Study On Photocatalytic CO₂ Reduction Over Supported ZnIn₂S₄ Catalysts

The environmental problems caused by huge amount of CO₂emission have attracted worldwide attention.Meanwhile,CO₂is also the most abundant carbon resource in the world.Effective utilization of CO₂and CO₂conversion into higher value-added fuels or chemicals is an important direction of sustainable development strategy.As renewable energy source which has abundant reserve,solar energy is clean and pollution-free.Using solar energy to carry out CO₂photocatalytic reaction has been widely concerned by scientists.As a visible light responsive semiconductor material with adjustable band gap,ZnIn₂S₄has been widely used in CO₂photocatalytic reduction.However,the bulk phase ZnIn₂S₄has some problems such as low carrier separation efficiency and lack of surface active sites.In order to improve the electron mobility in the bulk phase and provide rich CO₂adsorption active sites,two type of supported ZnIn₂S₄catalysts with amino modified silica and zinc aluminum composite metal oxide based on hydrotalcite were synthesized,respectively.Through a series of characterizations,the structure,morphology and optical properties of catalysts have been studied,and the photocatalytic activity of CO₂reduction was test.The research contents are as follows:1.SiO₂ carriers modified with different amine groups were prepared,and then supported ZnIn₂S₄materials were synthesized by solvothermal method.It was found that ZnIn₂S₄/NH-SiO₂catalyst with secondary amine modified SiO₂as the support had high catalytic activity in the photocatalytic reduction of CO₂to CO.Under the conditions of acetonitrile/water solvent system,triethylamine as hole sacrificial agent and visible light irradiation,the formation rate of CO reached 3262.0μmol?g^-1?h^-1,which was 13 times that of bulk ZnIn₂S₄and 10 times that of ZnIn₂S₄/SiO₂.In addition,the results of outdoor experiments with sunlight as light source showed that the reaction could be carried out under sunlight,and the best CO formation rate could reach 612.0μmol?g^-1?h^-1.The results of XRD,FT-IR,TEM,XPS and photoelectrichemical tests showed that the nanosheet structure of the catalyst reduced the bulk-to-face diffusion length,and accelerated the transport and separation efficiency of photogenerated carriers.Meanwhile,In-situ FT-IR test confirmed that the catalyst had excellent CO₂adsorption performance,and amine groups promoted the adsorption and activation of CO₂.DFT calculation results showed that the existence of zinc vacancy in the material can promote the reduction ability of the catalyst,and is conducive to the adsorption and activation of CO₂.2.ZnAl composite metal oxide（ZnAl O_x）was synthesized by hexamethylenetetramine method,and ZnIn₂S₄-ZnAl O_xcomposite was synthesized by solvothermal method.The results of XRD,TEM,photoelectrichemical and other tests showed that ZnIn₂S₄nanosheets were combined with the layered structure of ZnAl O_xsuccessfully,and ZnIn₂S₄was the photoactive component in the composite.ZnIn₂S₄-ZnAl O_xaccelerated the separation and transfer of photo-generated carriers.Through investigation of the effects of solvent ratio and additives on the formation rate of CO,it was found that when the ratio of acetonitrile/water was 9:1 and triethylamine was used as hole sacrificial agent,the composite had the best visible light catalytic CO₂reduction performance,and the CO formation rate reached 1100.5μmol?g^-1?h^-1,which was 4.4 times that of the bulk phase ZnIn₂S₄.In situ infrared experiments confirmed that the catalyst could promote the adsorption and activation of CO₂ at the catalyst surface.