The Study On Nickel-based Co-catalysts For Promoting Semiconductor Photocatalytic CO₂ Reduction Performance

In recent years,the rapid growth of the world’s population and the rapid development of the global economy have led to an increase in the use of fossil fuels,which has led to an accelerated depletion of fossil energy.This has led to an accelerated depletion of fossil energy sources.Furthermore,the burning of large amounts of fossil fuels has been accompanied by massive emissions of CO₂ gas,which in turn has led to serious climate problems.It is widely recognised that semiconductor photocatalysis is one of the most promising ways of solving energy and environmental problems,and the use of sunlight to reduce CO₂ to a range of hydrocarbon fuels and feedstocks for chemicals is considered to be the most effective way of solving these two problems.Photocatalysis also enables the photolysis of water for hydrogen production and the degradation of pollutants in water.Single semiconductor materials tend to have low photocatalytic activity,so they are often loaded with precious metals and photosensitisers to improve their photocatalytic performance,but there are still a number of problems with their large-scale use due to the high cost of precious metals and the tendency for photosensitisers to cause more serious secondary pollution to the environment.Based on these challenges,our work focuses on the effect of non-precious metal-nickel-based co-catalysts on the photocatalytic performance of semiconductors in a photosensitiser-free system,and on the design and synthesis of photocatalytic materials with reasonable band structure,good photostability,excellent catalytic activity and no precious metal elements.The non-precious metal nickel-based co-catalysts have low price,low toxicity,unique catalytic activity and good stability.The specific work is divided into three main parts.（1）A new double p-n junction catalyst of ZnIn₂S₄-Ni（OH）₂/NiO was successfully constructed by synthesizing a flower-like structure of ZnIn₂S₄ through a solvothermal method,loading Ni（OH）₂ on its surface and then converting Ni（OH）₂ into NiO through incomplete dehydration and oxidation by high temperature calcination at different temperatures.The results show that by loading Ni（OH）₂/NiO,not only the absorption of visible light by ZnIn₂S₄ is enhanced,but also a large number of basic sites are formed,thus providing more active sites for the adsorption of CO₂.The double p-n junction effectively suppresses the complexation of photo-induced electron-hole pairs,and the two are accelerated to move under the electric field force,thus extremely facilitating the effective separation of photogenerated carriers.By testing the photocatalytic CO₂ reduction performance of the material,the results show that the introduction of Ni（OH）₂/NiO significantly improves the efficiency of CO₂ reduction further on the surface of the material,where the efficiency of ZnIn₂S₄-Ni（OH）₂/NiO in generating CH₄and CO is 33.4μmol g^-1 h^-1 and 5.4μmol g^-1 h^-1,which is 11.1 and 9 times higher than that of ZnIn2S4,and it was tested for cyclic stability new,and the results showed that the catalytic efficiency could still be maintained at the initial 85%after 16 hours of photoreaction,indicating that the material has good cyclic stability.（2）In photocatalytic CO₂ reduction,poor product selectivity has been an important factor limiting its practical application,and improving product selectivity has a profound impact on photoreduction of CO₂.The Zn_0.5Cd_0.5S/NiMoO₄ composite photocatalytic material was successfully constructed by growing NiMoO₄ precursors on the surface of Zn_0.5Cd_0.5S using a simple solvothermal method and further calcined at high temperature to NiMoO₄.The photocatalytic performance was tested,and the experimental results showed that after doping with 25%NiMoO₄,only trace amounts of H₂ were produced in the products,and the yields of CH₄ and CO were enhanced,with the production rates of CH₄ and CO for the 25%sample of Zn_0.5Cd_0.5S/NiMoO₄ being 17.75μmol g^-1 h^-1 and 5.55μmol g^-1 h^-1,respectively and 5.55μmol g^-1 h^-1,which were 37.4 and 8.2 times higher than those of Zn_0.5Cd_0.5S.Further,the Zn_0.5Cd_0.5S/NiMoO4/CuNPs composite photocatalyst was successfully constructed by adding CuNPs during the synthesis of Zn_0.5Cd_0.5S/NiMoO₄/CuNPs 25%,and the photocatalytic performance of the Zn_0.5Cd_0.5S/NiMoO₄/CuNPs was tested by showing that only CH₄ was detected in the products CH₄ was detected in the products,and the CO and H₂ produced were negligible in trace amounts.The production rate of CH₄ was 23.1μmol g^-1 h^-1,which was 48.5times that of Zn_0.5Cd_0.5S.（3）CdIn₂S₄/NiS₂ composite photocatalysts were produced by hydrothermal growth of NiS₂ on the surface of microspherical CdIn₂S₄ as a substrate.NiS₂ is an ideal electron acceptor for capturing photogenerated electrons from CdIn₂S₄,while NiS₂ acts as an activation centre for the reaction,reducing the activation energy and overpotential required for the reaction.The photoreduction of CO₂ performance was tested and the results showed that the CO production rate of the CdIn₂S₄/NiS₂ 1.5wt%sample was 10.7μmol g^-1 h^-1,and the CO production rate was2.1μmol g^-1 h^-1,which showed a significant increase in photocatalytic activity compared to that of the single CdIn₂S₄.