Investigation Of Preparation,characterization And Application Of Novel High-performance Catalysts For Photoreduction Of CO₂

The massive consumption of fossil fuels such as oil and natural gas has led to an increase in CO₂emissions,and the accumulated CO₂can cause the greenhouse effect,which will lead to a series of environmental issues.Simultaneously,the continuous consumption of fossil fuels also accelerates the energy crisis because they are non-renewable energy sources and will remain an important energy source for human at present and for a long time in the future.To address these issues,human can make efforts in two ways:on one hand,reducing carbon emissions at the source,on the other hand,converting CO₂into energy compounds.In particular,photocatalytic reduction is an important way to alleviate environmental issues and energy crisis by converting CO₂into usable carbon-containing energy using renewable solar energy.This paper focuses on the design,synthesis,application and reaction mechanism of new catalysts for photoreduction of CO₂,and the main conclusions are as follows:Firstly,a highly stable metal-free material carbon doped boron nitride（BCN）was selected to synthesize a novel photocatalyst Ce O₂/BCN by combining cerium element in the form of cerium oxide using heating method and used for photocatalytic reduction of CO₂reaction.The characterization results of XPS and ESR showed that N-O-Ce bonds were formed in 30Ce O₂/BCN,which in turn formed a stable type II heterojunction.In addition,Ce³⁺and Ce⁴⁺coexisted in the material,and the high content of Ce³⁺contributed to the photocatalytic performance.Therefore,the yield of 30Ce O₂/BCN photoreduction of CO₂to CO was 17.58μmol g^-1with water as the reducing agent,and the catalytic performance was enhanced by 5.8-folds that of pure BCN(3.05μmol g^-1).Besides BCN,the metal organic framework NH₂-Ui O-66 is not only stable,but also has good catalytic performance.Based on its properties,this paper synthesized a new photocatalyst NH₂-Ui O-66/Ce CO₃OH by combining cerium element in the form of Ce CO₃OH using heating method,which is also used for photocatalytic CO₂reduction reaction.Both the coexistence of Ce³⁺/Ce⁴⁺and high content of Ce³⁺could contributed to performance enhancement due to the presence of cerium compounds.XPS and ESR characterization results showed that O-Zr-CO₃^2-bonds and direct Z-scheme heterojunction were formed between NH₂-Ui O-66 and Ce CO₃OH.Thus,more efficient separation of hole-electron pairs,delayed recombination,accelerated electron transfer efficiency enhanced catalytic performance.Meanwhile,the light absorption capacity and CO₂adsorption ability of composites were improved.Among them,NU/CC-1.6-90 had the best activity with the electron consumption rate of 152.8μmol g^-1h^-1,which was 5.1 times that of NH₂-Ui O-66.In addition,for the surface modification of NH₂-Ui O-66,the effect of calcination atmosphere was investigated in this paper.Relative to the untreated NH₂-Ui O-66,the photoreduction CO₂performance of NH₂-Ui O-66-N₂obtained by calcination with nitrogen at 250^oC was doubled.Preliminary characterization revealed that the performance improvement was attributed to the enhanced CO₂adsorption capacity and light absorption capacity,the detailed mechanism of which needs further study.In this paper,the synthesis of high-efficiency photocatalysts by heating and atmospheric calcination methods provides a new guide for the construction of CO₂photoreduction catalysts using cerium compounds.