Preparation Of Zinc-and Cadmium-Based Sulfide Photocatalysts For Photocatalytic Hydrogen Production

Powering the world without emitting greenhouse gases or producing additional pollutants is a challenging issue. Photocatalytic H2evolution through solar water splitting using semiconductor photocatalyst is one of the most attractive routes to achieve this goal. Among the photocatalysts, sulfide photocatalysts, including ZnS, CdS, received much attention because of their outstanding performance for photocatalytic H2production. Research in this field have received remarkable achievements. In this thesis, a series of Zinc-and Cadmium-based sulfide photocatalytic materials have been synthesized through facile routes. The relationship between crystal structure, morphology, separation of photo-generated charges and performance of photocatalytic H2production has been investigated systematically.Hierarchical porous Cd, In co-doped ZnS photocatalyst was firstly synthesized through the hydrothermal method. BET specific surface area of the as-prepared samples was up to127m2·g1. FESEM and TEM results demonstrated that the photocatalysts were composed of flower-like microsphere by assembly of nanoflakes. By adjusting the amount of Cd and In components in Cd, In co-doped ZnS photocatalyst, the crystal growth process would be in a competition between Ostwald ripening and orientation attachment, which makes the nanoflakes present wurtzite/sphalerite heterostructures. The wurtzite/sphalerite heterostructures could contribute to the separation of photo-generated charges. The visible-light absorption was mainly attributed to the doping of Cd element. Performance of photocatalyst with2%Pt loaded for photocatalytic H2production reached3.7mmol·h1, which is a good candidate for potential applications.ZnIn2S4/CdIn2S4composite photocatalysts were synthesized through hydrothermal method. Morphologies of ZnIn2S4and CdIn2S4corresponding to bigger flower-like microspheres with denser packed nanoflakes and smaller flower-like microspheres with looser packed nanoflakes. Due to the cross-doping of Cd and Zn into the ZnIn2S4and CdIn2S4, the absorption edges of composite photocatalysts were mainly located between540and550nm. Through introducing the Pt reduction cocatalyst and PdS oxidation cocatalyst into the ZnIn2S4/CdIn2S4composite photocatalyst, the rate-determining step of the total photocatalytic hydrogen evolution reaction was confirmed to the photocatalytic oxidative half reaction. Performance of the composite photocatalyst for photocatalytic H2production could reach780μmol·h1after loading PdS cocatalyst, which is3times higher than the pure ZnIn2S4photocatalyst.A series of CdxZn1xS solid solution photocatalysts have been synthesized through a facile, fast microwave-assisted route, the photocatalyst powder could be obtained in15min. The as-prepared photocatalyst was composed of irregular secondary particles by assembly of nanocrystals. Through introducing sodium dodecyl benzene sulfonate (SDBS) as the anionic surfactant, the nanocrystals presented twin structures which could effectively separate the photo-generated electrons and holes. The photocatalytic H2production performance of Cd0.6Zn0.4S solid solution photocatalyst synthesized in the presence of0.6mol·L1of SDBS reached3.6mmol·h1even without loading any cocatalyst. According to the phenomenon that the performance of Cd0.6Zn0.4S photocatalyst composed of nanocrystals increased after first cycle, an “activation effect” of the photocatalyst in assemble system at the initial stage of photocatalytic reaction was proposed, which provides theoretical evidence for the rational evaluation of the photocatalytic hydrogen evolution performance of the photocatalysts in assemble system.La was firstly doped into the space charge layer of Cd0.6Zn0.4S solid solution through solvothermal method. Mott–Schottky test indicated the depth of space charge layer of Cd0.6Zn0.4S solid solution could be adjusted by changing the amount of La doped. XPS results demonstrated La was doped into the space charge layer in the form of La–S–Zn bonds. Attributed to the La doping, light-absorbing property of Cd0.6Zn0.4S solid solution was greatly improved. Furthermore, the apparent quantum yield of CZS:2%La was up to93.3%under the irradiation of350nm monochromatic light. And the photocatalytic performance for H2production of CZS:2%La photocatalyst under the irradiation of the visible region of simulated sunlight (AM1.5) could reach1.39mmol·h1. Moreover, the promotion of La modification on the photocatalytic H2production performance has also been verified in the red TiO2system.