Preparation Of CdS Semiconductor Composite Photocatalysts And The Performance Of Photocatalytic Splitting Water Into Hydrogen

In this thesis the preparation of rare earth improved composite semiconductor photocatalyst CdS-Pt/RE/TiO₂ and Pt/CdS as well as their photocatalytic performance for hydrogen production was studied. The reseach is mainly composed of three parts:(1) The composite semiconductor photocatalyst CdS-Pt/TiO₂ was prepared by the method of grinding, and characterized by XRD, BET. Its photocatalytic activity for hydrogen evolution was investigated in aqueous Na₂S and Na₂SO₃ solution under visible light irradiation (λ≥420nm). The results indicated that the photocatalyst CdS-Pt/TiO₂ was active and stalbe for hydrogen producing mainly due to large surfacial area with mass active photocatalic dots. The optimalmol ratio CdS to TiO₂ was 4:1.(2)A series of CdS-Pt/RE/TiO₂ (RE=La, Eu, Er, Gd) composite photocatalysts were prepared by RE impregnation, Pt photodepositon and crashing-admixture process, and characterized by means of UV-vis, X-ray diffraction and electrochemistry. As a model reaction, photocatalytic hydrogen generation from water using Na₂S/Na₂SO₃ as electron donor was investigated. It has been found that the activities of all rare earth doped TiO₂ samples have been increased compared to those of CdS-Pt/TiO₂, and the order was La＞Eu＞Er＞Gd. The activity of CdS-Pt/La/TiO₂, comparing to CdS-Pt/TiO₂, increased 62.1% relatively, and the quantum efficiency was up to 8.02%. The data of lattice distortion implied that Ti⁴⁺ could anti-dope into rare earth oxide that existed on the surface of titanium dioxide. The data of electrochemistry experiment showed that the flat-band potential of conduction of RE/TiO₂ has been shifted negatively. The lattice distortion raised the Fermi level, which caused flat-band potential of the conduction of TiO₂ to shift negatively. Meanwhile, it generated oxygen hole or defect for Ti⁴⁺ substituted for RE³⁺, which induced charge imbalance on the TiO₂ surface. As a result, it facilitates the photoinduced electrons of the CdS conduction band to impregnate into TiO₂, and the photocatalytic activity of hydrogen generation was improved.(3) The photocatalyst Pt/CdS was prepared by precipitation of CdS with Colloid Pt which was deoxidized by H₄SiW₁₂O₄₀ (HPA) under UV light used H₂PtCl₆ as original material. The method was simple, energy saving. Colloid Pt was dispersed uniformly on the surface of cubic CdS, formed a mass of active dots, and H₄SiW₁₂O₄₀ could form Pt/HPA/CdS structure and act as electrons transferer and brige between CdS and Pt. As a result, the activity of hydrogen evolution was promoted.