Study On The Structural Regulation And Photocatalytic CO₂ Reduction Of NiO Semiconductor

The global greenhouse effect caused by carbon dioxide（CO₂）emission is an important problem to be solved urgently.Green and clean solar driven catalytic conversion of CO₂ into high value-added chemicals can solve both the greenhouse effect and the energy problem.The study of controllable fabrication and fine structure of nickel oxide（NiO）semiconductor composites is of great significance for understanding solar energy conversion technology.Due to the excellent conductivity,good chemical stability and non-toxicity,NiO semiconductor has been widely used in photocatalysis.However,due to the high degree of photocharges recombination,electrons and holes cannot be separated and transferred effectively,which greatly inhibits the application of NiO semiconductor in photocatalysis.Based on this,NiO semiconductor photocatalysts were modified by doping nonmetal and metal elements respectively and constructing heterojunction.The designed novel NiO-based photocatalysts achieved effective separation of photogenerated charge and efficient photoreduction of CO₂.The main research contents are as follows:1.Nitrogen doped NiO（N/NiO）semiconductor was prepared by molten salt method,and a CO₂ reduction system consisting of ruthenium dipyridine photosensitizer,acetonitrile/water/triethanolamine reaction medium and N/NiO photocatalyst was adopted.The transformation of NiO from p-type to n-type was caused by molten salt,which solved the problem of low performance for photoreduction of CO₂ to CO over p-type NiO.In addition,nitrogen doping enhances the physical adsorption of CO₂ and the separation of photocarriers on NiO.Thereout,they cooperated to optimize the CO₂ reduction system,the optimal nitrogen doped photocatalyst exhibited CO yield of 235μmol·g^-1·h^-1,which is 16.8 times that of p-type NiO and 2.4 times that of n-type NiO.2.Erbium-doped NiO(Er/NiO_1-x)semiconductor was prepared by molten salt method.Based on the above reaction system,Er/NiO_1-x was used as the photocatalyst of CO₂ reduction system.A series of characterization analysis showed that the highly dispersed Er doping changed the symmetry of NiO,enhanced its internal electric field and CO₂ adsorption activation,and promoted the separation of NiO photogenerated charge.In addition,according to density functional theory calculation,Er changed the NiO dipole moment and polarization,and reduced the CO₂ reduction energy barrier over NiO.Therefore,they synergically promoted the efficient photoreduction of CO₂ in the system.The CO yield of 2%Er doped photocatalyst showed CO yield of 368μmol·g^-1·h^-1,with the apparent quantum efficiency of7.4%.3.Z-scheme heterojunction is one of the effective methods to improve the photocatalytic performance.The K₂WO₈,NiO and Ni WO₄ ternary double Z-type heterojunction（W/NiO）semiconductor was prepared by one-step molten salt method.Ultraviolet-visible diffuse reflectance spectra（DRS）,photoluminescence（PL）spectra,photoelectric chemistry tests and other analysis showed that the double Z heterostructure broadens the spectral response range of NiO and promotes the separation of photocarriers over NiO.Compared with NiO,the double Z-scheme heterojunction enhanced the surface adsorption of water molecules and the accumulation of intermediate product of HCOO^-,optimized the CO₂ reduction system,and the CO yield reached 373μmol·g^-1·h^-1.The above studies showed that both the direct doping type and heterojunction type NiO can facilitate the efficient transfer and separation of photogenerated charges,achieving high activity and selectivity for CO₂ photoreduction.