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Recent advances in hybrid Cu2O-based heterogeneous nanostructures Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x 5

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Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties arise from the integrated interaction between the disparate components to generate promising potential for various significant applications including solar cell, carbon monoxide oxidation, photocatalyst, field emission, sensor, template and so on. With the rapid advancements in nanomaterial science and nanotechnology, hybrid Cu2O-based heterogeneous nanostructures with well-controlled compositions, shapes and sizes have been rationally designed and synthesized. This review attempts to summarize the important advances in the development of different types of hybrid Cu2O-based heterogeneous nanostructures, such as hybrid Cu2O-metal nanostructures, hybrid Cu2O-metal oxide nanostructures and hybrid Cu2O-carbon nanostructures. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are discussed based on some important and representative examples. Several key scientific issues and perspective research directions in this field are also given.

1. Introduction 20

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Semiconductor nanostructures have attracted considerable attention in the past decades because of their unexpected physical and chemical properties, as well as potentially significant applications in multidisciplinary fields such as energy conversion, electrics, catalysts, sensors and so on.1-10 It is well-recognized that the performances of semiconductor nanostructures strongly depend on a set of parameters such as the size, morphology, composition and crystallization.11-15 Furthermore, it has been demonstrated that hybrid semiconductor-based nanostructures can display new synergistic properties arise from the interaction between the disparate components to improve the performances of the original semconductors.16-25 Therefore, significant effort should be devoted to exploring effective methods for the rational design and synthesis of desired hybrid semiconductor-based nanostructures. Cuprous oxide (Cu2O), as a non-stoichiometic p-type semiconductor, is extensively attracted due to its perspective application in antibacterial activity,26 photocatalysts,27 gas sensor,28 and solar-driven water splitting,29 carbon monoxide (CO) oxidation,30,31 solar energy conversion,32 negative electrode material for lithium-ion battery,33,34 and metal-insulator-metal resistive switching memory35 and chemical template.36-56 The progress in nanomaterial science and nanotechnology has greatly accelerated the development of the synthesis and application of Cu2O nanostructures. So far, a number of Cu2O architectures with various morphologies have been successfully synthesized.57-137 Recently, progress and perspective on polyhedral Cu 2O This journal is © The Royal Society of Chemistry [year]

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nanostructures have been well-demonstrated.137,138 Especially, the facet-dependent properties of polyhedral Cu2O nanocrystals have been extensive attention.138,139 Although a better understanding of the facet-dependent property is necessary to prepare novel architectures with enhanced performances, the relative large sizes and instabilities of Cu2O crystals will limit their practical applications. Therefore, to expand the application of Cu 2O crystal is imperative. Hybrid Cu2O-based nanostructure, as a significant class of multicomponent heterogeneous architecture, could bring unexpected property for improving the potential application of Cu2O.140 The investigation of the synthetic strategy and formation mechanism of different hybrid Cu2O-based nanostructures offers a good opportunity to understand the fundamental principles for enhancing the desired performances. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are preliminarily uncovered. Therefore, a broad range of novel hybrid Cu2O-based nanostructures with enhanced performances has been controllably designed and fabricated. However, the systematic review on hybrid Cu2O-based nanostructures has not reported so far. In this review, we selectively summarize the synthesis strategy, principle for enhanced performance and application of different hybrid Cu2O-based nanostructure and cover the recent progress in this field (see Fig. 1). We start with a general survey in solutionbased synthetic strategies of hybrid Cu2O-metal heterostructures for tailoring their crystallographic facets and morphologies, especially the synthesis of metal decorated Cu2O heterostructures and metal@Cu2O core/shell architectures will be described in [journal], [year], [vol], 00–00 | 1

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Shaodong Sun*

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During the past decade, the extensive investigation of hybrid Cu2O–metal nanostructures is because multiple functions can be incorporated into one system for wide applications and for fascinating new properties induced by the hetero-interfaces.140 The electronic structures and physicochemical properties of the hybrid Cu2O–metal nanostructures strongly depend on the rational arrangement of the multi-components within the heterostructures. Thus, the spatially controllable synthesis of hybrid Cu2O–metal nanostructures is an urgent issue.141,142 So far, there are mainly two kinds of hybrid Cu 2O–metal heterogeneous systems, and a schematic illustration of the growth manner and geometrical model is shown in Fig. 2. The ability to controllably combine metal nanoparticles with Cu2O semiconductor is of special interest in that it can allow us to understand the interaction manner between the metal and the semiconductor to obtain preferred metal–semiconductor heterostructures.143 In this section, we will elaborate the Cu2O-reactanted strategies for synthesizing novel hybrid Cu2O–metal heterogeneous nanostructures. Firstly, the formation mechanism and application of the metal/Cu2O (metal decorated on Cu2O) heterogeneous nanostructures with controllable building blocks will be introduced. After this, we will especially discuss the synthesis method, formation mechanism and application of metal@Cu2O core/shell nanostructures. 2.1 Hybrid metal/Cu2O nanostructures

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Fig.1 Summary of main hybrid Cu2O-based heterogeneous nanostructures and their applications.

2. Hybrid Cu2O–metal nanostructures and their applications

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Fig.2 A schematic illustration of the growth manner and geometrical model of different hybrid Cu2O–metal heterogeneous nanostructures.

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It is well-demonstrated that the formation of a Schottky barrier at the metal–semiconductor interface can effectively prevent the recombination of the photo-electrons and photo-holes during a photocatalytic process, thus the photocatalytic efficiency of the original semiconductor can be obviously improved.144,145 Recently, hybrid metal/Cu2O nanostructures have been extensively investigated.140,146-157 Multifunctional metal/Cu2O heterogeneous nanostructures, such as Cu/Cu2O,140 Au/Cu2O,146150 Ag/Cu2O,151-155 Pt/Cu2O,156 and Pd/Cu2O,157 have been prepared by galvanic reactions or photo-irradiation between Cu2O and different metal salts. Therefore, precisely tailoring the metal/Cu2O heterogeneous nanostructures and thorough understanding of their formation mechanisms are imperative. Hybrid Cu/Cu2O heterogeneous nanostructures. In 2009, it has been reported that a copper rich or oxygen deficient surface can make a Schottky barrier for promoting the photocatalytic performance.158 Inspired by this viewpoint, the unique Cu/Cu2O heterogeneous nanostructures have been synthesized by a facile solution-phase reduction route.140 Low-magnification scanning electron microscopy (SEM) image of the polyhedral 26-facet Cu/Cu2O heterogeneous nanostructures is shown in Fig. 3a,140 and the selectively formation of rough Cu/Cu2O surfaces can be successfully achieved. From a crystallographic viewpoint, different exposed facets have different characteristic properties due to the difference in atomic arrangement, lattice symmetry and spacing. The reduction of a Cu2O generally initiates from the surface, thereby to shed light on the facet-dependent reducibility of Cu2O is necessary. The reducibility of a Cu2O can be uncovered by the bond length between the oxygen atom and copper atom. Previously, the density functional theory (DFT) calculations were performed to understand the structural properties of Cu2O(111), Cu2O(110) and Cu2O(100), which indicated that the bond length between the oxygen atom and This journal is © The Royal Society of Chemistry [year]

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detail. Next, hybrid Cu2O-metal oxide heterostructures and their potential applications are presented, and we also summarize the relationship of interface-property-performance. Finally, we illustrate the significance of using Cu2O component to prepare hybrid Cu2O-carbon heterostructures and their applications. Remarks on promising research directions of different hybrid Cu2O-based nanostructures are also given.

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copper atom in the (111) facet was larger than that of (110) and (100) facets (see Fig. 3b).140 Therefore, the results demonstrate that the (111) surface of Cu2O is much more facile to be reduced than the (110) and (100) surfaces, finally leading to the selective growth of Cu nanoparticles on Cu2O (111) surfaces. The successful preparation of Cu/Cu2O heterostructures provides an opportunity to extend the photocatalytic activities of non-noble metal–semiconductor materials. These novel Cu/Cu2O heterogeneous architectures show better adsorption and photodegradation of methyl orange (MO) than those of the original Cu2O architectures (see Fig. 3c). The formation of the Cu/Cu2O heterogeneous nanostructures not only makes the purposive crystal design of spatial arrangement possible, but also offers a good opportunity to understand the foundational importance of low-cost Cu nanoparticles for improve the photocatalytic activity of Cu2O. Typically, the above selective in-situ formation of Cu nanoparticles on Cu2O surfaces can be described by the following reaction: 2Cu2O + N2H4 → 4Cu + N2↑ + 2H2O (1) Notably, Cu2O can further be reduced to form pure Cu by increasing the reaction time and the amount of reducer in an aqueous solution at higher reaction temperature.159

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Fig.3 (a) Low-magnification SEM image of polyhedral 26-facet Cu/Cu2O heterogeneous nanostructures. (b) Optimized structures of Cu 2O(111), (110) and (100) surfaces, the red and blue balls represent oxygen and copper atoms, respectively. (c) A plot of the extent of adsorption and photodegradation of MO by different catalysts. Line A: the original polyhedral 26-facet Cu2O crystals. Line B: the as-prepared polyhedral 26facet Cu/Cu2O heterogeneous architectures. Reprinted with permission from ref. 140. Copyright RSC 2012.

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Hybrid Au/Cu2O heterogeneous nanostructures. On account of the redox pair of Cu2O/Cu2+ (+0.203 V, vs. SHE) is much lower than that of a noble metal redox pair, such as PtCl62–/Pt (+0.735 V, vs. SHE), AuCl4–/Au (+0.99 V, vs. SHE) and PdCl42– /Pd (+0.591 V, vs. SHE),160-162 Cu2O can be potentially used as the sacrificial precursors for the synthesis of hybrid noble metal/Cu2O nanostructures. The formation process of noble metal nanoparticles can be illustrated as the following reaction (eqn(2), which mainly involves two steps: (i) The desired growth of Cu2O This journal is © The Royal Society of Chemistry [year]

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crystals. (ii) The formation of M/Cu2O (M = Au, Pt and Pd) heterogeneous structures in AuCl4–, PtCl62– or PdCl42– aqueous solution (see eqn (2)). 3Cu2O + 2H+ + 2MClx– + H2O → 6Cu2+ + 2xCl– + 4OH– + 2M (2) Similar to that occurring in the above Cu/Cu2O system,140 Liu have demonstrated that the selective growth of Au nanoparticles on (111) surfaces of truncated octahedral and cuboctahedral Cu 2O crystals can also been achieved.146 The density and size of Au nanoparticle can be facilely controlled by tuning the concentration of Au precursor (see Fig. 4a). It can be clearly seen that a great number of Au nanoparticles were formed on (111) surfaces of the Cu2O crystals at lower concentration of HAuCl4, but almost none of the nanoparticles were produced on (100) surfaces. Upon increasing the concentration of HAuCl4, perfect Au/Cu2O core/shell heterostructures were obtained. So AuCl4– species can be preferentially absorbed on (111) surfaces and reduced by Cu(I) cites on these surfaces in an appropriate concentration of precursor. From the above results, it can be found that the (100) surfaces of Cu2O are difficult to reduce to form Au nanoparticles at a lower concentration of HAuCl4. However, when the Cu2O nanocube colloid (wholly exposed with six (100) facets) was injected into HAuCl4 at room temperature in the presence of ultrasound radiation, in-situ growth of Au nanoparticles on the surfaces of Cu2O nanocubes can be readily achieved.147 As for a (111) surface of Cu2O, it is interesting to understand the reaction activity of different specific position, such as apex, edge and facet. Du and coworkers have chosen octahedral Cu2O as templates for synthesizing Au/Cu2O heterogeneous nanostructures because the diversity of the surface energy distribution of octahedral Cu2O would result in the selective growth of Au nanoparticles at specific positions of {111} surfaces.148,149 The evolution of Au/Cu2O heterostructures involves the following four steps: (i) The selective adsorption of AuCl4– ions on vertices of octahedral Cu2O. (ii) The in-situ formation of Au nuclei through galvanic reaction and the selective growth of Au nanoparticles on the vertices. (iii) The change of selective growth route from along the crystal edges to along the {111} facets. (iv) The formation of Au nanoparticles. A schematic illustration of the surface-free-energy-distribution induced selective growth of Au nanoparticles on Cu2O octahedra with morphological evolutions is shown in Fig. 4b.148 The photocatalytic performances of the as-prepared Cu2O and Au/Cu2O heterostructures for the degradation of MO are investigated. As expected, the Au/Cu2O heterostructures exhibit higher photocatalytic performances than the pure Cu2O semiconductors. Notably, the formation Au/Cu2O heterostructures led to a dramatic improvement in the photocatalytic activities because of the electron–hole recombination being suppressed. However, the photocatalytic performances of the Au/Cu2O heterostructures were not improved with further increase of the loading amount of Au nanoparticles.148 The reduced photoactivity may be partially attributable to relatively higher Au loading in this system, which might decrease the total effective surface area of Cu2O semiconductor during the photocatalytic degradation of MO.

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Fig.4 (a) SEM images of selective growth of Au nanoparticles on truncated octahedral Cu 2O with morphological evolutions along with the increase of amount of HAuCl4. Reprinted with permission from ref. 146. Copyright ACS 2011. (b) A schematic illustration of the surface-free-energy-distribution induced selective growth of Au nanoparticles on truncated octahedral Cu 2O with morphological evolutions along with the increase of amount of HAuCl4. Reprinted with permission from ref. 148. Copyright RSC 2013. (c) SEM images of selective growth of Au nanoparticles on truncated octahedral Cu 2O with morphological evolutions along with the increase of amount of Au nanoparticles. Reprinted with permission from ref. 150. Copyright ACS 2012.

In addition of the above spontaneous redox reaction, Au/Cu 2O heterostructures with tunable coverage of Au were successfully synthesized by a facile method of mixing Au nanoparticles with Cu2O nanowires in a functional groups solution-phase system. Xu and coworkers have found that superhydrophobic poly(oanisidine)-capped Cu2O nanowires provide strong hydrophobic host−guest interactions with oleylamine-capped Au nanoparticles to form semiconductor-metal nanoparticles.150 When poly(oanisidine)-capped Cu2O nanowires and oleylamine-capped Au nanoparticles are mixed and dispersed in chloroform, their hydrophobic-hydrophobic interactions cause spontaneous formation of Au/Cu2O heterostructures. The oleylamine capped Au nanoparticles are immobilized onto the poly(o-anisidine)capped Cu2O nanowires so as to lower the surface energy through hydrophobic-hydrophobic interactions, leading to the formation of Au/Cu2O heterostructures (see Fig. 4c).150 Hybrid Ag/Cu2O heterogeneous nanostructures. Although Cu2O has been used as a weak reducing agent to synthesize Cu/Cu2O and Au/Cu2O heterostructures by the spontaneous redox route, it is difficult to obtain Ag/Cu2O heterostructures through the direct reaction between AgNO3 and Cu2O, so a modified synthetic strategy should be developed. Wang and coworkers have prepared uniform nanosheet-assembled silver hollow microcubes by using Cu2O cubes as template. In this reaction, This journal is © The Royal Society of Chemistry [year]

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AgNO3 acts as metal source and trisodium citrate acts as a stabilizer and shape-directing agent.151 The whole reaction process could be generally written as eqn (3). Clearly, both the concentrations of H+ ions and Ag+ ions strongly affect the reaction rate. Inspired by the above reaction mechanism, Ag+ ions can be reduced by the primary Cu2O nanospheres in the acidic solution, and the obtained Ag nanoparticles can be deposited on the surfaces of the Cu2O nanospheres. The corresponding SEM image, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) images are shown in Fig. 5a.152 Similarly, hollow Ag/Cu2O heterostructures with enhanced surface-enhanced Raman scattering (SERS) have been successfully designed and constructed by the reduction of AgNO3 with sodium citrate in a Cu2O-containing mother solution (see Fig. 5b).153 2H+ + Cu2O + 2Ag+ → 2Ag + 2Cu2+ + H2O (3) Cu + 2Ag+ → Cu2+ + 2Ag (4) Cu + Cu2+ + H2O → Cu2O + 2H+ (5) However, it is still necessary to develop a facile approach to synthesize novel Ag/Cu2O heterostructures. Recently, a one-step hydrothermal synthesis of Ag/Cu2O heterogeneous nanostructures grown on Cu foil was first reported, in which Cu foil and AgNO3 were the only reactants involved in the preparation process.154 [journal], [year], [vol], 00–00 | 4

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Fig.5 (a) SEM, TEM and HRTEM images of Ag/Cu2O nanospheres. Reprinted with permission from ref. 152. Copyright ACS 2014. (b) SEM, TEM and HRTEM images of truncated Ag/Cu2O heterostructures. Reprinted with permission from ref. 153. Copyright RSC 2014. (b) Different magnification SEM images and energy dispersive X-ray spectrum of octahedral Ag/Cu2O heterostructures. Reprinted with permission from ref. 155. Copyright RSC 2011. 5

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Ag and Cu2+ ion are generated by the reaction (4), and Cu2+ ion contacts with Cu substrate to form Cu2O on the Cu foil by a redox reaction (5). During this process, Cu2O may be inclined to absorb OH–, leading to the formation of negatively charged species on their surfaces. Ag nanoparticles with high surface energies tend to absorb Ag+ ions, and turn positively charged. Thus Cu2O and Ag are easy to interact with each other owing to the electrostatic attraction, finally the Ag/Cu2O heterogeneous nanostructures were formed.154 A photochemical irradiation method has also been successfully employed to deposit Ag nanoparticles onto the surfaces of Cu 2O octahedral crystals (see Fig. 5c).155 The procedure for the synthesis of Ag/Cu2O heterostructures is as follows: first, octahedral nanocrystals were dispersed into distilled water by sonication. The distilled water was pre-heated by a water bath. Then the suspension was irradiated with a 500 W column-like iodine tungsten lamp. Under continuous magnetic stirring, AgNO3 solution was injected into the suspension, and the This journal is © The Royal Society of Chemistry [year]

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suspension was further irradiated to finally synthesize Ag/Cu2O heterostructures. When Cu2O is illuminated under visible light, electrons and holes can be photogenerated (eqn (6)). Ag+ cations can be reduced by photogenerated electrons to form Ag/Cu 2O heterostructures (eqn (7)). The reactions can be proposed as follows: Cu2O + hν → Cu2O (ecb– + hvb+) (6) ecb– + Ag+ → Ag (7) 2.2 Hybrid metal@Cu2O core/shell nanostructures

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The metal@Cu2O core/shell architectures are highlighted in the following subsection because the electronic structures and catalytic properties of core–shell heterostructures can be substantially modified through the special interaction between shell atoms and core atoms.163,164 Hybrid metal@Cu2O core/shell nanocomposites were proposed to improve the photocatalytic performances of Cu2O by suppressing the charge recombination and increasing the formation of active species by trapping [journal], [year], [vol], 00–00 | 5

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photogenerated electrons.165 Therefore, understanding how the metal@Cu2O core/shell nanostructures cause the tunable synergistic properties is directly related to the capability to selectively implement desired performances into hybrid Cu 2Obased nanomaterials. Hybrid Cu@Cu2O core/shell nanostructures. In general, an oxidative reaction of pure Cu nanostructure has been widely used to generate a Cu2O-outside core/shell structure with a Cu core and a Cu2O shell (Cu@Cu2O). For example, core/shell heterostructured Cu@Cu2O nanowires with high aspect ratios were synthesized from Cu foams using a novel oxidation/reduction process in hydrogen and nitrogen atmosphere, which showed superior catalytic activities for the photodegradation of organic dyes under visible light irradiation.166 Core/shell heterostructured Cu@Cu2O nanodots can be prepared by the oxidation of Cu colloids (see Fig. 6a), which were found to be catalytically active for the generation of hydrogen from ammonia–borane.167 Core/shell Cu@Cu2O microspheres were synthesized by an interfacial hydrothermal method, which involved the in situ transformation from pure Cu to Cu2O.168 During this process, pure Cu microspheres were first formed through the reduction of copper(II) acetylacetonate. Then Cu surface was oxidized to transform into a Cu2O shell, leading to the formation of core/shell Cu@Cu2O microspheres. These core/shell Cu@Cu2O microspheres exhibited enhanced photocatalytic activity as compared to Cu2O on the degradation of gaseous nitrogen monoxide under visible light irradiation. However, the transition metal Cu is difficult to obtain by the reduction of copper oxides in solution.168-170 As a result, it is a challenging task to prepare the Cu-outside structure with a Cu2O core and a Cu shell (Cu2O@Cu). Actually, Cu is expected to play a vital role as a shell because of its high activity in diverse reaction.171 So far, literature on the successful synthesis of such a structure is very scarce. Therefore, the synthesis of Cu-outside core/shell Cu2O@Cu nanostructures is extremely desirable from both an academic and a practical viewpoint.

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Kou and coworkers have synthesized inside-out core/shell architectures (Cu2O@Cu) with a Cu2O core and a Cu shell by reduction of Cu2O templates in a mix solution of ethylene glycol/sodium hydroxide/glucose (see Fig. 6b).172 The obtained Cu2O@Cu core/shell structure exhibits excellent catalytic activity 6 | Journal Name, [year], [vol], 00–00

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in the Sonogashira coupling reaction, in which the high activity derived from the special architecture without a noble metal is fascinating. This Cu2O@Cu core/shell structure may provide a promising alternative of traditional noble metals for an economic Sonogashira coupling reaction. Recently, Ding and coworkers have found that three-dimensional (3D) binder-free Cu2O@Cu nanoneedle arrays electrode can exhibit a high specific capacitance and excellent cycling stability with high capacitance retention. And they have successfully constructed a Cu2O@Cu//AC supercapacitor, which possesses an energy density of 35.6 W h kg-1 at 0.9 kW kg-1 and excellent stability with a capacitance retention of 92% after 10000 cycles. Importantly, the in-series Cu2O@Cu//AC supercapacitors can light up LED arrays and even charge a mobile phone after being charged for dozens of seconds (see Fig. 7).173

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Fig.6 (a) TEM images of the inside-out Cu@Cu2O core/shell nanoparticles prepared by oxidation of Cu colloids; the inset is an HRTEM image of an individual nanoparticle. Reprinted with permission from ref. 167. Copyright RSC 2008. (b) TEM image of the inside-out Cu2O@Cu core/shell architectures; the inset is a SEM image of a typical individual particle. Reprinted with permission from ref. 172. Copyright RSC 2012.

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Fig.7 (a) Photograph of Cu2O@Cu//AC asymmetric supercapacitor (5cm × 5 cm). (b) Photographs showing that four supercapacitors in series can light up a 32-LEDs displayer for more than 20 minutes. (c) Photograph showing a mobile phone charged by two supercapacitors in series. (d) Photographs showing a 1 W yellow LED powered by two supercapacitors in series. Reprinted with permission from ref. 173. Copyright RSC 2014.

Hybrid Au@Cu2O core/shell nanostructures. As one typical combination of metal nanoparticles with localized surface plasmon resonance and oxide semiconductors, Au@Cu2O has attracted great attention because of its novel structure and potential application in solar energy conversion.165,174-181 Cu2O semiconductor has an appropriate high-refractive index (2.705 in visible region), resulting in a very strong influence of Cu2O toward the localized surface plasmon resonance of embedded metal nanoparticles.165 The plasmonic Au@Cu2O core/shell heterostructures provides several advantages.177 First, such core/shell heterostructures can effectively protect the metal nanoparticles from corrosion. Second, it can maximize the metal−support interaction through the three-dimensional contact between the metal core and the semiconductor shell, so facilitating the plasmonic energy transfer processes. Last, the local electromagnetic field of the localized surface plasmon resonance penetrates the shell, can be used to control the center wavelength of the localized surface plasmon resonance. Especially, the core/shell Au@Cu2O heterostructures displays interesting shell-dependent surface plasmon resonance light extinction on nanoscale.165 Therefore, to explore the cooperative This journal is © The Royal Society of Chemistry [year]

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interaction between plasmonic Au and Cu2O semiconductor as well as its special plasmon resonant property is imperative.

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Fig.8 (a) TEM image of Au@Cu2O core-shell nanoparticles with the shell thickness about 20 nm; The line scanning element analysis of one coreshell nanoparticle with Cu and Au distribution; UV−vis spectra of Au@Cu2O nanoparticles showing the red shift of localized surface plasmon resonance extinction. Reprinted with permission from ref. 178. Copyright ACS 2012. (b) Cross-sectional TEM images of the Au@Cu2O core-shell heterostructures with diffeent Au cores. Reprinted with permission from ref. 180. Copyright ACS 2009. (c) TEM images and energy dispersive X-ray mapping spectra of octahedral Au@Cu2O coreshell heterostructures. Reprinted with permission from ref. 176. Copyright RSC 2012. (d) SEM images showing two tungsten probes in contact with a single particle (pristine cube and octahedron, Au@Cu 2O core-shell cube Au@Cu2O core-shell octahedron, respectively) for I-V measurements. Reprinted with permission from ref. 174. Copyright ACS 2011.

Tian and coworkers have synthesized Au@Cu2O core/shell nanoparticles to demonstrate the dramatic effect of dielectric shell in both experimentally and theoretically.178 The extinction spectra of Au@Cu2O nanoparticles with controllable thickness of shells exhibit not only a tunable red shift of resonant peak but also distinctive enhanced absorption intensity and peak splitting (see Fig. 8a). The proper dielectric shell-coated plasmonic nanoparticles could be very perspective, especially for the application that needs effective enhancement of the plasmon resonant absorption. Wang and coworkers have developed a robust seed-mediated synthetic approach,165 which can fine-control several important geometrical parameters of the hybrid Au@Cu2O core/shell nanoparticles, including thickness of Cu2O shell, size of the Au core, and the spacing between the core and shell, to systematically and selectively fine-tune the synergistic light absorption and scattering property of the composite over a broad This journal is © The Royal Society of Chemistry [year]

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spectral range across the visible and near-infrared regions. They have performed Mie scattering calculations to theoretically interpret the correlation between the geometrical parameters and optical characteristics of the hybrid Au@Cu2O core/shell nanoparticles. Facet-dependent localized surface plasmon resonance properties of polyhedral Au@Cu2O core/shell nanocrystals are very interesting to be investigated. Huang and coworkers have found that the localized surface plasmon resonance absorption band positions of the Au cores in the Au@Cu2O core/shell heterostructures are highly dependent on the surface facets of the single-crystalline Cu2O shells.179 Within a considerably large Cu2O shell thickness range, the surface plasmon resonance band positions of the Au@Cu2O core/shell nanocrystals are independent of the thickness of shell, but shift progressively to the long wavelength side from octahedra to cuboctahedra and then cubes. Furthermore, novel Au@Cu2O with well-defined morphology can be easily synthesized by a seed-mediated aqueous solution method. Recent advances from Huang’s group demonstrate that the shape-directed growth of Cu2O can be achieved by using different Au seeds to prepare interesting Au@Cu2O nanostructures.175,180 They have synthesized various Au@Cu2O core/shell heterostructures through different Au nanostructures (including nanoplates, nanorods, octahedra, and highly faceted nanoparticles) as the structure-directing cores for the overgrowth of Cu2O shells (see Fig. 8b). The Au cores guide the growth of Cu2O shells with controlled morphologies, which can be attributed to an unusual hollow-shell refilled growth mechanism not reported previously. Systematic shape-evolution of the Cu2O shells can be easily achieved by simply adjusting the volume of added reducer. For example, truncated cubic to octahedral Cu2O shells were produced from octahedral Au nanocrystal cores.180 Unusual truncated stellated icosahedral and star column structures have also been synthesized. Au@Cu2O convex cubes, cuboctahedra, and octahedra were synthesized by using rhombic dodecahedral and highly edge- and corner-truncated octahedral Au cores, respectively.175 In spite of the shape-directed growth of Cu2O can be realized by using Au seeds to form Au@Cu2O structures, the size control of Cu2O (especially octahedral Cu2O) is more difficult in hydrophilic media. Huang and coworkers have used heterogeneous nucleation, rather than homogeneous nucleation, of Cu2O with Au nanorods as seeds to realize the subsequent uniform crystal growth. And nearly monodisperse octahedral Au@Cu2O nanocrystals with single-crystalline shells were successfully synthesized (see Fig. 8c), in which the size control of the Cu2O shell can be achieved by adjusting the amount of Au rods.176 The result of larger surface area and improved charge separation from core/shell interaction, made Au@Cu2O with different sizes exhibit excellent photocatalytic activity compared to that prepared without Au seeds toward MO degradation. Hybrid Au@Cu2O core/shell nanostructures have also become stronger candidates as gas sensors due to their controllable chemical and thermal stabilities within the protection of shells and effective charge separation between Au cores and Cu2O shells.181 In addition, the investigation of facet-dependent and Au core-enhanced electrical properties of Au@Cu2O heterostructures Journal Name, [year], [vol], 00–00 | 7

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have successfully been demonstrated (see Fig. 8d).174 Hybrid Ag@Cu2O core/shell nanostructures. The Ag@Cu2O core/shell heterostructure is demonstrated to be a candidate to solve the problem of corrosion or dissolution of the exposure of Ag nanoparticles. The electronic structures and properties of Ag@Cu2O core/shell heterostructures are substantially improved owing to the integrated interaction between the shell atoms and the core atoms. Ag@Cu2O core/shell nanostructures can also be prepared by a seed-mediated route. The controllable growth of Cu2O layers on Ag nanoplates can make different interfacial lengths in oxide-metal hybrid structures, leading to an excellent platform for investigating the effect of surface polarization on CO oxidation (see Fig. 9a).182 The geometry control of Ag@Cu2O core−shell nanoparticles can be synthesized through epitaxial growth of Cu2O nanoshells on the surfaces of various Ag nanostructures, which can exhibit geometry-dependent optical properties that are highly tunable across the visible and near-infrared spectral regions (see Fig. 9b).183 One-dimensional Ag@Cu2O core−shell heteronanowires have also been synthesized (see Fig. 9c), which display much higher plasmonic photocatalytic activities toward degradation of organic contaminants than Ag@Cu2O core−shell nanoparticles or pure Cu2O nanospheres under solar light irradiation. The enhancement in photocatalytic activity could be attributed to the surface plasmon resonance and the electron sink effect of the Ag nanowire core, and the unique one-dimensional (1D) core−shell nanostructure.184

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Fig. 9 (a) SEM image and EDS mapping of Ag@Cu2O core/shell nanoplates. Reprinted with permission from ref. 182. Copyright ACS 2014. (b) TEM image of Ag seeds and different Ag@Cu 2O core/shell nanostrucutres. Reprinted with permission from ref. 183. Copyright ACS 2014. (c) SEM and TEM images of one-dimensional Ag@Cu2O core/shell nanowires. Reprinted with permission from ref. 184. Copyright ACS 2014.

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The synthesis and applications of the above reported hybrid metal–Cu2O nanostructures are summarized in Table 1. However, the formation of multiple metal–Cu2O-based nanocomposites is less reported. Fortunately, hybrid Cu2O-based templates can be further used to synthesize a broad range of novel binary and ternary Cu2O-based heterostructures.56 For example, starting from monodisperse hybrid metal@Cu2O core/shell templates, metal@Cu2O@CuxE (E = S, Se, Te) nanocomposites will be synthesized through a replacement/etching approach. Based on the above result, metal@CuxE york-shell heterostructures can be converted from Cu2O shell through a modified Kirkendall process,184 and the obtained CuxE would then be employed as a solid precursor for further synthesizing new nanostructures through ion exchange mechansims. Significantly, hybrid metal– Cu2O-based templates might be in progress towards to fabricate novel multi-walled or multi-compositional hollow nanostructures through removing the Cu2O components, such as metal@metal, metal@oxide york/shell architectures.56 As demonstrated previously, charge separation is significant for improving the activity of semiconductor-based solar energy conversion.157,185 Spatial separation of photogenerated electrons and holes among different crystal facets of Cu2O should be further considered in future. An efficient charge separation might be achieved on different crystal facets under photo-irradiation due to the difference in electronic structures, leading to the appearance of a new concept of “surface heterojunction”.11,133 Based on the rule of charge separation, the selective deposition of desired cocatalysts on different crystal facets of Cu2O can be achieved by the reduction reaction with photogenerated electrons and the oxidation reaction with photogenerated holes, finally resulting in much higher activity compared with the photocatalyst decorated with random cocatalysts.185 Notably, the work functions of different Cu2O crystal facets and metals, the conduction band minimum (CBM) and the valance band maximum (VBM) of Cu2O and decorated semiconductors should be considered seriously, which can determine the selection of compatible cocatalysts and the final performances. This research direction will be useful to construct highly efficient solar energy conversion systems.

3. Hybrid Cu2O–metal oxide nanostructures and their applications The controllable synthesis of semiconductor–metal oxide heterojunctions is an exciting direction to pursue for highly active photoelectric beacons, and also offers an opportunity to investigate the relationship of structure-property-performance. Recently, considerable attention has been paid to construct highactivity hybrid Cu2O–metal oxide nanostructures with tunable interfaces for expanding their new applications.186-190 In this section, we will summarize the synthetic strategy and formation mechanism of different kind of hybrid Cu2O-metal oxide nanostructure. Firstly, recent advances in synthesis of Cu2O–ZnO heterogeneous nanostructures and their different applications (such as solar energy cell, photocatalyst and field emission) will be especially elaborated. After this, we will discuss the design and synthesis of Cu2O–TiO2 heterogeneous nanostructures for efficient photoelectrochemical water splitting in detailed. Then, we will introduce the synthetic strategies and This journal is © The Royal Society of Chemistry [year]

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principles of Cu2O–CuO heterogeneous nanostructures. In addition, other binary and ternary Cu2O-metal oxide heterogeneous nanostructures will also be mentioned. Finally, the synthesis and application of Cu2O–Cu2O p–n homogeneous nanostructures will be discussed. The applications of hybrid Cu2O–metal oxide nanostructures are summarized in Table 2.

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The design and fabrication of low-cost, efficient and reliable solar energy cells is a significant goal for solving the growing global energy demand and decreasing greenhouse gas emissions.191 Metal oxide semiconductors are ideal for constructing thin film solar cells, which can offer excellent characteristics for fabricating a wide range of heterojunction based devices.192,193 Cu2O has attracted interest as a good candidate material for solar cell because of its abundant availability, nontoxicity and low production cost.194,195 It has a higher absorption coefficient in the visible region and the minority carrier diffusion length is also suitable for acting as a solar cell absorber layer.196 Zinc oxide (ZnO), as one of the most successful n-type semiconductors because of its wide band gap (3.37 eV), relatively large exciton binding energy (60 meV), deep level defect, high charge carrier mobility (~ 120 cm2V–1s–1) and morphological diversity, has been widely investigated in solar cell, gas sensor and field emission device.197-199 The two semiconductors have a particularly relative position of the energy band, of which the CBM of Cu 2O is a little higher than the CBM of ZnO and the VBM of ZnO is lower than the VBM of Cu2O.200 This might promise that the p–n Cu2O–ZnO heterojunction has valuable applications in electrics and optoelectronics devices. Recently, p-Cu2O/n-ZnO heterojunction solar cells have been pursued. Although Shockley–Queisser theoretical value of the power conversion efficiency (PEC) of Cu2O-based solar cells is over 20%,201 the high recombination probability of photoinduced charge carriers and poor solar efficiency have hindered the practical application. So far, the highest PEC of reported pCu2O/n-ZnO-based devices (Al-doped ZnO/nondoped Ga2O3/Cu2O heterojunction) is about 5.83%.186 However, this efficiency is still much lower than the theoretical value. Therefore, further investigation devoted to this photo-adsorption Cu2O layer is imperative. Actually, because of the intrinsic crystallographic limitations, such as lattice mismatch (a = 0.4267 nm for cubic Cu2O and a=b= 0.3254 nm, c = 0.5210 nm for hexagonal ZnO) and relative instability of Cu2O, so most of the Cu2O–ZnO heterojunctions were combined by electrodeposition, electrochemical deposition and sputtering methods, which impose restrictions on the heterojunction that can only exist in the form of film with a simple planar interface.202-204 It leads to an inadequate minority carrier transport length, high recombination rate of the photogenerated electron–hole pairs and low sunlight utilizing efficiency. For example, Katayama et al. prepared Cu2O–ZnO film heterostructure and measured a PCE of 0.117% under a simulated solar light of 120 mW∙cm–2.202 Jeong and coworkers have studied the influence of electrodeposition conditions such as pH value and temperature on the cell performance.205 However, in the two cases, the PCE was still low at about 0.1%. In 2010, Cui and Musselman et al. have fabricated Cu2O–ZnO film/nanopillar heterojunctions by electrodeposition methods, and This journal is © The Royal Society of Chemistry [year]

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the efficiency of such nanopillar solar cells was improved to above 0.5%.206,207 In comparison with planar Cu2O/ZnO film solar cells, the introduction of nanowire arrays can lead to higher efficiency and short-circuit current improvement because nanowires have better charge carrier collection ability than film.208 Heterostructural p-Cu2O/n-ZnO nanowire arrays can be fabricated by the consecutive electrochemical deposition of an nZnO nanorod layer, followed by a p-Cu2O layer on a transparent conductive substrate. The performance of this heterojunction cell is able to achieve the PEC of 0.33% (see Fig. 10).187 Oxygen plasma can reduce the surface dangling bond and the density of defect sites of ZnO,209 resulting in an improved interface and a reduced charge recombination for higher device performance. Recently, Li and coworkers have also reported a highperformance Cu2O–ZnO nanowire heterojunction solar cell, fabricated solely by oxygen-plasma-assisted electrochemical deposition with the inclusion of Ga doping in aqueous solution. The use of electrochemically deposited ZnO powder-buffered Cu2O from a mixed Cu2+-ZnO powder solution and oxygen plasma treatment could reduce the density of defect sites in the interface to further increase PCE to 0.34%, leading to a little higher PEC among electrochemically fabricated Cu2O–ZnO nanowire solar cells.210

Fig.10 Cross-section SEM of Cu2O−ZnO heterojunction solar cell at applied potential of –0.4 V for (a) 5 min, (b) 10 min, (c) 20 min, (d) 30 min, (e) Current–voltage (I–V) characteristic curves and (f) external quantum efficiency of Cu2O−ZnO heterojunction solar cell under various growth time of Cu2O film. Reprinted with permission from ref. 187. Copyright RSC 2014.

However, the open-circuit voltage of the above devices is significantly below the theoretical limit of Cu2O, because of a low built-in potential caused by non-ideal band alignment between the absorber (Cu2O) and transparent conducting oxide (TCO), and a high recombination-current driven by the rapid Journal Name, [year], [vol], 00–00 | 9

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interfacial recombination.188,189 In order to further improve the open-circuit voltage, Buonassisi and coworkers have proposed to introduce a thin buffer layer between the absorber and the TCO.188,189 The buffer layer can act as an electron-blocking site, decreasing the recombination at the absorber–TCO interface. To date, some buffer layers have been introduced at the junction interface to offer ideal band alignment.186,188,189 For example, the introduction of an ultrathin non-toxic and scalable amorphous zinc tin oxide (a-ZTO) film (5 nm) as an electron-blocking layer can effectively inhibit charge recombination at the interface between the Cu2O absorber and the Al-doped ZnO TCO (see Fig. 11).188 The dark saturation current density reduces over an order of magnitude, and the open-circuit voltage improves to 0.553V and PEC is 2.65%.188 Moreover, Buonassisi and coworkers have found that the presence of a deleterious CuO layer at the a-ZTO/Cu2O interface can be minimized by optimizing the a-ZTO atomic layer deposition (ALD) process, enhancing the heterojunction open-circuit voltage, and leading to an independently verified PCE of 2.85%.189 The introduction of an n-type Ga2O3 film can greatly enhance the performance of n-ZnO/p-Cu2O heterojunction solar cells. The PEC of 5.38% can be obtained in an Al-doped ZnO/Ga2O3/Cu2O heterojunction solar cell.186

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Fig.11 (a) A schematic of the structure of the substrate type Cu2O-based solar cells with a-ZTO (or ZnO for the “control” device) buffer layers. (b) Cross-sectional scanning electron microscopy (SEM) image of the device, exhibiting a highly textured top surface stemming from (111) preferred growth of Cu2O. (c) Magnified SEM image near the junction interface. Conformal coating of a-ZTO and AZO layers is demonstrated. (d) HRTEM image near the junction interface. Dashed lines indicate phase boundaries between the amorphous ZTO layer (Zn/Sn=1/0.27) and surrounding crystalline Cu2O and AZO layers. Reprinted with permission from ref. 188. Copyright RSC 2013.

Although the PEC demonstrated in Al-doped ZnO/Ga2O3/Cu2O heterojunction solar cells represents a good starting point for the realization of low-cost solar cells, the intrinsic property of the ptype Cu2O is easy to generate acceptor defects, particularly in the form of copper vacancies, which leads to the Cu2O films with nanostructures have a high resistivity and low carrier mobility. Therefore, the improvement of the conductivity of Cu 2O component is necessary. Significantly, the modification of the electronic structure of Cu2O to fully absorb visible light and improve the separation and transfer of photoexcited charge

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carriers in the interfaces of semiconductors is greatly necessary. Doping is an useful strategy for modifying the electronic structures Cu2O, which could effectively improve their photovoltaic performances. A co-sputtering approach to dope Cu2O thin films might reduce the electrical resistivity and increase photo-induced current simultaneously.190,210 The construction of heterojunction is an exciting approach to obtain high-active photocatalysts. Coupling ZnO nanostructures with Cu2O nanostructures can tune the response of the photocatalysis in the visible region and accelerate the charge separation, which affects the injection rate of photo-induced charge carriers and the final photocatalytic activity. Although a number of investigations on Cu2O–ZnO films have been reported as photovoltaic devices, the construction of Cu2O–ZnO heterostructures on a substrate towards the degradation of organic pollutants has been scarcely reported. Recently, vertically aligned Cu2O–ZnO hetero-nanorod arrays were fabricated on indium-doped tin oxide (ITO) glass substrates using a simple hydrothermal method followed by an electrodeposition process.211,212 As shown in Fig. 12a~12f, uniform distribution of Cu2O over the individual ZnO nanorod can be achieved. The increase of the electrodeposition time can enhance the photocatalytic activities of the system until the Cu 2O nanoparticles nearly cover the entire periphery of the ZnO nanorods.211 The higher photocatalytic activities of the Cu2O– ZnO heterostructures can be possibly attributed to the improved optical absorption (Fig. 12g) and the specific 1D heterostructure (Fig. 12h). The Cu2O–ZnO heterostructure could expand the absorption range within the sunlight spectrum due to the narrow band gap of Cu2O. As shown in Fig. 12g, the sun light passing through the free space between the 1D nanorods may multiple scatterings in the free space between the nanorods and the ITO substrate, leading to the improvement of the light absorbance. Furthermore, the formation of a favorable Cu2O–ZnO p–n junction promotes the separation of photogenerated electron–hole pairs under visible light irradiation and reduces the charge recombination. As schematically shown in Fig. 12h, the photogenerated electrons in the conduction band (CB) of Cu2O can migrate into the CB of ZnO while the photogenerated holes migrate in the opposite direction from the valance band (VB) of ZnO to that of Cu2O. After the separation, the photogenerated electrons can very quickly come to the surface of the ZnO because of its onedimensional and single crystalline nature, which favors the degradation of the dye. The positive holes in the VB can react with H2O species adsorbed on the catalyst surface, forming high active ∙OH radicals in aqueous solution. The electron in the CB can transfer to oxygen adsorbed on the surface of the ZnO or Cu2O forming the HO2∙ superoxide radical, which oxidizes the adsorbed dye on the catalyst surface. Notably, when many Cu 2O nanoparticles covered on the surface of the ZnO nanorods, the effective surface of ZnO for photocatalytic degradation was eliminated, resulting in the photogenerated electrons derived from Cu2O cannot be depleted immediately and accumulate because of the poor electron mobility in nanocrystalline Cu2O, which accelerated the chance of charge recombination. Moreover, the

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Fig.12 (a) Low-magnification TEM image of a ZnO nanorod. (b) HRTEM image of a ZnO nanorod and (c) the corresponding SAED pattern of the ZnO nanorod. (d) Low-magnification TEM image of the Cu2O−ZnO nanorod hetero-structure. (e) HRTEM image of a Cu2O−ZnO nanorod heterostructure interface. (f) The corresponding SAED patterns of the marked area in (d). (g) Schematic of the Cu 2O−ZnO hetero-nanostructures that can act as a threedimensional light-harvester; (h) A schematic diagram showing the charge generation and transfer in the presence of light causing the degradation of the dye. Reprinted with permission from ref. 211. Copyright RSC 2014.

small size and amount of Cu2O nanoparticles covered on the ZnO nanorods were in favor of the holes transfer and depletion, thus the photocorrosion of Cu2O was effectively prevented.211 From the above mentioned result, it can be found that 3D branched heterostructures composed of 1D building blocks can tremendously improve the optical absorption and limit the charge recombination to enhance the photocatalytic performance. Furthermore, the increase of the overall aspect ratio will help to This journal is © The Royal Society of Chemistry [year]

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promote the field emission property.213 The heteronanobrushs comprising of Cu2O nanoneedles decorated with ZnO nanorods can be synthesized by a two-step chemical method.213 The Cu2O nanoneedle was grown directly on copper substrate by an electrodeposition and annealing method, subsequently, a seedassisted growth of ZnO on Cu2O was carried out to achieve brush-like morphology by pulsed laser deposition technique. A schematic of the growth procedure of Cu2O–ZnO hetero[journal], [year], [vol], 00–00 | 11

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Fig.13 (a) ~ (c) A schematic of the growth procedure of Cu2O−ZnO hetero-nanobrush. The bottom pictures show SEM images of each growth step. (d) Field emission current density–applied electric field (J–E) characteristics (inset shows turn-on value). (e) and (f) show the field emission micrographs of Cu2O nanoneedles and Cu2O−ZnO nanobrush, respectively. (g) Band diagram of Cu2O−ZnO heterojunction. Reprinted with permission from ref. 213. Copyright RSC 2012.

So far, it is less reported that normal hydrothermal methods can be developed for synthesizing Cu2O–ZnO heterojunctions. Recently, Yu and coworkers have reported a facile route for synthesizing ZnO decorated on different Cu2O microstructures by a low temperature hydrothermal and thermal annealing process with the assistance of polyethyleneimine.214 However, it still remains a challenge to develop facile solution-phase strategy to synthesize uniform 3D branched Cu2O–ZnO heterostructures composed of 1D building blocks to improve their potential 12 | Journal Name, [year], [vol], 00–00

applications.

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Sunlight-driven water splitting is a perspective research direction to meet the issue of worldwide energy demand. In a photoelectrochemical cell, photoexcitation of a p-type photocathode and an n-type photoanode provides electrons and holes, respectively, for water splitting. Previous report has demonstrated that Cu2O nanostructure is an ideal material component for efficient light harvesting.215 However, a major drawback of Cu2O as an electrode material is its short electron diffusion length (10–100 nm), and photo-instability in aqueous solution during illumination.216,217 In addition, the valence band position of Cu2O is slightly more positive than the potential of water oxidation, and coupling with an n-type semiconductor photoanode is therefore required for bias-free water splitting.29 Titanium dioxide (TiO2), as a typical n-type semiconductor, with excellent photo- and chemical stability, strong oxidizing activity, corrosion resistance and nontoxicity, can decompose water into oxygen and hydrogen without the application of an external voltage under certain conditions in the pioneering work of Fujishima and Honda four decades ago.218 Unfortunately, the common phases of TiO2 are wide band gaps (3.2 eV for the anatase phase and 3.0 eV for the rutile phase), which cannot be activated effectively under visible light radiation, and the photogenerate electron–hole pairs easily recombine.219 It has been demonstrated that narrow band-gap semiconductors can facilitate the electron transfer to large band-gap TiO2 in a narrow band-gap semiconductor/TiO2 heterostructure,220-224 thereby efficiently separating photogenerated charge carriers.225 Hence, the visible light absorption of TiO2 and the separation rate of photogenerated electron–hole pairs are substantially enhanced. Narrow band-gap (~ 2.17 eV) p-type Cu2O semiconductor allows for visible light absorption and conduction band electrons provide approximately 0.7 V driving force for proton reduction.219 Both the conduction and the valence bands of Cu2O are located above those of TiO2.226 Thus, when TiO2 is coupling with Cu2O, the photogenerated electrons transfer from the conduction band of Cu2O to that of TiO2 to form Ti3+ center,226 which prolongs the lifetime of photogenerated carriers. The merit of the Cu2O–TiO2 heterostructures can benefit from the attractive band gap of Cu2O as well as from the high stability of TiO2 in aqueous solutions.225, 227-237 Sun and coworkers have developed a robust ultrasonication-assisted sequential chemical bath deposition technique to yield p-type Cu2O nanoparticles on ntype TiO2 nanotube arrays (see Fig. 14).225 The synthesized Cu2O–TiO2 heterojunction photoelectrode exhibited a more effective photoconversion capability than TiO2 nanotube alone. Furthermore, the photoelectrode also possessed superior photoelectrocatalytic activity and stability towards to the degradation of Rhodamine B. Mesoporous TiO2 beads, produced by a metal-salt based hydrothermal process, can be successfully decorated with Cu 2O nanoparticles by a simple chemical bath deposition process.231 The structural advantages of high specific surface areas, large pore volumes and suitable pore sizes of the TiO2 beads in combination with the excellent charge separation realized through the decoration of band-structure-matched Cu2O nanoparticles, can achieve an ultra-high H2 evolution rate. Deng and coworkers This journal is © The Royal Society of Chemistry [year]

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nanobrush is displayed in Fig. 13a ~ Fig. 13c. The formation of Cu2O–ZnO p–n junction is an useful band alignment for the electron transport from the conduction band of Cu 2O core to the conduction band of ZnO shell, which exhibits an enhanced field emission property (see Fig. 13d ~ Fig. 13f). The Cu2O–ZnO p–n heterojunction greatly reduces the recombination of electron–hole pairs. Large quantities of free electrons from Cu2O can easily move along the bend energy band or jump into the interfacial states and continuously inject into ZnO, and then emit to a vacuum, which shows that the increased emission sites of the Cu2O–ZnO nanobrushs are more than that of the Cu2O nanoneedles (see Fig. 13g).

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have demonstrated that in situ loading of ultra-small Cu2O particles on TiO2 nanosheets can enhance the visible-light photoactivity.237 Other TiO2–Cu2O nanocomposites with increase the visible light absorption and photocatalytic performance are also been investigated.238-240

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capability to design necessary structures for expanding their potential applications. Coupling polyhedral Cu2O with Co3O4 nanoparticles was the most effective to avoid agglomerate formation of polyhedral Cu2O particles.241 Comparisons of the catalytic reactivity of Cu2O decorated with Co3O4 nanoparticles with different sizes and shapes for hydrogen evolution from ammonia borane hydrolysis suggested that the size of Co3O4 nanoparticles is more important than the shape to display high catalytic reactivity. Similarly, the photoelectrochemical and photoelectrocatalytic mechanisms of ntype TiO2 nanoparticles decorated on p-type Cu2O substrate are imperative to investigate. 3.3 Hybrid Cu2O–CuO heterogeneous nanostructures

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Fig.14 (a) and (b) Typical SEM images of Cu2O−TiO2 nanotube arrays prepared by the ultrasonication-assisted sequential chemical bath deposition technique. (c) TEM image of a Cu2O−TiO2 nanotube array (top view). (d) HRTEM image of the Cu2O−TiO2 architecture. Reprinted with permission from ref. 225. Copyright RSC 2013.

Fig.15 Band edges of the (TiO2)2(Cu2O) alloy and anatase TiO2 relative to the vacuum level. The green dot represents the hydrogen evolution potential, while the blue one represents the oxygen evolution potential. The insert is the atomic structures of (TiO2)2(Cu2O) alloys, the small red balls are O, the blue ones are Cu, while the Ti ions are located at the center of light blue octahedra. Reprinted with permission from ref. 219. Copyright RSC 2013.

Notably, Xiang and coworkers have investigated the stable structures of (TiO2)x(Cu2O)y solid-solutions with different compositions using a global optimization evolutionary algorithm, and examine their electronic properties by first-principles calculations.219 Their findings suggest predicted that (TiO2)2(Cu2O) are suitable for visible-light-driven photoelectrochemical water splitting applications due to their good optical absorption as well as their suitable band edge potentials (see Fig. 15). The layered structure of (TiO2)2(Cu2O) is expected to lead to high stability in aqueous solutions. 219 Therefore, better understanding of the controls of (TiO2)x(Cu2O)y solid-solution at the nanometer scale would bring about new This journal is © The Royal Society of Chemistry [year]

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Theoretically, Cu2O can be easily oxidized to form Cu2O@CuO core/shell structures in the oxygen condition due to the chemical valence of Cu(I).242 Moreover, CuO would be transformed into Cu2O by reduction principle. Therefore, the controllable synthesis of CuO–Cu2O heterojunctions is imperative for expanding the potential applications of Cu2O crystals. As expected, hybrid Cu2O–CuO heterogeneous nanostructures with improved performances have also been reported.242-247

Fig.16 A schematic illustration of the two-step synthesis of hybrid Cu2O−CuO nanorod arrays for solar photoelectrosynthesis of CH3OH from CO2: (1) thermal growth of CuO nanorods on a Cu foil and (2) cathodic electrodeposition of Cu2O for selected time periods from a cupric lactate solution, pH 9 (a). Morphology/composition of a Cu2O−CuO nanorod is sketched on the right side of panel (a). SEM images of thermally grown CuO nanorods before (b) and after Cu2O electrodeposition on them for 1 (c), 10 (d) and 30 min (e) respectively. (f) Energy band diagram of hybrid Cu2O−CuO nanorod arrays for solar photoelectrosynthesis of CH3OH from CO2. Semiconductor band edges and redox potentials are shown vs. the SHE ref. electrode. CB: conduction band; VB: valence band. Reprinted with permission from ref. 243. Copyright RSC 2013.

Recently, it has been demonstrated that solar photoelectronsynthesis of methanol can be driven by hybrid Cu2O–CuO semiconductor nanorod arrays for the first time.243 The Cu2O– Journal Name, [year], [vol], 00–00 | 13

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Moreover, the Cu2O–CuO heterogeneous structures show better catalytic activity towards catalytic oxidation of carbon monoxide (CO). The CO oxidation catalyzed by the CuO thin film restructured on different surface of Cu2O can involve different types of catalytically active sites, exhibiting different catalytic performance.242 Based on the anisotropic surfaces of Cu2O crystals, a broad range of novel hybrid Cu2O-CuO nanostructures with improved CO oxidation properties will be controllably designed and synthesized.

Fig.18 (a) TEM image of typical Fe3O4@C@Cu2O nanocomposites. Reprinted with permission from ref. 254. Copyright RSC 2014. (b) SEM image of typical Fe3O4−Cu2O−PANI nanocomposites. Reprinted with permission from ref. 255. Copyright RSC 2011. (c) and (d) SEM images of pine cone-like Fe3O4@Cu2O−Cu porous nanocomposites. Reprinted with permission from ref. 256. Copyright RSC 2014.

In addition to the above mentioned Cu2O–ZnO, Cu2O–TiO2 and Cu2O–CuO heterostructures, Cu2O–SnO,250 Cu2O–RuOx,251 Cu2O–CeO2,252 Cu2O–SiO2,253 and Cu2O–SrTiO3,254 were also investigated. Improved performances in photocatalysts and sensors have been observed in these heterostructures. Besides the binary systems, ternary composites with enhanced performances have also been synthesized.255-261 For example, magnetic Fe3O4@C@Cu2O with a bean-like core/shell nanostructure has been synthesized by a self-assembly approach (see Fig. 18a), and the bean-like core/shell nanocomposite exhibits universal and powerful visible-light-photocatalytic activity for the degradation of Rhodamine B, methyl orange, and alizarin red relative to commercial Cu2O.255 Multifunctional Fe3O4–Cu2O–polyaniline nanocomposite (see Fig. 18b) with room temperature superparamagnetism, excellent absorption ability and superhydrophobic and lipophilic property has been demonstrated.256 A stable, environmentally friendly and photomagnetic difunctional pine cone-like Fe3O4@Cu2O–Cu porous nanocomposite (see Fig. 18c and Fig. 18d) is also an ideal candidate in water treatment and environmental cleaning as well as in magnetic application.257 Moreover, the investigations of CuO–Cu2O–Ni nanocapsules,258 Cu2O–CuO–TiO2 core/shell nanowire arrays,259 Cu–Cu2O–TiO2 catalyst,260 TiO2–Pt– Cu2O,261 α–Fe2O3@SnO2@Cu2O heterostructures,262 were also achieved.

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CuO nanorod arrays were prepared on Cu substrates by a twostep approach consisting of the initial thermal growth of CuO nanorods followed by controlled electrodeposition of p-type Cu2O crystallites on their walls (see Fig. 16a). SEM images of thermally grown CuO nanorods before and after Cu 2O electrodeposition on them for different reaction time are shown in Fig. 16b ~ Fig. 16e. Fig. 16f displays the hypothetical energy band diagram and mechanism of hybrid Cu2O–CuO nanorod arrays for solar photoelectrosynthesis of CH3OH from CO2. It can be seen that the VB edge of CuO is located at a more positive potential than the corresponding level in Cu2O in full agreement with the photocurrent–potential response of a hybrid Cu2O–CuO nanorod electrode, so the differences in the band edges of the two oxides facilitate the transfer of photogenerated electrons from the Cu2O shells to the CuO cores. Moreover, the photogenerated electrons in Cu2O are also able to be directly transferred to CO2 because the Cu2O shell is also in contact with the electrolyte. This double pathway for injection of photoelectrons into CO2 likely leads to an enhanced photoelectrochemical performance of Cu2O–CuO nanorod array relative to a single Cu2O film.243 Moreover, highly stable and porous Cu2O–CuO cubes with enhanced gas sensing properties have been successfully synthesized by the calcination of the cupric oxalate and cubic Cu2O precursor at higher temperatures.244 Cu2O–CuO submicrospheres assembled by smaller particles show good selectivity to H2S gas as well as good stability and repeatability, can be easily prepared by a simple hydrothermal reduction method using Cu(CH3COO)2 as precursor.245 Cu2O–CuO hollow polyhedra with porous shells were fabricated by thermal decomposition of coordination compound [Cu3(btc)2]n (btc = benzene-1,3,5-tricarboxylate) polyhedra (see Fig.17a).246 When tested as anode materials for lithium-ion batteries, these hollow polyhedra exhibited a reversible lithium storage capacity. Notably, several approaches have been employed to synthesize hollow Cu2O cages by Oswald ripening or oxidation etching.73,80,85 Therefore, it is proposed that various Cu2O–CuO cages can be readily synthesized by partially oxidation of these morphologically hollow Cu2O cages. 2Cu2O + O2 + 4H2O → 4Cu(OH)2 (8) Cu(OH)2 + 2OH– → [Cu(OH)4]2– (9) [Cu(OH)4]2– → CuO + 2OH– + H2O (10) Typically, uniform Cu2O–CuO microframes have been prepared by an oxidation treatment of Cu2O microcubes in a hydrothermal condition (see Fig. 17b).247 The formation mechanism of the Cu2O–CuO microframes can be explained by the synergistic process of the Kirkendall effect and oxidation etching.49 In a hydrothermal condition, the surface of Cu 2O is firstly oxidized into divalent copper hydroxide (Cu(OH)2) in the presence of water and oxygen (see eqn (8)). However, the tetrahydroxo-cuprate(II) anion [Cu(OH)4]2− might be occurred from the copper hydroxide under a strong basic environment (see eqn (9)), because of the Jahn–Teller stabilization in square-planar copper(II) complexes.248 Then thermodynamically stable CuO is produced and precipitated to yield solid particles by the decomposition of [Cu(OH)4]2− species see eqn (10)). Thus CuO can be gradually precipitated on the inner wall of the hollow structure to form Cu2O–CuO frames. Hence, tailored synthesis of hollow Cu2O–CuO or pure CuO cages can be achieved.49,249

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Fig.17 (a) Left: A schematic illustration of the formation of Cu2O−CuO hollow polyhedra with a porous shell; Right: SEM images of typical Cu 2O−CuO hollow polyhedra. Reprinted with permission from ref. 246. Copyright RSC 2013 (b) SEM and TEM images of the shape-evolution from Cu2O to hybrid Cu2O−CuO cubes collected at different reaction stages; all the scale bars represent 1 µm. Reprinted with permission from ref. 247. Copyright RSC 2013. 5

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3.4 Hybrid Cu2O–Cu2O p–n homojunction The improvement of photo-induced charge separation is the key for light-harvesting systems in both photovoltaic and photoelectrochemical solar cells, which can convert light energy into electrical power or chemical fuel. To enhance the charge separation efficiency, an effective method is to construct appropriate junction structure within the semiconductors. Typically, Cu2O is synthesized as a p-type semiconductor.263 A p-type Cu2O based photodevices in which copper rich regions are usually fabricated at the Cu2O/metal or Cu2O/n-type semiconductor heterojunction, thus the performance of these devices were governed by the p-Cu2O/Cu0 Schottky junctions.264 Especially, the construction of a p–n Cu2O homojunction may have a unique advantage because the formation of Cu0 is not expected at the p-Cu2O/n-Cu2O rectifying junction where p-Cu2O and n-Cu2O layers have comparable chemical reactivities. Therefore, developing a facile and practical approach to fabricate highly photoactive n-type Cu2O electrodes can be beneficial as it This journal is © The Royal Society of Chemistry [year]

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will allow for building solar cells or photoelectrochemical cells based on a p–n Cu2O homojunction, which is predicted to achieve a higher efficiency than heterojunction solar cells constructed with p-type Cu2O.264 Currently, a handful of cases to prepare n-type Cu2O have been reported.265-269 Thus it enables people to construct various p–n Cu2O homojunction photoelectrodes for efficient visible light conversion.270 To date, only several p–n Cu2O homojunctions have been synthesized.271-273 These p–n Cu2O homojunction films were generally produced by two consecutive electrochemical deposition steps on subtracts. A better understanding of the effect of interfacial electric field in p–n Cu2O homojunction is very important because the built-in electric field in a junction region can promote the photo-induced charge separation and facilitate the charge transport to produce a high quantum yield.271,272 Xie and coworkers have reported that the p–n Cu2O homojunction films with controllable interfacial electric field were obtained by carefully adjusting the pH values of the electrolyte in each step of electrodeposition (see Fig. 19a [journal], [year], [vol], 00–00 | 15

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depositing an n-Cu2O layer on a p-Cu2O layer.273 The best cell assembled in this study achieved an efficiency of 1.06%, which is the highest efficiency reported to date for a Cu2O homojunction cell.274 However, the fabrication of p–n Cu2O homojunction solar cell is still thought to be a way to reach the theoretical efficiency of 12%.194 With continuing studies on optimizing the Fermi levels and conductivities of both the electrodeposited p- and nCu2O layers, the optimum contacts to Cu2O layers can be achieved, so the improvement of the p–n Cu2O homojunction solar cells is likely possible. In future, the hybrid p–n Cu2O– Cu2O homojunction might be used as a component for synthesizing perspective multilayer heterostructures.

Fig.19 SEM images of p–n Cu2O homojunction film (pH 7.0 + pH 4.9) (a), p–n Cu2O homojunction film (pH 8.0 + pH 4.9) (b), and p–n Cu2O homojunction film (pH 9.0 + pH 4.9) (c). (d) Mott-Schottky plots of p–n Cu2O homojunction films in the dark. (e) Photocurrent-potential characteristics in 0.5 M Na2SO4 solution (pH 6.7) of p–n Cu2O homojunction films under chopped (0.5 Hz) white light irradiation. The intensity of the white light is 100 mW/cm2, and the scan rate is 10 mV/s. (f) Concentrations of MV+• evolution over different p–n Cu2O homojunction films under visible light (λ > 400 nm) irradiation. Inset: Schematic diagram of photocatalytic reaction. Reprinted with permission from ref. 271. Copyright ACS 2013.

Although fascinating achievements in different types of hybrid Cu2O–metal oxide nanostructures have been reviewed above, some problems and challenges still exist and need to be solved. (i) To remarkably improve the performance of a hybrid Cu2Obased device, the tailored synthesis of Cu2O component with optimized size, morphology, dimension, crystal facet, and orientation is important. Although some “proof-of-concept” hybrid nanostructures were fabricated for studying the intrinsic properties of the devices, they are not possible for commercial applications. New integration technologies that can construct scalable and stable hybrid Cu2O–metal oxide nanostructures with good performances are still required. 275 (ii) For the solar energy conversion, Cu2O has relatively high carrier concentration, but the charge mobility and electric conductivity of Cu2O are poor. Especially, the high recombination of photo-induced charges and the poor solar efficiency have hindered the practical application. Therefore, both 16 | Journal Name, [year], [vol], 00–00

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the interfacial defect density and charge-transfer channel need to be well modulated by rational designing the structure of hybrid system. Further efforts are required to improve these characteristics by developing new growth route (e.g., selective doping of special chemical elements) and techniques for device design (e.g., use of special metal/oxide contacts according to energy band theory, which generally involves ultrathin protective layers of with strict thickness and composition on the Cu 2O surfaces). (iii) For the gas sensor and optoelectronic device applications, new technical approaches are necessary to directly grow uniform Cu2O aligned arrays onto flexible substrates with novel functionalities. (iv) The electronic structures and surface/interfacial properties of hybrid Cu2O-metal oxide heterogeneous nanostructures are still not well-known. Therefore, more advanced theoretical investigations should be implemented urgently. This journal is © The Royal Society of Chemistry [year]

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~Fig. 19c).271 The photoelectrochemical and surface photovoltage measurements were used to investigate the behaviors of photoinduced charge carriers in different p–n Cu2O homojunction films (see Fig. 19d and Fig. 19e). The results demonstrated that the p–n Cu2O homojunction film can exhibit higher charge separation efficiency, leading to the improved activity in photocatalytic reduction of methyl viologen (see Fig. 19f). In order to better understand the Fermi levels of the electrochemically grown polycrystalline p-Cu2O/n-Cu2O layers and maximize the overall cell performance, the back and front contacts of the Cu2O homojunction cells were systematically investigated.273 Choi and coworkers have electrochemically fabricated p–n Cu2O homojunction solar cells by consecutively

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It is well-known that solar energy is the largest source to availably convert into electricity through the photoelectric effect for directly use or storing in batteries.276 Carbon nanomaterials (graphene, carbon nanotubes (CNTs), and fullerene (C60)) are being largely investigated as smart supports for solar-to-energy conversion applications, due to their outstanding thermal and chemical stabilities, high conductivities, and high specific surface areas.277 When composited with semiconductor materials, these carbon nanostructures support act as good electron acceptors that can help improve charge separation within the semiconductors. As a result, the enhanced photocatalytic activities were achieved for semiconductor–carbon composites compared with the pristine semiconductor.278-287 So far, hybrid Cu2O–carbon nanostructure, as a promising composite, has attracted much attention because the application in energy conversion, sensing, catalyst and cancer therapy. The synthesis pathways and applications of reported hybrid Cu2O–carbon nanostructures are summarized in Table 3. In this section, we will summarize the reported strategies for controllable synthesis of Cu2O–carbon heterogeneous nanostructures. Firstly, recent advances in the synthesis of Cu2O– graphene heterogeneous nanostructures and their different applications will be especially elaborated. After this, we will discuss the design and synthesis of Cu2O–CNTs heterogeneous nanostructures. Finally, we will introduce the strategies which take advantage of different nanostructured carbon materials (such as carbon quantum dots, polypyrrole (PPy), carbon Vulcan XC-

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Graphene, a monolayer of sp2 hybridized carbon atoms arranged in a honeycomb lattice, is an important material with a range of unusual properties, including high mobility of charge carriers,288 large specific surface area,289 and excellent mechanical strength.290 Recently, graphene is attractive as a nanoscale building block for the synthesis of high-performance graphene-based composites, and extensive efforts have been employed to investigate the growth of nanoparticles on the graphene surface.291,292 In most cases, graphene oxide (GO), a layered material with unique oxygen-containing structure produced by oxidizing graphite, was taken as a sheet precursor for graphene.293 The oxygen functional groups on the GO surface would affect the synthesis and distribution of the nanoparticles on GO sheets. However, less study was considered to the relationship between the oxygen functional groups of GO and the surface structures of decorated nanoparticles. Cu2O is one of the most perspective candidate for studying Bose-Einstein condensation of excitons,294,295 because of the spin0 excitons in Cu2O. The electronic structure of Cu2O makes it a promising material with potential application in energy storage. The unusual electronic structures of both Cu2O and graphene inspired people to design and synthesize functional Cu2O-based graphene heterogeneous nanostructures.296

Fig.20 A graphical illustration of the synthesis of Cu2O−rGO nanocomposite. The GO sheets (a) were coordinated with Cu 2+ cations (b), and then converted to Cu(OH)2 on GO (c), and then Cu2O−rGO was obtained (d). The digital images show the color changes of the aqueous dispersions in each step. The inset is the high-magnification TEM image of the synthesized Cu2O−rGO nanocomposite. Reprinted with permission from ref. 293. Copyright RSC 2013.

General synthetic strategy of hybrid Cu2O–rGO nanostructures. It has demonstrated that the functional groups (hydroxyl and carboxyl groups) of GO can act as anchoring sites for the copper precursor. Recent studies have found that GO as a structural directing agent can be used to prepare unconventional polymeric matrices.297-299 Chen and co-workers have reported that the oxygen functional groups can induce the formation of Cu2O nanoparticles on the surface of reduced GO.293 This Cu2Oreduced GO (Cu2O–rGO) nanocomposite was prepared using different oxygenated GO by a wet-chemical method at low temperature. The formation of Cu2O–rGO is attributed to an interaction mechanism between Cu2+ cation and GO in aqueous solution. In a GO dispersion, Cu2+ ions tend to adsorb on the richoxygen atoms area of the GO sheet, leading to the formation of a

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high density of nanoparticles or even big microspheres at these sites after adding a precipitating agent. A schematic illustration of the synthetic pathway of Cu2O–rGO nanocomposites is shown in Fig. 20.293 A typical synthesis of Cu2O–rGO nanocomposites is as follows: The homogeneous suspension of exfoliated GO with sonication in water was prepared firstly (golden brown color, see Fig. 20a). Then, a blue copper(II) acetate monohydrate solution was added into the GO suspensions, resulting in a green aggregated mixture (see Fig. 20b). During this process, GO nanosheets have a strong interaction with Cu2+ ions as a result of their abundant oxygen functional groups, leading to the assembly of GO sheets into three-dimensional structure. Upon addition of sodium hydroxide aqueous solution, the above mixture turned dark blue because of

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and poor stability in oxidizing environments. To overcome these drawbacks, a few synthetic strategies aimed at controlling the size, crystal facet and stability of Cu2O nanocrystals have been reported.

Fig.21 (a) A schematic illustration of the synthesis of Cu2O−rGO nanocomposite; (b) SEM image of hybrid rhombic Cu 2O−rGO; (c) SEM image of hybrid cubic Cu2O−rGO. Reprinted with permission from ref. 305. Copyright RSC 2014.

GO supported Cu2O nanocrystals can exhibit shape-selective activity and stability.305 For example, Ren and coworkers have reported a novel aqueous synthesis route for the shape-controlled Cu2O nanocrystals that involves the preparation of an aqueous solution containing CuCl2, SDS, NH2OH· HCl, GO, and NaOH (see Fig. 21a). The hybrid Cu2O–GO nanocomposites exhibit improved shape uniformity and better dispersion as evident from the SEM images of both the rhombic 12-facet Cu2O architectures exposed with 12 {110} facets (see Fig. 21b) and cubic Cu2O architectures exposed with 6 {100} facets (see Fig. 21c). In this growth process, the dual role of GO as template and surfactant is essential for the formation of dispersed Cu2O nanoparticles. As reported, the negatively charged surface hydroxyl and carboxyl groups on the GO support facilitate their dispersion in aqueous solution, and favor binding with metal cations.303 The hydrolysis of Cu2+ precursor results in the nucleation of Cu(OH)2 precursor on the GO surface initially because of the strong electronic interaction between the cations and negatively charged functional groups. Upon addition of reactant NH2OH· HCl, the reduction of Cu2+ to Cu+ species occurred in the aqueous solution. As a result, the cubic Cu 2O–GO nanocomposites were formed at relatively low concentration of NH2OH· HCl, while rhombic Cu2O–GO nanocomposites were formed at relatively high concentration of NH2OH· HCl. Moreover, the GO support significantly improves the catalytic activity and stability of the Cu2O nanocrystals. The hybrid Cu2O– GO composite shows superior shape-dependent catalytic activity for both the photocatalytic reaction and the aqueous phase conversion of biomass-derived glycerol to lactic acid.305 Additionally, by taking advantages of the large surface area and high electronic conductivity of GO and high electrocatalytic activity of Cu2O, the fabricated hybrid Cu2O–GO composite could exhibit excellent performance as enzyme-free amperometric sensors.306 This journal is © The Royal Society of Chemistry [year]

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the formation of the blue Cu(OH)2 and the reduction of GO sheets at the same time (see Fig. 20c), as demonstrated in previous report.300 Afterwards, when the aqueous solution was heated, the Cu2O nanoparticles were prepared from the reduction of Cu(OH)2 by glucose (reducer), meanwhile the rGO sheets were also formed from the reduction of GO by glucose, and a dark red solid was formed (see Fig. 20d). The reduction of GO and deposition of Cu2O nanoparticles on rGO were carried out in one step. Finally, uniform Cu2O nanoparticles were spread on the surface of the rGO. The detailed chemical reactions that are involved in the growth of Cu2O-rGO heterostructures are suggested as follows: xGOa– + yCu2+ → (xGO-yCu)2y–ax (11) Cu2+ + 2OH– → Cu(OH)2 (12) GO + OH– → rGO (13) GO + nCu(OH)2 + mGlucose → Cu2O–rGO (14) Based on the above reaction mechanism, Cao and coworkers have successfully achieved ultra-small Cu2O nanoparticles monodispersely anchored on rGO.301 It can be found that the size of Cu2O nanoparticles on rGO is in a range of 5–8 nm as well as no aggregation of Cu2O nanoparticles. These Cu2O–rGO composites can afford high adsorption capacities for Rhodamine B and methylene blue. A reactive filtration film was assembled by the Cu2O–rGO composite, which can be applied to remove dye contaminants from waste water. Furthermore, Tran and co-workers have reported that the insitu growth and stabilization of Cu2O nanoparticles on graphene sheets are required to achieve a good p–n Cu2O–rGO junction, which can effectively improve the photocatalytic activity for hydrogen generation as well as the photostability of Cu2O.302 In this Cu2O–rGO composite, rGO acts as the electron acceptor to extract photogenerated electrons from Cu2O under visible light, leading to an enhanced charge separation within Cu 2O semiconductor, while limiting its self-photoreduction process. Hydrogen photogeneration activity and stability of the Cu2O– rGO composite in neutral aqueous solution were found to be significantly higher than those found for pristine Cu 2O. However, both higher rGO and lower rGO content have less harvesting efficiency. Increasing rGO content resulted in light absorption competition for Cu2O, whereas decreasing rGO content caused agglomeration of Cu2O. Both phenomena caused a decrease in the light harvesting efficiency of Cu2O that translated into lower catalytic efficiencies. Therefore, to achieve the highest activity for light-to-hydrogen conversion, the content of rGO within the composite should be optimized.302 Similarly, ultra-small Cu2O nanoparticles dispersed on rGO can be achieved by reducing copper acetate supported on graphite oxide using diethylene glycol as both solvent and reducing agent.303 The whole reaction was described as follows: Cu2+ + DEG + GO + Hydrothermal → Cu2O–rGO (15) Recently, a low-cost, fast, facile, green method, namely an ultrasound assisted approach, has been developed for the controlled synthesis of Cu2O–GO hybrid nanomaterials.304 The whole reaction was designed and carried out as below: Cu2+ + Glucose + GO + Ultrasound → Cu2O–rGO (16) Stable hybrid Cu2O–rGO nanostructures. Despite promising as catalytic materials, the major drawbacks of Cu2O nanocrystals include the rapid shape distortion under harsh reaction conditions

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hybrid architecture where porous three-dimensional framework structures interspersed among two-dimensional rGO sheets. Owing to high specific surface area and enhanced conductivity, the Cu2O–rGO mesocrystal achieved a higher sensitivity toward NO2 at room temperature, surpassing the performance of standalone systems of Cu2O nanowire networks and rGO sheets. The Cu2O–rGO mesocrystals not only provide an excellent model to study the 3D self-organization of 1D functional semiconductor nanowire but also open up new possibilities for designing GObased mesocrystals for various sensing applications.

Fig.22 (a) ~ (b) Different magnification TEM image of Cu 2O–FGS nanocomposite; (c) HRTEM images of an individual Cu 2O nanoparticle grown on FGS; (d) The dynamic H2S sensing behaviour of the Cu2O– FGS-based sensor device. Reprinted with permission from ref. 309. Copyright RSC 2013.

According to the formation mechanism as shown in eqn (11) ~ eqn (14), Chen and coworkers have synthesized stable Cu2O nanoparticles with the size of around 3 nm, which were uniformly and densely grown on functionalized graphene sheets (FGS).307,308 The distribution density of Cu2O nanoparticles can be easily controlled by FGS with different carbon and oxygen ratios (see Fig. 22a ~ Fig. 22c).309 Compared to bulk Cu2O, the as-synthesized Cu2O–FGS nanocomposite exhibits enhanced stability against oxidation in ambient atmosphere, which is attributed to not only finite-size effect, but also interfacial effect between Cu2O and FGS. Surfactant-free capped Cu2O nanoparticles grown on the FGS is favor of providing more active sites for the adsorption of gaseous molecules; while the FGS can not only be used instead of surfactant or ligand for synthesis of two dimensional nanocomposite, but also acted as a conducting network for promoting the electron transfer. Therefore, stable Cu2O–FGS nanocomposites show fantastic sensitivity toward H2S at room temperature (see Fig. 22d). 3D hybrid Cu2O–rGO nanostructures. Quasi-two-dimensional structure of GO exposed with abundant functional groups offers dual molecule-colloid properties,310 which elicits multivalent interaction with Cu2+ as well as polymer additive, both inducing and stabilizing the aggregation for subsequent particle-mediated crystallization.311 Inspired by this viewpoint, Fan and coworkers have prepared rGO-conjugated 3D Cu2O nanowire mesocrystals (see Fig. 23) using a one-pot hydrothermal treatment of copper(II) acetate in the presence of oanisidine and GO.312 The obtained octahedral Cu2O mesocrystals possess high intracrystal porosities as a result of highly oriented interpenetrating nanowire with high aspect ratios as building blocks. The formation mechanism is proposed as follows: First, GO-promoted agglomeration of amorphous spherical Cu2O nanoparticles by means of particle-mediated aggregation under diffusion-limited condition; Second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals with a high degree of orientation by Ostwald ripening; Third, large-scale selforganization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, leading to an integrated This journal is © The Royal Society of Chemistry [year]

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Fig.23 SEM images of octahedron Cu2O nanowire mesocrystals. (a) Overall product morphology of the octahedron Cu2O nanowire mesocrystals. (b) X-ray diffraction pattern of the Cu2O mesocrystals. The inset shows a schematic illustration of crystal structure of octahedron Cu2O nanowire mesocrystal, with crystal orientations of hexapod branching shown. (c) An octahedron Cu 2O mesocrystal along the [111] view, and (d) interior morphology with overlaid hexapod grid. (e−g) SEM images of rGO-Cu2O mesocystal composites of higher GO loading content. Reprinted with permission from ref. 312. Copyright ACS 2012.

Despite a number of reports focusing on the environmental and energy storage applications, so far little has been developed to explore the application of hybrid Cu2O–GO in biological systems. Wang and coworkers have synthesized and functionalize Cu2O– GO composite using biocompatible poly-(sodium 4styrensulfonate) (PSS) to render a novel water-dispersible hybrid for cancer therapy under both visible and near-infrared light in vitro.313 Experimentally, PSS-coated Cu2O–rGO composites were synthesized by the reduction of the GO aqueous dispersion in the presence of Cu(NO3)2, PSS, and hydrazine hydrate under reflux at high temperature. The average size of the Cu2O nanocrystals deposited on rGO sheets was about 4 nm. The material can stable as a homogeneous suspension in biological solutions. Under nearJournal Name, [year], [vol], 00–00 | 19

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infrared light irradiation, in vitro photothermal killing of both cancer and normal cells was demonstrated. Under visible light irradiation, it demonstrated in vitro selective photocatalytic killing of cancer cells. Hence, the PSS-coated Cu2O–rGO composites can be used as applicable cancer therapy agents. Based on the above discussions, low-cost and facilesynthesized Cu2O nanomaterials, in conjunction with more efficient GO-templated synthetic strategies, hold great perspective for the controlled synthesis of Cu2O–GO nanocomposites with potential applications in catalysts, sensors, cancer therapeutic agent as well as energy storage devices such as solar cells, and lithium-ion batteries (see Table 3).

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Due to the unusual one-dimensional hollow tubular structure, high specific surface area, and special chemical and electronic property, carbon nanotubes (CNTs) acted as supports for preparing nanosized catalysts is feasible.314 CNTs are largely inert, so the activation of their surfaces is essential. Thus it has motivated numerous investigations to improve metal nanoparticles dispersions on CNTs through functionalization of the carbon surface.315 The aromatic ring system of CNTs can be disrupted by the assistance of oxidation reagents including HNO3 or HNO3/H2SO4 mixture, thus the CNTs can be functionalized with groups such as hydroxyl, carboxyl and carbonyl, which can act as anchoring sites for metal oxide nanoparticles and induce the impregnation of small and large particles.316,317 Moreover, the grafting of chemical functionalities on the CNTs surfaces can impart negative charges, resulting in the creation of the electrostatic stability required for a colloidal dispersion, which will decrease the strong tendency to agglomerate because of their high surface energies. As a result, the unique chemical and electrical properties of CNTs can be transferred to the CNT-based composites. It has been demonstrated that the physical and chemical properties of the CNTs deposited nanoparticles could be improved to obtain desired performances.316,317 Therefore, more and more investigations of CNTs have focused on depositing metal or metal oxide nanoparticles onto their surfaces to form highactivity CNTs-based nanocomposites. Copper oxide can exhibit an excellent performance in amperometric sensing,318-320 so it is expected that Cu2O–CNTs hybrid nanostructures will be greater ability to promote electrontransfer and large specific surface area, which can be potentially used to prepare high-performance amperometric sensors. Although there are several complex and high-cost methods for the synthesis of Cu2O/multi-walled carbon nanotubes (MWCNTs) nanocomposites,321,322 the sensing properties of the as-prepared products are often limited because of the poor deposition of Cu2O nanoparticles on the MWCNTs surfaces. Therefore, it is highly desirable to achieve the synthesis of uniform Cu2O nanoparticles dispersed on the surface of MWCNTs. Cu2O–MWCNTs nanocomposites were successfully prepared in large quantities by a new fixure-reduction method under low temperature.323 The Cu2O–MWCNTs modified electrode displays high electrocatalytic activity towards the oxidation of glucose. During this synthesis process, MWCNTs were chemically acidified by circumfluence agitation in a mixture of sulfuric acid and nitric acid at first. Second, copper ions were fixed onto the 20 | Journal Name, [year], [vol], 00–00

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surface of MWCNTs by chemical and physical adsorption. Third, the copper ions fixed on the surface of the MWCNTs were reduced by sodium sulfite. Finally, the Cu2O–MWCNTs nanocomposites were synthesized. Furthermore, Zhang and coworkers have elucidated the growth mechanism of Cu2O– MWCNTs (see Fig. 24) synthesized by a spontaneous redox reaction.324 During this formation process, it has been found that defect densities of MWCNTs and pH value of the reaction system are crucial for the spontaneous redox, and high defect density is thermodynamically and dynamically favorable to the formation of Cu2O–MWCNTs. For spontaneous redox, Cu2O nanoparticles are located on the defect sites of MWCNTs, and a strong interaction is formed between defects and Cu2O, which could promote electron-transfer in catalyst. So the Cu2O–MWCNTs nanocomposite shows a catalytic performance superior to that of the catalyst prepared by a hydrothermal method or other methods in the hydrogenation of benzene to cyclohexane. However, the above mentioned methods involved harshly tangled MWCNTs, which might decrease the electrical conductivity and result in the poor sensitivity for glucose detection.

Fig.24 TEM images of three kinds of Cu2O nanoparticles located on MWCNTs. Reprinted with permission from ref. 324. Copyright ACS 2010.

Huang and coworkers have successfully prepared a type of nanospindle-like Cu2O/straight multi-walled carbon nanotubes (SMWNTs) hybrid nanostructure by a precipitation method, which can exhibit an enzyme-free glucose sensor with high electrocatalytic activity and excellent reproducibility.325 In this hybrid system, SMWNTs act as the conductions for dispersing and connecting nanospindle-like Cu2O catalysts. Comparing with the tangled MWCNTs widely applied in nonenzymatic sensors, SMWNTs can be more easily dispersed in solution after mild sonication pretreatment because of the weaker van der waals attraction force between the SMWNTs bundles, and keep high electrical conductivity. Moreover, Cu2O nanospindles can be homogeneously distributed in the SMWNTs conductive networks, which can be easily accessing to glucose, and amplifying the electrochemical signal for glucose determination. Thus the formation of an efficient conductive network between Cu2O This journal is © The Royal Society of Chemistry [year]

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nanospindles and SMWNTs can promote the electron transfer rate and improve the sensitivity of glucose detection. Hence, this nanocomposite combined the advantageous features of both SMWNTs and nanospindle-like Cu2O, and greatly improved the electrocatalytic property of glucose detection. However, the size of nanospindle-like Cu2O is much larger, which will lose high electrical conductivity and high surface energy, thus the sensitivity for glucose detection is still difficulty to be completely enhanced. Therefore, the unique dispersion of SMWNTs inspired us to design and synthesize ultra-small Cu2O–SMWNTs nanocomposites in the future. 4.3 Other hybrid Cu2O–carbon heterogeneous nanostructures

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As a novel class of recently discovered carbon nanostructures, carbon quantum dots (CQDs) can exhibit promising photophysical or chemical properties (photoinduced electron transfer and redox properties, luminescence and so on).326,327 Especially, the up-converted photoluminescence (PL) of CQDs offers the possibility to construct a CQDs-based near infrared (NIR) and IR light (collectively called (N)IR) sensitive photocatalytic system. In light of its relatively narrow band gap, Cu2O was a potential candidate for designing the CQDs-based (N)IR light sensitive photocatalyst.

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Fig.25 (a–c) SEM, (inset of a) TEM, (d) HRTEM images of the Cu2O−CQDs composite prepared by one-step ultrasonic treatment, (e) SEM image of a single Cu2O−CQDs particle for energy dispersive X-ray spectrum (EDX); (f–h) EDX element mapping data of Cu, O and C elements throughout a single Cu2O−CQDs particle; (i) a schematic photocatalytic mechanism for the Cu2O−CQDs composite under (N)IR light irradiation. Reprinted with permission from ref. 328. Copyright RSC 2012.

Liu and coworkers have reported a one-step ultrasonic method for the fabrication of hybrid Cu2O–CQDs composites (see Fig. This journal is © The Royal Society of Chemistry [year]

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25a~Fig. 25h).328 When the Cu2O–CQDs photocatalyst is illuminated (see Fig. 24i (1)), the protruding nanostructures allow multiple reflections of (N)IR light between the vacant spaces of these protruding particles, leading to a better use of the source light and therefore exhibit an enhanced photocatalytic performance.329 Furthermore, CQDs can absorb (N)IR light ( >700 nm), and then emit shorter wavelength light (390 ~ 564 nm) as a result of up-conversion, which in turn further excites Cu2O to form electron/hole pairs (see Fig. 25i (2)). The electronhole pairs can react with the adsorbed oxidants/reducers (usually O2/OH–) to generate active oxygen radicals, which subsequently results in the photodegradation of organic dye. Significantly, when CQDs are attached onto the surface of Cu2O semiconductors, the position of the CQDs band edge permits the transfer of electrons from the Cu2O surfaces, leading to the charge separation, and hindering the recombination of electronhole pairs.330 Thus the electrons will be shuttled freely along the conducting network of CQDs, and the longer-lived holes on the Cu2O will account for the higher activity of the Cu2O–CQDs composite photocatalyst. Therefore, the Cu2O–CQDs could use (N)IR light to enhance the photocatalytic activity based on the synergistic effect of the superior light reflecting ability of the Cu2O nanostructures and the up-converted PL property of CQDs.

Fig.26 (a) SEM image of Cu2O/C60 heterogeneous architectures, reprinted with permission from ref. 331. Copyright ACS 2012; (b) SEM image of Cu2O@PPy nanowires. Reprinted with permission from ref. 332. Copyright RSC 2009.

Besides the above mentioned Cu2O–GO, Cu2O–CNTs, Cu2O– CQDs nanocomposites, a few other Cu2O–carbon nanomaterials with special applications have been synthesized (see Fig. 26). For example, hybrid Cu2O diode with orientation-controlled C60 polycrystal has been synthesized by a vacuum evaporation approach.331 Spontaneous self-assembly of Cu2O@PPy nanowires have been achieved by hydrothermal reduction of commercial CuO by pyrrole monomers in solution.332 Cu2O/carbon Vulcan XC-72 as non-enzymatic sensor for glucose determination has been synthesized using NaBH4 as the reducing agent by an impregnation method.333 An efficient and reusable Cu2O–PPh3–TBAB system for the cross-couplings of aryl halides and heteroaryl halides with terminal alkynes has also been reported.334 As mentioned above, coupling Cu2O with different carbon nanostructures (such as CNTs, GO, and CQDs) can remarkably promote electron-transfer reactions to achieve the desired properties compared to the bare Cu2O components. The rapid emergence of various binary Cu2O–carbon heterogeneous nanostructures is expected to offer new opportunities to expand our understanding of the fundamental significance of Cu2O crystals as well as to enhance the potential applications of the Journal Name, [year], [vol], 00–00 | 21

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Cu2O-based nanocomposites. However, the intrinsic factors related to the kinetically controlled synthesis of well-morphological Cu2O with highenergy facets decorated on carbon substrates should be elucidated thoroughly, and the relationship between carbon-copper-oxygen interfacial structure and performance is unclear. Furthermore, the development of ternary or multiple Cu2O–carbon-based nanocomposites with multi-performances is still a challenge. Decorating Cu2O@metal/metal oxide on carbon substrates can reduce the damage of Cu2O component during the chemical reactions, and further enhance the stability of the nanostructures. Especially, an unique Cu2O–metal–graphene stack has been demonstrated to harness charger flow for photocatalysis, which will open new windows to rationally designing hybrid materials for solar energy conversion.335 In addition, other layered 2-D nanomaterials similar to graphene (such as boron nitride and molybdenum disulfide) decorated with Cu2O should be further investigated.

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Hybrid Cu2O-based nanostructure has become a rapidly growing research field due to its significant contribution to both fundament study and multifunctional application. In this review, the synthesis strategies and the principles for enhancing performances have been demonstrated for different types of hybrid Cu2O-based nanostructures, including hybrid Cu2O–metal nanostructure (Cu@Cu2O, Au@Cu2O, Ag@Cu2O core/shell architecture and Cu, Au, Ag decorated Cu2O heterostructure), hybrid Cu2O–metal oxide nanostructure (including Cu2O–ZnO, Cu2O–TiO2, Cu2O–CuO heterojunction and Cu2O–Cu2O homojunction) and hybrid Cu2O–carbon nanostructure (including Cu2O–rGO, Cu2O–CNTs and Cu2O–CQDs). So far, novel hybrid Cu2O-based nanostructures with improved performances (such as solar cell, carbon monoxide oxidation, photocatalyst, field emission, sensor, template and so on) have attracted much attention. Although significant progress has been made in the fabrication and application of various hybrid Cu2O-based nanostructures, several challenges and perspective research directions still need to be addressed. Rapid advancements in nanoscience and nanotechnology have enabled the fabrication of hybrid Cu2O-based nanostructures with tunable characteristics. Actually, the rational design and sophisticated synthesis of morphological Cu2O-based nanostructure has been paid more attention. Various synthetic strategies have been employed to prepare hybrid Cu2O-based nanostructures with desired morphologies and even multidimensional interfaces to meet the specific requirements for practical applications. From this sense, the concept of “morphology-dependent nanostructure” provides a top priority for finely tuning the physiochemical performances. However, some promising research directions should be proposed. For example, polyhedral Cu2O nanostructures wholly exposed with high-energy surfaces could be introduced into the hybrid Cu2Obased heterogeneous architectures, especially for the hybrid metal@Cu2O core/shell and metal nanoparticles decorated Cu2O heterojunctions. Furthermore, much attention should be paid to synthesize hybrid Cu2O-based nanostructures with highly uniform one-dimensional or two-dimensional Cu2O building 22 | Journal Name, [year], [vol], 00–00

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blocks. The application of hybrid Cu2O-based templates for synthesizing multicomponent heterostructures or hollow cages should be further considered. Previously, we have demonstrated that Cu2O-templated growth of definable nanostructures is of special interest from both theoretical and practical perspectives, and different hollow cages, including metal, metal oxide and copper sulfide, can be selectively designed and synthesized.56 Inspired by this Cu2O-templated strategy, hybrid Cu2O-based templates can also be expanded to synthesize a broad range of new binary and ternary Cu2O-based heterostructures. It can be confidently anticipated that the syntheses engineering on new M– Cu2O–metal, M–Cu2O–metal oxide and M–Cu2O–carbon (M = sulphide, selenide, metal oxide, and metal) heterogeneous nanostructures will be successfully achieved through Cu2O–metal, Cu2O–metal oxide and Cu2O–carbon heterogeneous templates, respectively. Subsequently, the novel multi-walled or multicompositional hollow york/shell nanostructures can be obtained after removing the Cu2O components. Significantly, in-depth investigations of the electronic structures and interfacial properties of hybrid Cu2O-based nanostructures could consult us to rationally design and synthesize functional Cu2O-based nanocomposites with exceptional performances. However, some future research directions towards to the modification of the electronic structures and interfacial properties of hybrid Cu2O-based nanostructures should be highlighted. (i) The illumination of the facet-dependent surface/interface properties to substantially promote the performances is a significant task, and the concept of “surface heterojunction” should be further applied in the design and fabrication of novel heterojunctions. Moreover, we would like to emphasize that more advanced theoretical investigations and experimental studies on the electronic structures and interfacial properties of hybrid Cu2O-based nanostructures should be conducted to offer a better understanding of the structure-related properties and to further develop the interface-dependent applications. (ii) Selected-doping and selected-heterostructuring on specific facets of Cu2O are very meaningful to improve the electronic conductivity and charge separation for enhancing the photochemical performances, which would also bring about new capability to design necessary structures for potential applications. Especially, the work functions of metal and different crystal facets of Cu2O, and the conduction band minimum and the valance band maximum of Cu2O and decorated semiconductors should be considered, which directly determines the appropriate selection of compatible cocatalysts for charge separation. (iii) Rational design and selection of ultrathin protective layers with strict thickness and composition on the Cu2O surfaces should be taken seriously, which can effectively enhance the structural stability of the nanocomposite. Moreover, the surface restructuring of Cu2O to in-situ form new CuO or Cu thin films during oxidation or reduction condition should be considered for optimizing the Cu2O-based energy conversion systems. (iv) With regard to the Cu2O component in a hybrid system, the synthesis of low-cost, uniform-size, well-shaped, welldispersed, and high-purity nanoparticles still remains an obstacle. Therefore, attention should be employed on the exploration of This journal is © The Royal Society of Chemistry [year]

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new synthetic routes to prepare the desirable Cu2O nanoparticles on a design substrate. Overall, the investigation of hybrid Cu2O-based nanocomposites with tailored features offers a meritorious platform for uncovering the relationship of structure-propertyperformance and accelerating the practical applications. Given the continuous development of the growth and synthesis techniques, more novel hybrid Cu2O-based nanostructures with interesting properties and promising applications will be achieved in the near future.

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S. D. Sun would like to acknowledge the support by the National Science Foundation of China (NSFC No. 51302213 and 51272209), Shaanxi Province Science and Technology Innovation Team Project (2013KCT-05), Doctoral Fund of Ministry of Education of China (No. 20120201120051), and Fundamental Research Funds for the Central Universities of China (2014gjhz31).

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Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 E-mail: [email protected] (S. D. Sun) 1 X. B. Chen, C. Li, M. Grätzel, R. Kostecki and S. S. Mao, Chem. Soc. Rev., 2012, 41, 7909–7937. 2 X. B. Chen, S. H. Shen, L. J. Guo and S. S. Mao, Chem. Rev., 2010, 110, 6503–6570. 3 C. Burda, X. B. Chen, R. Narayanan and M. A. El-Sayed, Chem. Rev., 2005, 105, 1025–1102. 4 A. I. Hochbaum and P. D. Yang, Chem. Rev., 2010, 110, 527–546. 5 H. K. Wang and A. L. Rogach, Chem. Mater., 2014, 26, 123–133. 6 X. Wang, W. Tian, T. Y. Zhai, C. Y. Zhi, Y. Bando and D. Golberg, J. Mater. Chem., 2012, 22, 23310–23326. 7 Q. F. Zhang, E. Uchaker, S. L. Candelaria and G. Z. Cao, Chem. Soc. Rev., 2013, 42, 3127–3171. 8 Z. Li, Q. Sun, X. D. Yao, Z. H. Zhu and G. Q. Lu, J. Mater. Chem., 2012, 22, 22821–22831. 9 L. Q. Jing, W. Zhou, G. H. Tian and H. G. Fu, Chem. Soc. Rev., 2013,42, 9509–9549. 10 X. Liu and M. T. Swihart, Chem. Soc. Rev., 2014, 43, 3908–3920. 11 J. G. Yu, J. X. Low, W. Xiao, P. Zhou, and M. Jaroniec, J. Am. Chem. Soc., 2014, 136, 8839–8842. 12 Y. Li and W. J. Shen, Chem. Soc. Rev., 2014, 43, 1543–1574. 13 H. B. Wu, J. S. Chen, H. H. Hng and X. W. Lou, Nanoscale, 2012, 4, 2526–2542. 14 X. W. Lou, L. A. Archer and Z. C. Yang, Adv. Mater., 2008, 20, 3987–4019. 15 Z. Y. Wang, L. Zhou and X. W. Lou, Adv. Mater., 2012, 24, 1903– 1911. 16 L. C. Chen, Mater. Sci. Semicond. Process., 2013, 16, 1172–1185. 17 P. Thiyagarajan, H. J. Ahn, J. S. Lee, J. C. Yoon and J. H. Jang. Small, 2013, 9, 2341–2347. 18 Y. J. Lin, G. B. Yuan, R. Liu, S. Zhou, S. W. Sheehan and D. W. Wang, Chem. Phys. Lett., 2011, 507, 209–215. 19 R. S. Selinsky, Q. Ding, M. S. Faber, J. C. Wright and S. Jin, Chem.

This journal is © The Royal Society of Chemistry [year]

80

85

90

95

100

105

110

View Article Online

DOI: 10.1039/C5NR02178B

Soc. Rev., 2013, 42, 2963–2985. 20 D. Savateeva, D. Melnikau, V. Lesnyak, N. Gaponik and Y. P. Rakovich, J. Mater. Chem., 2012, 22, 10816–10820. 21 R. Smith, B. Liu, J. Bai and T. Wang, Nano Lett., 2013, 13, 3042– 3047. 22 B. P. Khanal, A. Pandey, L. Li, Q. L. Lin,W. K. Bae, H. M. Luo, V. I. Klimov and J. M. Pietryga, ACS Nano, 2012, 6, 3832–3840. 23 X. H. Zhao, P. Wang and B. J. Li, Nanoscale, 2011, 3, 3056–3059. 24 Y. Q. Qu and X. F. Duan, Chem. Soc. Rev., 2013, 42, 2568–2580. 25 Y. Q. Qu and X. F. Duan, J. Mater. Chem., 2012, 22, 16171–16181. 26 H. Pang, F. Gao and Q. Y. Lu, Chem. Commun., 2009, 1076–1078. 27 D. Barreca, G. Carraro, V. Gombac, A. Gasparotto, C. Maccato, P. Fornasiero and E. Tondello, Adv. Funct. Mater., 2011, 21, 2611–2623. 28 H. G. Zhang, Q. S. Zhu, Y. Zhang, Y. Wang, L. Zhao and B. Yu, Adv. Funct. Mater., 2007, 17, 2766–2771 29 A. Paracchino, V. Laporte, K. Sivula, M. Grätzel and E. Thimsen, Nature. Mater., 2011, 10, 456–461. 30 Q. Hua, T. Cao, H. Z. Bao, Z. Q. Jiang and W. X. Huang, ChemSusChem, 2013, 6, 1966–1972. 31 X. Wang, C. Liu, B. J. Zheng, Y. Q. Jiang, L. Zhang, Z. X. Xie and L.S. Zheng, J. Mater. Chem. A, 2013, 1, 282–287. 32 R. N. Briskman, Sol. Energy Mater. Sol. Cells, 1992, 27, 361–368. 33 P. Poizot, S. Laruelle, S. Grugeon, L. Dupont and J. M. Taracon, Nature, 2000, 407, 496–499. 34 W. P. Kang, F. L. Liu, Y. L. Su, D. J. Wang and Q. Shen, CrystEngComm, 2011, 13, 4174–4180. 35 A. Chen, S. Haddad, Y. C. Wu, T. N. Fang, S. Kaza and Z. Lan, Appl. Phys. Lett., 2008, 92, 013503. 36 J. W. Nai, S. Q. Wang , Y. Bai and L. Guo, Small, 2013, 9, 3147–3152. 37 F. Hong, S. D. Sun, H. J. You, S. C. Yang, J. X. Fang, S. W. Guo, Z. M. Yang, B. J. Ding and X. P. Song, Cryst. Growth Des., 2011, 11, 3694– 3697. 38 J. N. Gao, Q. S. Li, H. B. Zhao, L. S. Li, C. L. Liu, Q. H. Gong and L. M. Qi, Chem. Mater., 2008, 20, 6263–6269. 39 S. D. Sun, D. C. Deng, C. C. Kong, X. P. Song and Z. M. Yang, Dalton Trans., 2012, 41, 3214–3222. 40 S. D. Sun, X. P. Song, C. C. Kong, S. H. Liang, B. J. Ding and Z. M. Yang, CrystEngComm, 2011, 13, 6200–6205. 41 S. D. Sun, X. P. Song, C. C. Kong, D. C. Deng and Z. M. Yang, CrystEngComm, 2012, 14, 67–70. 42 S. D. Sun, X. P. Song, D. C. Deng, X. Z. Zhang and Z. M. Yang, Catal. Sci. Technol., 2012, 2, 1309–1314. 43 S. D. Sun, S. R. L. Wang, D. C. Deng, and Z. M. Yang, New J. Chem., 2013, 37, 3679–3684. 44 S. D. Sun, D. C. Deng, X. P. Song and Z. M. Yang, Phys.Chem. Chem. Phys., 2013, 15, 15964–15970. 45 J. H. Sohn, H. G. Cha, C. W. Kim, D. K. Kim and Y. S. Kang, Nanoscale, 2013, 5, 11227–11233. 46 Z. Y. Wang, D. Y. Luan, C. M. Li, F. B. Su, S. Madhavi, F. Y. C. Boey and X. W. Lou, J. Am. Chem. Soc., 2010, 132, 16271–16277. 47 J. W. Nai, Y. Tian, X. Guan and L. Guo, J. Am. Chem. Soc., 2013, 135, 16082–16091. 48 Z. Y. Wang, D. Y. Luan, F. Y. C. Boey and X. W. Lou, J. Am. Chem. Soc., 2011, 133, 4738–4741. 49 J. C. Park, J. H. Kim, H. Kwon and H. Song, Adv. Mater., 2009, 21, 803–807. 50 Y. Cudennec and A. Lecerf, Solid State Sci., 2003, 5, 1471–1474. 51 S. D. Sun, C. C. Kong, L. Q. Wang, S. C. Yang, X. P. Song, B. J. Ding,

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10

15

20

25

30

35

40

45

50

55

and Z. M. Yang, CrystEngComm, 2011, 13, 1916–1921. 52 C. H. Kuo, Y. T. Chu, Y. F. Song and M. H. Huang, Adv. Funct. Mater., 2011, 21, 792–797. 53 H. L. Cao, X. F. Qian, C. Wang, X. D. Ma, J. Yin and Z. K. Zhu, J. Am. Chem. Soc., 2005, 127, 16024–16025. 54 W. X. Zhang, Z. X. Chen and Z. H. Yang, Phys. Chem. Chem. Phys., 2009, 11, 6263–6268. 55 S. H. Jiao, L. F. Xu, K. Jiang and D. S. Xu, Adv. Mater., 2006, 18, 1174–1177. 56 S. D. Sun and Z. M.Yang, Chem. Commun., 2014, 50, 7403–7415. 57 H. G. Zhang, Q. S. Zhu, Y. Zhang, Y. Wang, L. Zhao and B. Yu, Adv. Funct. Mater., 2007, 17, 2766–2771. 58 Y. S. Luo, S. Q. Li, Q. F. Ren, J. P. Liu, L. L Xing, Y. Wang, Y. Yu, Z. J. Jia and J. L. Li, Cryst. Growth Des., 2007, 7, 87–92. 59 H. W. Zhang, X. Zhang, H. Y. Li, Z. K. Qu, S. Fan and M. Y. Ji, Cryst. Growth Des., 2007, 7, 820–824. 60 L. N. Guan, H. Pang, J. J. Wang, Q. Y. Lu, J. Z. Yin and F. Gao, Chem. Commun., 2010, 46, 7022–7024. 61 X. Y. Meng, G. H. Tian, Y. J. Chen, Y. Qu, J. Zhou, K. Pan, W. Zhou, G. L. Zhang and H. G. Fu, RSC Adv., 2012, 2, 2875–2881. 62 S. K. Li, X. Guo, Y. Wang, F. Z. Huang, Y. H. Shen, X. M. Wang and A. J. Xie, Dalton Trans., 2011, 40, 6745–6750. 63 W. Z. Wang, G. H. Wang, X. S. Wang, Y. J. Zhan, Y. K. Liu and C. L. Zheng, Adv. Mater., 2002, 14, 67–69. 64 Y. J. Xiong, Z. Q. Li, R. Zhang, Y. Xie, J. Yang and C. Z. Wu, J. Phys. Chem. B, 2003, 107, 3697–3702. 65 Y. K. Hsu, C. H. Yu, Y. C. Chen and Y. G. Lin, RSC Adv., 2012, 2, 12455–12459. 66 Y. W. Tan, X. Y. Xue, Q. Peng, H. Zhao, T. H. Wang and Y. D. Li, Nano Lett., 2007, 7, 3723–3728. 67 X. Y. Liu, R. Z. Hu, S. L. Xiong, Y. K. Liu, L. L. Chai, K. Y. Bao and Y. T. Qian, Mater. Chem. Phys., 2009, 114, 213–216. 68 C. H. Lu, L. M. Qi, J. H. Yang, X. Y. Wang, D. Y. Zhang, J. L. Xie and J. M. Ma, Adv. Mater., 2005, 17, 2562–2567. 69 J. Shi, J. Li, X. J. Huang and Y.W. Tan, Nano Res., 2011 4, 488–493. 70 C. H. Kuo and M. H. Huang, J. Am. Chem. Soc., 2008, 130, 12815– 12820. 71 Y. Chang and H. C. Zeng, Cryst. Growth Des., 2004, 4, 273–278. 72 J. S. Xu and D. F. Xue, Acta Mater. 2007, 55, 2397–2406. 73 Y. Y. Ma, Z. Y. Jiang, Q. Kuang, S. H. Zhang, Z. X. Xie, R. B. Huang and L. S. Zheng, J. Phys. Chem. C, 2008, 112, 13405–13409. 74 H. R. Liu, W. F. Miao, S. Yang, Z. M. Zhang and J. F. Chen, Cryst. Growth Des., 2009, 9, 1733–1737. 75 M. J. Siegfried and K. S. Choi, Angew. Chem. Int. Ed., 2005, 44, 3218–3223. 76 J. Li, Y. Shi, Q. Cai, Q. Y. Sun, H. D. Li, X. H. Chen, X. P. Wang, Y. J. Yan and E. G. Vrieling, Cryst. Growth Des., 2008, 8, 2652–2659. 77 S. D. Sun, X. Z. Zhang, X. P. Song, S. H. Liang, L. Q. Wang and Z. M. Yang, CrystEngComm, 2012, 14, 3545–3553. 78 J. T. Zhang, J. F. Liu, Q. Peng, X. Wang and Y. D. Li, Chem. Mater., 2006, 18, 867–871. 79 M. L. Pang and H. C. Zeng, Langmuir, 2010, 26, 5963–5970. 80 L. H. Yang, Y. M. Sui, W. Y. Zhao, W. Y. Fu, H. B. Yang, L. N. Zhang, X. M. Zhou, S. L. Cheng, J. W. Ma, H. Zhao and M. H. Li, CrystEngComm, 2011, 13, 6265–6270. 81 Y. M. Sui, W. Y. Fu, Y. Zeng, H. B. Yang, Y. Y. Zhang, H. Chen, Y. G. Li, M. H. Li and G. T. Zou, Angew. Chem. Int. Ed., 2010, 49, 4282– 4285.

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82 Y. Chang, J. J. Teo and H. C. Zeng, Langmuir, 2005, 21, 1074–1079. 83 Y. H. Tsai, C.Y. Chiu and M. H. Huang, J. Phys. Chem. C, 2013, 117, 24611–24617. 84 L. Zhang and H. Wang, J. Phys. Chem. C, 2011, 115, 18479–18485. 85 L. Zhang and H. Wang, ACS Nano, 2011, 5, 3257–3267. 86 H. L. Xu and W. Z. Wang, Angew. Chem. Int. Edit., 2007, 46, 1489– 1492. 87 H. L. Xu, W. Z. Wang and L. Zhou, Cryst. Growth Des., 2008, 8, 3486–3489. 88 W. Z. Wang, P. C. Zhang, L. Peng, W. J. Xie, Gu. L. Zhang, Y. Tu and W. J. Mai, CrystEngComm, 2010, 12, 700–701. 89 Z. H. Wang, H. Wang, L. L. Wang and L. Pan, J. Phys. Chem. Solids, 2009, 70, 719–722. 90 Z. H. Wang, X. Y. Chen, J. W. Liu, M. S. Mo, L. Yang and Y. T. Qian, Solid State Commun.,2004, 130, 585–589. 91 H. T. Zhu, J. X. Wang and G. Y. Xu, Cryst. Growth Des., 2009, 9, 633–638. 92 J. Xu, Y. B. Tang, W. X. Zhang, C. S. Lee, Z. H. Yang and S. T. Lee, Cryst. Growth Des., 2009, 9, 4524–4528. 93 Y. M. Sui, Y. Y. Zhang, W. Y. Fu, H. B.Yang, Q. Zhao, P. Sun, D. Ma, M. X. Yuan, Y. X. Li and G. T. Zou, J. Cryst. Growth, 2009, 311, 2285– 2290. 94 M. Q. Yang, Y. W. Zhang, G. S. Pang and S. H. Feng, Eur. J. Inorg. Chem., 2007, 3841–3844. 95 Z. Y. Gao, J. L. Liu, J. L. Chang, D. P. Wu, J. J. He, K. Wang, F. Xu and K. Jiang, CrystEngComm, 2012, 14, 6639–6646. 96 H. Liu, Y. Zhou, S. A. Kulinich, J. J. Li, L. L. Han, S. Z. Qiao and X. W. Du, J. Mater. Chem. A, 2013, 1, 302–307. 97 Y. X. Zhao, W. T. Wang, Y. P. Li, Y. Zhang, Z. F. Yan and Z. Y. Huo, Nanoscale, 2014, 6, 195–198. 98 L. F. Gou and C. J. Murphy, Nano Lett., 2003, 3, 231–234. 99 Y. B. Cao, J. M. Fan, L. Y. Bai, F. L. Yuan and Y. F. Chen, Cryst. Growth Des., 2010, 10, 232–236. 100 Y. M. Sui, W. Y. Fu, H. B. Yang, Y. Zeng, Y. Y. Zhang, Q. Zhao, Y. G. Li, X. M. Zhou, Y. Leng, M. H. Li and G. T. Zou, Cryst. Growth Des., 2010, 10, 99–108. 101 H. Y. Zhao, Y. F.Wang and J. H. Zeng, Cryst. Growth Des., 2008, 8, 3731–3734. 102 C. H. Kuo, C. H. Chen and M. H. Huang, Adv. Funct. Mater., 2007, 17, 3773–3780. 103 D. F. Zhang, H. Zhang, L. Guo, K. Zheng, X. D. Han and Z. Zhang, J. Mater. Chem., 2009, 19, 5220–5225. 104 M. J. Siegfried and K. S. Choi, J. Am. Chem. Soc., 2006, 128, 10356– 10357. 105 I. C. Chang, P. C. Chen, M. C. Tsai, T. T. Chen, M. H. Yang, H. T. Chiu and C. Y. Lee, CrystEngComm, 2013, 15, 2363–2366. 106 X. Zhao, Z. Y. Bao, C. T. Sun and D. F. Xue, J. Cryst. Growth 2009, 311, 711–715. 107 M. H. Kim, B. K. Lim, E. P. Lee and Y. N. Xia, J. Mater. Chem., 2008, 18, 4069–4073. 108 H. L. Xu, W. Z. Wang and W. Zhu, J. Phys. Chem. B, 2006, 110, 13829–13834. 109 Y. Xu, H. Wang, Y. F. Yu, L. Tian, W. W. Zhao and B. Zhang, J. Phys. Chem. C, 2011, 115, 15288–15296. 110 W. Y. Zhao, W. Y. Fu, H. B. Yang, C. J. Tian, M. H. Li, Y. X. Li, L. N. Zhang, Y. M. Sui, X. M. Zhou, H. Chen and G. T. Zou, CrystEngComm, 2011, 13, 2871–2877. 111 H. Pang, F. Gao and Q. Y. Lu, CrystEngComm, 2010, 12, 406–412.

This journal is © The Royal Society of Chemistry [year]

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15

20

25

30

35

40

45

50

55

Nanoscale

112 G. Prabhakaran and R. Murugan, CrystEngComm, 2012, 14, 8338– 8341. 113 K. F. Chen and D. F. Xue, CrystEngComm, 2013, 15, 1739–1746. 114 X. Zhang, Y. Xie, F. Xu, X. H. Liu and D. Xu, Inorg. Chem. Commun., 2003, 6, 1390–1391. 115 X. D. Liang, L. Gao, S. W. Yang and J. Sun, Adv. Mater., 2009, 21, 2068–2071. 116 X. Lan, J. Y. Zhang, H. Gao and T. M. Wang, CrystEngComm, 2011, 13, 633–636. 117 W. C. Huang, L. M. Lyu, Y. C. Yang and M. H. Huang, J. Am. Chem. Soc., 2012, 134, 1261–1267. 118 K. X. Yao, X. M. Yin, T. H. Wang and H. C. Zeng, J. Am. Chem. Soc., 2010, 132, 6131–6144. 119 C. H. Kuo and M. H. Huang, J. Phys. Chem. C, 2008, 112, 18355– 18360. 120 K. F. Chen and D. F. Xue, CrystEngComm, 2012, 14, 8068–8075. 121 Z. M. Yang, S. D. Sun, C. C. Kong, X. P. Song and B. J. Ding, J. Nanomater., 2010, 710584. 122 Y. Zhang, B. Deng, T. R. Zhang, D. M. Gao and A. W. Xu, J. Phys. Chem. C, 2010, 114, 5073–5079. 123 M. Leng, C. Yu and C. Wang, CrystEngComm, 2012, 14, 8454–8461. 124 W. W. Zhou, B. Yan, C. W. Cheng, C. X. Cong, H. L. Hu, H. J. Fan and T. Yu, CrystEngComm, 2009, 11, 2291–2296. 125 S. D. Sun, F. Y. Zhou, L. Q. Wang, X. P. Song and Z. M. Yang, Cryst. Growth Des., 2010, 10, 541–547. 126 S. D. Sun, C. C. Kong, S. C. Yang, L. Q. Wang, X. P. Song, B. J. Ding and Z. M. Yang, CrystEngComm, 2011, 13, 2217–2221. 127 S. D. Sun, D. C. Deng, C. C. Kong, Y. Gao, S. C. Yang, X. P. Song, B. J. Ding and Z. M. Yang, CrystEngComm, 2011, 13, 5993–5997. 128 S. D. Sun, X. P. Song, Y. X. Sun, D. C. Deng and Z. M. Yang, Catal. Sci. Technol., 2012, 2, 925–930. 129 Y. H. Liang, L. Shang, T. Bian, C. Zhou, D. H. Zhang, H. J. Yu, H. T. Xu, Z. Shi, T. R. Zhang, L. Z. Wu and C. H. Tung, CrystEngComm, 2012, 14, 4431–4436. 130 X. P. Wang, S. H. Jiao, D. P. Wu, Q. Li, J. G. Zhou, K. Jiang and D. S. Xu, CrystEngComm, 2013, 15, 1849–1852. 131 S. D. Sun, H. Zhang, X. P. Song, S. H. Liang, C. C. Kong and Z. M. Yang, CrystEngComm, 2011, 13, 6040–6044. 132 S. D. Sun, X. P. Song, C. C. Kong and Z. M. Yang, CrystEngComm, 2011, 13, 6616–6620. 133 L. Z. Zhang, J. W. Shi, M. C. Liu, D. W. Jing and L. J. Guo, Chem. Commun., 2013, 50, 192–194. 134 Q. Hua, D. L. Shang,W. H. Zhang, K. Chen, S. J. Chang, Y. S. Ma, Z. Q. Jiang, J. L. Yang and W. X. Huang, Langmuir, 2011, 27, 665–671. 136 S. D. Sun, H. J. You, C. C. Kong, X. P. Song, B. J. Ding and Z. M. Yang, CrystEngComm, 2011, 13, 2837–2840. 137 S. D. Sun and Z. M. Yang, RSC Adv., 2014, 4, 3804–3822. 138 M. H. Huang, S. Rej and S. C. Hsu, Chem. Commun., 2014, 50, 1634–1644. 139 C. H. Kuo and M. H. Huang, Nano Today., 2010, 2, 106–116. 140 S. D. Sun, C. C. Kong, H. J. You, X. P. Song, B. J. Ding and Z. M. Yang, CrystEngComm, 2012, 14, 40–43. 141 G. Shen and D. Chen, J. Phys. Chem. C, 2010, 114, 21088–21093. 142 F. R. Fan, Y. Ding, D. Y. Liu, Z. Q. Tian and Z. L. Wang, J. Am.Chem. Soc., 2009, 131, 12036–12037. 143 C. G. Read, E. M. P. Steinmiller and K. S. Choi, J. Am.Chem. Soc., 2009, 131, 12040–12041. 144 P. Wang, B. B. Huang, X. Y. Qin, X. Y. Zhang, Y. Dai, J. Y. Wei

This journal is © The Royal Society of Chemistry [year]

60

65

70

75

80

85

90

95

100

105

110

115

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DOI: 10.1039/C5NR02178B

and M. H. Whangbo, Angew. Chem., Int. Ed., 2008, 47, 7931–7933. 145 H. C. Yatmaz, A. Akyol and M. Bayramoglu, Ind. Eng. Chem. Res.,2004, 43, 6035–6039. 146 X. W. Liu, Langmuir, 2011, 27, 9100–9104. 147 X. W. Liu, F. Y. Wang, F. Zhen and J. R. Huang, RSC Advances, 2012, 2, 7647–7651. 148 H. Zhu, M. L. Du, D. L. Yu, Y. Wang, L. N. Wang, M. L. Zou, M. Zhang and Y. Q. Fu, J. Mater. Chem. A, 2013, 1, 919–923. 149 H. Zhu, M. L. Du, D. L. Yu, Y. Wang, M. L. Zou, C. S. Xu and Y. Q. Fu, Dalton Trans., 2012, 41, 13795–13799. 150 Y. L. Pan, S. Z. Deng, L. Polavarapu, N. Y. Gao, P. Y. Yuan, C. H. Sow and Q. H. Xu, Langmuir, 2012, 28, 12304–12310. 151 Y. Q. Wang, T. Gao, K. Wang, X. P. Wu, X. J. Shi, Y. B. Liu, S. Y. Lou and S. M. Zhou, Nanoscale, 2012, 4, 7121–7126. 152 W. X. Zhang, X. M. Yang, Q. Zhu, K. Wang, J. B. Lu, M. Chen, and Z. H. Yang, Ind. Eng. Chem. Res., 2014, 53, 16316–16323. 153 L. H. Yang, J. Lv, Y. M. Sui, W. Y. Fu, X. M. Zhou, J. W. Ma, S. Su, W. J. Zhang, P. Lv, D. Wu, Y. N. Mu and H. B. Yang, CrystEngComm, 2014,16, 2298–2304. 154 R. Ji, W. D. Sun and Y. Chu, RSC Adv., 2014, 4, 6055–6059. 155 Z. H. Wang, S. P. Zhao, S. Y. Zhu, Y. L. Sun and M. Fang, CrystEngComm, 2011, 13, 2262–2267. 156 N. Meir, I. J. L. Plante, K. Flomin, E. Chockler, B. Moshofsky, M. Diab, M. Volokh and T. Mokari, J. Mater. Chem. A, 2013, 1, 1763–1769. 157 L. L. Wang, J. Ge, A. L. Wang, M. S. Deng, X. J. Wang, S. Bai, R. Li, J. Jiang, Q. Zhang, Y. Luo and Y. J. Xiong, Angew. Chem. Int. Ed., 2014, 53, 5107–5111. 158 Y. Abdu and A.O Musa, Bayero Journal of Pure and Applied Sciences, 2009, 2, 8–12. 159 S. D. Sun, C. C. Kong, D. C. Deng, X. P. Song, B. J. Ding and Z. M. Yang, CrystEngComm, 2011, 13, 63–66. 160 J. Y. Kim, Y. W. Kwon and H. J. Lee, J. Mater. Chem. A, 2013, 1, 14183–14188. 161 X. W. Liu, RSC Adv., 2011, 1, 1119–1125. 162 K. Y. Lee, S. W. Han and H. C. Choi, Bull. Korean Chem. Soc., 2009, 30, 3113–3116. 163 S. Alayoglu, A. U. Nilekar, M. Mavrikakis and B. Eichhorn, Nat. Mater., 2008, 7, 333–338. 164 S. H. Zhou, B. Varughese, B. Eichhorn, G. Jackson and K. McIlwrath, Angew. Chem. Int. Ed., 2005, 44, 4539–4543. 165 L. Zhang, D. A. Blom and H. Wang, Chem. Mater., 2011, 23, 4587– 4598. 166 W. Chen, Z. L. Fan and Z. P. Lai, J. Mater. Chem. A, 2013, 1, 13862–13868. 167 S. B. Kalidindi, U. Sanyal and B. R. Jagirdar, Phys. Chem. Chem. Phys., 2008, 10, 5870–5874. 168 Z. Ai, L. Zhang, S. Lee and W. Ho, J. Phys. Chem. C, 2009, 113, 20896–20902. 169 A. Radi, D. Pradhan, Y. Sohn and K. T. Leung, ACS Nano, 2010, 4, 1553–1560. 170 D. B. Pedersen, S. Wang and S. H. Liang, J. Phys. Chem. C, 2008, 112, 8819–8826. 171 R. Chinchilla and C. Najera, Chem. Rev., 2007, 107, 874–922. 172 J. H. Kou, A. Saha, C. Bennett-Stamper and R. S. Varma, Chem. Commun., 2012, 48, 5862–5864. 173 C. Q. Dong,Y. Wang, J. L. Xu, G. H. Cheng, W. F. Yang, T. Y. Kou, Z. H. Zhang and Y. Ding, J. Mater. Chem. A, 2014, 2, 18229–18235. 174 C. H. Kuo, Y. C. Yang, S. Gwo and M. H. Huang, J. Am. Chem. Soc.,

Journal Name, [year], [vol], 00–00 | 25

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Page 25 of 33

5

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10

15

20

25

30

35

40

45

50

55

2011, 133, 1052–1057. 175 W. C. Wang, L. M. Lyu and M. H. Huang, Chem. Mater., 2011, 23, 2677–2684. 176 L. N. Kong, W. Chen, D. K. Ma, Y. Yang, S. S. Liu and S. M. Huang, J. Mater. Chem., 2012, 22, 719–724. 177 J. T. Li, S. K. Cushing, J. Bright, F. K. Meng, T. R. Senty, P. Zheng, A.D. Bristow and N. Q. Wu, ACS Catal., 2013, 3, 47–51. 178 D. Y. Liu, S. Y. Ding, H. X. Lin, B. J. Liu, Z. Z. Ye, F. R. Fan, B. Ren and Z. Q. Tian, J. Phys. Chem. C, 2012, 116, 4477–4483. 179 Y. C. Yang, H. J. Wang, J. Whang, J. S. Huang, L. M. Lyu, P. H. Lin, S. Gwo and M. H. Huang, Nanoscale, 2014, 6, 4316–4324. 180 C. H. Kuo, T. E. Hua and M. H. Huang, J. Am. Chem. Soc., 2009, 131, 17871–17878. 181 P. Rai, R. Khan, S. Raj, S. M. Majhi, K. K. Park, Y. T. Yu, I. H. Lee and P. K. Sekhar, Nanoscale, 2014, 6, 581–588. 182 Y. Bai, W. H. Zhang, Z. H. Zhang, J. Zhou, X. J. Wang, C. M. Wang, W. X. Huang, J. Jiang and Y. J. Xiong, J. Am. Chem. Soc., 2014, 136 14650–14653. 183 H. Jing, N. Large, Q. F. Zhang and H. Wang, J. Phys. Chem. C, 2014, 118, 19948–19963. 184 J. Y. Xiong, Z. Li, J. Chen, S. Q. Zhang, L. Z. Wang and S. X. Dou, ACS Appl. Mater. Interfaces, 2014, 6, 15716–15725. 185 R. G. Li, F. X. Zhang, D. E. Wang, J. X. Yang, M. R. Li, J. Zhu, X. Zhou, H. X. Han and C. Li, Nat. Comm., 2013, 4, 1432. 186 T. Minami, Y. Nishi and T. Miyata, Appl. Phys. Express, 2013, 6, 044101. 187 Y. K. Hsu, H. H. Lin, J. R. Wu, M. H. Chen, Y. Ch. Chen, and Y. G. Lin, RSC Adv., 2014, 4, 7655–7659. 188 Y. S. Lee, J. Y. Heo, S. C. Siah, J. P. Mailoa, R. E. Brandt, S. B. Kim, R. G. Gordon and T. Buonassisi, Energy Environ. Sci., 2013, 6, 2112– 2118. 189 S. W. Lee, Yun S. Lee, J. Y. Heo, S. C. Siah, D. Chua, R. E. Brandt, S. B. Kim, J. P. Mailoa, T. Buonassisi and R. G. Gordon, Adv. Energy Mater., 2014, 4, 1301916. 190 Y. S. Lee, J. Y. Heo, M. T. Winkler, S. C. Siah, S. B. Kim, R. G. Gordon and T. Buonassisi, J. Mater. Chem. A, 2013, 1, 15416–15422. 191 V. Fthenakis, J. E. Mason and K. Zweibel, Energy Policy, 2009, 37, 387–399. 192 K. L. Chopra, P. D. Paulson and V. Dutta, Prog. Photovoltaics, 2004, 12, 69–92. 193 J. Jasieniak, B. I. MacDonald, S. E. Watkins and P. Mulvaney, Nano Lett., 2011, 11, 2856–2864. 194 B. P. Rai, Sol. Cells, 1988, 25, 265–272. 195 W. W. Zhou, B. Yan, C. W. Cheng, C. X. Cong, H. L. Hu, H. J. Fan and T. Yu, CrystEngComm, 2009, 11, 2291–2296. 196 K. Akimoto, S. Ishizuka, M. Yanagita, Y. Nawa, G. K. Paul and T. Sakurai, Sol. Energy, 2006, 80, 715–722. 197 S.H. Ko, D. Lee, H.W. Kang, K.H. Nam, J.Y. Yeo, S.J. Hong, C.P. Grigoropoulos and H. J. Sung, Nano Lett., 2011, 11, 666–671. 198 Y. Wang, G. She, H. Xu, Y. Liu, L. Mu and W. Shi, Mater. Lett., 2012, 67, 110–112. 199 C.Y. Kao, C.L. Hsin, C.W. Huang, S.Y. Yu, C.W. Wang, P.H. Yeh and W. W. Wu, Nanoscale, 2012, 4, 1476–1480. 200 K.P. Musselman, A. Marin, A. Wisnet, C. Scheu, J. L. MacManusDriscoll and L. Schmidt-Mende, Adv. Funct. Mater., 2011, 21, 573–582. 201 A. E. Rakhshani, Solid-State Electron., 1986, 29, 7–17. 202 J. Katayama, K. Ito, M. Matsuoka and J. Tamaki, J. Appl. Electrochem., 2004, 34, 687–692.

26 | Journal Name, [year], [vol], 00–00

60

65

70

75

80

85

90

95

100

105

110

115

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Page 26 of 33

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203 T. Jiang, T. Xie, Y. Zhang, L. Chen, L. Peng, H. Li and D. Wang, Phys. Chem. Chem. Phys., 2010, 12, 15476–15481. 204 M. Izaki, T. Shinagawa, K. T. Mizuno, Y. Ida, M. Inaba and A. Tasaka, J. Phys. D: Appl. Phys., 2007, 40, 3326–3329. 205 S. S. Jeong, A. Mittiga, E. Salza, A. Masci and S. Passerini, Electrochim. Acta, 2008, 53, 2226–2231. 206 J. B. Cui and U. J. Gibson, J. Phys. Chem. C, 2010, 114, 6408–6412. 207 K. P. Musselman, A. Wisnet and D. C. Iza, Adv. Mater., 2010, 22, 254–258. 208 H. M. Wei, H. B. Gong, Y. Z.Wang, X. L. Hu, L. Chen, H. Y. Xu, P. Liu and B. Q. Cao, CrystEngComm, 2011, 13, 6065–6070. 209 L. J. Brillson, H. L. Mosbacker, M. J. Hetzer, Y. Strzhemechny, G. H. Jessen, D. C. Look, G. Cantwell, J. Zhang and J. J. Song, Appl. Phys. Lett., 2007, 90, 203515. 210 J. L. Xie, C. X. Guo and C. M. Li, Phys.Chem. Chem. Phys., 2013, 15, 15905–15911. 211 X. W. Zou, H. Q. Fan, Y. M. Tian and S. J. Yan, CrystEngComm, 2014, 16, 1149–1156. 212 T. F. Jiang, T. F. Xie, L. P. Chen, Z. W. Fu and D. J. Wang, Nanoscale, 2013, 5, 2938–2944. 213 M. Deo, D. Shinde, A. Yengantiwar, J. Jog, B. Hannoyer, X. Sauvage, M. More and S. Ogale, J. Mater. Chem., 2012, 22, 17055–17062. 214 Y. Wang, S. C. Li, H. Shi and K. Yu, Nanoscale, 2012, 4, 7817–7824. 215 C. Y. Lin, Y. H. Lai, D. Mersch and E. Reisner, Chem. Sci., 2012, 3, 3482–3487. 216 P. E. de Jongh, D. Vanmaekelbergh and J. J. Kelly, Chem. Mater., 1999, 11, 3512–3517. 217 P. E. de Jongh, D. Vanmaekelbergh and J. J. Kelly, J. Electrochem. Soc., 2000, 147, 486–489. 218 A. Fujishima and K. Honda, Nature, 1972, 238, 37–38. 219 H. R. Liu, J. H. Yang, Y. Y. Zhang, S. Y. Chen, A. Walsh, H. J. Xiang, Xi. G. Gong and S. H. Wei, Phys.Chem. Chem. Phys., 2013, 15, 1778–1781. 220 S. H. Liu, L. X. Yang, S. H. Xu, S. L. Luo and Q. Y. Cai, Electrochem. Commun., 2009, 11, 1748–1751. 221 Y. K. Lai, J. Y. Huang, H. F. Zhang, V. P. Subramaniam, Y. X. Tang, D. G. Gong, L. Sundar, L. Sun, Z. Chen and C. J. Lin, J. Hazard. Mater., 2010, 184, 855–863. 222 W. T. Sun, Y. Yu, H. Y. Pan, X. F. Gao, Q. Chen and L. M. Peng, J. Am. Chem. Soc., 2008, 130, 1124–1125. 223 L. X. Yang, B. B. Chen, S. L. Luo, J. X. Li, R. H. Liu and Q. Y. Cai, Environ. Sci. Technol., 2010, 44, 7884–7889. 224 W. Zhu, X. Liu, H. Q. Liu, D. L. Tong, J. Y. Yang and J. Y. Peng, J. Am. Chem. Soc., 2010, 132, 12619–12626. 225 M. Y. Wang, L. Sun, Z. Q. Lin, J. H. Cai, K. P. Xie and C. J. Lin, Energy Environ. Sci., 2013, 6, 1211–1220. 226 Y. Hou, X. Y. Li, Q. D. Zhao, X. Quan and G. H. Chen, Appl. Phys. Lett., 2009, 95, 093108. 227 Y. Hou, X. Y. L i, X. J. Zou, X. Quan and G. H. Chen, Environ. Sci. Technol., 2009, 43, 858–863. 228 Y. G. Zhang, L. L. Ma, J. L. Li and Y. Yu, Environ. Sci. Technol., 2007, 41, 6264–6269. 229 L. X. Yang, S. L. Luo, Y. Li , Y. Xiao, Q. Kang and Q. Y. Cai, Environ. Sci. Technol., 2010, 44, 7641–7646. 230 A. Mazare, N. Liu, K. Y. Lee, M. S. Killian and P. Schmuki, ChemistryOpen, 2013, 2, 21–24. 231 W. Y. Cheng, T. H. Yu, K. J. Chao and S.Y. Lu, ChemCatChem, 2014, 6, 293–300.

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232 C. Wang, J. C. Wu, P. F. Wang, Y. H. Ao, J. Hou, J. Qian, Sens. Actuators B, 2013, 181, 1–8. 233 Y. B. Wang, Y. N. Zhang, G. H. Zhao, H. Y. Tian, H. J. Shi and T. C. Zhou, ACS Appl. Mater. Interfaces, 2012, 4, 3965–3972. 234 J. Y. Zhang, H. L. Zhu, S. K. Zheng, F. Pan and T. M. Wang, ACS Appl. Mater. Interfaces, 2009, 1, 2111–2114. 235 S. Z. Kang, H. Liu, X. Q. Li, M. J. Sun and J. Mu, RSC Adv., 2014, 4, 538–543. 236 K. Lalitha, G. Sadanandam, V. D. Kumari, M. Subrahmanyam, B. Sreedhar and N. Y. Hebalkar, J. Phys. Chem. C, 2010, 114, 22181–22189. 237 L. C. Liu, X. R. Gu, C. Z. Sun, H. Li, Y. Deng, F. Gao and L. Dong, Nanoscale, 2012, 4, 6351–6359. 238 L. Xiong, F. Yang, L. Yan, N. Yan, X. Yang, M. Qiu and Y. Yu, J. Phys. Chem. Solids, 2011, 72, 1104–1109. 239 J. P. Yasomanee and J. Bandara, Solar Energy Mater. Solar Cells, 2008, 92, 348–352. 240 Y. W. Chen, J. D. Prange, S. Dühnen, Y. Park, M. Gunji, C. E. D. Chidsey and P. C. McIntyre, Nat. Mater., 2011, 10, 539–544. 241 Y. Yamada, K.Yano and S. Fukuzumi, Energy Environ. Sci., 2012, 5, 5356–5363. 242 H. Z. Bao, W. H. Zhang, Q. Hua, Z. Q. Jiang, J. L. Yang, and W. X. Huang, Angew. Chem. Int. Ed., 2011, 50, 12294–12298. 243 G. Ghadimkhani, N. R. de Tacconi, W. Chanmanee, C. Janakya and K. Rajeshwar, Chem. Commun., 2013, 49, 1297–1299. 244 L. J. Zhou, Y. C. Zou, J. Zhao, P. P. Wang, L. L. Feng, L. W. Sun, D. J. Wang and G. D. Li, Sens. Actuators B, 2013, 188, 533–539. 245 F. N. Meng, X. P. Di, H. W. Dong, Y. Zhang, C. L. Zhu, C. Y. Li, Y. J. Chen, Sens. Actuators B, 2013, 182, 197–204. 246 L. Hu, Y. M. Huang, F. P. Zhang and Q. W. Chen, Nanoscale, 2013, 5, 4186–4190. 247 L. Zhang, Z. M. Cui, Q. Wu, D. Guo, Y. Xu and L. Guo, CrystEngComm, 2013, 15, 7462–7467. 248 Y. Cudennec and A. Lecerf, Solid State Sci., 2003, 5, 1471–1479. 249 C. C. Kong, L. L. Tang, X. Z. Zhang, S. D. Sun, S. C. Yang, X. P. Song and Z. M. Yang, J. Mater. Chem. A, 2014, 2, 7306–7312. 250 H. A. Al-Jawhari, J. A. Caraveo-Frescas, M. N. Hedhili and H. N. Alshareef, ACS Appl. Mater. Interfaces, 2013, 5, 9615–9619. 251 E. Pastor, F. M. Pesci, A. Reynal, A. D. Handoko, M. J. Guo, X. Q. An, A. J. Cowan, D. R. Klug, J. R. Durrant and J. W.Tang, Phys. Chem. Chem. Phys., 2014, 16, 5922–5926. 252 H. Z. Bao, Z. H. Zhang, Q. Hua and W. X. Huang, Langmuir, 2014, 30, 6427–6436. 253 X.Yang, R. Yuan, Y. Q. Chai, Y. Zhuo, C. L. Hong, Z. Y. Liu and H. L. Su, Talanta, 2009, 78, 596–601. 254 D. Sharma, S. Upadhyay, V. R. Satsangi, R. Shrivastav, U. V. Waghmare and S. Dass, J. Phys. Chem. C, 2014, 118, 25320–25329. 255 S. K. Li, F. Z. Huang, Y. Wang, Y. H. Shen, L. G. Qiu, A. J. Xie and S. J. Xu, J. Mater. Chem., 2011, 21, 7459–7466. 256 J. Cao, J. C. Li, L. Liu, A. J. Xie, S. K. Li, L.G. Qiu, Y. P. Yuan and Y. H. Shen, J. Mater. Chem. A, 2014, 2, 7953–7959. 257 H. S. Wang, Y. A. Hu, Y. Jiang, L. G. Qiu, H. B. Wu, B. Guo,Y. H. Shen, Y. Wang, L. Zhu and A. J. Xie, Dalton Trans., 2013, 42, 4915– 4921. 258 X. G. Liu, C. Feng, S. W. Or, Y. P. Sun, C. G. Jin, W. H. Li and Y. H. Lv, RSC Adv., 2013, 3, 14590–14594. 259 Q. Huang, F. Kang, H. Liu, Q. Li and X. D. Xiao, J. Mater. Chem. A, 2013, 1, 2418–2425. 260 G. J. Wu, N. J. Guan and L. D. Li, Catal. Sci. Technol., 2011, 1, 601–

This journal is © The Royal Society of Chemistry [year]

60

65

70

75

80

85

90

95

100

105

110

115

View Article Online

DOI: 10.1039/C5NR02178B

608. 261 Q. G. Zhai, S. J. Xie, W. Q. Fan, Q. H. Zhang, Y. Wang, W. P. Deng, and Y. Wang, Angew. Chem. Int. Ed., 2013, 52, 5776–5779. 262 Q. Y. Tian, W. Wu, L. L. Sun, S. L. Yang, M. Lei, J. Zhou, Y. Liu, X. H. Xiao, F. Ren, C. Z. Jiang, and V. A. L. Roy, ACS Appl. Mater. Interfaces, 2014, 6, 13088–13097. 263 A. E. Rakhshani, Solid-State Electron. 1986, 29, 7–17. 264 L. C. Olsen, F. W. Addis and W. Miller, Sol. Cells, 1982, 7, 247–279. 265 W. Siripala and J. R. P. Jayakody, Sol. Energy Mater., 1986, 14, 23– 27. 266 R. P. Wijesundara, L. D. R. D. Perera, K. D. Jayasuriya, W. Siripala, K. T. L. de Silva, A. P. Samantilleke and I. M. Dharmadasa, Sol. Energy Mater. Sol., 2000, 61, 277–282. 267 C. A. N. Fernando, T. M. W. J. Bandara and S. K. Wethasingha, Sol. Energy Mater., 2001, 70, 121–129. 268 C. A. N. Fernando, P. H. C. de Silva, S. K. Wethasingha, I. M. Dharmadasa, T. Delsol and M. C. Simmonds, Renewable Energy, 2002, 26, 521–529. 269 L. Wang and M. Tao, Electrochem. Solid-State Lett., 2007, 10, 248– 250. 270 C. M. McShane and K. S. Choi, J. Am. Chem. Soc., 2009, 131, 2561– 2569. 271 T. F. Jiang, T. F. Xie, W. S. Yang, L. P. Chen, H. M. Fan and D. J. Wang, J. Phys. Chem. C, 2013, 117, 4619–4624. 272 L. C. K. Liau, Y. C. Lin and Y. J. Peng, J. Phys. Chem. C, 2013, 117, 26426–26431. 273 C. M. McShane and K. S. Choi, Phys. Chem. Chem. Phys., 2012, 14, 6112–6118. 274 C. M. McShane, W. P. Siripala and K. S. Choi, J. Phys. Chem. Lett., 2010, 1, 2666–2670. 275 L. C. Chen, Mater. Sci. Semicond. Process., 2013, 16, 1172–1185. 276 A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, Chem. Rev., 2010, 110, 6595–6663. 277 D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marksab and M. C. Hersam, Chem. Soc. Rev., 2013, 42, 2824–2860. 278 P. Gao, J. Liu, S. Lee, T. Zhang and D. D. Sun, J. Mater. Chem., 2012, 22, 2292–2298. 279 X. J. Lv, W. F. Fu, H. X. Chang, H. Zhang, J. S. Cheng, G. J. Zhang, Y. Song, C. Y. Hu and J. H. Li, J. Mater. Chem., 2012, 22, 1539–1546. 280 L. Sheeney-Haj-Ichia, B. Basnar and I. Willner, Angew. Chem., Int. Ed., 2005, 44, 78–83. 281 I. Robel, B. A. Bunker and P. V. Kamat, Adv. Mater., 2005, 17, 2458–2463. 282 K. Woan, G. Pyrgiotakis and W. Sigmund, Adv. Mater., 2009, 21, 2233–2239. 283 G. Williams and P. V. Kamat, Langmuir, 2009, 25, 13869–13873. 284 Q. Li, B. Guo, J. Yu, J. Ran, B. Zhang, H. Yan and J. R. Gong, J. Am.Chem. Soc., 2011, 133, 10878–10884. 285 A. Iwase, Y. H. Ng, Y. Ishiguro, A. Kudo and R. Amal, J. Am. Chem. Soc., 2011, 133, 11054–11057. 286 P. V. Kamat, J. Phys. Chem. Lett., 2011, 2, 242–251. 287 N. J. Bell, Y. H. Ng, A. Du, H. Coster, S. C. Smith and R. Amal, J. Phys. Chem. C, 2011, 115, 6004–6009. 288 X. Du, I. Skachko, A. Barker and E. Y. Andrei, Nat. Nanotechnol., 2008, 3, 491–495. 289 S. Park and R. S. Ruoff, Nat. Nanotechnol., 2009, 4, 217–224. 290 C. G. Lee, X. D. Wei, J. W. Kysar and J. Hone, Science, 2008, 321, 385–388.

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10

15

20

25

30

35

40

45

291 Z. T. Luo, L. A. Somers, Y. Y. Dan, T. Ly, N. J. Kybert, E. J. Mele and A. T. C. Johnson, Nano Lett., 2010, 10, 777–781. 292 C. Pak and D. C. Lee, ACS Appl. Mater. Interfaces, 2012, 4, 1021– 1029. 293 Y. S. Zhou, G. Chen, Y. G. Yu, L. X. Hao, Z. H. Han and Q. L. Yu, New J. Chem., 2013, 37, 2845–2850. 294 L. V. Butov, C. W. Lai, A. L. Ivanov, A. C. Gossard and D. S. Chemla, Nature, 2002, 417, 47–52. 295 D. Snoke, Science, 2002, 298, 1368–1372. 296 D. Li and R. B. Kaner, Science, 2008, 320, 1170–1171. 297 C. Petit, and T. J. Bandosz, Adv. Mater., 2009, 21, 4753–4757. 298 F. Guo, F. Kim, T. H. Han, V. B. Shenoy, J. X. Huang and R. H. Hurt, ACS Nano, 2011, 5, 8019–8025. 299 K. Jasuja and V. Berry, ACS Nano, 2009, 3, 2358–2366. 300 X. B. Fan, W. C. Peng, Y. Li, X. Y. Li, S. L. Wang, G. L. Zhang and F. B. Zhang, Adv. Mater., 2008, 20, 4490–4493. 301 B. J. Li, H. Q. Cao, G. Yin, Y. X. Lu and J. F. Yin, J. Mater. Chem., 2011, 21, 10645–10648. 302 P. D. Tran, S. K. Batabyal, S. S. Pramana, J. Barber, L. H. Wong and S. C. J. Loo, Nanoscale, 2012, 4, 3875–3878. 303 X.Y. Yan, X. L. Tong, Y. F. Zhang, X. D. Han, Y. Y. Wang, G. Q. Jin, Y. Qin and X. Y. Guo, Chem. Commun., 2012, 48, 1892–1894. 304 Y. Zhang, X. W. Liang Zeng, S. Y. Song and D. P. Liu, Dalton Trans., 2012, 41, 4316–4319. 305 C. Hong, X. Jin, J. Totleben, J. Lohrman, E. Harak, B. Subramaniam, R. V. Chaudhari and S. Ren, J. Mater. Chem. A, 2014, 2, 7147–7151. 306 M. M. Liu, R. Liu and W. Chen, Biosens. Bioelectron., 2013, 45, 206–212. 307 G. Eda and M. Chhowalla, Adv. Mater., 2010, 22, 2392–2415. 308 T. F. Yeh, J. M. Syu, C. Cheng, T. H. Chang and H. Teng, Adv. Funct. Mater., 2010, 20, 2255–2262. 309 L. S. Zhou, F. P. Shen, X. K. Tian, D. H. Wang, T. Zhang and W. Chen, Nanoscale, 2013, 5, 1564–1569. 310 J. Y. Kim, L. J. Cote, F. Kim, W. Yuan, K. R. Shull and J. X. Huang, J. Am. Chem. Soc., 2010, 132, 8180–8186. 311 S. T. Yang, Y. L. Chang, H. F. Wang, G. B. Liu, S. Chen, Y. W. Wang, Y. F. Liu and A. N. Cao, J. Colloid Interface Sci., 2010, 351, 122– 127. 312 S. Z. Deng, V. Tjoa, H. M. Fan, H. R. Tan, D. C. Sayle, M. Olivo, S. Mhaisalkar, J. Wei and C. H. Sow, J. Am. Chem. Soc., 2012, 134, 4905– 4917. 313 C. Y. Hou, H. C. Quan, Y. Y. Duan, Q. H. Zhang, H. Z. Wang and Y. G. Li, Nanoscale, 2013, 5, 1227–1232. 314 I. Yu, L. L. Ma, W. Y. Huang, F. P. Du, J. C. Yu, J. G. Yu, J. B. Wang and P. K. Wong, Carbon, 2005, 43, 670–674. 315 G.W. Yang, G.Y. Gao, G.Y. Zhao, H.L. Li, Carbon, 2007, 45, 3036– 3041.

50

55

60

65

70

75

80

85

90

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Page 28 of 33

DOI: 10.1039/C5NR02178B

316 N. Rajalakshmi, H. Ryu, M. M. Shaijumon and S. Ramaprabhu, J. Power. Sources, 2005, 140, 250–257. 317 G. Ovejero, J. L. Sotelo, M. D. Romero, A. Rodriguez, M. A. Ocana and G. Rodriguez, Ind. Eng. Chem. Res., 2006, 45, 2206–2212. 318 M.C. Batchelor, G.G. Wildgoose, R.G. Compton, L.D. Shao and M. L. H. Green, Sens. Actuators B: Chem., 2008, 132, 356–360. 319 X.J. Zhang, G.F. Wang, W. Zhang, N.J. Hu, H.Q. Wu and B. Fang, J. Phys. Chem. C, 2008, 112, 8856–8862. 320 Z. J. Zhuang, X. D. Su, H.Y. Yuan, Q. Sun, D. Xiao and M. M. F. Choi, Analyst, 2008, 133, 126–132. 321 P. Martis, A. Fonseca, Z. Mekhalif and J. Delhalle, J. Nanopart. Res., 2010, 12, 439–448. 322 Y. S. Luo, Q. F. Ren, J. L. Li, Z. J. Jia, Q. R. Dai, Y. Zhang and B. H. Yu, Nanotechnology, 2006, 17, 5836–5840. 323 X. J. Zhang, G. F. Wang, W. Zhang, Y. Wei and B. Fang, Biosens. Bioelectron., 2009, 24, 3395–3398. 324 S. Q. Song, R. C. Rao, H. X. Yang and A. M. Zhang, J. Phys. Chem. C, 2010, 114, 13998–14003. 325 X. M. Zhou, H. G. Nie, Z. Yao, Y. Q. Dong, Z. Yang and S. M. Huang, Sens. Actuators B, 2012, 168, 1–7. 326 H. T. Li, X. D. He, Z. H. Kang, H. Huang, Y. Liu, J. L. Liu, S. Y. Lian, C. H. A. Tsang, X. B. Yang and S. T. Lee, Angew. Chem., Int. Ed., 2010, 49, 4430–4434. 327 S. N. Baker and G. A. Baker, Angew. Chem., Int. Ed., 2010, 49, 6726–6744. 328 H. T. Li, R. H. Liu, Y. Liu, H. Huang, H. Yu, H. Ming, S. Y. Lian, S. T. Lee and Z. H. Kang, J. Mater. Chem., 2012, 22, 17470–17475. 329 G. L. Li, J. Y. Liu and G. B. Jiang, Chem. Commun., 2011, 47, 7443– 7745. 330 Y. Yao, G. H. Li, S. Ciston, R. M. Lueptow and K. A. Gray, Environ.Sci. Technol., 2008, 42, 4952–4957. 331 M. Izaki, T. Saito, T. Ohata, K. Murata, B. M. Fariza, J. Sasano, T. Shinagawa and S. Watase, ACS Appl. Mater. Interfaces, 2012, 4, 3558– 3565. 332 D. Muňoz-Rojas, J. Oró-Solé and P. Gómez-Romero, Chem. Commun., 2009, 5913–5915. 333 K. M. El Khatib and R.M. Abdel Hameed, Biosens. Bioelectron., 2011, 26, 3542–3548. 334 B. X. Tang, F. Wang, J. H. Li,Y. X. Xie and M. B. Zhang, J. Org. Chem., 2007, 72, 6294–6297. 335 S. Bai, J. Ge, L. L. Wang, M. Gong, M. S. Deng, Q. Kong, L. Song, J. Jiang, Q. Zhang, Y. Luo, Y. Xie, and Y. J. Xiong, Adv. Mater., 2014, 26, 5689–5695.

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Table 1

Table 1 Synthesis, structures and applications of hybrid Cu2O–metal nanostructures

Products

Reactants

Structures

Applications

Ref.

Cu/Cu2O

Cu2O, N2H4∙H2O

26-facet polyhedra

photocatalyst

140

Au/Cu2O

Cu2O, HAuCl4

14-facet polyhedra

H2O2 detection

146

Au/Cu2O

Cu2O, HAuCl4

nanocubes

sensors

147

Au/Cu2O

Cu2O, HAuCl4

octahedra

photocatalyst

148,149

Au/Cu2O

Cu2O, HAuCl4

nanowires

photocatalyst

150

Ag/Cu2O

AgNO3,sodium citrate

hollow nanoframes

SERS

152

nanocubes

SERS

153

2+

Ag/Cu2O

AgNO3, Cu, Cu

Ag/Cu2O

AgNO3, Cu2O

octahedra

photocatalyst

154

Cu@Cu2O

Cu, O2, N2, H2, Ar

nanowires

photocatalyst

166

Cu@Cu2O

Cu(acac)2, toluene

microspheres

photocatalyst

168

Cu2O@Cu

Cu, O2

nanoparticles

hydrogen production

167

Cu2O@Cu

Cu2O, ethylene glycol,

nanospheres

Sonogashira coupling

172

sodium hydroxide,

reaction

glucose Cu2O@Cu

electrodeposition

nanoneedle arrays

supercapacitor

173

Au@Cu2O

2+

nanospheres

plasmon resonant

165

Au, Cu , PVP, N2H4∙H2O 2+

Au@Cu2O

Au, Cu , SDS, NaOH,

Au@Cu2O

Au, Cu2+, SDS,

absorption polyhedra

photocatalyst

175

ocahedra

photocatalyst

176

nanospheres

plasmon resonant

178

NH2OH3∙HCl N2H4∙H2O Au@Cu2O

Au, Cu2+, PVP, ascorbic acid

Au@Cu2O

2+

Au, Cu , SDS,

absorption polyhedra

optical property

179

polyhedra

electrical, photocatalytic

180

N2H4∙H2O Au@Cu2O

Au, Cu2+, SDS,

Au@Cu2O

Au, Cu2+, PVP,

N2H4∙H2O

properties nanospheres

sensors

181

nanoplates

CO oxidation

182

Ag, PVP, Cu(NO3)2,

quasi-spherical nanoparticles,

optical property

183

N2H4

nanocubes, and nanocuboids

Ag, Cu(NO3)2, N2H4

nanowires

photocatalyst

184

N2H4∙H2O Ag@Cu2O

Ag, PVP, CuCl2, NaOH, AA

Ag@Cu2O Ag@Cu2O

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Table 2

Products

Structures

Applications

Ref.

ZnO:Al/nondoped

nanofilms

solar cells

186

Cu2O/ZnO

nanofilms

solar cells

187

ZnO:Al/a-ZTO/Cu2O

nanofilms

solar cells

188

ZnO:Al/CuO/Cu2O

nanofilms

solar cells

189

Cu2O/ZnO

nanorods arrays

solar cells

190

Cu2O/ZnO

nanofilms

solar cells

203

Cu2O/ZnO

nanopillar

solar cells

206

Cu2O/ZnO

nanofilms

solar cells

208

Cu2O/ZnO

nanorods arrays

solar cells

210

Cu2O/ZnO

nanorod arrays

photocatalyst

211

Cu2O/ZnO

nanorods

photocatalyst

212

Cu2O/ZnO

nanobrush

field emission and

213

Ga2O3/Cu2O

photocatalytic properties Cu2O/ZnO

multipods

field emission and

214

photocatalytic properties Cu2O/TiO2

nanotube arrays

photoelectrocatalytic

225

properties Cu2O/TiO2

nanotube arrays

photocatalyst

227

Cu2O/TiO2

multipods

photocatalyst

228

Cu2O/TiO2

networks

photocatalyst

229

Cu2O/TiO2

nanotube arrays

photocatalyst

230

Cu2O/TiO2

micorspheres

hydrogen production

231

Cu2O/TiO2

nanotube arrays

photocatalyst

232

Cu2O/TiO2

nanocubes

photocatalyst

233

Cu2O/TiO2

nanofilms

photocatalyst

234

Cu2O/TiO2

nanotubes

eugenol detection

235

Cu2O/TiO2

nanoparticles

hydrogen production

236

Cu2O/TiO2

nanoparticles

photocatalyst

237

Cu2O/CuO

polyhedra

CO oxidation

242

Cu2O/CuO

nanorod arrays

methanol production

243

Cu2O/CuO

microcubes

gas sensors

244

Cu2O/CuO

sub-microspheres

gas sensors

245

Cu2O/CuO

14-facet polyhedra

lithium-ion battery anodes

246

Cu2O/CuO

microcubes

gas sensors

247

Cu2O/CuO

nanofilms

photoelectrocatalytic

248

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Table 2 Structures and applications of hybrid Cu2O–metal oxide nanostructures

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properties Cu2O/SnO

nanofilms

transistors

250

Cu2O/RuxO

nanofilms

catalyst

251

Cu2O/CeO2

hollow core/shell

CO oxidation

252

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Cu2O/SiO2

nanofilms

sensor

253

Cu2O/SrTiO3

nanofilms

photoelectrode

254

Fe3O4@C@Cu2O

bean-like

photocatalyst

255

Fe3O4–Cu2O–polyaniline

dandelion-like

photocatalyst

256

Fe3O4@Cu2O–Cu

pine cone-like

photocatalyst

257

CuO–Cu2O–Ni

nanocapsules

microwave absorbers

258

Cu2O–CuO–TiO2

nanowire arrays

photoelectrolysis

259

Cu–Cu2O–TiO2

nanoparicles

CO oxidation

260

Fe2O3@SnO2@Cu2O

single core-double shell

photocatalyst

261

heterostructures Cu2O–Cu2O

nanofilms

photocatalyst

271

Cu2O–Cu2O

nanofilms

solar cells

273

20

25

30

35

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Table 3 Table 3 Synthesis, structures and applications of hybrid Cu2O–carbon nanostructures

Products

Reactants

Structures of Cu2O

Applications

Ref.

Cu2O–rGO

GO, glucose,

nanoparticles (5~8 nm)

supercapacitors

301

nanoparticles (~ 20 nm)

photocatalyst

302

nanoparticles (~ 4 nm)

electrocatalyst

303

nanospheres (150~200 nm)

lithium-ion battery anodes

304

polyhedral (~ 200 nm)

photocatalyst

305

nanocubes (~ 227 nm)

detection of glucose and

306

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Cu(CH3COO)2,NaOH Cu2O–rGO

GO, glucose,

Cu2O–rGO

GO, diethylene glycol, Cu(CH3COO)2,

Cu2O–rGO

GO, glucose, Cu(CH3COO)2, glycol

Cu2O–rGO

GO, CuCl2, SDS, NaOH, NH2OH3∙HCl

Cu2O–rGO

GO, CuCl2, SDS, NaOH, NH2OH3∙HCl

Cu2O–functionalized graphene

functionalized

hydrogen peroxide nanoparticles (~ 3 nm)

H2S gas sensing

309

GO, o-anisidine, KOH

octahedral constructing of

gas sensor

312

Cu(CH3COO)2

nanowires

GO, Cu(NO3)2, PSS,

nanoparticles (~ 4 nm)

cancer

313

graphene, glucose, Cu(CH3COO)2,NaOH

Cu2O–rGO Cu2O–rGO–PSS

N2H4∙H2O Cu2O–MWCNTs

Cu(CH3COO)2, DMF,

therapeutic agent nanospheres (~ 200 nm)

optical property

322

nanoparticles (~ 10 nm)

glucose sensor

323

nanoparticles (~ 4 nm)

catalyst

324

nanospindle

glucose sensor

325

nanospheres (~ 2 μm)

(near) infrared

328

nanofilms

photovoltaic performance

331

PVP and NaBH4, MWCNTs Cu2O–MWCNTs

Cu(CH3COO)2, Na2SO3, MWCNTs

Cu2O–MWCNTs

Cu(CH3COO)2, NH3∙H2O, MWCNTs

Cu2O–SMWNTs

SMWNTs, Cu(NO3)2, NaOH

Cu2O–CQDs

CuSO4, NaOH, PVP,

Cu2O–C60

C60, Au,Si wafer and

glucose, CQDs

photocatalyst

quartz glass Cu2O@PPy

CuO, pyrrole

nanowires

none

332

Cu2O/Carbon Vulcan

CuCl2, NaBH4, Cu,

nanoparticles (~ 40 nm)

glucose sensor

333

XC-72

Carbon Vulcan XC-72

5

32 | Journal Name, [year], [vol], 00–00

This journal is © The Royal Society of Chemistry [year]

Nanoscale Accepted Manuscript

Cu(CH3COO)2,NaOH,

Page 33 of 33

Nanoscale

View Article Online

DOI: 10.1039/C5NR02178B

Nanoscale Accepted Manuscript

Published on 11 May 2015. Downloaded by Carleton University on 11/05/2015 12:53:51.

Biography

(Shaodong Sun) 5

10

Dr. Shaodong Sun received his PhD degrees in Materials Science and Engineering from Xi’an Jiaotong University in 2011, and then joined in School of Science and MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter at Xi’an Jiaotong University. Currently, he is a Research Fellow in Department of Chemistry, National University of Singapore. His research interests focus on the designated synthesis of metal oxide based photocatalytic hybrid nanomaterials.

This journal is © The Royal Society of Chemistry [year]

Journal Name, [year], [vol], 00–00 | 33

Recent advances in hybrid Cu2O-based heterogeneous nanostructures.

Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties that arise from the integrated interaction between the disparate c...
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