Visible-light-induced H2 evolution from an aqueous solution containing sulfide and sulfite over a ZnS-CuInS2-AgInS2 solid-solution photocatalyst.
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Biomedical subjects
Issei Tsuji
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Photocatalytic H2 evolution under visible-light irradiation over band-structure-controlled (CuIn)xZn2(1-x)S2 solid solutions.
(CuIn)(x)Zn2(1-x)S2 solid solutions between a ZnS photocatalyst with a wide band gap and CuInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents SO(3)(2-) and S(2-) under visible-light irradiation (lambda >/= 420 nm). Pt (0.5 wt %)-loaded (CuIn)(0.09)Zn(1.82)S(2) with a 2.3-eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 12.5%. H(2) evolved at a rate of 1.5 L h(-1) m(-2) under irradiation with a solar simulator (AM 1.5). Diffuse reflection and photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side, as the ratio of CuInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the composition as well as the photophysical properties. DFT calculations suggested that the visible-light response should be derived from the contribution of Cu 3d and S 3p orbitals to the valence band and that of In 5s5p and Zn 4s4p orbitals to the conduction band, respectively. The contribution of these orbitals to the energy bands affected the photophysical and photocatalytic properties.
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Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(1-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures.
(AgIn)(x)Zn(2(1-x))S(2) solid solutions between ZnS photocatalyst with a wide band gap and AgInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents, SO(3)(2)(-) and S(2)(-), under visible-light irradiation (lambda >or= 420 nm) even without Pt cocatalysts. Loading of the Pt cocatalysts improved the photocatalytic activity. Pt (3 wt %)-loaded (AgIn)(0.22)Zn(1.56)S(2) with a 2.3 eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 20%. H(2) gas evolved at a rate of 3.3 L m(-2) x h(-1) under irradiation using a solar simulator (AM 1.5). The diffuse reflection and the photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side as the ratio of AgInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the compositions as well as the photophysical properties. The dependence of the photophysical and photocatalytic properties upon the composition was mainly due to the change in the band position caused by the contribution of the Ag 4d and In 5s5p orbitals to the valence and conduction bands, respectively. It was found from SEM and TEM observations that the solid solutions partially had nanostep structures on their surfaces. The Pt cocatalysts were selectively photodeposited on the edge of the surface nanosteps. It was suggested that the specific surface nanostructure was effective for the suppression of recombination between photogenerated electrons and holes and for the separation of H(2) evolution sites from oxidation reaction sites.
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AgInZn7S9 solid solution photocatalyst for H2 evolution from aqueous solutions under visible light irradiation.
AgInZn7S9 with a 2.3 eV band gap, which was a solid solution of AgInS2 and ZnS semiconductors, showed photocatalytic activity for H2 evolution from an aqueous solution containing sacrificial reagents SO3(2-) and S2- under visible light irradiation (lambda > 420 nm) even without a Pt cocatalyst, and loading of the Pt cocatalyst improved the photocatalytic activity.
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