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This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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DOI: 10.1039/C4NR05749J
Synthesis of Scaly Sn3O4/TiO2 Nanobelts Heterostructure for Enhanced UV-Visible Light Photocatalytic Activity Guohui Chen‡a, Shaozheng Ji‡a, Yuanhua Sanga, Sujie Changa, Yana Wanga, Pin Haoa, Jerome Claveriec, Hong Liua,b*, Guangwei Yu a* A novel scaly Sn 3 O4/TiO 2 nanobelts heterostructured photocatalyst was fabricated via a facile hydrothermal route. The scaly Sn 3 O4 nanoflakes can be synthesized in situ and assembled on surface coarsened TiO 2 nanobelts through a hydrothermal process. The morphology and distribution of Sn 3O4 nanoflakes can be well-controlled by simply tuning Sn/Ti molar ratio of the reactants. Compared with single phase nanostructures of Sn 3 O4 and TiO2, the scaly hybrid nanobelts exhibited markedly enhanced photoelectrochemical (PEC) response, which caused higher photocatalytic hydrogen evolution even without the assistance of Pt as co-catalyst, and enhanced degradation ability of organic pollutants under both UV and visible light irradiation. In addition to the increased exposure of active facets and broad light absorption, the outstanding performance is ascribed to matched energy band structure between Sn 3O4 and TiO 2 at the two sides of the heterostructure, which efficiently reduce the recombination of photo-excited electron-hole pairs, and prolong the lifetime of charge carriers. Both photocatalytic assessment and PEC tests revealed that Sn 3O4 /TiO 2 heterostructures with a molar ratio Sn/Ti of 2/1 exhibited the highest photocatalytic activity. This research provides a facile and low-cost method for large scale production of Sn 3 O4 based materials in various applications.
1. Introduction Semiconductor photocatalysts have aroused much attention as a potential solution to the growing worldwide energy crisis and increasing environmental pollution problems,1,2 by virtue of their sustainable conversion of solar energy into clean hydrogen fuel and their ability to photochemically oxidize pollutants. Early discoveries of photocatalysts were focused on semiconductors with wide band gaps such as TiO23 and ZnO,4 that solely can be activated by high-energy ultraviolet (UV) light, which accounts for only 4% of the sunlight, greatly limiting their applicability. Over the past 20 years, research has focused on the discovery of highly-active photocatalysts with broad spectrum absorption, in particular in the visible range. Progress has been made on Ag2O,5 WO3,6 PbO2,7 etc..8,9 They are mostly efficient for degrading organic pollutants, but their ability to catalyze water splitting is negligible due to their inappropriate band structures. Moreover, they are based on expensive (Ag) or toxic (Pb) materials. Most recently, Sn3O4 was shown to possess outstanding visible light photocatalytic activity for both dye degradation 10 and hydrogen evolution.11 Similar to other heterovalent oxides like Fe3O412 and Co3O4,13 Sn3O4 is composed by mixed valences of Sn2+ and Sn4+.14 One-third of the Sn atoms are in Sn (II) tetrahedral coordination sites and two-thirds are in Sn (IV) octahedral sites.15
This journal is © The Royal Society of Chemistry [year]
Sn3O4 belongs to (101)-layered structures based on the rutile structure,16 and the stability of the crystalline structure has been verified by theoretical calculations.14,17 Recently, stable Sn3O4 with nanobelt,18, 19 nanosphere10 and nanosheet11 morphologies were successfully synthesized. However, its hydrogen production property under visible light irradiation is highly relied on noble metal deposition as co-catalyst,11 which is a severe cost limitation. The discovery of practical and cost-effective conditions for using Sn3O4 under solar light to degrade organic pollutants and to split water for hydrogen generation should be of great utility for photocatalysis research. Theoretical analysis on the band structures of TiO2 and Sn3O4 can suggest that combining visible light active Sn3O4 with UV light active TiO2 could not only yield a UV-visible broad spectrum photocatalyst, but also enhance the separation of photo-excited holes and electrons. As discussed in our recent review paper, the design of heterostructured photocatalyst should follow one or more principles, including enhancing light active facets, broadening light absorption region, and enhancing the separation of photoexcited charge carrriers.20 Among the various oxide, onedimensional (1D) TiO2, such as nanorods, nanotubes and nanobelts, have been among the most widely studied for the design and fabrication of hierarchical nanostructures.21 Thank to its high aspect ratio, 1D TiO2 provides a large surface area for the Nanoscale, 2014, [vol], 00–00 | 1
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growth of other oxides, and facilitates interfacial charge transfer and effectively inhibits aggreation.22 Coupling 1D TiO2 with other narrow band-gap photocatalysts is expected to prohibit charge carrier recombination and enhance light harvesting, resulting in high photocatalytic activities. Based on this concept, many heterostructure based on 1D TiO2 were reported, such as Ag2O/TiO2,5 CeO2/TiO2,23 Bi2O3/ TiO2,24 and so on.25 Herein, we report the synthesis of novel scaly Sn 3O4/TiO2 nanobelts heterostructures prepared through a two-step hydrothermal process. By assembling Sn3O4 on TiO2 nanobelts, the photocatalytic hydrogen generation ability is dramatically improved. The presence of a heterojunction between Sn3O4 and TiO2 with energy band matching causes greater separation of photoexcited charge carriers and enhancement of the photodegradation activiy both under UV and visible light irradiation. We believe this broad spectrum photocatalyst will have great practical applications in photocatalytic water splitting for hydrogen generation and photodegradation of organic pollutant.
2. Experimental 2.1 Materials Titania P25 (TiO2: ca. 80% anatase and 20% rutile), sodium hydroxide (NaOH), hydrochloric acid (HCl), sulfuric acid (H2SO4), tin (II) chloride dehydrate (SnCl2·2H2O), sodium citrate dehydrate (Na3C6H5O7·2H2O), ethanol (C2H5OH), and methyl orange (MO) were purchased from Sinopharm. All the chemicals were used as received without further purification. Deionized water was used throughout this study. 2.2 Synthesis of photocatalysts Scaly Sn3O4/TiO2 nanobelts heterostructure was prepared by two steps, (1) pre-synthesis of TiO2 nanobelts:26 0.8 g P25 was mixed with 80 mL of 10 M NaOH aqueous solution and stirred for 30 min. Then the mixture was transferred into a 100 mL Teflonlined stainless steel autoclave, heated at 180 °C for 72 h. After naturally cooling down to room temperature, obtained Na2Ti3O7 powder was washed thoroughly with deionized water to remove the excess NaOH. The obtained Na2Ti3O7 nanobelts were then immersed in 100 mL of 0.1 M HCl for 24 h and then washed thoroughly with deionized water to produce H2Ti3O7 nanobelts, then mixed with 40 mL of 0.02 M H2SO4 aqueous solution in 50 mL Teflon-lined stainless steel autoclave by heating at 100 °C for 12 h to get surface coarse nanobelts. Finally, the products were isolated from the solution by centrifugation, sequentially washed with deionized water for several times, and dried at 70 °C for 10 h, followed by thermal annealing at 600 °C for 2 h; (2) synthesis of Sn3O4/TiO2 system: scaly Sn3O4/TiO2 nanobelts were prepared by a simple hydrothermal co-precipitation method. In a typical process, 5.0 mmol SnCl2·2H2O and 12.5 mmol Na3C6H5O7·2H2O were dissolved in 12.5 mL of deionized water and stirred for 5 min to obtain a transparent solution, to which a certain amount of pre-synthesized TiO2 nanobelts (molar ratio Sn/Ti= 2/1) were added. Then 12.5 mL of 0.2 M NaOH aqueous solution was added to the above solution while continuously stirring and followed by ultrasonic treatment to obtain a homogeneous solution. The solution was transferred to 50 mL Teflon-lined stainless steel autoclave and maintained at 180 °C for 12 h. The
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DOI: 10.1039/C4NR05749J
obtained powder was washed with deionized water and ethanol and dried at 60 °C for 12 h. Different Sn3O4/TiO2 heterostructure were synthesized by varying molar ratio of Sn/Ti from 1/1 to 3/1. Pure Sn3O4 was prepared without the addition of TiO2 nanobelts. 2.3 Characterizations Crystal structures were recorded on a Bruke D8 Advance powder X-ray diffractometer (XRD) with Cu Kα (λ = 0.15406 nm) irradiation. Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) were measured on a HITACHI S-4800 field emission scanning electron microscope. High resolution transmission electron microscopic (HRTEM) images and element mapping were acquired from a JOEL JEM 2100 microscope. UV–vis diffuse reflectance spectra (DRS) of the samples were recorded on a UV–vis spectrophotometer (UV2550, Shimadzu) with an integrating sphere attachment within the wavelength range from 200 to 800 nm and with BaSO4 as the reflectance standard. The photoluminescence (PL) spectra were measured at room temperature with a FLS920 fluorescence spectrometer under the excitation wavelength of 300 nm. The specific surface area was calculated with the Brunauer-EmmettTeller (BET) method by the instrument (Micromeritics, ASAP2020). 2.4 Photoelectrochemical measurements PEC analyses were performed on an electrochemical workstation (Gamry Reference 600, USA) with a standard three-electrode cell, Ag/AgCl as reference electrode, Pt wire as the counter electrode and Na2SO4 solution (0.1 M, pH = 6.8) as electrolyte. To obtain the working electrodes, TiO2, Sn3O4, and Sn3O4/TiO2 (molar ratio Sn/Ti = 2/1) slurries in terpineol solvent were coated on a clean fluorine doped tin oxide (FTO) glass, and subsequent heat at 400 °C for 2 h with N2 flowing to form a better electronic connection between the samples and the FTO substrate. All the working electrodes investigated in this study were of similar thickness and area (1 cm×1 cm). A 400 W Xenon lamp was used as light source for PEC measurement, the dark current and the photocurrent of the anode in the range of bias from -0.6 V to 0.2 V were recorded and compared. The photocurrent response (I–t) curves were measured at -0.35 V. FTO glass was used as blank sample, all electrochemical experiments were carried out at room temperature. Mott-Schottky (M-S) plots were obtained with a Gamry electrochemical station (Reference 3000, USA), impedance spectroscopy was measured at different frequencies of 10 Hz, 100 Hz and 1000 Hz, respectively. 2.5 Photocatalytic hydrogen evolution The photocatalytic hydrogen evolution experiments were performed in a closed gas circulation system (CEL-SPO2, AULTT). Typically, 200 mg photocatalyst was suspended in the mixture of water (220 mL) and methanol (80 mL) and irradiated for 5 hours with a 300W Xe arc lamp (HXUV 300). The evolved hydrogen was analyzed by an online gas chromatograph equipped with a thermal conductivity detector (HP-GC1490, N2 carrier, TDX-01 carbon molecular sieve column). The 1 wt % Pt cocatalyst was photo-deposited on the Sn3O4/TiO2 catalysts by mixed a calculated amount of H2PtCl6 (10g/L) in ethanol aqueous solution (20 mL ethanol and 80 mL water), followed by irradiation of a Mercury lamp (300 W) for 30 min.27 Cycling tests
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of photocatalytic hydrogen generation were conducted over successive 20 h irradiation without renewing the sacrificial agents.
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DOI: 10.1039/C4NR05749J
thus inhibit the recombination of the photoexcited electrons and holes.29
The photocatalytic degradation activities of the samples was evaluated by monitoring the decomposition process of the methyl orange aqueous solution (MO, 20 mg/L). The experiments were carried out in a photoreaction apparatus XPA-II photochemical reactor (XPA-II, Nanjing Xujiang Machine-electronic Plant). Typically, 30 mg photocatalyst was mixed with 30 mL MO solution and stirred for 30 min in the dark to reach the adsorptiondesorption equilibrium. The suspension was then irradiated with the three different light sources under constant stirring. UV and simulated solar lights were obtained by a 300 W Mercury lamp and a 500 W Xenon lamp, respectively, and visible light was also obtained from Xenon lamp by using cutoff to remove light of λ
Nanoscale Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: G. Chen, S. Ji, Y. Sang, S. Chang, Y. Wang, P. Hao, J. P. Claverie, H. Liu and G. Yu, Nanoscale, 2015, DOI:
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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DOI: 10.1039/C4NR05749J
Synthesis of Scaly Sn3O4/TiO2 Nanobelts Heterostructure for Enhanced UV-Visible Light Photocatalytic Activity Guohui Chen‡a, Shaozheng Ji‡a, Yuanhua Sanga, Sujie Changa, Yana Wanga, Pin Haoa, Jerome Claveriec, Hong Liua,b*, Guangwei Yu a* A novel scaly Sn 3 O4/TiO 2 nanobelts heterostructured photocatalyst was fabricated via a facile hydrothermal route. The scaly Sn 3 O4 nanoflakes can be synthesized in situ and assembled on surface coarsened TiO 2 nanobelts through a hydrothermal process. The morphology and distribution of Sn 3O4 nanoflakes can be well-controlled by simply tuning Sn/Ti molar ratio of the reactants. Compared with single phase nanostructures of Sn 3 O4 and TiO2, the scaly hybrid nanobelts exhibited markedly enhanced photoelectrochemical (PEC) response, which caused higher photocatalytic hydrogen evolution even without the assistance of Pt as co-catalyst, and enhanced degradation ability of organic pollutants under both UV and visible light irradiation. In addition to the increased exposure of active facets and broad light absorption, the outstanding performance is ascribed to matched energy band structure between Sn 3O4 and TiO 2 at the two sides of the heterostructure, which efficiently reduce the recombination of photo-excited electron-hole pairs, and prolong the lifetime of charge carriers. Both photocatalytic assessment and PEC tests revealed that Sn 3O4 /TiO 2 heterostructures with a molar ratio Sn/Ti of 2/1 exhibited the highest photocatalytic activity. This research provides a facile and low-cost method for large scale production of Sn 3 O4 based materials in various applications.
1. Introduction Semiconductor photocatalysts have aroused much attention as a potential solution to the growing worldwide energy crisis and increasing environmental pollution problems,1,2 by virtue of their sustainable conversion of solar energy into clean hydrogen fuel and their ability to photochemically oxidize pollutants. Early discoveries of photocatalysts were focused on semiconductors with wide band gaps such as TiO23 and ZnO,4 that solely can be activated by high-energy ultraviolet (UV) light, which accounts for only 4% of the sunlight, greatly limiting their applicability. Over the past 20 years, research has focused on the discovery of highly-active photocatalysts with broad spectrum absorption, in particular in the visible range. Progress has been made on Ag2O,5 WO3,6 PbO2,7 etc..8,9 They are mostly efficient for degrading organic pollutants, but their ability to catalyze water splitting is negligible due to their inappropriate band structures. Moreover, they are based on expensive (Ag) or toxic (Pb) materials. Most recently, Sn3O4 was shown to possess outstanding visible light photocatalytic activity for both dye degradation 10 and hydrogen evolution.11 Similar to other heterovalent oxides like Fe3O412 and Co3O4,13 Sn3O4 is composed by mixed valences of Sn2+ and Sn4+.14 One-third of the Sn atoms are in Sn (II) tetrahedral coordination sites and two-thirds are in Sn (IV) octahedral sites.15
This journal is © The Royal Society of Chemistry [year]
Sn3O4 belongs to (101)-layered structures based on the rutile structure,16 and the stability of the crystalline structure has been verified by theoretical calculations.14,17 Recently, stable Sn3O4 with nanobelt,18, 19 nanosphere10 and nanosheet11 morphologies were successfully synthesized. However, its hydrogen production property under visible light irradiation is highly relied on noble metal deposition as co-catalyst,11 which is a severe cost limitation. The discovery of practical and cost-effective conditions for using Sn3O4 under solar light to degrade organic pollutants and to split water for hydrogen generation should be of great utility for photocatalysis research. Theoretical analysis on the band structures of TiO2 and Sn3O4 can suggest that combining visible light active Sn3O4 with UV light active TiO2 could not only yield a UV-visible broad spectrum photocatalyst, but also enhance the separation of photo-excited holes and electrons. As discussed in our recent review paper, the design of heterostructured photocatalyst should follow one or more principles, including enhancing light active facets, broadening light absorption region, and enhancing the separation of photoexcited charge carrriers.20 Among the various oxide, onedimensional (1D) TiO2, such as nanorods, nanotubes and nanobelts, have been among the most widely studied for the design and fabrication of hierarchical nanostructures.21 Thank to its high aspect ratio, 1D TiO2 provides a large surface area for the Nanoscale, 2014, [vol], 00–00 | 1
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growth of other oxides, and facilitates interfacial charge transfer and effectively inhibits aggreation.22 Coupling 1D TiO2 with other narrow band-gap photocatalysts is expected to prohibit charge carrier recombination and enhance light harvesting, resulting in high photocatalytic activities. Based on this concept, many heterostructure based on 1D TiO2 were reported, such as Ag2O/TiO2,5 CeO2/TiO2,23 Bi2O3/ TiO2,24 and so on.25 Herein, we report the synthesis of novel scaly Sn 3O4/TiO2 nanobelts heterostructures prepared through a two-step hydrothermal process. By assembling Sn3O4 on TiO2 nanobelts, the photocatalytic hydrogen generation ability is dramatically improved. The presence of a heterojunction between Sn3O4 and TiO2 with energy band matching causes greater separation of photoexcited charge carriers and enhancement of the photodegradation activiy both under UV and visible light irradiation. We believe this broad spectrum photocatalyst will have great practical applications in photocatalytic water splitting for hydrogen generation and photodegradation of organic pollutant.
2. Experimental 2.1 Materials Titania P25 (TiO2: ca. 80% anatase and 20% rutile), sodium hydroxide (NaOH), hydrochloric acid (HCl), sulfuric acid (H2SO4), tin (II) chloride dehydrate (SnCl2·2H2O), sodium citrate dehydrate (Na3C6H5O7·2H2O), ethanol (C2H5OH), and methyl orange (MO) were purchased from Sinopharm. All the chemicals were used as received without further purification. Deionized water was used throughout this study. 2.2 Synthesis of photocatalysts Scaly Sn3O4/TiO2 nanobelts heterostructure was prepared by two steps, (1) pre-synthesis of TiO2 nanobelts:26 0.8 g P25 was mixed with 80 mL of 10 M NaOH aqueous solution and stirred for 30 min. Then the mixture was transferred into a 100 mL Teflonlined stainless steel autoclave, heated at 180 °C for 72 h. After naturally cooling down to room temperature, obtained Na2Ti3O7 powder was washed thoroughly with deionized water to remove the excess NaOH. The obtained Na2Ti3O7 nanobelts were then immersed in 100 mL of 0.1 M HCl for 24 h and then washed thoroughly with deionized water to produce H2Ti3O7 nanobelts, then mixed with 40 mL of 0.02 M H2SO4 aqueous solution in 50 mL Teflon-lined stainless steel autoclave by heating at 100 °C for 12 h to get surface coarse nanobelts. Finally, the products were isolated from the solution by centrifugation, sequentially washed with deionized water for several times, and dried at 70 °C for 10 h, followed by thermal annealing at 600 °C for 2 h; (2) synthesis of Sn3O4/TiO2 system: scaly Sn3O4/TiO2 nanobelts were prepared by a simple hydrothermal co-precipitation method. In a typical process, 5.0 mmol SnCl2·2H2O and 12.5 mmol Na3C6H5O7·2H2O were dissolved in 12.5 mL of deionized water and stirred for 5 min to obtain a transparent solution, to which a certain amount of pre-synthesized TiO2 nanobelts (molar ratio Sn/Ti= 2/1) were added. Then 12.5 mL of 0.2 M NaOH aqueous solution was added to the above solution while continuously stirring and followed by ultrasonic treatment to obtain a homogeneous solution. The solution was transferred to 50 mL Teflon-lined stainless steel autoclave and maintained at 180 °C for 12 h. The
View Article Online
Page 2 of 8
DOI: 10.1039/C4NR05749J
obtained powder was washed with deionized water and ethanol and dried at 60 °C for 12 h. Different Sn3O4/TiO2 heterostructure were synthesized by varying molar ratio of Sn/Ti from 1/1 to 3/1. Pure Sn3O4 was prepared without the addition of TiO2 nanobelts. 2.3 Characterizations Crystal structures were recorded on a Bruke D8 Advance powder X-ray diffractometer (XRD) with Cu Kα (λ = 0.15406 nm) irradiation. Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) were measured on a HITACHI S-4800 field emission scanning electron microscope. High resolution transmission electron microscopic (HRTEM) images and element mapping were acquired from a JOEL JEM 2100 microscope. UV–vis diffuse reflectance spectra (DRS) of the samples were recorded on a UV–vis spectrophotometer (UV2550, Shimadzu) with an integrating sphere attachment within the wavelength range from 200 to 800 nm and with BaSO4 as the reflectance standard. The photoluminescence (PL) spectra were measured at room temperature with a FLS920 fluorescence spectrometer under the excitation wavelength of 300 nm. The specific surface area was calculated with the Brunauer-EmmettTeller (BET) method by the instrument (Micromeritics, ASAP2020). 2.4 Photoelectrochemical measurements PEC analyses were performed on an electrochemical workstation (Gamry Reference 600, USA) with a standard three-electrode cell, Ag/AgCl as reference electrode, Pt wire as the counter electrode and Na2SO4 solution (0.1 M, pH = 6.8) as electrolyte. To obtain the working electrodes, TiO2, Sn3O4, and Sn3O4/TiO2 (molar ratio Sn/Ti = 2/1) slurries in terpineol solvent were coated on a clean fluorine doped tin oxide (FTO) glass, and subsequent heat at 400 °C for 2 h with N2 flowing to form a better electronic connection between the samples and the FTO substrate. All the working electrodes investigated in this study were of similar thickness and area (1 cm×1 cm). A 400 W Xenon lamp was used as light source for PEC measurement, the dark current and the photocurrent of the anode in the range of bias from -0.6 V to 0.2 V were recorded and compared. The photocurrent response (I–t) curves were measured at -0.35 V. FTO glass was used as blank sample, all electrochemical experiments were carried out at room temperature. Mott-Schottky (M-S) plots were obtained with a Gamry electrochemical station (Reference 3000, USA), impedance spectroscopy was measured at different frequencies of 10 Hz, 100 Hz and 1000 Hz, respectively. 2.5 Photocatalytic hydrogen evolution The photocatalytic hydrogen evolution experiments were performed in a closed gas circulation system (CEL-SPO2, AULTT). Typically, 200 mg photocatalyst was suspended in the mixture of water (220 mL) and methanol (80 mL) and irradiated for 5 hours with a 300W Xe arc lamp (HXUV 300). The evolved hydrogen was analyzed by an online gas chromatograph equipped with a thermal conductivity detector (HP-GC1490, N2 carrier, TDX-01 carbon molecular sieve column). The 1 wt % Pt cocatalyst was photo-deposited on the Sn3O4/TiO2 catalysts by mixed a calculated amount of H2PtCl6 (10g/L) in ethanol aqueous solution (20 mL ethanol and 80 mL water), followed by irradiation of a Mercury lamp (300 W) for 30 min.27 Cycling tests
Nanoscale Accepted Manuscript
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of photocatalytic hydrogen generation were conducted over successive 20 h irradiation without renewing the sacrificial agents.
View Article Online
DOI: 10.1039/C4NR05749J
thus inhibit the recombination of the photoexcited electrons and holes.29
The photocatalytic degradation activities of the samples was evaluated by monitoring the decomposition process of the methyl orange aqueous solution (MO, 20 mg/L). The experiments were carried out in a photoreaction apparatus XPA-II photochemical reactor (XPA-II, Nanjing Xujiang Machine-electronic Plant). Typically, 30 mg photocatalyst was mixed with 30 mL MO solution and stirred for 30 min in the dark to reach the adsorptiondesorption equilibrium. The suspension was then irradiated with the three different light sources under constant stirring. UV and simulated solar lights were obtained by a 300 W Mercury lamp and a 500 W Xenon lamp, respectively, and visible light was also obtained from Xenon lamp by using cutoff to remove light of λ
