Synthesis Of Ag@Imidazole Functionalized Polymer Nanoparticles For Photocatalytic Reduction Of CO₂

With the rapid development of world industrialization,human demand for energy is increasing.The use and combustion of a large number of fossil energy leads to the increase of CO₂content in the atmospheric environment year by year,and the living environment of human beings is also deteriorating.At present,mankind is facing the dual problems of energy shortage and environmental degradation.It’s urgent to change the energy supply structure and reduce carbon emissions.In order to solve the problems of energy shortage and environmental degradation,scientists have carried out a lot of exploration and research.Among them,CO₂catalytic reduction and its recycling have attracted the interest of researchers.The methods of CO₂catalytic reduction mainly include electrocatalysis,photocatalysis and thermochemical catalysis,among which the photocatalytic reduction of CO₂is the most promising method.The photocatalytic performance mainly depends on the adsorption and activation of CO₂,the absorption and utilization of light energy,the generation and separation of photogenerated carriers and so on.Generally speaking,in order to obtain more CO₂reduction products per unit time,the reaction system needs to have good capture performance and high reduction efficiency CO₂.The CO₂reduction efficiency is affected by the performance of the catalyst and the light utilization.Therefore,this paper focused on the CO₂capture capacity and light utilization performance of the catalyst.According to literature reports,imidazole based materials have good capture performance of CO₂,and Ag nanoparticles have the advantages of enhancing the absorption and utilization of visible light,inhibiting the recombination of photogenerated"electron-hole pairs"and promoting photogenerated charge transfer.In addition,Ag nanoparticles will produce hot electrons to participate in the reduction reaction of CO₂after being excited by light.Based on this,this paper designed and synthesized a kind of metal organic composite nanoparticles with Ag nanoparticles as the core and imidazole based polymer as the shell,which combined the excellent properties of Ag nanoparticles and imidazole based materials,and explore the feasible strategies and methods to obtain higher CO₂photocatalytic reduction performance.This paper mainly included the following research contents:The first chapter,we summarized the research status and progress of photocatalytic reduction of CO₂in recent years,introduced the basic principle of photocatalytic reduction of CO₂and the method of optimizing the performance of photocatalyst,and reviewed the application research progress of different types of photocatalysts,imidazole functional materials and metal nanoparticles in photocatalytic reduction of CO₂.The Second chapter,we designed and synthesized Ag nanoparticles as the core and imidazole functional polymer as the shell Ag@P（CMST-co-DVB）-IMI core-shell metal organic composite nanoparticles.In the synthesis of composite nanoparticles,in order to avoid the agglomeration of metal nanoparticles,we first loaded a layer of Si O₂on the surface of Ag nanoparticles.Then it was modified by MPS（3-（isobutyryloxy）propyltrimethoxysilane）to possess surface polymerization properties.Then,p-vinyl benzyl chloride functional monomer and divinylbenzene crosslinker were polymerized on the surface of nanoparticles by distillation precipitation polymerization to construct the polymer shell layer Ag@Si O₂@P（CMST-co-DVB）nanoparticles.Si O₂was selectively etched and synthesized by hydrofluoric acid Ag@P（CMST-co-DVB）nanoparticles.Finally,1-Methylimidazole functional group was modified to the outer polymer of composite nanoparticles Ag@P（CMST-co-DVB）-IMI nanoparticles.Then,the structure,morphology,thermal stability,elements,specific surface area and pore diameter of the composite nanoparticles were tested and characterized by infrared spectrum,UV-Vis spectrum,transmission electron microscope,thermogravimetric analysis,X-ray photoelectron spectroscopy,X-ray powder diffraction and nitrogen adsorption-desorption test.The third chapter,we studied and characterized the photocatalytic reduction of CO₂by composite nanoparticles.The results showed that Ag core nanoparticles and imidazole based polymers in the composite nanoparticles had a good synergistic effect:firstly,imidazole based polymers played a good role in CO₂adsorption and enrichment,enriching CO₂around Ag nanoparticles.Then,under light irradiation,Ag nanoparticles played a good role in light energy absorption and utilization,and directly produce photoelectrons.Under the condition of appropriate propagation distance,photoinduced electrons were effectively transmitted to CO₂,and CO₂was reduced to formate with the participation of H⁺,so as to complete the photocatalytic reduction process of CO₂.Through the preliminary qualitative and quantitative analysis of the product by ion chromatography and nuclear magnetic resonance,it was determined that the main product was formic acid,and its maximum conversion efficiency was about 395.6μmol·g^-1_cat·h^-1.The cycle experiment showed that the composite nanoparticles had excellent recycling performance of CO₂photocatalytic reduction.In order to further explore the photoelectrochemical properties of composite nanoparticles,we characterized and calculated the transient photocurrent,electrochemical impedance,motschottky curve and solid-state UV-Vis diffuse reflection spectrum,and preliminarily proposed the possible working principle of CO₂photocatalytic reduction of composite nanoparticles.