Preparation Of Heterojunction Copper-based Compound Nanoparticles And Their Applications On Hydrogen Production

As energy shortages and environmental issues become increasingly severe,people urgently need to seek environmentally friendly new energy sources in order to solve the above problems.Since 1972 Fujishima and Honda discovered for the first time that the use of ultraviolet light to irradiate n-type semiconductor TiO₂photoanodes can catalyze the splitting of water,photocatalytic water splitting under the excitation of sunlight to produce renewable hydrogen attracts widespread attention.In recent years,researchers have reported the use of the compound semiconductor CuInS₂ for the preparation of hydrogen.CuInS₂ is a direct bandgap p-type semiconductor material with a band gap of 1.5 e V and a light absorption coefficient of 10⁴ cm^-1.Compared with TiO₂,it can greatly broaden the absorption range of sunlight spectrum.It is an ideal photocatalytic hydrogen production material.However,the efficiency of photocatalytic hydrogen production of CuIn S₂ is still relatively low,improve the hydrogen production efficiency has become the focus of current research.This thesis proposes a new method for improving the hydrogen conversion efficiency of CuInS₂.The idea is based on the use of n-type semiconductors and p-type CuInS₂ semiconductor materials to form a pn heterostructure.This method can effectively achieve the tailoring of the surface properties of CuInS₂ particles and improve the stability and dispersion.Based on the study of the photocatalytic activity of p-type chalcopyrite CuIn S₂,this thesis synthesized CuIn S₂ nanomaterials with pn-junction heterostructures and studied the photocatalytic properties of hydrogen evolution,and explored the optimization of CuInS₂ structure in order to reduce surface recombination and improve hydrogen production performance.The main contents are as follows:1.The preparation of nano-scale CuInS₂/XS?X=Cd?Zn?In?heterojunction materials using a hot injection method and the study of their hydrogen production performance.In this chapter,p-type chalcopyrite CuIn S₂ nanocrystals modified with n-type binary sulfide?CdS?ZnS?In₂S₃?were fabricated by hot injection method using oleylamine as a ligand and solvent.The characterization results of X-ray diffraction?XRD?,Raman,and High-resolution transmission electron microscope?HRTEM?,exhibits the nanoparticles with heterostructure and high crystallinity were obtained.The Ultraviolet visible spectroscopy?UV-Vis?results indicates that the absorption limit of heterostructure has a blue shift,expanding the spectrum absorption range.The photocatalytic hydrogen production performance of the heterostructure CuInS₂ nano-photocatalysts modified with different compounds was compared.The results show that CuInS₂/Zn S photocatalyst has the best hydrogen production efficiency with the maximum efficiency of 19.20?mol·g^-1·h^-1,and the calculated quantum efficiency is 0.35%.The pn junction heterostructure promotes the effective separation and transfer of electrons and holes is the main reason for the increase of efficiency compared with pure phase CuInS₂.2.The preparation of micronano-scale CuIn S₂/TiO₂ heterojunction materials using mechanochemical method and the study of their hydrogen production performance.The mechanochemical method converts mechanical energy into heat through crushing,grinding,and compression.Compared with the hot injection method,it has the advantages of high energy efficiency,high output,and short cycle time because it provides instantaneous heat release under solid-state reaction to produce a target product.In this chapter,we grinded the Cu,In and S elemental of stoichiometric ratio by mechanochemical method to synthesize micro-nanometer CuInS₂ particles.The results of XRD,Raman and HRTEM showed that the micro-nanocrystals had a high degree of crystallinity.UV-Vis results show that the product has better visible light absorption properties.Furthermore,n-type TiO₂ was modified on the surface of micro-nanocrystalline CuInS₂ by means of mechanical ball milling using hydrolyzed titanium source,and its hydrogen performance was tested.The hydrogen production effect of the heterostructure was significantly higherthanthatofpurephasemicro-nanocrystals CuIn S₂ when bis?acetylacetonato?diisopropyl titanate?TDAA?was used as a titanium source.In this thesis,n-type semiconductors and p-type CuInS₂ semiconductor materials are used to prepare pn heterostructure materials.This method provides an effective approach to tail the surface of CuIn S₂ particles.These results of this thesis provide experimental and theoretical support to improving the hydrogen conversion efficiency of CuInS₂ materials.