Preparation Of COF-316 Composites And Application Of Artificial Photosynthesis For CO₂ Reduction

Carbon negative technologies that convert CO2 into energy or high value chemicals are an effective way to reduce CO2 in the air to achieve the goal of’carbon neutrality’,as the high consumption of fossil energy has led to CO2 concentrations in the air exceeding the alarming level(350 ppm).Artificial photosynthesis for CO2 reduction is a green way of reducing CO2,driven by the inexhaustible power of sunlight.Covalent organic frameworks(COFs)materials have become an excellent catalyst for CO2 reduction by artificial photosynthesis due to their high stability,large specific surface area and adjustable structure and energy bands.However,the photogenerated carrier complexation of singlecomponent COFs is still relatively serious,which limits the improvement of their artificial photosynthesis performance.In this paper,complexes of Nafion,nonprecious metal bismuth nanoparticles(Bi Nps)and COFs were prepared to promote the electron separation ability of COFs and improve the photocatalytic reaction activity.The main studies are as follows:In this paper,COF-316 was synthesized using an irreversible nucleophilic substitution to improve photocatalytic reaction activity by compounding with perfluorosulfonic acid-based polymer Nafion and non-precious bismuth nanoparticles(Bi Nps),respectively,for the purpose of promoting electron transfer capability and light absorption.The main studies are as follows:Nafion,a perfluorosulfonic acid polymer with high proton conductivity,was loaded into the pores of COF-316 to facilitate CO2 hydrogenation at the active site under the gas-solid reaction by using the proton conductivity of Nafion,thus improving the performance of CO production by CO2 reduction and low concentration CO2 reduction.COF-316 was synthesized by solvothermal method using 2,3,6,7,10,11-hexahydroxytriphenyl and tetrafluoro--phenyl ene dihydrocyanide as ligands.Then Nafion was loaded into the pores of COF-316 by solvent concentration method to prepare Nafion@COF-316 composites.The structure and morphology were determined by X-ray powder diffraction,transmission electron microscopy and scanning electron microscopy.The N2 adsorption test proved the successful loading of the polymer in the pores.In the gas-solid photocatalytic CO2 reduction test,the conversion rate of CO2-CO by Nafion@COF-316 was as high as 215.03 μmol·g-1·h-1,which was 4.28 times higher than that of pure COF-316.Electrochemical and photophysical characterisation tests have demonstrated the superior electron transfer,proton conduction and charge separation efficiency of the Nafion@COF-3 16 composite.In order to improve the light absorption of the material,non-noble metal bismuth nanoparticles with plasma resonance effect(SPR)were selected to compound with COF-316,which improved the light absorption range and charge separation efficiency of COF-316,and improved the performance of CO2 reduction to CO.Firstly,Bi Nps with a diameter of about 10 nm was prepared by wet chemical method.In the process of solvothermal synthesis of COF-316,Bi Nps was added in situ to successfully prepare Bi@COF-316 composites.Through Xray powder diffraction characterization,it is proved that the structure of COF-3 16 and Bi Nps is complete.In the morphology characterization of scanning electron microscopy and transmission electron microscopy,it can be observed that Bi Nps with a particle size of about 10 nm are uniformLy distributed in COF-316.In the photocatalytic CO2 reduction performance test of gas-liquid phase system,the conversion rate of CO2-CO by Bi@COF-3 16 is as high as 185.42 μmol·g-1·h-1,and the selectivity is 85%,which is 4.38 times higher than that of pure COF-316.UVVis diffuse reflectance spectroscopy confirmed that Bi@COF-316 had a wider light absorption range and SPR characteristic peak was observed at 563 nm wavelength,indicating that 10 nm Bi Nps produced plasma resonance effect in COF-316 and improved light absorption.Photoelectrochemical tests proved that the introduction of Bi Nps reduced the electron-hole recombination problem.Subsequently,an attempt was made to introduce Nafion polymer into the Bi@COF-316 complex to prepare the ternary composite catalyst Nafion/Bi@COF316.The shortcomings of its catalytic environment and performance were investigated and discussed,and the preparation of COF-316-based composites and artificial photosynthesis for CO2 reduction applications were comprehensively investigated.