Synthesis And Property Of Efficient Zn_xCd_1-xS Photocatalytic Semiconductor Material

The increasing serious global energy crisis and growing environmental pollution caused by fossil oil are affecting human survival and development. Photocatalytic hydrogen production from water splitting has received intense attention because of its environmental friendliness and economical utility in converting solar energy to valuable hydrogen energy. As a semiconductor with narrow band gap, ZnxCd1-xS semiconductor exhibits an excellent oxidation capability and photocorrosion resistance. In addition, ZnxCd1-xS, as a visible light driven photocatalyst, has excellent performance in photocatalytic hydrogen production extensively. However, aggregate on ZnxCd1-xS surface area and recombination of photogenerated electrons and holes have reduced the photocatalytic efficiency. Up to now, by loading cocatalyst to trap the photogenerated electrons or holes, the photocatalytic activity can be notably improved.Perylene tetracarboxylic diimide (PDI) is a kind of larger π-conjugate structure molecules, highly light stability and thermal stability. Excitedly, as a photosensitive material, PDIs have found use in a wide range of applications, including fluorescent sensors, liquid crystals, supramolecular assemblies, photovoltaics and electron-transfer systems. Synthesis of PDIs compound with different groups at the bay position makes it possible to affect the molecular energy levels of HOMO and LUMO, and thus tune the ability of grasping electrons. Moreover, different functional groups have been introduced at the imide nitrogen atoms of PDIs aimd at modifying the packing in solid state and thus regulating the intermolecular interactions and the charge transfer process.This thesis aims to control the synthesis of specific structure ZnxCd1-xS and PDI doped ZnxCd1-xS semiconductor, research on the effect of structure and PDI doped on the band gap of ZnxCd1-xS semiconductor and recombination of photogenerated electron-hole, to clarify the mechanism of the visible light catalytic hydrogen production, preparation of efficient photocatalytic materials of ZnxCd1-xS semiconductor. Paper mainly includes three parts:In chapter 1, Prologue. Overview the research status and problems of ZnxCd1-xS solid solution as photocatalytic hydrogen production material. Overview the structure, synthesis, properties and applications of perylene diimide derivatives.In chapter 2, Research on PDIs doped ZnxCd1-xS solid solution. Overview the synthesis, structure, and photocatalytic H2-production performance and mechanism of ZnxCd1-xS semiconductor. Overview the synthesis of three PDI derivatives of different groups at the bay position and PDIs doped ZnxCd1-xS nanocomposites. This paper studies the structure and photocatalytic performance of PDIs modified Zn0.5Cd0.5S semiconductor when x=0.5. The X-ray diffraction and the UV-visible diffuse absorption spectra indicate the PDIs had no effect on the lattice structure of Zn0.5Cd0.5S. The TEM and SEM suggest the heterojunction formation between the Zn0.5Cd0.5S and PDIs with occurrence of a compact and abundant interfacial contact. FT-IR and Raman Scattering measurements are carried out to reveal the connection between Zn0.5Cd0.5S and PDIs in Zno.sCdo.sS-PDIs nanocomposite. The Brunauer-Emmett-Teller and the pore distribution indicate more surface active sites of Zno.sCdo.sS-PDIs increased by doping PDIs. The transient photocurrent responses and the electrochemical impedance spectroscopy (EIS) Nyquist plots indicate the doping PDIs effectively suppress the recombination of photogenerated electrons and holes, and thus greatly improve the efficiency of photocatalytic hydrogen production. The comparative study of structure of doping different PDIs, reveals the electron transfer process and mechanism of photocatalytic hydrogen production of PDIs and Zn0.5Cd0.5S. Doping the conjugate small molecules, effectively restrains the recombination of photogenerated carriers, effectively improves the rate of photocatalytic hydrogen production.In chapter 3, Research on synthesis and property of Zn0.5Cd0.5S/ZnS core-shell structure. Overview the synthesis of core-shell structure of Zn0.5Cd0.5S/ZnS and the research of photocatalytic H2-production performance. Prepare Zn0.5Cd0.5S/ZnS nanostructures core-shell structure with the core structure of Zn0.5Cd0.5S and the shell structure of ZnS. The structure and composition were characterized. Photocatalytic H2-production activities reveal the rate of photocatalytic H2-production of Zn0.5Cd0.5S/ZnS is 6 times higher than the pristine Zn0.5Cd0.5S. The mechanism of photocatalytic H2-production activities has been put forward.