Preparation Of Polyimine-based Catalyst For Photocatalytic CO₂ Reduction

Inspired by natural photosynthesis,using solar energy to convert CO₂ and H₂O into high value-added chemicals such as CH₄,CO,and CH₃OH is considered an ideal and effective way to solve energy shortage and environmental pollution.Therefore,the development and design of a stable and efficient photocatalyst is the key to achieve artificial photosynthesis.However,for single-component polyimide（PI）,it is difficult to further improve its photocatalytic CO₂ reduction activity by adjusting its structure or band gap.This is mainly due to its highly ordered conjugated molecular structure,which results in high efficiency of photogenerated electron-hole complexation within single-component PI materials and the lack of reactive sites limiting its application in photocatalysis.To solve the above problems,this paper constructs an organic-inorganic heterojunction system and chelates transition metal ions to promote the separation and migration of photogenerated carriers,provide reactive sites,and thus improve the photocatalytic CO₂reduction performance of the materials.A series of structural and photoelectric tests of the prepared materials were characterized,combined with in situ infrared tests and so on,were used to investigate the reaction mechanism of photocatalytic CO₂ reduction.The main studies is divided into the following two parts:（1）Preparation of PI/CdS heterojunctions and their photocatalytic CO₂ reduction performance studies.The heterojunction system with a tightly bound interface was constructed by in situ growth of CdS nanoparticles on the nanosheet surface through the preparation of nanosheet PI by the solvothermal method.The photocatalytic CO₂ reduction performances were tested in the gas-liquid system,and the results showed that the best photocatalytic CO₂ reduction performance of PI/CdS-20%reached 88.7μmol/g/h（CO,76.3%）when the CdS loading was at 20 wt%,which was about 3 times that of a single PI and 2 times that of CdS,respectively,while the material still maintained stable performance under four cycles.The corresponding XRD,FT-IR,and XPS characterizations confirmed the successful preparation of 0D/1D heterojunctions.Photoelectric tests as well as fluorescence spectroscopy tests confirmed that the construction of heterojunctions could effectively improve the electron-hole separation efficiency,which in turn improved the photocatalytic activity of the catalysts.（2）Preparation of PI-M and their photocatalytic CO₂ reduction performance studies.The catalytic materials PI-M with more active centers(M=Co²⁺,Zn²⁺,or Ni²⁺)were prepared by hydrothermal method by chelating different kinds of transition metal ions（TMI）in the PI backbone,respectively.The catalytic reduction performance tests showed that the introduction of TMI could significantly improve the photocatalytic activity of the materials,in which PI-Zn had a high yield of photocatalytic reduction of CO₂to CO,reaching 66.3μmol/g/h,which was about 2.4 times that of pure PI.It was confirmed that the chelation of TMI as the reactive site with PI could improve the light absorption capability of the materials and effectively promote the separation of photogenerated electron-hole pairs of the material,in combination with the characterization by XPS,UV-vis diffuse reflectance spectra and photoelectric performance tests.