Polymeric photocatalysts based on graphitic carbon nitride.

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Polymeric Photocatalysts Based on Graphitic Carbon Nitride Shaowen Cao, Jingxiang Low, Jiaguo Yu,* and Mietek Jaroniec* fuels,[5] decomposition and mineralization of organic pollutants,[6] selective organic synthesis,[7] and even disinfection of bacteria.[8] Research on semiconductor photocatalysis was initiated in 1972 by the pioneering work co-authored by Fujishima and Honda on TiO2 electrodes for photoelectrochemical water splitting.[9] Four years later, Carey et al. reported the photocatalytic decomposition of organic pollutants in the presence of a TiO2 photocatalyst.[10] After that, in 1979, Inoue et al. reported the photocatalytic reduction of CO2 in aqueous suspensions of semiconductor powders such as TiO2, ZnO, CdS, GaP, and SiC.[11] Since then, a huge number of research articles has been published on the development of highly efficient and stable semiconductor photocatalysts. Through this research, many semiconductors have been identified as potential photocatalysts under UV or visible light, such as TiO2,[12,13] ZnO,[14,15] SnO2,[16,17] Fe2O3,[18,19] BiVO4,[20,21] Cu2O,[22,23] and CdS[24,25] etc. Each photocatalytic reaction basically involves three processes: photon absorption; electron–hole-pair generation and separation; and catalytic surface reactions.[26] Thus, any improvement of the photocatalytic performance requires enhancement of the three aforementioned processes. So far, researchers have made numerous efforts to develop novel visible-light active photocatalysts because visible light is abundant in the solar spectrum. For example, respectively, Zou et al.[27] and Liu et al.[28] reported In1−xNixTaO4 and Y2Ta2O5N2 as novel visible-light photocatalysts for hydrogen production from water splitting. Maeda et al.[29] also found that the solid solution Ga1−xZnxO1−xNx could split water under visible light. On the other hand, doping of existing semiconductors (especially TiO2) has been shown to be an effective way of extending their light absorption to visible region.[30] However, a serious drawback of existing photocatalysts is usually their low photocatalytic efficiency due to the fast recombination of charge carriers. To improve the charge-carrier separation, an option is to develop suitable semiconductor composites that assure the opposite migration of electrons and holes by conduction-band (CB) and valence-band (VB) offsets.[31] Another choice is the immobilization of cocatalysts onto the surface of photocatalysts, which not only can improve the charge separation by capturing electrons or holes, but also favors the surface catalytic reaction by reducing the activation energy.[32] In this regard, noble metals usually serve as highly efficient cocatalysts. For instance, Yan et al.[33] developed a Pt– PdS/CdS composite photocatalyst, with a robust quantum efficiency of 93% at 420 nm. Recently, noble-metal-free cocatalysts

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4-based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4-based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4, bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4-based semiconductor composites. Also, the photocatalytic applications of g-C3N4-based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4-based photocatalysts are highlighted.

1. Introduction The increasing global crisis of energy shortage and environmental issues are becoming serious threats to the long-term development of human society. Governments and scientists are trying to find green technologies as sustainable ways to address these aforementioned concerns. Among potential solutions, semiconductor-based photocatalysis has emerged with inestimable superiority because it is considered as an economic, renewable, clean, and safe technology,[1,2] which requires only the inexhaustible solar light as a driving force, and a suitable semiconductor as a photocatalyst to conduct catalytic reactions for a variety of applications, such as hydrogen production from water splitting,[3,4] CO2 reduction into hydrocarbon

Prof. S. W. Cao, J. X. Low, Prof. J. G. Yu State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology 122 Luoshi Road, Wuhan 430070, PR China E-mail: [email protected] Prof. J. G. Yu Department of Physics Faculty of Science King Abdulaziz University Jeddah 21589, Saudi Arabia Prof. M. Jaroniec Department of Chemistry and Biochemistry Kent State University Kent, OH 44242, USA E-mail: [email protected]

DOI: 10.1002/adma.201500033

Adv. Mater. 2015, DOI: 10.1002/adma.201500033

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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have also been explored and some of them show competitive performance, as compared with noble-metal cocatalysts.[34] Graphitic carbon nitride, generally known as g-C3N4, is recognized as the most stable allotrope among various carbon nitrides under ambient conditions. The history of g-C3N4 can be traced back to the embryonic form, “melon”, found by Berzelius and Liebig in the 1830s (as described in refs.[35,36]) “Melon” is a linear polymer consisting of interconnected tri-s-triazines via secondary nitrogens, while g-C3N4 is in the form of 2D sheets consisting of tri-s-triazines interconnected via tertiary amines.[37] However, the introduction of g-C3N4 into the field of heterogeneous catalysis occurred not long ago, in 2006.[38,39] Especially, the utilization of g-C3N4 for photocatalysis was firstly reported by Wang et al. for visible-light photocatalytic water splitting.[40] Unlike TiO2, which is only active in the UV region, g-C3N4 possesses a bandgap of ca. 2.7 eV, with the CB and VB positions respectively at ca. −1.1 eV and ca. +1.6 eV vs normal hydrogen electrode (NHE).[40,41] This enables it to be a visiblelight-active photocatalyst for a range of reactions. Thermogravimetric analysis (TGA) reveals that g-C3N4 is thermally stable even in air up to 600 °C, which can be attributed to its aromatic C–N heterocycles. Due to strong van der Waals interactions between the layers, g-C3N4 is chemically stable in most solvents such as water, alcohols, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), diethyl ether, and toluene, as well as glacial acetic acid and 0.1 M NaOH aqueous solution.[42,43] Due to the similar layered structure as in graphite, the theoretical specific surface area for ideal monolayer g-C3N4 could be as high as 2500 m2 g−1.[44] More importantly, g-C3N4 is only composed of two earth-abundant elements: carbon and nitrogen. This not only suggests that it can be easily prepared at low cost, but also its properties can be tuned by simple strategies without significant alteration of the overall composition.[36,42] Moreover, its polymeric nature allows control over the surface chemistry via molecular-level modification and surface engineering. Also, the polymeric nature of g-C3N4 assures sufficient flexibility of the structure, which can serve as a host matrix of outstanding compatibility to various inorganic nanoparticles; this latter feature is very beneficial for the fabrication of g-C3N4-based composite materials. The unique aforementioned characteristics of g-C3N4 makes this material a very promising photocatalyst for various applications.[45] In recent years, great and fruitful efforts have been made in the field of g-C3N4-based photocatalysis. Herein, we present a comprehensive overview on the recent advances in the design, preparation, and applications of g-C3N4based photocatalysts. Firstly, the fabrication and nanostructure design of pristine g-C3N4 photocatalysts are introduced, followed by a thorough discussion of their bandgap engineering in terms of atomic-level doping and molecular-level modification. Next, preparation of g-C3N4-based photocatalysts is thoroughly discussed with a special emphasis on heterostructure formation. Another section of this review presents photocatalytic applications of g-C3N4-based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection; especially, those demonstrating the enhancement of photocatalytic processes by the presence of carbon materials and non-noble-metal cocatalysts and those involving Z-scheme heterojunction-enhanced photocatalysis. Finally, some concluding remarks and perspectives

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Shaowen Cao received his BS in Geochemistry in 2005 from the University of Science and Technology of China, and his Ph.D. in Materials Chemistry & Physics in 2010 from the Shanghai Institute of Ceramics, Chinese Academy of Sciences. He then worked as a Research Fellow at the School of Materials Science and Engineering, Nanyang Technological University until Feb 2014. He is now a Professor at Wuhan University of Technology. His current research interests include the design and fabrication of photocatalytic materials for energy and environmental applications. See more details at: http://www.researcherid.com/rid/I-8050-2013. Jiaguo Yu received his BS and MS in chemistry from Central China Normal University and Xi’an Jiaotong University, respectively, and his Ph.D. in Materials Science in 2000 from Wuhan University of Technology. In 2000, he became a Professor at Wuhan University of Technology. He was a postdoctoral fellow at the Chinese University of Hong Kong from 2001 to 2004, a visiting scientist from 2005 to 2006 at University of Bristol, a visiting scholar from 2007 to 2008 at University of Texas at Austin. His current research interests include semiconductor photocatalysis, photocatalytic hydrogen production, CO2 reduction to hydrocarbon fuels, for example. For more details see: http://www.researcherid.com/rid/G-4317-2010. Mietek Jaroniec received his MS and Ph.D. from M. Curie-Sklodowska University (Poland) in 1972 and 1976; afterward, he was appointed as a faculty at the same University. Since 1991, he has been Professor of Chemistry at Kent State University, Kent, Ohio (USA). His research interests include interfacial chemistry and the chemistry of materials, especially adsorption at the gas/solid and liquid/solid interfaces, and nanoporous materials. At Kent State he has established a vigorous research program in the area of nanomaterials, such as ordered mesoporous silicas, organosilicas, inorganic oxides, carbon nanostructures, and nanostructured catalysts/photocatalysts, focusing on their synthesis, characterization and environmental and energy-related applications.




REVIEW Figure 1. Schematic illustration of the main routes for the synthesis of g-C3N4 by condensation of cyanamide,[46] dicyandiamide,[47] melamine,[48] thiourea[49] and urea;[50] the color code used in chemical structures: C, black; N, red; H, blue; S, purple; O, white.

on the future exploration of g-C3N4-based photocatalysts are presented.

2. Design of g-C3N4-Based Photocatalysts 2.1. Synthesis of Pristine g-C3N4 2.1.1. Effect of Precursors and Reaction Parameters g-C3N4 can be simply prepared by the thermal condensation of several low-cost nitrogen-rich precursors (Figure 1) such

as cyanamide,[46] dicyandiamide,[47] melamine,[48] thiourea,[49] urea,[50] or mixtures thereof.[51] X-ray powder diffraction (XRD) patterns are usually used to determine the phase of carbon nitrides. The XRD patterns of g-C3N4 feature two pronounced diffraction peaks at ca. 27.4 and ca. 13.0° (Figure 2a). For graphitic materials, the former can be indexed as the 002 peak characteristic for interlayer stacking of aromatic systems, and the latter can be indexed as the 100 peak that corresponds to the interplanar separation. X-ray photoelectron spectroscopy (XPS) measurements are used to investigate the status of carbon (Figure 2b) and nitrogen elements (Figure 2c) in g-C3N4, including sp2-bonded carbon in C–C (ca. 284.6 eV) and N–C=N

Figure 2. a) XRD pattern of g-C3N4. Reproduced with permission.[40] Copyright 2009, Nature Publishing Group. b,c) High-resolution XPS spectra of C1s (b) and N1s (c) of g-C3N4. Reproduced with permission.[49] Copyright 2012, Royal Society of Chemistry.




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(ca. 288.1 eV), the sp2-bonded nitrogen in C–N=C (ca. 398.7 eV), the nitrogen in tertiary N–(C)3 groups (ca. 400.3 eV), and the presence of amino groups (C–N–H, ca. 401.4 eV) caused by imperfect polymerization. Consequently, elemental analysis is employed to determine the elemental content of g-C3N4 materials such as the C and N percentages and the C/N ratio. UV– vis diffuse reflectance spectra are commonly used to evaluate the bandgaps (Eg) of g-C3N4 samples. Roughly, Eg can be estimated by using the following simple equation: Eg = 1240/λ, in which λ [nm] is the absorption band edge of a given sample. Generally, the physicochemical properties of g-C3N4 are related to the type of the precursors and reaction parameters used. Yan et al.[48] heated melamine in a semiclosed system at different temperatures, and found that the C/N ratio of the product increased from 0.721 to 0.742, and the bandgaps decreased from 2.8 to 2.75 eV as the heating temperature increased from 500 to 580 °C. For smaller values of the C/N molar ratio than that of an ideal g-C3N4 (0.75), amine groups can be present due to incomplete condensation. It is noteworthy that the fabrication of an ideal g-C3N4 with a C/N stoichiometric ratio of 0.75 is difficult. However, a trace amount of defects in g-C3N4 could be beneficial for adjusting its bandgap. On the other hand, the existing amine groups could partially reduce the surface inertness of g-C3N4 and promote its interaction with target reactants. Nevertheless, too low a C/N stoichiometric ratio is disadvantageous and should be avoided because the excessive defects caused by incomplete condensation can negatively affect charge migration and separation. The specific surface area of g-C3N4 depends on the precursors and synthesis conditions used; for instance, a small surface area (of ca. 8 m2 g−1) was reported for melamine-derived g-C3N4.[48] Zhang et al.[49] reported the fabrication of g-C3N4 by heating thiourea at different temperatures. An increase in temperature from 450 to 600 °C favored polycondensation of g-C3N4 and subsequently improved the structural interconnectivity and increased electron delocalization in aromatic sheets. However, a higher temperature than 650 °C could cause the decomposition of g-C3N4 and thus reduce the particle size. As a result, the bandgap first decreased and then increased from 2.71 to 2.58 and 2.76 eV for the g-C3N4 prepared at 450, 550, and 650 °C, respectively. As compared with melamine-derived g-C3N4, the Brunauer–Emmett–Teller (BET) specific-surface area of thiourea-derived g-C3N4 was enhanced to 52 m2 g−1. Recently, urea was found to be a superior precursor for preparing g-C3N4 with high specific-surface area because it produces sheet-like g-C3N4 of much smaller thickness.[50,52–56] Dong et al.[50] heated urea at 550 °C for different time periods and found that the thickness of the obtained g-C3N4 was reduced from 36 to 16 nm, and the specific-surface area was enhanced from 31 to 288 m2 g−1 as the pyrolysis time (excluding heating-up time) increased from 0 to 240 min. It has been indicated from other work that g-C3N4 with a relatively higher specific-surface area could be prepared by modifying the above-mentioned precursors before their thermal treatment. For instance, Yan et al.[57] demonstrated that the g-C3N4 prepared from sulfuric-acid-treated melamine possessed higher specific-surface area (ca. 16 m2 g−1) than that prepared from untreated melamine (ca. 9 m2 g−1). The authors suggested that the modification of melamine with sulfuric acid led to a different condensation process during which

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Table 1. Bandgaps and specific surface areas for the typical g-C3N4 samples. Precursor

Reaction temperature, time and atmosphere

Band gap [eV]

Surface area [m2 g−1]

Ref.

Cyanamide

550 °C, 4 h, air

2.70

ca. 10

[46]

Melamine

500 °C, 2 h, air

2.80

ca. 8

[48]

580 °C, 2 h, air

2.75

Dicyandiamide

550 °C, 2 h, air

2.75

ca. 10

[49]

Thiourea

450 °C, 2 h, air

2.71

ca. 11

[49]

550 °C

2.58

ca. 18 ca. 52

650 °C

2.76

550 °C, 0 h, air

2.72

ca. 31

550 °C

2.68

ca. 62

550 °C

2.72

ca. 75

550 °C

2.78

ca. 288

Sulfuric-acidtreated-melamine

600 °C, 4 h, Ar gas

2.69

ca. 16

[57]

Sulfur-mixed melamine

650 °C, 2 h, N2 gas

2.65

ca. 26

[58]

Guanidine thiocyanate

550 °C, 2 h, N2 gas

2.74

ca. 8

[59]

700 °C, 2 h, N2 gas

2.89

ca. 42

Urea

[50]

the sublimation of melamine was suppressed. Zhang et al.[58] treated a mixture of melamine and sulfur (S8) at 650 °C in a N2 flow for 2 h to obtain g-C3N4 materials with higher surface areas and narrower bandgaps than those of the g-C3N4 prepared from melamine only. Interestingly, such sulfur-mediated synthesis did not cause the doping effect of sulfur but just affected the polymerization process. Long et al.[59] also reported that heat treatment of guanidine thiocyanate at 700 °C induces its desulfurization and polymerization, which leads to the formation of pristine g-C3N4 with a high crystallinity and a low density of surface defects, as well as a relatively high specific surface area, 42 m2 g−1. Table 1 summarizes the bandgaps and specific surface areas of typical g-C3N4 samples prepared by using different precursors and reaction conditions. These examples suggest that the selection of different precursors, combined with suitable control over the reaction parameters, such as the time and temperature of the thermal treatment, is an effective strategy for optimizing the electronic structure and specific surface area of g-C3N4. Among various precursors used for synthesis of g-C3N4, urea is an effective chemical to prepare thin-layer g-C3N4 with high specific surface area. However, to simplify the synthesis of g-C3N4 materials and further improve their properties, various precursors and experimental conditions should be explored, for instance as the recently reported exfoliation methods.[40,60–67]

2.1.2. Exfoliation of Bulk g-C3N4 Despite the huge theoretical specific-surface area for ideally layered g-C3N4, as-prepared bulk g-C3N4 materials usually exhibit very low specific-surface areas due to the stacking





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of the polymeric layers. To advance the utilization of g-C3N4, it is necessary to find ways to separate those stacking layers. Fortunately, existing work in the literature,[44,60–67] devoted to bulk carbon nitride, shows that this material can be exfoliated to thin layers by using appropriate methods. Actually, mechanical exfoliation, such as Scotch-tape-assisted exfoliation, which is known for the preparation of graphene from graphite, has been successfully employed for exfoliation of carbon nitride poly(triazine imide) with intercalated bromide ions.[60] However, it has not been reported yet for processing tri-s-triazinebased carbon nitrides. Here we briefly summarize various exfoliation methods for g-C3N4. Yang et al.[61] reported a sonication-assisted liquid-exfoliation method to prepare thin-layer g-C3N4 nanosheets from bulk g-C3N4. It was found that isopropyl alcohol, having a low boiling point, is an excellent solvent to exfoliate bulk g-C3N4 on a large scale under continuous sonication. The thickness of the resultant g-C3N4 nanosheets was very small (ca. 2 nm), which is essential for achieving the high surface area of this material, 384 m2 g−1. Electrochemical impedance spectroscopy (EIS) studies have shown that the electron transfer resistance (estimated from semicircular Nyquist plots) of the thin-layer g-C3N4 nanosheets was decreased by 75% as compared to the bulk g-C3N4, suggesting an improvement in the charge transport and separation ability of these nanosheets. This was further evidenced by photoluminescence (PL) spectra of g-C3N4, in which a significantly weaker PL intensity corresponding to a lower recombination rate of photoinduced electrons and holes was observed after exfoliation. In other work, She et al.[62] sonicated bulk g-C3N4, which had a surface area of ca. 3 m2 g−1, in 1,3-butanediol and obtained thin-layer g-C3N4 that had a thickness of ca. 3–6 atoms (ca. 0.9–2.1 nm). An increased surface area of ca. 32 m2 g−1 was thus achieved. Similarly, EIS studies revealed that the electron-transfer resistance of g-C3N4 was decreased by 60% after exfoliation. Also, transient photocurrent measurements showed that a higher photocurrent was obtained for thin-layer g-C3N4 under visible-light irradiation. This combined photo-electrochemical analysis indicated an improvement in the transport and separation of photoinduced charge carriers in the thin-layer g-C3N4 nanosheets. Kumar et al.[63] have also simply fabricated mesoporous g-C3N4 by sonicating melamine-derived bulk-g-C3N4 suspensions in mixed solvents of ethanol and water. The surface area of this mesoporous g-C3N4 was ca. 112 m2 g−1, which is much higher than that of bulk g-C3N4 (ca. 8 m2 g−1). In addition to the exfoliation methods in the presence of organic solvents, acid or base solutions can also be used to exfoliate bulk g-C3N4 into g-C3N4 thin layers. Xu et al.[64] mixed dicyandiamide-derived g-C3N4 with concentrated H2SO4 in deionized water and sonicated for exfoliation. This exfoliation process assured intercalation of H2SO4 into the interlayers of the bulk g-C3N4, successfully generating g-C3N4 nanosheets that had a thickness of a single atomic layer (ca. 0.4 nm). These g-C3N4 nanosheets showed a much higher surface area (ca. 206 m2 g−1) than the bulk g-C3N4 (ca. 4 m2 g−1). Photocurrent and EIS measurements revealed improved transport and separation of the photogenerated charge carriers in these single-atomic-layer g-C3N4 nanosheets. Sano et al.[44] hydrothermally treated melamine-derived g-C3N4 with NaOH solution. The grain size of the resulting g-C3N4 was significantly reduced, along with the

formation of a mesoporous structure, and the surface area was enlarged from ca. 8 to 65 m2 g−1. Niu et al.[65] applied a simple thermal-oxidation etching route to exfoliate the dicyandiamide-derived bulk g-C3N4 into ca. 2 nm g-C3N4 nanosheets with a high surface area of 306 m2 g−1. Current–voltage characteristics analysis indicated an improved electron-transfer ability across the in-plane direction of these nanosheets. Time-resolved fluorescence decay spectra revealed an increased lifetime of the photoinduced charge carriers due to the quantum-confinement effect. Xu et al.[66] first intercalated NH4Cl into the interlayers of dicyandiamide-derived g-C3N4. The resulting g-C3N4-based intercalation compound (g-C3N4/NH4Cl) was then treated via a thermal exfoliation process. This process resulted in nanosheets of g-C3N4 that were 6–9 atomic layers thick (thickness of ca. 2–3 nm), showing a surface area of ca. 30 m2 g−1 and an improved electron-transport ability. The aforementioned thermal exfoliation methods are considered to be low-cost, large-scale, and environmentally friendly ways of preparing thin-layer g-C3N4. Furthermore, Zhao and co-workers[67,68] combined the thermal exfoliation method with a sonication process in organic solvents such as isopropyl alcohol and methanol, which resulted in single-atomic-layer g-C3N4 nanosheets with a thickness of 0.4–0.5 nm. Such ultra-thin layers of g-C3N4 assure a short distance for the migration of charge carriers. Consequently, a much higher charge-separation efficiency was obtained for the ultrathin g-C3N4, as evidenced by its 17-times-higher photocurrent and lower charge-transfer resistance. Moreover, time-resolved fluorescence decay spectra revealed a longer lifetime of the photoinduced charge carriers as compared to that of bulk g-C3N4. In summary, an effective exfoliation of bulk g-C3N4 into thinlayer g-C3N4 nanosheets can be achieved in organic solvents, or acid or base media via liquid-type exfoliation or by simple thermal exfoliation, as illustrated in Figure 3. Importantly, almost single layers of g-C3N4 can be obtained by these simple methods, which allows for better understanding of the physicochemical properties of g-C3N4. Generally, the superiority of the resultant g-C3N4 thin layers can be related to the enlarged specific surface area, improved electron transport ability, and enhanced charge separation efficiency.

2.1.3. Nanostructure Design of g-C3N4 As a polymer, g-C3N4 has a flexible structure and is thus well suited to form different morphologies with the assistance of different templates. Indeed, several typical nanostructures of g-C3N4 have been obtained, such as porous g-C3N4, hollow spheres and 1D nanostructures; a brief overview of these structures is presented below. Porous g-C3N4: Porous photocatalysts are extremely fascinating, because the porous structure can provide a large surface area and numerous channels to facilitate mass diffusion, as well as charge migration and separation. Hard and soft templating methods are often used because they allow tuning of the porous structure of g-C3N4 by choosing different templates. Mesoporous g-C3N4 has been successfully obtained by using various precursors such as cyanamide,[69,70] ammonium thiocyanate,[71,72] thiourea,[73] and urea[74] in the presence of silica nanoparticles used as a hard template, the removal of which generated a 3D



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Figure 3. a) Schematic illustration of different routes for exfoliation of the bulk g-C3N4 to a few-layer g-C3N4. b,c) AFM image (b) and the corresponding thickness analysis (c) taken around the white line in (b) for g-C3N4 nanosheets prepared by sonication-assisted liquid-exfoliation method Reproduced with permission.[61] Copyright 2013, Wiley-VCH. d,e) TEM image (d) and AFM image (e) of g-C3N4 nanosheets prepared by thermal oxidation etching route. The inset in panel (e) is the height curve determined along the line between P1 and P4. Reproduced with permission.[65] Copyright 2012, WileyVCH. f,g) SEM image (f) and AFM image (g) of g-C3N4 nanosheets prepared by combined thermal exfoliation-sonication process. Reproduced with permission.[67] Copyright 2014, Elsevier.

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REVIEW Figure 4. a) Illustration of the SBA-15-hard templating route for the preparation of ordered mesoporous g-C3N4. CA stands for cyanamide. b) TEM image of the resulting material. Reproduced with permission.[76] Copyright 2013, Wiley-VCH.

interconnected structure of g-C3N4 with a large surface area up to 373 m2 g−1. The resulting pore size was consistent with the size of the silica nanoparticles used as the template. Hexagonally ordered mesoporous silica, SBA-15, has also been used as a hard template to synthesize ordered mesoporous g-C3N4.[75] The resulting g-C3N4 is actually an inverse replica of the SBA-15 template. Accordingly, Chen et al.[75] reported the synthesis of ordered mesoporous g-C3N4 with a large surface area of 239 m2 g−1 and pore volume of 0.34 cm3 g−1 using cyanamide as the precursor. The pore size of this material was ca. 5.3 nm, which is smaller than that of the SBA-15 template (10.4 nm). This is not surprising, because the size of the pores in an inverse replica of SBA-15 do not correspond to the pore size, rather to the pore-wall thickness of the template. To improve the interaction between the silica template and the cyanamide, Zhang et al.[76] pre-treated SBA-15 with dilute HCl. Then, sonication and vacuum was applied to enhance the infiltration of cyanamide molecules into the pores of SBA-15 (Figure 4). As a result, ordered mesoporous g-C3N4 with a much higher surface area of 517 m2 g−1 and a larger pore volume of 0.49 cm3 g−1 was prepared. Fukasawa et al.[77] applied close-packed uniform-sized silica-nanosphere assemblies as a template and cyanamide as a precursor to prepare inverse opal g-C3N4 ordered mesostructures. This strategy allowed tuning of the average pore size of g-C3N4 from 13 to 70 nm by changing the size of the primary silica nanospheres from 20 to 80 nm. The highest surface area of 230 m2 g−1 was obtained for the sample having 20 nm pores, while the largest pore volume of 1.70 cm3 g−1 was obtained for the sample having 70 nm pores. Interestingly, the g-C3N4 ordered porous structures could further serve as hard templates to prepare regularly arranged and size-tunable Ta3N5 nanoparticles. Also, porous g-C3N4 has been successfully prepared without hard templates. For instance, soft template such as Pluronic P123 was used to prepare a melamine-derived mesoporous g-C3N4 with a high surface area of 90 m2 g−1 and an extended range of light absorption up to 800 nm.[78] A facile and nontoxic bubble-templating method was recently developed to fabricate nanoporous g-C3N4. In this method, dicyandiamide was used as a precursor, and thiourea[79] or urea[80] served as the bubble-forming template. The decomposition of the thiourea or urea generated gas bubbles during thermal treatment and induced the formation of a g-C3N4 porous structure, which showed a much higher surface area than g-C3N4 prepared from pure dicyandiamide. Other studies


indicate that, in some cases, porous g-C3N4 can be obtained by template-free methods. For example, Dong and Zhang[81] found that replacing melamine with melamine hydrochloride as a precursor could generate porous g-C3N4 with a surface area of 69 m2 g−1. Han et al.[82] controlled the inherent decomposition of the dicyandiamide according to Le Chatelier's principle in a semiclosed system with different window sizes. The surface area and the pore volume of the obtained porous g-C3N4 could reach 201–209 m2 g−1 and 0.50–0.52 cm3 g−1, respectively. Shen et al.[83] used cyanuric acid as a polymerization inhibitor of melamine and obtained hierarchically structured porous g-C3N4. Hollow Spheres: Photocatalysts in the form of hollow spheres are attractive because they are able to harvest more incident light through successive reflections within the hollow structure and can produce more photoinduced charge carriers. However, the preparation of hollow g-C3N4 spheres is difficult because of the layered structure of polymeric g-C3N4, which is susceptible to collapse during processing. Nevertheless, several attempts toward the preparation of hollow g-C3N4 spheres have been quite successful. Sun et al.[84] coated monodisperse silica nanoparticles with thin mesoporous silica shells. These core–shell structures were then used as hard templates to prepare g-C3N4 hollow nanospheres. Namely, the aforementioned mesoporous shells were infiltrated with cyanamide, followed by its thermal condensation and the subsequent removal of the whole silica core–shell template; the resulting uniform g-C3N4 hollow nanospheres are shown in Figure 5. The shell thickness of the hollow g-C3N4 nanospheres could be tuned from 56 to 85 nm simply by varying the thickness of the mesoporous silica shells. g-C3N4 hollow nanospheres can serve as light-harvesting antennas and also an excellent platform for the construction of specific photocatalytic systems. Very recently, the supramolecular chemistry of triazine molecules was shown to be attractive for the preparation of g-C3N4 hollow structures. In this case, the molecular cooperative assembly of the triazine molecules resulted in the formation of a hydrogen-bonded supramolecular network precursor such as the cyanuric acid–melamine complex. This complex can be prepared in different morphological forms depending on the solvent used; for example, 3D macroscopic assemblies[85] or flower-like layered spherical aggregates[86] in dimethyl sulfoxide, and an ordered pancake-like structure[87] in ethanol have been obtained. After thermal polycondensation, these initial morphological forms of the precursor were partially preserved along with the creation of



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1D Nanostructures: 1D nanostructured photocatalysts such as nanorods, nanowires, nanobelts, and nanotubes continue to attract special attention because, through tuning their length, diameter, and aspect ratio, unique chemical, optical and electronic properties can be achieved, which is beneficial for optimizing their photocatalytic activity. Li et al.[88] prepared condensed g-C3N4 nanorods with an average diameter of 260 nm by the thermal condensation of cyanamide in the presence of an anodic aluminum oxide (AAO) template. The confinement effect of the AAO template was crucial for improving both the crystallinity and the orientation of the g-C3N4 to enhance the charge-carrier mobility. The resultant g-C3N4 nanorods also possessed a more-positive VB position, essential for a stronger oxidation power. Furthermore, the authors used SBA-15 nanorods as a template to prepare mesoporous g-C3N4 nanorods via a nanocasting process (Figure 6).[89] The obtained g-C3N4 nanorods had a diameter of ca. 100 nm, a large surface area of 110–200 m2 g−1, and well-defined Figure 5. a) An illustration of the preparation of g-C3N4 hollow nanospheres and metal/g-C3N4 mesochannels; thus, they were well suited for hollow nanosphere composites (CY stands for cyanamide). b–d) TEM images of g-C3N4 hollow loading various uniform metal nanoparticles nanospheres with different thickness. Scale bars equal 0.5 µm. a–d) Reproduced with permisfor different catalytic/photocatalytic applicasion.[84] Copyright 2012, Nature Publishing Group. tions. Bai et al.[90] reported a template-free preparation of g-C3N4 nanorods via a simple reflux process in hollow interiors within them. The resulting products were shown to be hollow 3D assemblies, mesoporous hollow spheres, and mixed solvents of methanol and H2O using g-C3N4 nanoplates hollow boxes, which exhibited excellent photocatalytic activity. as precursors, which were synthesized by thermal treatment

Figure 6. a) Schematic diagram for the synthesis of mesoporous g-C3N4 nanorods using SBA-15 nanorods as a template. CA stands for cyanamide. Adapted with permission.[89] Copyright 2012, Royal Society of Chemistry. b) Typical TEM image of mesoporous g-C3N4 nanorods. The inset shows the particle size distribution. Reproduced with permission.[89] Copyright 2012, Royal Society of Chemistry.

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of dicyandiamide at 550 °C for 4 h. The original g-C3N4 nanoplates were transformed to nanorods with a diameter of 100–150 nm, possibly via an exfoliation–regrowth and rolling mechanism. It was shown for the g-C3N4 nanorods that the active lattice face was increased and surface defects were decreased, which is beneficial for photocatalytic reactions. g-C3N4 nanorod networks were fabricated by a solvothermal method using cyanuric chloride and melamine in a sub-critical acetonitrile solvent.[91] This synthetic route only required a temperature of 180 °C, which is much lower than that used for traditional solidstate syntheses (normally 500–600 °C). The nanorod content was more than 90% in the produced sample, with an average size of 50–60 nm and a length of several micrometers, which was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging (Figure 7). While at a lower reaction temperature of 160 or 140 °C, the morphological features are less pronounced. To ensure a


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Figure 7. a,b) SEM (a) and TEM (b) images of g-C3N4 nanorod networks. The inset of (a) shows a corresponding digital photograph. a,b) Reproduced with permission.[91] Copyright 2012, Wiley-VCH.

sufficient thermodynamic driving force for the formation of such g-C3N4 nanorod networks, a solvothermal time of 96 h was necessary. Shorter times of 48 or 24 h were not sufficient to ensure covalent crosslinking and assembly of the molecular tectons. Acetonitrile, as a more-polar solvent, was required in this solvothermal process. It could facilitate the condensation and crystallization of carbon nitrides, whereas nonpolar solvents such as benzene, cyclohexane, and carbon tetrachloride led only to a low polymerization yield of 400 nm) using triethanolamine as a sacrificial agent. The light intensity was measured to be ca. 180 mW cm−2. The Ni(OH)2/g-C3N4 composites exhibited efficient hydrogen-evolution activity under visible-light irradiation with a rate of 7.6 μmol h−1 (for 0.05 g of catalyst in 80 mL of 10 vol% triethanolamine aqueous solution) at the optimal loading of 0.5 mol% Ni(OH)2. The corresponding apparent quantum efficiency was 1.1% at 420 nm. Such a cocatalytic performance of Ni(OH)2 was attributed to the lower potential of Ni2+/Ni than the CB of g-C3N4, which enables Ni(OH)2 to trap the photogenerated electrons from the g-C3N4. Meanwhile, the potential of Ni2+/Ni was still negative enough to drive the water-reduction process. Moreover, these Ni(OH)2/g-C3N4 composites showed good photocatalytic stability as demonstrated by cycling experiments. Hong et al.[288] prepared a NiS/g-C3N4 photocatalyst by a simple hydrothermal method. The maximum visiblelight photocatalytic hydrogen-production rate of 48.2 μmol h−1 for 0.1 g of catalyst in 100 mL of 15 vol% triethanolamine aqueous solution was obtained with 1.1 wt% NiS as a cocatalyst, using a 300 W Xenon lamp equipped with a 420 nm cutoff filter as the light source. The corresponding apparent quantum efficiency was 1.9% at 440 nm. A 2D composite of g-C3N4 and MoS2 was prepared by Hou et al.[294] The resulting layered nanojunctions showed a large contact area that favored interfacial electron transfer. The well-matched positions between the CB of g-C3N4, the CB of MoS2, and the water-reduction potential also favored electron transfer from g-C3N4 to MoS2 and the subsequent water reduction reaction on the surface of MoS2. The resulting visiblelight photocatalytic hydrogen rate of the optimal 0.2 wt% MoS2/ g-C3N4 was more than 25 μmol h−1 (for 0.02 g of catalyst in 100 mL of 10 vol% lactic acid aqueous solution) under irradiation of a Xenon 300 W lamp equipped with a 420 nm cutoff filter and a water IR filter, with an apparent quantum efficiency of 2.1% at 420 nm. It is noteworthy that the cocatalytic performances of Ni(OH)2, NiS, and MoS2 are competitive with that of platinum (see Table 3). This gives strong confidence for the future development of low-cost photocatalytic systems for clean energy production. In summary, polymeric g-C3N4-based photocatalysts are considered as a viable alternative for hydrogen production under visible-light irradiation with the assistance of appropriate cocatalysts. However, noble-metal cocatalysts are unsuitable if one consider a fully economical system for clean energy production. Thus, it would be ideal to use carbon materials and nonnoble-metal cocatalysts for visible-light-induced photocatalytic hydrogen evolution over g-C3N4-based photocatalysts. 3.2. Photocatalytic CO2 Reduction Apart from photocatalytic hydrogen production, photoreduction of CO2 into hydrocarbon fuels using semiconductor photocatalysts has been considered as an optional technique to solve the global energy shortage, which will also reduce the greenhouse effect. As shown in Reactions 1 to 5,[5,301] CO2 reduction is a multielectron transfer process for converting CO2 into formic acid, carbon monoxide, methanal, methanol and methane with appropriate reduction potential requirements, respectively.



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www.MaterialsViews.com Table 3. Photocatalytic H2 evolution on g-C3N4 with non-noble-metal cocatalysts. Mass fraction of cocatalysts

Total mass of catalysts

Reactant solution

Light source (wavelength [nm])

Activitya) [µmol h−1]

Quantum efficiency [%]

Reference cocatalyst; Photocatalytic activity [µmolh−1]

Ref.

0.5 mol%

0.05 g

80 mL of 10 vol% triethanolamine aqueous solution

350 W Xe lamp (>400 nm)

7.6

1.1 (420 nm)

1.0 wt% Pt; 8.2

[287]

NiS

1.1 wt%

0.10 g


300 W Xe lamp (>420 nm)

48.2

1.9 (440 nm)

Pt; ca. 1.43 times that of NiSb)

[288]

NiS

1.5 mol%

0.10 g


300 W Xe lamp (>420 nm)

44.77

\

2.0 wt% Pt; 47.61

[289]

NiS2

2.0 wt%

0.01 g


300 W Xe lamp (>420 nm)

4.06

\

1.0 wt% Pt; 1.07

[290]

2.0 wt% of Ni2+

0.002 g g-C3N4 + 0.68 µmol cocatalyst


500 W Xe lamp (>400 nm)

4.87

1.51 (400 nm)

Pt; Quantum efficiency 1.83% (400 nm)

[291]

\

0.10 g g-C3N4 + 0.05 mmol cocatalyst

90 mL of H2O + 20 mL of triethanolamine

300 W Xe lamp (simulated solar light)

51

0.2 (420 nm)

3.0 wt% Pt; 59

[292]

Ni(dmgH)2

3.5 wt%

0.005 g


300 W Xe lamp (>420 nm)

1.18

\

\

[293]

MoS2

0.2 wt%

0.02 g

100 mL of 10 vol% lactic acid aqueous solution

300 W Xe lamp (>420 nm)

>25

2.1 (420 nm)

2.0 wt% Pt; >20

[294]

WS2

0.3 at%

0.05 g

100 mL of 10 vol% lactic acid aqueous solution

300 W Xe lamp (>420 nm)

ca. 12

\

\

[296]

0.34 mol%

0.10 g

80 mL of 25 vol% methanol aqueous solution

300 W Xe lamp (>400 nm)

4.87

\

\

[297]

\

0.01 g g-C3N4 + 0.002 g cocatalyst


300 W Xe lamp (350–740 nm)

2.6

0.62 (365 nm)

\

[298]

Cocatalysts

Ni(OH)2

[Ni(TEOA)2]Cl2c)

Ni–Tu–TETNd)

Cu(OH)2 CoIII(dmgH)2pyCl

a)Determined by using a gas chromatography with a thermal conductivity detector; b)Calculated from the original ref. [288]; c)Formed in situ during the photocatalytic reaction; d)Formed in situ during the photocatalytic reaction.

CO2 + 2H+ + 2e − → HCOOH 0 = −0.61V ( vs. NHE at pH 7 ) E redox

(1)

CO2 + 2H+ + 2e − → CO + H2 O 0 = −0.53V ( vs. NHE at pH 7 ) E redox

(2)

CO2 + 4H+ + 4e − → HCHO + H2 O 0 = −0.48V ( vs. NHE at pH 7 ) E redox

(3)

CO2 + 6H+ + 6e − → CH3 OH + H2 O 0 = −0.38V ( vs. NHE at pH 7 ) E redox

(4)

CO2 + 8H+ + 8e − → CH4 + 2H2 O 0 = −0.24 V ( vs.NHE at pH 7 ) E redox

(5)

Recent work[81,168,302–309] in this area demonstrates that g-C3N4 can serve as a potential candidate to drive the photocatalytic reaction of CO2 reduction. Dong and Zhang[81] found that g-C3N4 prepared from melamine hydrochloride could effectively photocatalyze the reduction of CO2 into CO in the presence of water vapor under visible-light irradiation and without any

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cocatalyst. Mao et al.[302] revealed that urea-derived g-C3N4 (u-gC3N4) exhibited better visible-light photocatalytic CO2 reduction performance than the melamine-derived g-C3N4 (m-g-C3N4), due to its mesoporous flake-like structure, larger surface area, and smaller crystal size. More interestingly, the photocatalytic product over u-g-C3N4 was CH3OH and C2H5OH, while it was only C2H5OH over m-g-C3N4 (Figure 17). Our work suggests that the introduction of a Pt cocatalyst onto g-C3N4 could improve both the photoactivity and selectivity for CO2 reduction into CH4, CH3OH, and HCHO under UV–vis light irradiation.[303] Bai et al.[304] loaded Pd cocatalysts with different facets onto g-C3N4 and found that the CO2 reduction occurred better on Pd{111} facets rather than Pd{100} facets. Maeda et al.[305] coupled g-C3N4 with a small amount of a molecular ruthenium complex, cis,trans-[Ru{4,4′-(CH2PO3H2)2-2,2′-bipyridine} (CO)2Cl2] as a catalytic center. As a result, efficient photocatalytic CO2 reduction into HCOOH with a selectivity of >80% was achieved under visible light. Lin et al.[306] constructed a photoreaction system composed of g-C3N4 as a photocatalyst, CoOx as an oxidative cocatalyst, and Co-bipyridine complex (Co(bpy)32+) as an electron mediator (Figure 18). This inexpensive system exhibited efficient visible-light photocatalytic activity for the reduction of CO2 into CO. In addition, the wavelengthdependent CO production matched well with the UV−vis




REVIEW Figure 16. a) TEM image of the Ni0.5 sample. b) Schematic illustration of visible-light photocatalytic mechanism for the Ni(OH)2/g-C3N4 composites. c) Comparison of the photocatalytic H2 production from triethanolamine aqueous solution using the Ni(OH)2 and Pt-deposited g-C3N4 samples. Nix stands for Ni(OH)2/g-C3N4 with x mol% of Ni(OH)2. d) Cycling test for photocatalytic H2 evolution activity of the Ni0.5 sample. a,c,d) Reproduced with permission.[287] Copyright 2013, Royal Society of Chemistry. b) Adapted with permission.[287] Copyright 2013, Royal Society of Chemistry.

diffuse reflectance spectrum of g-C3N4, which suggested that the CO2 photoreduction is associated with the charge-generation–separation-transfer dominated catalysis. Moreover, an excellent stability was observed for this photocatalytic system. Our work shows that the semiconductor heterojunctions such as g-C3N4/In2O3[168] and g-C3N4/red phosphor[309] are capable of photocatalyzing the conversion of CO2 into CH4. The aforementioned work indicate that the photocatalytic efficiency and selectivity of CO2 reduction are highly dependent on the structures of g-C3N4-based photocatalysts and cocatalysts. Non-noble-metal cocatalysts have been also successfully coupled with g-C3N4 to fabricate low-cost systems for the photoreduction of CO2. However, current studies are highly limited by the efficiency and stability of these materials; a sustained effort over a long period is expected to be required to advance the development of both photocatalysts and cocatalysts. 3.3. Photocatalytic Removal of Pollutants Semiconductor photocatalysis is an effective and economic strategy to deal with the environmental problems caused by organic pollutants. Due to the unique electronic structure and physicochemical properties, g-C3N4 has been widely used for the


photocatalytic degradation of various contaminants, including methyl orange (MO),[48,95,105,127,180,243,310–315] rhodamine B (RhB),[41,86,109,158,316–331] methylene blue (MB),[52,66,147,153,202,332–342] aromatic compounds,[47,72,74,80,97,108,143,150,152,154,162,166,175,198,220,221,223,343–346] aldehydes,[141,142,161,163,344] and so on. The removal of inorganic toxic gas NO[44,50,73,218,250,347,348] in air and the reduction of heavy metal ion Cr(VI)[144,155,341,346,349] have also been investigated. Particularly, g-C3N4 loaded with Au[312] or Ag nanoparticles[313] showed excellent photocatalytic activity for the decomposition of methyl orange (MO) due to the synergistic action of surface plasmon resonance and the electron-sink effect of Au or Ag nanoparticles. In another report, Han et al.[315] introduced Co3O4 into g-C3N4 to trap the photogenerated holes of g-C3N4, which resulted in efficient MO degradation. A ternary-layered nanojunction of g-C3N4/nitrogen-doped graphene/MoS2 was prepared by Hou et al.[341] and it exhibited efficient visible-light photocatalytic performance toward the degradation of MB and the reduction of Cr(VI), which could be attributed to enhanced light absorption, effective charge migration and interfacial charge separation. g-C3N4/carbon composites have been shown to be advantageous for the degradation of various pollutants, e.g., g-C3N4/ ordered mesoporous carbon for RhB degradation,[326] g-C3N4/ graphene for RhB degradation,[328] g-C3N4/C60 for RhB[327]



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Figure 17. a,b) TEM images of u-g-C3N4 (a) and m-g-C3N4 (b). a,b) Reproduced with permission.[302] Copyright 2013, Royal Society of Chemistry. c) The photocatalytic CO2 conversion over different samples (0.2 g) under 12 h visible-light irradiation (λ > 420 nm). c) Adapted with permission.[302] Copyright 2013, Royal Society of Chemistry.

and MB degradation,[339] g-C3N4/CNT for MB degradation,[338] g-C3N4/graphene oxide for RhB and 2,4-dichlorophenol degradation,[329] and so on. This can be mainly attributed to several reasons listed below. Firstly, the conductive carbon materials can serve as efficient electron-transfer channels and acceptors to improve the separation of photogenerated electron–hole pairs. Secondly, carbon materials may act as cocatalysts to provide sufficient catalytic sites for photocatalytic degradation. Lastly, black carbon materials can absorb more light with a longer wavelength. Although the longerwavelength light is not able to excite g-C3N4 to generate electrons and holes, it may result in a photothermal effect that is beneficial for catalytic reactions. However, the amount of the loaded black carbon should be carefully controlled because its excess may cause a negative shielding effect for light harvesting. It should be emphasized that g-C3N4-based all-solid-state Z-scheme heterojunctions exhibit extremely superior photocatalytic activity for organic-pollutant degradation as compared with

pure g-C3N4. For example, the decomposition of methanal and ethanal was hardly noticed with pure g-C3N4, whereas it was efficient with the Z-scheme heterojunctions of g-C3N4-TiO2,[142] g-C3N4-sulfur-doped TiO2,[141] and g-C3N4-WO3.[163] In another case, the g-C3N4-MoO3 Z-scheme heterojunction[174] showed its universality for the degradation of different dyes including MO, RhB and MB. It is known that photogenerated holes (h+), hydroxyl radicals (•OH) and superoxide anion radicals (•O2−) are the main reactive species to oxidize organic pollutants during photocatalytic reactions. However, pure g-C3N4 is not able to drive the oxidation process of H2O to generate •OH due to its less-positive VB position than the •OH/H2O potential (ca. 2.27 V),[350] which results in an insufficient oxidation ability. Contrarily, in a Z-scheme heterojunction such as g-C3N4− TiO2,[142] the photogenerated electrons and holes remain in the CB of the g-C3N4 and the VB of the TiO2 respectively, which not only enables effective spatial separation of the charge carriers, but also preserves the strong reduction and oxidation ability of the photogenerated electrons and holes (Figure 19a). Thus, the optimal g-C3N4–TiO2 sample exhibited a methanal decomposition rate more than twice higher as compared with that of P25 (Figure 19b). Therefore, it is not surprising that a much higher photocatalytic efficiency can be obtained for g-C3N4-based allsolid-state Z-scheme heterojunctions toward the degradation of organic pollutants due to the high spatial-charge-separation efficiency, together with excellent redox ability. 3.4. Photocatalytic Organic Syntheses

Figure 18. Synergistic action of Co-bipyridine complex and CoOx in the case of CO2 photoreduction over g-C3N4 (g-CN). Reproduced with permission.[306] Copyright 2013, American Chemical Society.

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Recently, g-C3N4-based photocatalysts have been shown to have great potential for selective organic transformation under mild conditions. Wang and co-workers reported a series of work demonstrating the effective photocatalytic oxidation of aromatic compounds on g-C3N4-based photocatalysts, including the selective oxidation of benzene to phenol,[351–353] aromatic alcohols to aldehydes,[354,355] aromatic amines to imines,[356] and so on. It was found that under visible-light irradiation, g-C3N4 modified by iron complexation, i.e., Fe/g-C3N4 showed remarkably improved activity to convert benzene to phenol in the presence of H2O2, as compared with the case without visible-light irradiation.[351,352] In another report, Zhang et al.[357] revealed that a 38% conversion of benzene to phenol with 97%




REVIEW

occur either with or without the electron mediator. Particularly, a 100% yield of 1,4-NADH could be achieved in the presence of [Cp*Rh(bpy)H2O]2+ as an electron mediator. The resultant NADH could be further applied to reduce H2O2 to H2O, mediated by horseradish peroxidase. Other work has indicated the effective photocatalytic esterification of benzaldehyde and alcohol in the presence of g-C3N4,[362] oxidative cleavage of the carbon–carbon bond of α-hydroxy ketones in the presence of mesoporous g-C3N4,[363] and allylic oxidation in the presence of g-C3N4 and N-hydroxy compounds.[364] A composite CdS/g-C3N4 photocatalyst was used to selectively catalyze the oxidation of aromatic alcohols into aldehydes and the reduction of nitrobenzene into aniline.[365] Photocatalytic selective production of hydrogen peroxide that is an important clean oxidant for organic synthesis, has also been achieved on g-C3N4 under visible-light irradiation, in an alcohol/water mixture in the presence of O2.[366]

3.5. Photocatalytic Disinfection

Figure 19. a) Schematic illustration of Z-scheme mechanism for g-C3N4– TiO2 photocatalyst under UV light irradiation. Reproduced with permission.[142] Copyright 2013, Royal Society of Chemistry. b) Rate constant of the photocatalytic decomposition of HCHO for different samples. Ux stands for urea (precursor for g-C3N4) with certain weight percentage ratios against P25. Adapted with permission.[142] Copyright 2013, Royal Society of Chemistry.

selectivity could be achieved using FeCl3-modified mesoporous carbon nitride as a visible-light photocatalyst to activate H2O2. Mesoporous carbon nitride was also able to activate O2 under visible light to oxidize benzyl alcohols to benzaldehydes,[354] various amines to imines,[356] and methyl phenyl sulfide to methyl phenyl sulfoxide[358] with a high selectivity up to 99%, as well as the formation of new C–C bonds through connecting N-aryltetrahydroisoquinolines with nitroalkanes or dimethyl malonate.[359] Li et al.[360] developed a Mott–Schottky photocatalyst consisting of mesoporous carbon nitride with Pd nanoparticles. The efficient electron transfer from the g-C3N4 to the Pd resulted in a high photocatalytic activity and selectivity for the room-temperature C–C bond formation by coupling aryl halides with different coupling partners. Liu and Antonietti[361] employed diatom-structured g-C3N4 to photocatalyze the regeneration of nicotinamide adenine dinucleotide hydrogen (NADH) from the reduction of NAD+, which could


As a nontoxic, efficient, and stable method, photocatalytic disinfection has been shown to be superior in comparison with traditional disinfection methods, such as chlorination and UV disinfection. Recent studies have demonstrated that g-C3N4based photocatalysts exhibit antibacterial activity under visiblelight irradiation. Wang et al.[367] revealed the photocatalytic inactivation of Escherichia coli cells by graphene and g-C3N4 nanosheets co-wrapped with cyclo-octasulfur (α-S8); the composites with different wrapping sequences possessed different inactivation abilities. Under visible-light irradiation, both g-C3N4 and α-sulfur were excited. In the case of reduced graphene oxide (rGO) (middle layer) sandwiched in g-C3N4 (outer layer) and α-S8 (inner layer), a fast spatial charge separation between g-C3N4 and α-S8 was achieved via rGO, which acted as a charge-transfer mediator, and the photoinduced electrons were accumulated in the CB of the α-S8, while the photoinduced holes were accumulated in the VB of the g-C3N4. However, in the case of a g-C3N4 (middle layer) sandwiched between rGO (outer layer) and α-S8 (inner layer), rGO was unable to be an effective charge-transfer mediator for such spatial separation. As a result, the former structure showed a much higher photocatalytic inactivation activity of E. coli cells in aerobic conditions due to the effective formation of reactive oxidative species such as OH•, O2•− and H2O2. Zhao et al.[67] also indicated that complete destruction of E. coli bacteria could be achieved on atomic single-layer g-C3N4. In a very recent report, Huang et al.[368] found that mesoporous g-C3N4 is effective and recyclable for visible-light photocatalytic inactivation of E. coli bacteria, more likely following a hole-dominant oxidative pathway. These examples reveal the good antibacterial activity of g-C3N4-based photocatalysts under visible-light irradiation. However, studies in this area are at the initial stage, and intensive investigations of the photocatalytic disinfection over various g-C3N4-based photocatalysts are highly encouraged.

4. Summary and Outlook This review shows that g-C3N4 is a promising visible-light photocatalyst due to its unique electronic structure with both



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a narrow bandgap and appropriate CB and VB positions, as well as high stability against high temperature, acids, bases, and organic solvents. The preparation of g-C3N4 can be simply accomplished by thermal condensation of low-cost nitrogenrich precursors, and thus, it is economic and environmentally friendly. Although g-C3N4 exists usually in the form of stacked polymeric nanosheets, which results in its small surface area, this disadvantage can be easily diminished by choosing different precursors, liquid-exfoliation or thermal-exfoliation methods to reduce the thickness of g-C3N4. Nanostructural design based on templating strategies, supramolecular-chemistry methods, and even template-free routes can afford highly porous structures, hollow spheres, and 1D nanostructures of g-C3N4 with large surface area and/or enhanced light-harvesting capability, also sometimes with improved charge-carrier mobility. Its simple chemical composition from carbon and nitrogen also enables it to be effective in the modification of g-C3N4 at the atomic level (such as elemental doping) and the molecular level (such as copolymerization) to modulate its band structure for better light-absorption ability or stronger redox ability. In addition, g-C3N4-based semiconductor composites can be effectively developed to promote charge transfer and separation for photocatalytic reactions, mostly in the form of traditional type-II heterojunctions and all-solid-state Z-scheme heterojunctions. These modification strategies give rise to a series of g-C3N4based photocatalysts that can be used for various photocatalytic applications, such as water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacteria disinfection. Remarkable accomplishments have been already achieved in the area of the g-C3N4-based photocatalytic hydrogen evolution by dye sensitization, hybridization with carbon materials, and introduction of non-noble-metal cocatalysts. Also, g-C3N4/ carbon composites and g-C3N4-based all-solid-state Z-scheme heterojunctions have been shown to be superior for the photocatalytic degradation of organic pollutants. In view of the reported literature, significant progress has been made in the area of g-C3N4-based photocatalysis. However, visible-light photocatalytic efficiency is still relatively low and far from the requirements of practical applications. Although there are numerous reports on the preparation of single-layer g-C3N4 nanosheets, their surface areas are much less than the theoretical value. This implies a large potential for improving the surface structure of single-layer g-C3N4 nanosheets to create abundant active sites. In this regard, it is necessary to develop novel synthetic and exfoliation methods for the preparation of a perfect single-layer g-C3N4. Moreover, g-C3N4 nanosheets usually serve as an anchoring support for nanoparticles, while it is now difficult to control the particle size on the g-C3N4 support. Therefore, fine tuning of the interface contact is hard to achieve. This seriously limits the construction of g-C3N4-based heterojunctions for more-efficient charge separation and migration. At this point, various strategies for surface functionalization of g-C3N4 with specific chemical groups should be explored to amplify the anchoring ability of g-C3N4. Moreover, g-C3N4-based Z-scheme heterojunctions possess both excellent charge-separation efficiency and strong redox ability. As such, the enrichment of g-C3N4-based photocatalysts with Z-scheme heterojunctions is highly encouraged. On the other hand, the current applications of g-C3N4-based Z-scheme heterojunctions 22


are focused mainly on photocatalytic degradation of organic pollutants and rarely on hydrogen evolution. Hence, expanding the spectrum of photocatalytic applications of g-C3N4-based Z-scheme heterojunctions is also highly expected. Analogous polymeric structures to g-C3N4, such as C3N3S3,[369] g-C4N3,[370] and poly(triazine imide)[371–373] can be also very active under visible-light irradiation. This should open new possibilities in the modification of the molecular structure of g-C3N4 and lead to more exciting findings. In addition, the modification of g-C3N4 and the design of non-noble-metal cocatalysts usually follow their own ways. To obtain a low-cost photocatalytic system with high efficiency, it is required that high-performance g-C3N4-based photocatalysts be developed, which match well with non-noble-metal cocatalysts. Finally, a comprehensive understanding of the photocatalytic mechanism is helpful for its further optimization. Thus, in situ observations based on advanced material characterization and fundamental studies based on computer simulations are highly desirable to advance further developments in this exciting area of research.

Acknowledgements This work was supported by the 973 program (2013CB632402), and NSFC (51472191, 21407115, 51272199, 51320105001 and 21433007). This work was also financially supported by the Natural Science Foundation of Hubei Province of China (2014CFB164), the General Financial Grant from the China Postdoctoral Science Foundation (2014M552101), the Deanship of Scientific Research (DSR) of King Abdulaziz University (90-130-35-HiCi), the Fundamental Research Funds for the Central Universities (WUT: 2014-VII-010, 2014-IV-058, 2014-IV155), the Self-determined and Innovative Research Funds of SKLWUT (2013-ZD-1), and a WUT Start-Up Grant. Received: November 1, 2014 Revised: December 13, 2014 Published online:

[1] A. J. Bard, Science 1980, 207, 139. [2] M. R. Hoffmann, S. T. Martin, W. Choi, D. W. Bahnemann, Chem. Rev. 1995, 95, 69. [3] A. Kudo, Y. Miseki, Chem. Soc. Rev. 2009, 38, 253. [4] X. Chen, S. Shen, L. Guo, S. S. Mao, Chem. Rev. 2010, 110, 6503. [5] S. N. Habisreutinger, L. Schmidt-Mende, J. K. Stolarczyk, Angew. Chem. Int. Ed. 2013, 52, 7372. [6] D. Chatterjee, S. Dasgupta, J. Photochem. Photobiol. C 2005, 6, 186. [7] X. Lang, X. Chen, J. Zhao, Chem. Soc. Rev. 2014, 43, 473. [8] P. K. Robertson, J. M. Robertson, D. W. Bahnemann, J. Hazard. Mater. 2012, 211–212, 161. [9] A. Fujishima, K. Honda, Nature 1972, 238, 37. [10] J. H. Carey, J. Lawrence, H. M. Tosine, Bull. Environ. Contam. Toxicol. 1976, 16, 697. [11] T. Inoue, A. Fujishima, S. Konishi, K. Honda, Nature 1979, 277, 637. [12] J. Yu, Q. Li, S. Liu, M. Jaroniec, Chem. Eur. J. 2013, 19, 2433. [13] J. Yu, J. Low, W. Xiao, P. Zhou, M. Jaroniec, J. Am. Chem. Soc. 2014, 136, 8839. [14] E. S. Jang, J. H. Won, S. J. Hwang, J. H. Choy, Adv. Mater. 2006, 18, 3309. [15] X. Wang, M. Liao, Y. Zhong, J. Y. Zheng, W. Tian, T. Zhai, C. Zhi, Y. Ma, J. Yao, Y. Bando, D. Golberg, Adv. Mater. 2012, 24, 3421.





REVIEW

[16] S. Wu, H. Cao, S. Yin, X. Liu, X. Zhang, J. Phys. Chem. C 2009, 113, 17893. [17] S. Liu, G. Huang, J. Yu, T. W. Ng, H. Y. Yip, P. K. Wong, ACS Appl. Mater. Interfaces 2014, 6, 2407. [18] S. W. Cao, Y. J. Zhu, J. Phys. Chem. C 2008, 112, 6253. [19] X. Zhou, Q. Xu, W. Lei, T. Zhang, X. Qi, G. Liu, K. Deng, J. Yu, Small 2014, 10, 674. [20] S. Liu, K. Yin, W. Ren, B. Cheng, J. Yu, J. Mater. Chem. 2012, 22, 17759. [21] S. W. Cao, Z. Yin, J. Barber, F. Y. Boey, S. C. Loo, C. Xue, ACS Appl. Mater. Interfaces 2012, 4, 418. [22] W. C. Huang, L. M. Lyu, Y. C. Yang, M. H. Huang, J. Am. Chem. Soc. 2012, 134, 1261. [23] X. An, K. Li, J. Tang, ChemSusChem 2014, 7, 1086. [24] Y. Hu, X. Gao, L. Yu, Y. Wang, J. Ning, S. Xu, X. W. Lou, Angew. Chem. Int. Ed. 2013, 52, 5636. [25] Q. Xiang, B. Cheng, J. Yu, Appl. Catal., B 2013, 138–139, 299. [26] Y. Tachibana, L. Vayssieres, J. R. Durrant, Nat. Photonics 2012, 6, 511. [27] Z. Zou, J. Ye, K. Sayama, H. Arakawa, Nature 2001, 414, 625. [28] M. Liu, W. You, Z. Lei, G. Zhou, J. Yang, G. Wu, G. Ma, G. Luan, T. Takata, M. Hara, K. Domen, C. Li, Chem. Commun. 2004, 2192. [29] K. Maeda, K. Teramura, D. Lu, T. Takata, N. Saito, Y. Inoue, K. Domen, Nature 2006, 440, 295. [30] W. Zhou, H. Fu, ChemCatChem 2013, 5, 885. [31] Y. Wang, Q. Wang, X. Zhan, F. Wang, M. Safdar, J. He, Nanoscale 2013, 5, 8326. [32] J. Yang, D. Wang, H. Han, C. Li, Acc. Chem. Res. 2013, 46, 1900. [33] H. Yan, J. Yang, G. Ma, G. Wu, X. Zong, Z. Lei, J. Shi, C. Li, J. Catal. 2009, 266, 165. [34] J. Ran, J. Zhang, J. Yu, M. Jaroniec, S. Z. Qiao, Chem. Soc. Rev. 2014, 43, 7787. [35] J. V. Liebig, Ann. Pharm. 1834, 10, 10. [36] Y. Wang, X. Wang, M. Antonietti, Angew. Chem. Int. Ed. 2012, 51, 68. [37] Y. Zheng, J. Liu, J. Liang, M. Jaroniec, S. Z. Qiao, Energy Environ. Sci. 2012, 5, 6717. [38] F. Goettmann, A. Fischer, M. Antonietti, A. Thomas, Angew. Chem. Int. Ed. 2006, 45, 4467. [39] F. Goettmann, A. Fischer, M. Antonietti, A. Thomas, Chem. Commun. 2006, 4530. [40] X. C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. A. Domen, M. Antonietti, Nat. Mater. 2009, 8, 76. [41] S. C. Yan, S. B. Lv, Z. S. Li, Z. G. Zou, Dalton Trans. 2010, 39, 1488. [42] X. Wang, S. Blechert, M. Antonietti, ACS Catal. 2012, 2, 1596. [43] G. P. Dong, Y. H. Zhang, Q. W. Pan, J. R. Qiu, J. Photochem. Photobiol. C 2014, 20, 33. [44] T. Sano, S. Tsutsui, K. Koike, T. Hirakawa, Y. Teramoto, N. Negishi, K. Takeuchi, J. Mater. Chem. A 2013, 1, 6489. [45] Z. W. Zhao, Y. J. Sun, F. Dong, Nanoscale 2015, 7, 15. [46] K. Maeda, X. Wang, Y. Nishihara, D. Lu, M. Antonietti, K. Domen, J. Phys. Chem. C 2009, 113, 4940. [47] H. Ji, F. Chang, X. Hu, W. Qin, J. Shen, Chem. Eng. J. 2013, 218, 183. [48] S. C. Yan, Z. S. Li, Z. G. Zou, Langmuir 2009, 25, 10397. [49] G. Zhang, J. Zhang, M. Zhang, X. Wang, J. Mater. Chem. 2012, 22, 8083. [50] F. Dong, Z. Wang, Y. Sun, W. K. Ho, H. Zhang, J. Colloid Interface Sci. 2013, 401, 70. [51] A. B. Jorge, D. J. Martin, M. T. S. Dhanoa, A. S. Rahman, N. Makwana, J. Tang, A. Sella, F. Corà, S. Firth, J. A. Darr, P. F. McMillan, J. Phys. Chem. C 2013, 117, 7178. [52] J. Liu, T. Zhang, Z. Wang, G. Dawson, W. Chen, J. Mater. Chem. 2011, 21, 14398.

[53] F. Dong, L. Wu, Y. Sun, M. Fu, Z. Wu, S. C. Lee, J. Mater. Chem. 2011, 21, 15171. [54] Y. Sakata, K. Yoshimoto, K. Kawaguchi, H. Imamura, S. Higashimoto, Catal. Today 2011, 161, 41. [55] Y. Zhang, J. Liu, G. Wu, W. Chen, Nanoscale 2012, 4, 5300. [56] Y. P. Yuan, W. T. Xu, L. S. Yin, S. W. Cao, Y. S. Liao, Y. Q. Tng, C. Xue, Int. J. Hydrogen Energy 2013, 38, 13159. [57] H. Yan, Y. Chen, S. Xu, Int. J. Hydrogen Energy 2012, 37, 125. [58] J. Zhang, M. Zhang, G. Zhang, X. Wang, ACS Catal. 2012, 2, 940. [59] B. Long, J. Lin, X. Wang, J. Mater. Chem. A 2014, 2, 2942. [60] M. J. Bojdys, N. Severin, J. P. Rabe, A. I. Cooper, A. Thomas, M. Antonietti, Macromol. Rapid Commun. 2013, 34, 850. [61] S. Yang, Y. Gong, J. Zhang, L. Zhan, L. Ma, Z. Fang, R. Vajtai, X. Wang, P. M. Ajayan, Adv. Mater. 2013, 25, 2452. [62] X. She, H. Xu, Y. Xu, J. Yan, J. Xia, L. Xu, Y. Song, Y. Jiang, Q. Zhang, H. Li, J. Mater. Chem. A 2014, 2, 2563. [63] S. Kumar, T. Surendar, B. Kumar, A. Baruah, V. Shanker, RSC Adv. 2014, 4, 8132. [64] J. Xu, L. Zhang, R. Shi, Y. Zhu, J. Mater. Chem. A 2013, 1, 14766. [65] P. Niu, L. Zhang, G. Liu, H.-M. Cheng, Adv. Funct. Mater. 2012, 22, 4763. [66] H. Xu, J. Yan, X. She, L. Xu, J. Xia, Y. Xu, Y. Song, L. Huang, H. Li, Nanoscale 2014, 6, 1406. [67] H. Zhao, H. Yu, X. Quan, S. Chen, Y. Zhang, H. Zhao, H. Wang, Appl. Catal., B 2014, 152–153, 46. [68] H. Zhao, H. Yu, X. Quan, S. Chen, H. Zhao, H. Wang, RSC Adv. 2014, 4, 624. [69] X. Wang, K. Maeda, X. Chen, K. Takanabe, K. Domen, Y. Hou, X. Fu, M. Antonietti, J. Am. Chem. Soc. 2009, 131, 1680. [70] J.-H. Yang, G. Kim, K. Domen, J.-H. Choy, J. Nanosci. Nanotechnol. 2013, 13, 7487. [71] Y. Cui, J. Zhang, G. Zhang, J. Huang, P. Liu, M. Antonietti, X. Wang, J. Mater. Chem. 2011, 21, 13032. [72] Y. Cui, J. Huang, X. Fu, X. Wang, Catal. Sci. Technol. 2012, 2, 1396. [73] F. Dong, Y. Li, W. Ho, H. Zhang, M. Fu, Z. Wu, Chin. Sci. Bull. 2014, 59, 688. [74] S. C. Lee, H. O. Lintang, L. Yuliati, Chem. Asian J. 2012, 7, 2139. [75] X. Chen, Y.-S. Jun, K. Takanabe, K. Maeda, K. Domen, X. Fu, M. Antonietti, X. Wang, Chem. Mater. 2009, 21, 4093. [76] J. Zhang, F. Guo, X. Wang, Adv. Funct. Mater. 2013, 23, 3008. [77] Y. Fukasawa, K. Takanabe, A. Shimojima, M. Antonietti, K. Domen, T. Okubo, Chem. Asian J. 2011, 6, 103. [78] H. Yan, Chem. Commun. 2012, 48, 3430. [79] J. Xu, Y. Wang, Y. Zhu, Langmuir 2013, 29, 10566. [80] M. Zhang, J. Xu, R. Zong, Y. Zhu, Appl. Catal., B 2014, 147, 229. [81] G. Dong, L. Zhang, J. Mater. Chem. 2012, 22, 1160. [82] K. K. Han, C. C. Wang, Y. Y. Li, M. M. Wan, Y. Wang, J. H. Zhu, RSC Adv. 2013, 3, 9465. [83] B. Shen, Z. Hong, Y. Chen, B. Lin, B. Gao, Mater. Lett. 2014, 118, 208. [84] J. Sun, J. Zhang, M. Zhang, M. Antonietti, X. Fu, X. Wang, Nat. Commun. 2012, 3, 1139. [85] Y. S. Jun, J. Park, S. U. Lee, A. Thomas, W. H. Hong, G. D. Stucky, Angew. Chem. Int. Ed. 2013, 52, 11083. [86] Y.-S. Jun, E. Z. Lee, X. Wang, W. H. Hong, G. D. Stucky, A. Thomas, Adv. Funct. Mater. 2013, 23, 3661. [87] M. Shalom, S. Inal, C. Fettkenhauer, D. Neher, M. Antonietti, J. Am. Chem. Soc. 2013, 135, 7118. [88] X.-H. Li, J. Zhang, X. Chen, A. Fischer, A. Thomas, M. Antonietti, X. Wang, Chem. Mater. 2011, 23, 4344. [89] X.-H. Li, X. Wang, M. Antonietti, Chem. Sci. 2012, 3, 2170. [90] X. Bai, L. Wang, R. Zong, Y. Zhu, J. Phys. Chem. C 2013, 117, 9952. [91] Y. Cui, Z. Ding, X. Fu, X. Wang, Angew. Chem. Int. Ed. 2012, 51, 11814.



23

www.advmat.de

REVIEW

www.MaterialsViews.com [92] J. Liu, J. Huang, D. Dontosova, M. Antonietti, RSC Adv. 2013, 3, 22988. [93] M. Tahir, C. Cao, N. Mahmood, F. K. Butt, A. Mahmood, F. Idrees, S. Hussain, M. Tanveer, Z. Ali, I. Aslam, ACS Appl. Mater. Interfaces 2014, 6, 1258. [94] M. Tahir, C. Cao, F. K. Butt, S. Butt, F. Idrees, Z. Ali, I. Aslam, M. Tanveer, A. Mahmood, N. Mahmood, CrystEngComm 2014, 16, 1825. [95] M. Tahir, C. Cao, F. K. Butt, F. Idrees, N. Mahmood, Z. Ali, I. Aslam, M. Tanveer, M. Rizwan, T. Mahmood, J. Mater. Chem. A 2013, 1, 13949. [96] S. Wang, C. Li, T. Wang, P. Zhang, A. Li, J. Gong, J. Mater. Chem. A 2014, 2, 2885. [97] G. Liu, P. Niu, C. Sun, S. C. Smith, Z. Chen, G. Q. M. Lu, H.-M. Cheng, J. Am. Chem. Soc. 2010, 132, 11642. [98] J. Zhang, J. Sun, K. Maeda, K. Domen, P. Liu, M. Antonietti, X. Fu, X. Wang, Energy Environ. Sci. 2011, 4, 675. [99] L. Ge, C. Han, X. Xiao, L. Guo, Y. Li, Mater. Res. Bull. 2013, 48, 3919. [100] X. Ma, Y. Lv, J. Xu, Y. Liu, R. Zhang, Y. Zhu, J. Phys. Chem. C 2012, 116, 23485. [101] G. Chen, S.-P. Gao, Chin. Phys. B 2012, 21, 107101. [102] S. Stolbov, S. Zuluaga, J. Phys.: Condens. Matter 2013, 25, 085507. [103] J. Hong, X. Xia, Y. Wang, R. Xu, J. Mater. Chem. 2012, 22, 15006. [104] Y. Wang, Y. Di, M. Antonietti, H. Li, X. Chen, X. Wang, Chem. Mater. 2010, 22, 5119. [105] S. C. Yan, Z. S. Li, Z. G. Zou, Langmuir 2010, 26, 3894. [106] G. Zhang, M. Zhang, X. Ye, X. Qiu, S. Lin, X. Wang, Adv. Mater. 2014, 26, 805. [107] J. Li, B. Shen, Z. Hong, B. Lin, B. Gao, Y. Chen, Chem. Commun. 2012, 48, 12017. [108] G. Dong, Z. Ai, L. Zhang, RSC Adv. 2014, 4, 5553. [109] G. Dong, K. Zhao, L. Zhang, Chem. Commun. 2012, 48, 6178. [110] L. Zhang, X. Chen, J. Guan, Y. Jiang, T. Hou, X. Mu, Mater. Res. Bull. 2013, 48, 3485. [111] H. Pan, Y.-W. Zhang, V. B. Shenoy, H. Gao, ACS Catal. 2011, 1, 99. [112] H. Gao, S. Yan, J. Wang, Z. Zou, Dalton Trans. 2014, 43, 8178. [113] X. Wang, X. Chen, A. Thomas, X. Fu, M. Antonietti, Adv. Mater. 2009, 21, 1609. [114] Z. Ding, X. Chen, M. Antonietti, X. Wang, ChemSusChem 2011, 4, 274. [115] J. Tian, Q. Liu, A. M. Asiri, A. H. Qusti, A. O. Al-Youbi, X. Sun, Nanoscale 2013, 5, 11604. [116] X. Song, H. Tao, L. Chen, Y. Sun, Mater. Lett. 2014, 116, 265. [117] S. Z. Hu, R. R. Jin, G. Lu, D. Liu, J. Z. Gui, RSC Adv. 2014, 4, 24863. [118] S. Tonda, S. Kumar, S. Kandula, V. Shanker, J. Mater. Chem. A 2014, 2, 6772. [119] B. Yue, Q. Li, H. Iwai, T. Kako, J. Ye, Sci. Technol. Adv. Mater. 2011, 12, 034401. [120] H. Gao, S. Yan, J. Wang, Y. A. Huang, P. Wang, Z. Li, Z. Zou, Phys. Chem. Chem. Phys. 2013, 15, 18077. [121] D. Xu, X. Li, J. Liu, L. Huang, J. Rare Earth. 2013, 31, 1085. [122] J. Zhang, X. Chen, K. Takanabe, K. Maeda, K. Domen, J. D. Epping, X. Fu, M. Antonietti, X. Wang, Angew. Chem. Int. Ed. 2010, 49, 441. [123] J. Zhang, G. Zhang, X. Chen, S. Lin, L. Mohlmann, G. Dolega, G. Lipner, M. Antonietti, S. Blechert, X. Wang, Angew. Chem. Int. Ed. 2012, 51, 3183. [124] H.-R. Zheng, J.-S. Zhang, X.-C. Wang, X.-Z. Fu, Acta Phys.-Chim. Sin. 2012, 28, 2336. [125] G. Zhang, X. Wang, J. Catal. 2013, 307, 246. [126] J. Zhang, M. Zhang, S. Lin, X. Fu, X. Wang, J. Catal. 2014, 310, 24. [127] S. Chu, Y. Wang, Y. Guo, J. Feng, C. Wang, W. Luo, X. Fan, Z. Zou, ACS Catal. 2013, 3, 912.

24


[128] Y. Guo, S. Chu, S. Yan, Y. Wang, Z. Zou, Chem. Commun. 2010, 46, 7325. [129] Y. Guo, J. Yang, S. Chu, F. Kong, L. Luo, Y. Wang, Z. Zou, Chem. Phys. Lett. 2012, 550, 175. [130] Y. Guo, F. Kong, C. Wang, S. Chu, J. Yang, Y. Wang, Z. Zou, J. Mater. Chem. A 2013, 1, 5142. [131] X. Lu, Q. Wang, D. Cui, J. Mater. Sci. Technol. 2010, 26, 925. [132] X. Zhou, F. Peng, H. Wang, H. Yu, Y. Fang, Chem. Commun. 2011, 47, 10323. [133] N. Yang, G. Li, W. Wang, X. Yang, W. F. Zhang, J. Phys. Chem. Solids 2011, 72, 1319. [134] H. Yan, H. Yang, J. Alloys Compd. 2011, 509, L26. [135] X. Zhou, B. Jin, L. Li, F. Peng, H. Wang, H. Yu, Y. Fang, J. Mater. Chem. 2012, 22, 17900. [136] Y. Guo, F. Kong, S. Chu, L. Luo, J. Yang, Y. Wang, Z. Zou, RSC Adv. 2012, 2, 5585. [137] J. Wang, W.-D. Zhang, Electrochim. Acta 2012, 71, 10. [138] S. Zhao, S. Chen, H. Yu, X. Quan, Sep. Purif. Technol. 2012, 99, 50. [139] B. Chai, T. Peng, J. Mao, K. Li, L. Zan, Phys. Chem. Chem. Phys. 2012, 14, 16745. [140] X.-J. Wang, W.-Y. Yang, F.-T. Li, Y.-B. Xue, R.-H. Liu, Y.-J. Hao, Ind. Eng. Chem. Res. 2013, 52, 17140. [141] K. Kondo, N. Murakami, C. Ye, T. Tsubota, T. Ohno, Appl. Catal., B 2013, 142–143, 362. [142] J. Yu, S. Wang, J. Low, W. Xiao, Phys. Chem. Chem. Phys. 2013, 15, 16883. [143] C. Miranda, H. Mansilla, J. Yáñez, S. Obregón, G. Colón, J. Photochem. Photobiol. A 2013, 253, 16. [144] K. Sridharan, E. Jang, T. J. Park, Appl. Catal., B 2013, 142–143, 718. [145] S. Zhou, Y. Liu, J. Li, Y. Wang, G. Jiang, Z. Zhao, D. Wang, A. Duan, J. Liu, Y. Wei, Appl. Catal., B 2014, 158–159, 20. [146] Q. Li, L. Zong, Y. Xing, X. Wang, L. Yu, J. Yang, Sci. Adv. Mater. 2013, 5, 1316. [147] K. Dai, L. Lu, C. Liang, Q. Liu, G. Zhu, Appl. Catal., B 2014, 156–157, 331. [148] N. Boonprakob, N. Wetchakun, S. Phanichphant, D. Waxler, P. Sherrell, A. Nattestad, J. Chen, B. Inceesungvorn, J. Colloid Interface Sci. 2014, 417, 402. [149] J. Wang, J. Huang, H. Xie, A. Qu, Int. J. Hydrogen Energy 2014, 39, 6354. [150] L. Gu, J. Wang, Z. Zou, X. Han, J. Hazard. Mater. 2014, 268, 216. [151] L. Zhang, D. Jing, X. She, H. Liu, D. Yang, Y. Lu, J. Li, Z. Zheng, L. Guo, J. Mater. Chem. A 2014, 2, 2071. [152] S. Obregón, G. Colón, Appl. Catal., B 2014, 144, 775. [153] Y. Wang, R. Shi, J. Lin, Y. Zhu, Energy Environ. Sci. 2011, 4, 2922. [154] J. X. Sun, Y. P. Yuan, L. G. Qiu, X. Jiang, A. J. Xie, Y. H. Shen, J. F. Zhu, Dalton Trans. 2012, 41, 6756. [155] W. Liu, M. Wang, C. Xu, S. Chen, Chem. Eng. J. 2012, 209, 386. [156] W. Liu, M. Wang, C. Xu, S. Chen, X. Fu, J. Mol. Catal. A: Chem. 2013, 368–369, 9. [157] D. Chen, K. Wang, D. Xiang, R. Zong, W. Yao, Y. Zhu, Appl. Catal., B 2014, 147, 554. [158] S. Kumar, A. Baruah, S. Tonda, B. Kumar, V. Shanker, B. Sreedhar, Nanoscale 2014, 6, 4830. [159] X. Li, M. Li, J. Yang, X. Li, T. Hu, J. Wang, Y. Sui, X. Wu, L. Kong, J. Phys. Chem. Solids 2014, 75, 441. [160] Y. Zang, L. Li, Y. Zuo, H. Lin, G. Li, X. Guan, RSC Adv. 2013, 3, 13646. [161] K. Katsumata, R. Motoyoshi, N. Matsushita, K. Okada, J. Hazard. Mater. 2013, 260, 475. [162] L. Huang, H. Xu, Y. Li, H. Li, X. Cheng, J. Xia, Y. Xu, G. Cai, Dalton Trans. 2013, 42, 8606. [163] Z. Jin, N. Murakami, T. Tsubota, T. Ohno, Appl. Catal., B 2014, 150–151, 479.





REVIEW

[164] S. Chen, Y. Hu, S. Meng, X. Fu, Appl. Catal., B 2014, 150–151, 564. [165] H. Katsumata, Y. Tachi, T. Suzuki, S. Kaneco, RSC Adv. 2014, 4, 21405. [166] Y. Tian, B. Chang, J. Fu, B. Zhou, J. Liu, F. Xi, X. Dong, J. Solid State Chem. 2014, 212, 1. [167] J. Chen, S. Shen, P. Guo, M. Wang, P. Wu, X. Wang, L. Guo, Appl. Catal., B 2014, 152–153, 335. [168] S.-W. Cao, X.-F. Liu, Y.-P. Yuan, Z.-Y. Zhang, Y.-S. Liao, J. Fang, S. C. J. Loo, T. C. Sum, C. Xue, Appl. Catal., B 2014, 147, 940. [169] L.-Y. Chen, W.-D. Zhang, Appl. Surf. Sci. 2014, 301, 428. [170] S. Ye, L.-G. Qiu, Y.-P. Yuan, Y.-J. Zhu, J. Xia, J.-F. Zhu, J. Mater. Chem. A 2013, 1, 3008. [171] K. Sridharan, T. Kuriakose, R. Philip, T. J. Park, Appl. Surf. Sci. 2014, 308, 139. [172] Y. Liu, Y.-X. Yu, W.-D. Zhang, Int. J. Hydrogen Energy 2014, 39, 9105. [173] L. Huang, H. Xu, R. Zhang, X. Cheng, J. Xia, Y. Xu, H. Li, Appl. Surf. Sci. 2013, 283, 25. [174] Y. He, L. Zhang, X. Wang, Y. Wu, H. Lin, L. Zhao, W. Weng, H. Wan, M. Fan, RSC Adv. 2014, 4, 13610. [175] L. Huang, Y. Li, H. Xu, Y. Xu, J. Xia, K. Wang, H. Li, X. Cheng, RSC Adv. 2013, 3, 22269. [176] Y. Zang, L. Li, X. Li, R. Lin, G. Li, Chem. Eng. J. 2014, 246, 277. [177] X. Wang, G. Chen, C. Zhou, Y. Yu, G. Wang, Eur. J. Inorg. Chem. 2012, 1742. [178] L. Sun, X. Zhao, C.-J. Jia, Y. Zhou, X. Cheng, P. Li, L. Liu, W. Fan, J. Mater. Chem. 2012, 22, 23428. [179] Y. Wang, Z. Wang, S. Muhammad, J. He, CrystEngComm 2012, 14, 5065. [180] S. Zhang, J. Li, M. Zeng, G. Zhao, J. Xu, W. Hu, X. Wang, ACS Appl. Mater. Interfaces 2013, 5, 12735. [181] J. Chen, S. Shen, P. Guo, P. Wu, L. Guo, J. Mater. Chem. A 2014, 2, 4605. [182] L. Sun, Y. Qi, C. J. Jia, Z. Jin, W. Fan, Nanoscale 2014, 6, 2649. [183] X. Xu, G. Liu, C. Randorn, J. T. S. Irvine, Int. J. Hydrogen Energy 2011, 36, 13501. [184] Y. Liu, G. Chen, C. Zhou, Y. Hu, D. Fu, J. Liu, Q. Wang, J. Hazard. Mater. 2011, 190, 75. [185] Y. He, J. Cai, T. Li, Y. Wu, Y. Yi, M. Luo, L. Zhao, Ind. Eng. Chem. Res. 2012, 51, 14729. [186] Y. He, J. Cai, T. Li, Y. Wu, H. Lin, L. Zhao, M. Luo, Chem. Eng. J. 2013, 215–216, 721. [187] Y. He, J. Cai, L. Zhang, X. Wang, H. Lin, B. Teng, L. Zhao, W. Weng, H. Wan, M. Fan, Ind. Eng. Chem. Res. 2014, 53, 5905. [188] J. Cai, Y. He, X. Wang, L. Zhang, L. Dong, H. Lin, L. Zhao, X. Yi, W. Weng, H. Wan, RSC Adv. 2013, 3, 20862. [189] S. Kumar, B. Kumar, T. Surendar, V. Shanker, Mater. Res. Bull. 2014, 49, 310. [190] G. Li, N. Yang, W. Wang, W. F. Zhang, J. Phys. Chem. C 2009, 113, 14829. [191] H. Pan, X. Li, Z. Zhuang, C. Zhang, J. Mol. Catal. A: Chem. 2011, 345, 90. [192] Q. Li, B. Yue, H. Iwai, T. Kako, J. Ye, J. Phys. Chem. C 2010, 114, 4100. [193] K. Li, L. Yan, Z. Zeng, S. Luo, X. Luo, X. Liu, H. Guo, Y. Guo, Appl. Catal., B 2014, 156–157, 141. [194] M. Yang, Q. Huang, X. Jin, Mater. Sci. Eng. B 2012, 177, 600. [195] L. Ge, F. Zuo, J. Liu, Q. Ma, C. Wang, D. Sun, L. Bartels, P. Feng, J. Phys. Chem. C 2012, 116, 13708. [196] S.-W. Cao, Y.-P. Yuan, J. Fang, M. M. Shahjamali, F. Y. C. Boey, J. Barber, S. C. Joachim Loo, C. Xue, Int. J. Hydrogen Energy 2013, 38, 1258. [197] J. Zhang, Y. Wang, J. Jin, Z. Lin, F. Huang, J. Yu, ACS Appl. Mater. Interfaces 2013, 5, 10317.

[198] J. Fu, B. Chang, Y. Tian, F. Xi, X. Dong, J. Mater. Chem. A 2013, 1, 3083. [199] F. Jiang, T. Yan, H. Chen, A. Sun, C. Xu, X. Wang, Appl. Surf. Sci. 2014, 295, 164. [200] F. Yang, V. Kuznietsov, M. Lublow, C. Merschjann, A. Steigert, J. Klaer, A. Thomas, T. Schedel-Niedrig, J. Mater. Chem. A 2013, 1, 6407. [201] F. Yang, M. Lublow, S. Orthmann, C. Merschjann, T. Tyborski, M. Rusu, S. Kubala, A. Thomas, R. Arrigo, M. Havecker, T. SchedelNiedrig, ChemSusChem 2012, 5, 1227. [202] C. Pan, J. Xu, Y. Wang, D. Li, Y. Zhu, Adv. Funct. Mater. 2012, 22, 1518. [203] Z. Li, S. Yang, J. Zhou, D. Li, X. Zhou, C. Ge, Y. Fang, Chem. Eng. J. 2014, 241, 344. [204] Y. Tian, B. Chang, Z. Yang, B. Zhou, F. Xi, X. Dong, RSC Adv. 2014, 4, 4187. [205] Y. Ji, J. Cao, L. Jiang, Y. Zhang, Z. Yi, J. Alloys Compd. 2014, 590, 9. [206] C. Li, S. Wang, T. Wang, Y. Wei, P. Zhang, J. Gong, Small 2014, 10, 2783. [207] L. Ge, C. Han, J. Liu, Appl. Catal., B 2011, 108–109, 100. [208] Y. Wang, X. Bai, C. Pan, J. He, Y. Zhu, J. Mater. Chem. 2012, 22, 11568. [209] Y. Tian, B. Chang, J. Lu, J. Fu, F. Xi, X. Dong, ACS Appl. Mater. Interfaces 2013, 5, 7079. [210] M.-S. Gui, P.-F. Wang, D. Yuan, Y.-K. Yang, Chin. J. Inorg. Chem. 2013, 29, 2057. [211] H. Wang, J. Lu, F. Wang, W. Wei, Y. Chang, S. Dong, Ceram. Int. 2014, 40, 9077. [212] X.-J. Wang, Q. Wang, F.-T. Li, W.-Y. Yang, Y. Zhao, Y.-J. Hao, S.-J. Liu, Chem. Eng. J. 2013, 234, 361. [213] S. Shi, M. A. Gondal, A. A. Al-Saadi, R. Fajgar, J. Kupcik, X. Chang, K. Shen, Q. Xu, Z. S. Seddigi, J. Colloid Interface Sci. 2014, 416, 212. [214] Y. Bai, P.-Q. Wang, J.-Y. Liu, X.-J. Liu, RSC Adv. 2014, 4, 19456. [215] J. Fu, Y. Tian, B. Chang, F. Xi, X. Dong, J. Mater. Chem. 2012, 22, 21159. [216] L. Ye, J. Liu, Z. Jiang, T. Peng, L. Zan, Appl. Catal., B 2013, 142–143, 1. [217] J. Di, J. Xia, S. Yin, H. Xu, M. He, H. Li, L. Xu, Y. Jiang, RSC Adv. 2013, 3, 19624. [218] Y. Sun, W. Zhang, T. Xiong, Z. Zhao, F. Dong, R. Wang, W. K. Ho, J. Colloid Interface Sci. 2014, 418, 317. [219] D. Jiang, L. Chen, J. Zhu, M. Chen, W. Shi, J. Xie, Dalton Trans. 2013, 42, 15726. [220] C. Chang, L. Zhu, S. Wang, X. Chu, L. Yue, ACS Appl. Mater. Interfaces 2014, 6, 5083. [221] J. Di, J. Xia, S. Yin, H. Xu, L. Xu, Y. Xu, M. He, H. Li, J. Mater. Chem. A 2014, 2, 5340. [222] M. Xiong, L. Chen, Q. Yuan, J. He, S. L. Luo, C. T. Au, S. F. Yin, Dalton Trans. 2014, 43, 8331. [223] S. Zhang, Y. Yang, Y. Guo, W. Guo, M. Wang, M. Huo, J. Hazard. Mater. 2013, 261, 235. [224] M. Xu, L. Han, S. Dong, ACS Appl. Mater. Interfaces 2013, 5, 12533. [225] L. Shi, L. Liang, J. Ma, F. Wang, J. Sun, Catal. Sci. Technol. 2014, 4, 758. [226] S. Kumar, T. Surendar, A. Baruah, V. Shanker, J. Mater. Chem. A 2013, 1, 5333. [227] F.-J. Zhang, F.-Z. Xie, S.-F. Zhu, J. Liu, J. Zhang, S.-F. Mei, W. Zhao, Chem. Eng. J. 2013, 228, 435. [228] K. Shen, M. A. Gondal, R. G. Siddique, S. Shi, S. Wang, J. Sun, Q. Xu, Chin. J. Catal. 2014, 35, 78. [229] Z. Xiu, H. Bo, Y. Wu, X. Hao, Appl. Surf. Sci. 2014, 289, 394. [230] D. Jiang, J. Zhu, M. Chen, J. Xie, J. Colloid Interface Sci. 2014, 417, 115.



25

www.advmat.de

REVIEW

www.MaterialsViews.com [231] P. He, L. Song, S. Zhang, X. Wu, Q. Wei, Mater. Res. Bull. 2014, 51, 432. [232] H. Katsumata, T. Sakai, T. Suzuki, S. Kaneco, Ind. Eng. Chem. Res. 2014, 53, 8018. [233] S. Wang, D. Li, C. Sun, S. Yang, Y. Guan, H. He, Appl. Catal., B 2014, 144, 885. [234] D. Jiang, L. Chen, J. Xie, M. Chen, Dalton Trans. 2014, 43, 4878. [235] Y. Lan, X. Qian, C. Zhao, Z. Zhang, X. Chen, Z. Li, J. Colloid Interface Sci. 2013, 395, 75. [236] J. Yan, H. Xu, Y. Xu, C. Wang, Y. Song, J. Xia, H. Li, J. Nanosci. Nanotechnol. 2014, 14, 6809. [237] T. Zhou, Y. Xu, H. Xu, H. Wang, Z. Da, S. Huang, H. Ji, H. Li, Ceram. Int. 2014, 40, 9293. [238] Y. Xu, H. Xu, J. Yan, H. Li, L. Huang, J. Xia, S. Yin, H. Shu, Colloids Surf. A 2013, 436, 474. [239] J. Cao, Y. Zhao, H. Lin, B. Xu, S. Chen, Mater. Res. Bull. 2013, 48, 3873. [240] Y.-S. Xu, W.-D. Zhang, ChemCatChem 2013, 5, 2343. [241] S. Yang, W. Zhou, C. Ge, X. Liu, Y. Fang, Z. Li, RSC Adv. 2013, 3, 5631. [242] L. Xu, J. Xia, H. Xu, J. Qian, J. Yan, L. Wang, K. Wang, H. Li, Analyst 2013, 138, 6721. [243] Y. Yang, W. Guo, Y. Guo, Y. Zhao, X. Yuan, J. Hazard. Mater. 2014, 271, 150. [244] H. Xu, J. Yan, Y. Xu, Y. Song, H. Li, J. Xia, C. Huang, H. Wan, Appl. Catal., B 2013, 129, 182. [245] H. Yan, Y. Huang, Chem. Commun. 2011, 47, 4168. [246] S. Gawande, S. R. Thakare, ChemCatChem 2012, 4, 1759. [247] Y. Sui, J. Liu, Y. Zhang, X. Tian, W. Chen, Nanoscale 2013, 5, 9150. [248] F. He, G. Chen, Y. Yu, S. Hao, Y. Zhou, Y. Zheng, ACS Appl. Mater. Interfaces 2014, 6, 7171. [249] J. Zhang, M. Zhang, R. Q. Sun, X. Wang, Angew. Chem. Int. Ed. 2012, 51, 10145. [250] F. Dong, Z. Zhao, T. Xiong, Z. Ni, W. Zhang, Y. Sun, W. K. Ho, ACS Appl. Mater. Interfaces 2013, 5, 11392. [251] P. Zhou, J. Yu, M. Jaroniec, Adv. Mater. 2014, 26, 4920. [252] J. Zhang, M. Grzelczak, Y. Hou, K. Maeda, K. Domen, X. Fu, M. Antonietti, X. Wang, Chem. Sci. 2012, 3, 443. [253] L. Ge, C. Han, X. Xiao, L. Guo, Appl. Catal., B 2013, 142–143, 414. [254] R.-L. Lee, P. D. Tran, S. S. Pramana, S. Y. Chiam, Y. Ren, S. Meng, L. H. Wong, J. Barber, Catal. Sci. Technol. 2013, 3, 1694. [255] S. Cao, J. Yu, J. Phys. Chem. Lett. 2014, 5, 2101. [256] S. Martha, A. Nashim, K. M. Parida, J. Mater. Chem. A 2013, 1, 7816. [257] Y. Zhong, Z. Wang, J. Feng, S. Yan, H. Zhang, Z. Li, Z. Zou, Appl. Surf. Sci. 2014, 295, 253. [258] D. J. Martin, K. Qiu, S. A. Shevlin, A. D. Handoko, X. Chen, Z. Guo, J. Tang, Angew. Chem. Int. Ed. 2014, 53, 9240. [259] P. Niu, G. Liu, H.-M. Cheng, J. Phys. Chem. C 2012, 116, 11013. [260] Z. Hong, B. Shen, Y. Chen, B. Lin, B. Gao, J. Mater. Chem. A 2013, 1, 11754. [261] X. L. Wang, W. Q. Fang, S. Yang, P. Liu, H. Zhao, H. G. Yang, RSC Adv. 2014, 4, 10676. [262] X. L. Wang, W. Q. Fang, H. F. Wang, H. Zhang, H. Zhao, Y. Yao, H. G. Yang, J. Mater. Chem. A 2013, 1, 14089. [263] M. Schwarze, D. Stellmach, M. Schroder, K. Kailasam, R. Reske, A. Thomas, R. Schomacker, Phys. Chem. Chem. Phys. 2013, 15, 3466. [264] J. Liu, Y. Zhang, L. Lu, G. Wu, W. Chen, Chem. Commun. 2012, 48, 8826. [265] D. Hollmann, M. Karnahl, S. Tschierlei, K. Kailasam, M. Schneider, J. Radnik, K. Grabow, U. Bentrup, H. Junge, M. Beller, S. Lochbrunner, A. Thomas, A. Brückner, Chem. Mater. 2014, 26, 1727. [266] K. Kailasam, J. D. Epping, A. Thomas, S. Losse, H. Junge, Energy Environ. Sci. 2011, 4, 4668. [267] K. Takanabe, K. Kamata, X. Wang, M. Antonietti, J. Kubota, K. Domen, Phys. Chem. Chem. Phys. 2010, 12, 13020.

26


[268] [269] [270] [271] [272] [273] [274] [275] [276] [277] [278] [279] [280] [281] [282] [283] [284] [285] [286] [287] [288] [289] [290] [291] [292] [293] [294] [295] [296] [297] [298] [299] [300] [301] [302] [303] [304] [305] [306] [307]

S. Min, G. Lu, J. Phys. Chem. C 2012, 116, 19644. J. Xu, Y. Li, S. Peng, G. Lu, S. Li, Phys. Chem. Chem. Phys. 2013, 15, 7657. Y. Wang, J. Hong, W. Zhang, R. Xu, Catal. Sci. Technol. 2013, 3, 1703. X. Zhang, L. Yu, C. Zhuang, T. Peng, R. Li, X. Li, ACS Catal. 2014, 4, 162. L. Yu, X. Zhang, C. Zhuang, L. Lin, R. Li, T. Peng, Phys. Chem. Chem. Phys. 2014, 16, 4106. Q. Xiang, J. Yu, M. Jaroniec, Chem. Soc. Rev. 2012, 41, 782. Q. Xiang, J. Yu, J. Phys. Chem. Lett. 2013, 4, 753. A. Du, S. Sanvito, Z. Li, D. Wang, Y. Jiao, T. Liao, Q. Sun, Y. H. Ng, Z. Zhu, R. Amal, S. C. Smith, J. Am. Chem. Soc. 2012, 134, 4393. X. Li, Y. Dai, Y. Ma, S. Han, B. Huang, Phys. Chem. Chem. Phys. 2014, 16, 4230. J. Low, S. Cao, J. Yu, S. Wageh, Chem. Commun. 2014, 50, 10768. Q. Xiang, J. Yu, M. Jaroniec, J. Phys. Chem. C 2011, 115, 7355. L. Ge, C. Han, Appl. Catal., B 2012, 117–118, 268. Y. Chen, J. Li, Z. Hong, B. Shen, B. Lin, B. Gao, Phys. Chem. Chem. Phys. 2014, 16, 8106. Z. Wu, H. Gao, S. Yan, Z. Zou, Dalton Trans. 2014, 43, 12013. Z. Xing, Z. Chen, X. Zong, L. Wang, Chem. Commun. 2014, 50, 6762. Y. Di, X. Wang, A. Thomas, M. Antonietti, ChemCatChem 2010, 2, 834. S. Samanta, S. Martha, K. Parida, Chem. Cat. Chem 2014, 6, 1453. J. Chen, S. Shen, P. Guo, M. Wang, J. Su, D. Zhao, L. Guo, J. Mater. Res. 2014, 29, 64. X. Bai, R. Zong, C. Li, D. Liu, Y. Liu, Y. Zhu, Appl. Catal., B 2014, 147, 82. J. Yu, S. Wang, B. Cheng, Z. Lin, F. Huang, Catal. Sci. Technol. 2013, 3, 1782. J. Hong, Y. Wang, W. Zhang, R. Xu, ChemSusChem 2013, 6, 2263. Z. Chen, P. Sun, B. Fan, Z. Zhang, X. Fang, J. Phys. Chem. C 2014, 118, 7801. L. Yin, Y.-P. Yuan, S.-W. Cao, Z. Zhang, C. Xue, RSC Adv. 2014, 4, 6127. J. Dong, M. Wang, X. Li, L. Chen, Y. He, L. Sun, ChemSusChem 2012, 5, 2133. D. Wang, Y. Zhang, W. Chen, Chem. Commun. 2014, 50, 1754. S.-W. Cao, Y.-P. Yuan, J. Barber, S. C. J. Loo, C. Xue, Appl. Surf. Sci. 2014, 319, 344. Y. Hou, A. B. Laursen, J. Zhang, G. Zhang, Y. Zhu, X. Wang, S. Dahl, I. Chorkendorff, Angew. Chem. Int. Ed. 2013, 52, 3621. L. Ge, C. Han, X. Xiao, L. Guo, Int. J. Hydrogen Energy 2013, 38, 6960. Y. Hou, Y. Zhu, Y. Xu, X. Wang, Appl. Catal., B 2014, 156–157, 122. X. Zhou, Z. Luo, P. Tao, B. Jin, Z. Wu, Y. Huang, Mater. Chem. Phys. 2014, 143, 1462. S. W. Cao, X. F. Liu, Y. P. Yuan, Z. Y. Zhang, J. Fang, S. C. Loo, J. Barber, T. C. Sum, C. Xue, Phys. Chem. Chem. Phys. 2013, 15, 18363. X.-W. Song, H.-M. Wen, C.-B. Ma, H.-H. Cui, H. Chen, C.-N. Chen, RSC Adv. 2014, 4, 18853. X. B. Li, A. J. Ward, A. F. Masters, T. Maschmeyer, Chem. Eur. J. 2014, 20, 7345. M. Marszewski, S. W. Cao, J. G. Yu, M. Jaroniec, Mater. Horiz. 2015, DOI: 10.1039/c4mh00176a. J. Mao, T. Peng, X. Zhang, K. Li, L. Ye, L. Zan, Catal. Sci. Technol. 2013, 3, 1253. J. Yu, K. Wang, W. Xiao, B. Cheng, Phys. Chem. Chem. Phys. 2014, 16, 11492. S. Bai, X. Wang, C. Hu, M. Xie, J. Jiang, Y. Xiong, Chem. Commun. 2014, 50, 6094. K. Maeda, K. Sekizawa, O. Ishitani, Chem. Commun. 2013, 49, 10127. J. Lin, Z. Pan, X. Wang, ACS Sustainable Chem. Eng. 2014, 2, 353. P. Niu, Y. Q. Yang, J. C. Yu, G. Liu, H.-M. Cheng, Chem. Commun. 2014, 50, 10837.





REVIEW

[308] S. B. Wang, J. L. Lin, X. C. Wang, Phys. Chem. Chem. Phys. 2014, 16, 14656. [309] Y.-P. Yuan, S.-W. Cao, Y.-S. Liao, L.-S. Yin, C. Xue, Appl. Catal., B 2013, 140–141, 164. [310] S. Zhang, L. Zhao, M. Zeng, J. Li, J. Xu, X. Wang, Catal. Today 2014, 224, 114. [311] Q. Li, N. Zhang, Y. Yang, G. Z. Wang, D. H. L. Ng, Langmuir 2014, 30, 8965. [312] N. Cheng, J. Tian, Q. Liu, C. Ge, A. H. Qusti, A. M. Asiri, A. O. AlYoubi, X. Sun, ACS Appl. Mater. Interfaces 2013, 5, 6815. [313] Y. Yang, Y. Guo, F. Liu, X. Yuan, Y. Guo, S. Zhang, W. Guo, M. Huo, Appl. Catal., B 2013, 142–143, 828. [314] W.-C. Peng, X.-Y. Li, Catal. Commun. 2014, 49, 63. [315] C. Han, L. Ge, C. Chen, Y. Li, X. Xiao, Y. Zhang, L. Guo, Appl. Catal., B 2014, 147, 546. [316] Y. Ishida, L. Chabanne, M. Antonietti, M. Shalom, Langmuir 2014, 30, 447. [317] R. C. Pawar, V. Khare, C. S. Lee, Dalton Trans. 2014, 43, 12514. [318] F. Dong, Y. Sun, L. Wu, M. Fu, Z. Wu, Catal. Sci. Technol. 2012, 2, 1332. [319] Y. Cui, Z. Ding, P. Liu, M. Antonietti, X. Fu, X. Wang, Phys. Chem. Chem. Phys. 2012, 14, 1455. [320] D. Wang, H. Sun, Q. Luo, X. Yang, R. Yin, Appl. Catal., B 2014, 156–157, 323. [321] M. Shalom, S. Inal, D. Neher, M. Antonietti, Catal. Today 2014, 225, 185. [322] J. S. Xu, T. J. K. Brenner, Z. P. Chen, D. Neher, M. Antonietti, M. Shalom, ACS Appl. Mater. Interfaces 2014, 6, 16481. [323] S. Z. Hu, L. Ma, J. G. You, F. Y. Li, Z. P. Fan, G. Lu, D. Liu, J. Z. Gui, Appl. Surf. Sci. 2014, 311, 164. [324] S. Kumar, S. T. B. Kumar, A. Baruah, V. Shanker, J. Phys. Chem. C 2013, 117, 26135. [325] Y. Bu, Z. Chen, W. Li, Appl. Catal., B 2014, 144, 622. [326] L. Shi, L. Liang, J. Ma, F. Wang, J. Sun, Dalton Trans. 2014, 43, 7236. [327] B. Chai, X. Liao, F. Song, H. Zhou, Dalton Trans. 2014, 43, 982. [328] Y. Min, X. F. Qi, Q. Xu, Y. Chen, CrystEngComm 2014, 16, 1287. [329] G. Liao, S. Chen, X. Quan, H. Yu, H. Zhao, J. Mater. Chem. 2012, 22, 2721. [330] Y. Li, H. Zhang, P. Liu, D. Wang, H. Zhao, Small 2013, 9, 3336. [331] J. Oh, S. Lee, K. Zhang, J. O. Hwang, J. Han, G. Park, S. O. Kim, J. H. Park, S. Park, Carbon 2014, 66, 119. [332] J. F. Zhang, Y. F. Hu, X. L. Jiang, S. F. Chen, S. G. Meng, X. L. Fu, J. Hazard. Mater. 2014, 280, 713. [333] Y.-P. Zhu, M. Li, Y.-L. Liu, T.-Z. Ren, Z.-Y. Yuan, J. Phys. Chem. C 2014, 118, 10963. [334] Y. Li, J. Zhan, L. Huang, H. Xu, H. Li, R. Zhang, S. Wu, RSC Adv. 2014, 4, 11831. [335] F. Chang, Y. Xie, C. Li, J. Chen, J. Luo, X. Hu, J. Shen, Appl. Surf. Sci. 2013, 280, 967. [336] L. Ge, C. Han, J. Liu, J. Mater. Chem. 2012, 22, 11843. [337] Y. Meng, J. Shen, D. Chen, G. Xin, Rare Metals 2011, 30, 276. [338] Y. Xu, H. Xu, L. Wang, J. Yan, H. Li, Y. Song, L. Huang, G. Cai, Dalton Trans. 2013, 42, 7604. [339] X. Bai, L. Wang, Y. Wang, W. Yao, Y. Zhu, Appl. Catal., B 2014, 152–153, 262. [340] Q. Yu, S. Guo, X. Li, M. Zhang, Mater. Technol. 2014, 29, 172. [341] Y. Hou, Z. Wen, S. Cui, X. Guo, J. Chen, Adv. Mater. 2013, 25, 6291.

[342] K. Dai, L. Lu, Q. Liu, G. Zhu, X. Wei, J. Bai, L. Xuan, H. Wang, Dalton Trans. 2014, 43, 6295. [343] Z. Y. Zhang, J. D. Huang, M. Y. Zhang, Q. Yuan, B. Dong, Appl. Catal., B 2015, 163, 298. [344] C. Liu, L. Jing, L. He, Y. Luan, C. Li, Chem. Commun. 2014, 50, 1999. [345] C. Chang, Y. Fu, M. Hu, C. Wang, G. Shan, L. Zhu, Appl. Catal., B 2013, 142–143, 553. [346] X. Hu, H. Ji, F. Chang, Y. Luo, Catal. Today 2014, 224, 34. [347] F. Dong, Z. Y. Wang, Y. H. Li, W.-K. Ho, S. C. Lee, Environ. Sci. Technol. 2014, 48, 10345. [348] F. Dong, M. Ou, Y. Jiang, S. Guo, Z. Wu, Ind. Eng. Chem. Res. 2014, 53, 2318. [349] G. Dong, L. Zhang, J. Phys. Chem. C 2013, 117, 4062. [350] A. Fujishima, X. Zhang, C. R. Chim. 2006, 9, 750. [351] X. Chen, J. Zhang, X. Fu, M. Antonietti, X. Wang, J. Am. Chem. Soc. 2009, 131, 11658. [352] X. Ye, Y. Cui, X. Qiu, X. Wang, Appl. Catal., B 2014, 152–153, 383. [353] X. Ye, Y. Cui, X. Wang, ChemSusChem 2014, 7, 738. [354] F. Su, S. C. Mathew, G. Lipner, X. Fu, M. Antonietti, S. Blechert, X. Wang, J. Am. Chem. Soc. 2010, 132, 16299. [355] B. Long, Z. Ding, X. Wang, ChemSusChem 2013, 6, 2074. [356] F. Su, S. C. Mathew, L. Mohlmann, M. Antonietti, X. Wang, S. Blechert, Angew. Chem. Int. Ed. 2011, 50, 657. [357] P. Zhang, Y. Gong, H. Li, Z. Chen, Y. Wang, RSC Adv. 2013, 3, 5121. [358] P. Zhang, Y. Wang, H. Li, M. Antonietti, Green Chem. 2012, 14, 1904. [359] L. Möhlmann, M. Baar, J. Rieß, M. Antonietti, X. Wang, S. Blechert, Adv. Synth. Catal. 2012, 354, 1909. [360] X.-H. Li, M. Baar, S. Blechert, M. Antonietti, Sci. Rep. 2013, 3, 1743. [361] J. Liu, M. Antonietti, Energy Environ. Sci. 2013, 6, 1486. [362] L. Song, S. Zhang, X. Wu, H. Tian, Q. Wei, Ind. Eng. Chem. Res. 2012, 51, 9510. [363] H. Zhan, W. Liu, M. Fu, J. Cen, J. Lin, H. Cao, Appl. Catal., A 2013, 468, 184. [364] P. Zhang, Y. Wang, J. Yao, C. Wang, C. Yan, M. Antonietti, H. Li, Adv. Synth. Catal. 2011, 353, 1447. [365] X. Dai, M. Xie, S. Meng, X. Fu, S. Chen, Appl. Catal., B 2014, 158–159, 382. [366] Y. Shiraishi, S. Kanazawa, Y. Sugano, D. Tsukamoto, H. Sakamoto, S. Ichikawa, T. Hirai, ACS Catal. 2014, 4, 774. [367] W. Wang, J. C. Yu, D. Xia, P. K. Wong, Y. Li, Environ. Sci. Technol. 2013, 47, 8724. [368] J. Huang, W. Ho, X. Wang, Chem. Commun. 2014, 50, 4338. [369] Z. Zhang, J. Long, L. Yang, W. Chen, W. Dai, X. Fu, X. Wang, Chem. Sci. 2011, 2, 1826. [370] X. Li, S. Zhang, Q. Wang, Phys. Chem. Chem. Phys. 2013, 15, 7142. [371] K. Schwinghammer, M. B. Mesch, V. Duppel, C. Ziegler, J. Senker, B. V. Lotsch, J. Am. Chem. Soc. 2014, 136, 1730. [372] E. J. McDermott, E. Wirnhier, W. Schnick, K. S. Virdi, C. Scheu, Y. Kauffmann, W. D. Kaplan, E. Z. Kurmaev, A. Moewes, J. Phys. Chem. C 2013, 117, 8806. [373] K. Schwinghammer, B. Tuffy, M. B. Mesch, E. Wirnhier, C. Martineau, F. Taulelle, W. Schnick, J. Senker, B. V. Lotsch, Angew. Chem. Int. Ed. 2013, 52, 2435.



27

Triazine-based graphitic carbon nitride: a two-dimensional semiconductor.

Increasing the visible light absorption of graphitic carbon nitride (melon) photocatalysts by homogeneous self-modification with nitrogen vacancies.

Oxygen functional groups in graphitic carbon nitride for enhanced photocatalysis.

Graphitic carbon nitride: synthesis, properties, and applications in catalysis.

Graphitic Carbon Nitride Supported Catalysts for Polymer Electrolyte Fuel Cells.

Graphitic carbon nitride embedded hydrogels for enhanced gel electrophoresis.

Enhanced electrochemiluminescence sensor for detecting dopamine based on gold nanoflower@graphitic carbon nitride polymer nanosheet-polyaniline hybrids.

A novel multi-amplification photoelectrochemical immunoassay based on copper(II) enhanced polythiophene sensitized graphitic carbon nitride nanosheet.

carbon nitride containing graphitic carbon nanocapsule hybrid as a Pt-free electrocatalyst for oxygen reduction.

Graphitic carbon nitride nanosheet-carbon nanotube three-dimensional porous composites as high-performance oxygen evolution electrocatalysts.

The effect of water on the structural, electronic and photocatalytic properties of graphitic carbon nitride.

Photoelectrochemical Immunosensor for Detection of Carcinoembryonic Antigen Based on 2D TiO2 Nanosheets and Carboxylated Graphitic Carbon Nitride.

RGO) for superior photodegradation of organic pollutants under UV and visible light.

Dispersing molecular cobalt in graphitic carbon nitride frameworks for photocatalytic water oxidation.

Ion coordination significantly enhances the photocatalytic activity of graphitic-phase carbon nitride.

Urea-derived graphitic carbon nitride (u-g-C3N4) films with highly enhanced antimicrobial and sporicidal activity.

A highly active and durable Co-N-C electrocatalyst synthesized using exfoliated graphitic carbon nitride nanosheets.

Preparation and characterization of photoactive antimicrobial graphitic carbon nitride (g-C3N4) films.

Conductive Graphitic Carbon Nitride as an Ideal Material for Electrocatalytically Switchable CO2 Capture.

Synthesis of potassium-modified graphitic carbon nitride with high photocatalytic activity for hydrogen evolution.

Rational design of carbon nitride photocatalysts by identification of cyanamide defects as catalytically relevant sites.

Iodine modified carbon nitride semiconductors as visible light photocatalysts for hydrogen evolution.

Macroscopic 3D Porous Graphitic Carbon Nitride Monolith for Enhanced Photocatalytic Hydrogen Evolution.

Graphitic Carbon Nitride Sensitized with CdS Quantum Dots for Visible-Light-Driven Photoelectrochemical Aptasensing of Tetracycline.