Preparation Of Visible-Light-Responsive Catalytic Materials And Their Photocatalytic Hydrogen Production Properties

Highly efficient, low-cost and environment friendly photocatalytic hydrogen productionover semiconductors become an extremely defiant and strategic issue. Up to now, TiO₂as aphotocatalyst, is intensively investigated in the photocatalytic hydrogen production becauseof its exceptional optical and electronic properties, chemical stability, low-cost andnon-toxicity. However, TiO₂is only active under ultraviolet light, while the visible lightenergy occupies around43%of the received solar energy. Consequently, exploring thevisible-light-responsive, highly efficient and stable photocatalysts has become the focus inthis field. In this case, we carried out the investigations into controlling synthesis andphotocatalytic hydrogen produciton activity over novel visible-light-responsive catalyticmaterials. The main contents and conclusion are as follows:1. Walnut-like cubic In₂S₃microsphere with the average diameter of5-10μm isprepared through an ionic liquid-assisted solvothermal method for the first time. Thehierarchical microspheres are constituted with much cross-linking nanosheets of10-50nmthickness, which exhibit the considerable stable photocatatlytic H₂production activity undervisible light irradiation. The component, crystal phase and morphology of products can beeffectively regulated by means of the addition amount of ionic liquid, solvothermaltemperature and reaction time, which offers a reference for other metal sulfide controllingsynthesis with micro/nanometer structure.2. The cubic floriated In₂S₃microsphere with the average diameter of1μm issynthesized through combining hydrothermal method with post-annealing process using theIn（NO₃）₃and L-cysteine as original materials. The hierarchical microspheres areself-aggregation by nanosheets with10-20nm thickness. The visible light responsiveIn₂S₃/TiO₂nanocomposites are obtained by ball-milling In₂S₃and TiO₂. The photocatalyticH₂production rate over In₂S₃/TiO₂nanocomposites has been enhanced by14timescomparing with that over pure In₂S₃. Band-gap calculation and photoluminescence testsconfirm that only Pt deposition on TiO₂can benefit to promote the photogenerated electrondirectional migration and significantly improve charge separation. The above results providea reference for designing the composite micro/nanometer structure and co-catalyst loadingposition. It is important to develope new type, high efficient and visible-light-drivenphotocatalysts. 3. The hexagonal phase floriated ZnIn₂S₄microsphere with the average diameter of3-6μm is fabricated by hydrothermal method using In（NO₃）₃·4.5H₂O, Zn（NO₃）₂·6H₂O andthioacetamide as original materials. The MWCNTs/ZnIn₂S₄nanocomposites are firstlyprepared in the hydrothermal process when multiwalled carbon nanotubes（MWCNTs） areintroduced. The photocatalytic H₂production rate over1.0wt%Pt-loaded ZnIn₂S₄andMWCNTs/ZnIn₂S₄nanocomposite improves90%and55%respectively, comparing withbare ZnIn₂S₄. Although introducing MWCNTs exhibit lower enhancement photocatalyticactivity than Pt-loading products, the MWCNTs/ZnIn₂S₄composites still have excellentphotocatalytic H₂production performance and stability. Considering Pt as scarce resources,the MWCNTs/ZnIn₂S₄composites can be regarded as a new class, highly efficient and visiblelight responsive photocatalytic materials, which have greatly practical application value.4. The stannite-type multicomponent sulfides Ag₂ZnSnS₄nanoparticle with the diameterof100-200nm is synthesized through combining solvothermal method with post-annealingprocess at N2atmosphere. It is found that the Pt-loaded Ag₂ZnSnS₄displays significantlyenhanced and steady photoactivity for H₂evolution with an apparent quantum efficiency ashigh as15.2%under420nm light irradiation. The results show that Ag₂ZnSnS₄as a kind ofnew type photocatalyst has considerably practical application value and can replace thehighly toxic and unstable CdS in photocataytic H₂production field.5. The AgIn₅S₈/TiO₂nanocomposite, which is used for photocatalytic hydrogenproduction under visible light irradiation for the first time, is prepared through one stephydrothermal method using AgNO₃, In（NO₃）₃·4.5H₂O, thioacetamide and TiO₂（P25） asoriginal materials,. The effects of molar ratio in the AgIn₅S₈/TiO₂nanocomposites on crystalphase, microstructure, optical absorption properties and photocatalytic H₂evolution activityare investigated comparatively. The AgIn₅S₈shows the sharp absorption edge at about705nm, corresponding bandgap around1.76eV. As a result, the AgIn₅S₈/TiO₂nanocompositesexhibit the wide spectrum response performance. The photocatalytic activity for H₂production of AgIn₅S₈/TiO₂nanocomposites has been improved by6.7times comparing withthat of single AgIn₅S₈. The enhanced photocatalytic activity is ascribed to the ultrafineAgIn₅S₈nanoparticles uniformly and closely attaching on the surface of TiO₂to formheterojunction structure, which is benefitial to play synergistic effect of various compositionand significantly enhance the charge separation. The above results have a very importantguiding significance for selecting semiconductors with different band structure and propertiesto construct a wide spectrum responsive, highly efficient and stable heterojunction system. 6. The carbon nanobuds consisting of C₆₀decorated on the surface ofSWCNTs(denoted as C₆₀-d-CNTs) and peapod-like nanostructure carbon with C₆₀trappedinside SWCNTs（assigned as Peapod） is fabricated by a simple solution method and a hightemperature vacuum calcining method respectively. The nanocomposites couplingnanostructured carbon with TiO₂exhibit effectively photocatalytic H₂production underUV light spectrum of Xe-lamp, without H₂production under visible light（λ≥420nm）irradiation. Experimental results suggest that C₆₀-d-CNTs is the most effective carbonmaterial for improving TiO₂photocatalytic H₂production activity among SWCNTs, C₆₀and peapod-like nanostructure carbon. The photocatalytic activity for H₂production ofC₆₀-d-CNTs/TiO₂nanocomposite is enhanced by2.1times comparing with that of pure TiO₂.The reasons may be that C₆₀and SWCNTs have intensive chemical interaction, whichbenefits the photogenerated electron transfer from TiO₂to SWCNTs, and then to C₆₀. As aresult, the photogenerated carriers recombination can be effectively inhibitted. Although theaforesaid nanostructure carbon materials have not expanded the visible-light-response rangeof TiO₂, they can promote the photogenerated electron directional migration and suppresscharge recombination. The above results offer some new ideas for designing and synthesizingphotocatalysts with the effective electronic injection and separation.7. The layered and multiporous polymeric graphitic-like carbon nitride（g-C₃N₄） can belarge-scale prepared by calcining urea in an alumina crucible with a cover. Following theg-C₃N₄/（Pt-TiO₂） nanocomposite is fabricated via a simple chemical adsorption method. It isfound that the g-C₃N₄/（Pt-TiO₂） nanocomposite with mass ratio of70:30has the maximumphotocatalytic hydrogen production rate and excellent photostability under visible lightirradiation, while bare g-C₃N₄and Pt-TiO₂have no H₂production in the same conditions. Theexperimental results show that the photogenerated electron can directionally migrate to carryon photocatalytic H₂production when g-C₃N₄hybridizes Pt-TiO₂. The above results pave anew way for large-scale preparation of cheap, novel, steady and visible-light-responsivephotocatalytic materials.