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Yijun Xu - One of the best experts on this subject based on the ideXlab platform.
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toward improving the graphene semiconductor composite Photoactivity via the addition of metal ions as generic interfacial mediator
ACS Nano, 2014Co-Authors: Nan Zhang, Minquan Yang, Zirong Tang, Yijun XuAbstract:We report a simple and general approach to improve the transfer efficiency of photogenerated charge carriers across the interface between graphene (GR) and semiconductor CdS by introducing a small amount of metal ions (Ca2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) as “mediator” into their interfacial layer matrix, while the intimate interfacial contact between GR and CdS is maintained. This simple strategy can not only significantly improve the visible-light-driven Photoactivity of GR–CdS semiconductor composites for targeting selective photoredox reaction, including aerobic oxidation of alcohol and anaerobic reduction of nitro compound, but also drive a balance between the positive effect of GR on retarding the recombination of electron–hole pairs photogenerated from semiconductor and the negative “shielding effect” of GR resulting from the high weight addition of GR. Our current work highlights that the significant issue on improving the Photoactivity of GR–semiconductor composites via strengtheni...
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basic principles for observing the photosensitizer role of graphene in the graphene semiconductor composite photocatalyst from a case study on graphene zno
Journal of Physical Chemistry C, 2013Co-Authors: Minquan Yang, Yijun XuAbstract:The graphene–ZnO (GR–ZnO) nanocomposites have been fabricated via a facile, low-temperature in situ wet chemistry process, during which the reduction of graphene oxide and intimate interfacial contact between ZnO nanoparticles and GR nanosheets are achieved simultaneously. The GR–ZnO nanocomposites exhibit visible light Photoactivity toward reduction of Cr(VI) in aqueous solution under ambient conditions. The large band gaps of GR–ZnO composites suggest that the visible light irradiation cannot photoexcite electrons in the valence band (VB) to conduction band (CB) of ZnO, thus ruling out the possibility that the visible light Photoactivity of GR–ZnO is induced by the band gap photoexcitation of ZnO. Instead, under visible light irradiation, the GR sheet in GR–ZnO can be photoexcited from ground-state GR to excited-state GR* to generate electrons, which then inject into the CB of ZnO to make the GR–ZnO composites exhibit visible light Photoactivity. Our results provide new robust proof of the role of GR as...
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fast and spontaneous reduction of gold ions over oxygen vacancy rich tio2 a novel strategy to design defect based composite photocatalyst
Applied Catalysis A-general, 2013Co-Authors: Yijun XuAbstract:Abstract A novel strategy has been developed for spontaneous reduction of gold ions on the TiO2 with oxygen vacancies (TiO2-OV) to obtain defect-based composite photocatalyst, during which neither additional reducing agents nor surfactants are required. The as-formed metallic gold nanoparticles are partially embedded into the surface of TiO2 resulting from the binding with OV on the TiO2 surface. Such an intimate interfacial contact between gold nanoparticles and TiO2 can contribute to improving the separation and transport of charge carriers photogenerated from Au-TiO2-OV hybrids under visible light irradiation as well as stabilizing gold nanoparticles on TiO2. It is revealed that the electron transfer from OV states of TiO2-OV to gold ions is responsible for the spontaneous formation of metallic gold nanoparticles. The results show that Au-TiO2-OV shows enhanced visible light Photoactivity toward Rhodamine B (RhB) degradation compared to the original TiO2 and TiO2-OV. The wavelength dependent Photoactivity analysis further clarifies that the surface plasmon resonance (SPR) due to the excitation of gold nanoparticles under visible light irradiation is the driving force for the enhanced visible light Photoactivity. It is hoped that our current work would provide a simple, fast strategy to synthesize defect-based composite photocatalysts for target applications.
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graphene transforms wide band gap zns to a visible light photocatalyst the new role of graphene as a macromolecular photosensitizer
ACS Nano, 2012Co-Authors: Yanhui Zhang, Zirong Tang, Nan Zhang, Yijun XuAbstract:We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS–GR nanocomposites exhibit visible light Photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure–Photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS–GR nanocomposites acts as an organic dye-like macromolecular “photosensitizer” for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR–semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept ...
Ling Zan - One of the best experts on this subject based on the ideXlab platform.
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effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic co2 reduction under visible light
Catalysis Science & Technology, 2013Co-Authors: Jin Mao, Tianyou Peng, Xiaohu Zhang, Ling ZanAbstract:Two kinds of graphitic carbon nitride (g-C3N4) were synthesized through a pyrolysis process of urea or melamine. It is found that the obtained g-C3N4, as photocatalysts, can reduce CO2 to organic fuels under visible light, and exhibit different Photoactivity and selectivity on the formation of CH3OH and C2H5OH. The product derived from the urea (denoted as u-g-C3N4) shows a mesoporous flake-like structure with a larger surface area and higher Photoactivity for the CO2 reduction than the non-porous flaky product obtained from melamine (denoted as m-g-C3N4). Moreover, using u-g-C3N4 as a photocatalyst can result in the formation of a mixture containing CH3OH and C2H5OH, while m-g-C3N4 only leads to the selective formation of C2H5OH. The present interesting findings could shed light on the design of efficient, eco-friendly and convenient photocatalysts and the tuning of their photoreactivity in the field of sustainable light-to-energy conversion.
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preparation of agin5s8 tio2 heterojunction nanocomposite and its enhanced photocatalytic h2 production property under visible light
ACS Catalysis, 2013Co-Authors: Bo Chai, Tianyou Peng, Jing Mao, Ling ZanAbstract:AgIn5S8/TiO2 nanocomposite is prepared through a one-pot hydrothermal method, which is used for photocatalytic H2 production under visible-light irradiation. The effects of AgIn5S8/TiO2 molar ratio in the nanocomposites on the crystal phase, microstructure, optical absorption properties, and photocatalytic H2 evolution activity are investigated comparatively. The pristine AgIn5S8 shows a sharp absorption edge at ∼705 nm, corresponding to a bandgap of ∼1.76 eV, and its visible-light-driven Photoactivity for H2 production can be remarkably enhanced by coupling with TiO2. The AgIn5S8/TiO2 nanocomposite with molar ratio of 1:10 has the maximum Photoactivity for H2 production, improved by 7.7 times as compared with the pristine AgIn5S8. The enhanced Photoactivity can be ascribed to some AgIn5S8 nanoparticles closely contacting the TiO2 nanoparticles to form heterojunction structure. This configuration of the composite photocatalyst results in an efficient charge separation at the interface, followed by fast di...
Qian Zhang - One of the best experts on this subject based on the ideXlab platform.
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effects of calcination on the photocatalytic properties of nanosized tio2 powders prepared by ticl4 hydrolysis
Applied Catalysis B-environmental, 2000Co-Authors: Qian ZhangAbstract:Abstract The ultra fine nanosized TiO2 photocatalysts in the anatase, rutile, and both phases were prepared by the hydrolysis of TiCl4 solution. The resulting materials have been characterized by HREM, XRD, BET and UV–VIS absorption spectroscopy. The Photoactivity, effective degradation, and the selectivity for complete mineralization of these catalysts were tested in the photocatalytic degradation of phenol. For this reaction, the quantum-sized catalyst particles (4 nm) in the anatase phase shows the highest selectivity, the concentrations of p-benzoquinone and hydroquinol as the photocatalytic products were at very low level. However, the selectivity of the quantum-sized crystallites in the rutile phase was not improved in comparison with that of catalysts which bandgap corresponding bulk rutile. HREM micrographs show the quantum-sized catalysts were crystallized partially or many defects occurred on their crystal planes, they are responsible for their relative low Photoactivity. Calcination is an effective treatment to increase the Photoactivity of nanosized TiO2 photocatalysts resulting from the improvement of crystallinity. Mixtures of both phases exhibit higher Photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts. To the best of our knowledge, we are first to report that the quantum-sized TiO2 crystallite exhibit high selectivity for complete mineralization in the photocatalytic degradation of phenol solution.
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effects of calcination on the photocatalytic properties of nanosized tio2 powders prepared by ticl4 hydrolysis
Applied Catalysis B-environmental, 2000Co-Authors: Qian ZhangAbstract:Abstract The ultra fine nanosized TiO2 photocatalysts in the anatase, rutile, and both phases were prepared by the hydrolysis of TiCl4 solution. The resulting materials have been characterized by HREM, XRD, BET and UV–VIS absorption spectroscopy. The Photoactivity, effective degradation, and the selectivity for complete mineralization of these catalysts were tested in the photocatalytic degradation of phenol. For this reaction, the quantum-sized catalyst particles (4 nm) in the anatase phase shows the highest selectivity, the concentrations of p-benzoquinone and hydroquinol as the photocatalytic products were at very low level. However, the selectivity of the quantum-sized crystallites in the rutile phase was not improved in comparison with that of catalysts which bandgap corresponding bulk rutile. HREM micrographs show the quantum-sized catalysts were crystallized partially or many defects occurred on their crystal planes, they are responsible for their relative low Photoactivity. Calcination is an effective treatment to increase the Photoactivity of nanosized TiO2 photocatalysts resulting from the improvement of crystallinity. Mixtures of both phases exhibit higher Photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts. To the best of our knowledge, we are first to report that the quantum-sized TiO2 crystallite exhibit high selectivity for complete mineralization in the photocatalytic degradation of phenol solution.
Tianyou Peng - One of the best experts on this subject based on the ideXlab platform.
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effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic co2 reduction under visible light
Catalysis Science & Technology, 2013Co-Authors: Jin Mao, Tianyou Peng, Xiaohu Zhang, Ling ZanAbstract:Two kinds of graphitic carbon nitride (g-C3N4) were synthesized through a pyrolysis process of urea or melamine. It is found that the obtained g-C3N4, as photocatalysts, can reduce CO2 to organic fuels under visible light, and exhibit different Photoactivity and selectivity on the formation of CH3OH and C2H5OH. The product derived from the urea (denoted as u-g-C3N4) shows a mesoporous flake-like structure with a larger surface area and higher Photoactivity for the CO2 reduction than the non-porous flaky product obtained from melamine (denoted as m-g-C3N4). Moreover, using u-g-C3N4 as a photocatalyst can result in the formation of a mixture containing CH3OH and C2H5OH, while m-g-C3N4 only leads to the selective formation of C2H5OH. The present interesting findings could shed light on the design of efficient, eco-friendly and convenient photocatalysts and the tuning of their photoreactivity in the field of sustainable light-to-energy conversion.
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preparation of agin5s8 tio2 heterojunction nanocomposite and its enhanced photocatalytic h2 production property under visible light
ACS Catalysis, 2013Co-Authors: Bo Chai, Tianyou Peng, Jing Mao, Ling ZanAbstract:AgIn5S8/TiO2 nanocomposite is prepared through a one-pot hydrothermal method, which is used for photocatalytic H2 production under visible-light irradiation. The effects of AgIn5S8/TiO2 molar ratio in the nanocomposites on the crystal phase, microstructure, optical absorption properties, and photocatalytic H2 evolution activity are investigated comparatively. The pristine AgIn5S8 shows a sharp absorption edge at ∼705 nm, corresponding to a bandgap of ∼1.76 eV, and its visible-light-driven Photoactivity for H2 production can be remarkably enhanced by coupling with TiO2. The AgIn5S8/TiO2 nanocomposite with molar ratio of 1:10 has the maximum Photoactivity for H2 production, improved by 7.7 times as compared with the pristine AgIn5S8. The enhanced Photoactivity can be ascribed to some AgIn5S8 nanoparticles closely contacting the TiO2 nanoparticles to form heterojunction structure. This configuration of the composite photocatalyst results in an efficient charge separation at the interface, followed by fast di...
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hydrothermal preparation of multiwalled carbon nanotubes mwcnts cds nanocomposite and its efficient photocatalytic hydrogen production under visible light irradiation
Energy & Fuels, 2011Co-Authors: Tianyou Peng, Peng Zeng, Xiaojing Liu, Xiaohu ZhangAbstract:Multiwalled carbon nanotubes (MWCNTs)/CdS nanocomposites containing different MWCNT contents were synthesized hydrothermally via direct growth of CdS nanoparticles on the functionalized MWCNT surface. The effects of the hydrothermal temperature and MWCNT content in the nanocomposites on the Photoactivity for hydrogen production were investigated comparatively under visible light (λ ≥ 420 nm) irradiation. It was found that 10 wt % MWCNTs/CdS showed much higher photocatalytic hydrogen production efficiency and photostability than the pure CdS nanoparticles. The significantly enhanced Photoactivity of the nanocomposite was attributed to the synergetic effect of the intrinsic properties of its components, such as excellent charge transfer and separation on the interfaces between the modified MWCNTs and CdS nanoparticles, resulting from the direct growth of CdS nanoparticles on the MWCNT surface during the hydrothermal process. The present MWCNTs/CdS nanocomposite reveals obvious predominance, such as enhanced...
Roel Van De Krol - One of the best experts on this subject based on the ideXlab platform.
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efficient solar water splitting by enhanced charge separation in a bismuth vanadate silicon tandem photoelectrode
Nature Communications, 2013Co-Authors: Fatwa F Abdi, Lihao Han, Arno H M Smets, Miro Zeman, B Dam, Roel Van De KrolAbstract:The Photoactivity of metal oxide electrodes for water splitting is often limited by poor charge separation. Abdi et al. improve the solar-to-hydrogen efficiency in a hybrid device that comprises a gradient-doped bismuth vanadate photoanode and a double-junction amorphous silicon tandem solar cell.