Construction Of Zr-MOFs Based Composite Photocatalyst And Study On Its Performance And Mechanism Of Photocatalytic Reduction Of Carbon Dioxide

Global awareness of the need for carbon neutrality has driven research on the carbon cycle based on CO₂ capture,utilization,and storage technologies.Photocatalytic conversion of CO₂ technology is a typical low energy consumption CO₂ conversion technology that emulates nature,builds an artificial photosynthesis system,utilizes solar energy to drive CO₂ photoreduction at normal temperature and pressure,and converts CO₂into high value-added chemicals or fuels.It is an effective strategy to achieve the goals of"carbon peak"and"carbon harmony".However,traditional inorganic semiconductor photocatalysts have problems such as poor CO₂ adsorption capacity and low multi-electron reduction efficiency,which seriously limit the further development of photocatalytic conversion of CO₂.In this context,metal organic frameworks（MOFs）composed of metal ions/clusters and organic ligands provide a more promising platform for solar-driven CO₂ conversion.The adjustable pore structure of MOFs makes MOFs a potential CO₂ adsorption and catalytic material.However,the photocatalytic activity of MOFs is currently plagued by insufficient effective photogenerated electrons and fewer active sites.How to construct multiple catalytic sites on the surface of MOFs and make the active sites have a high electron density are two key factors in CO₂ reduction of MOFs based photocatalysts.Based on this,this thesis focuses on the reduction of CO₂ using Zr-MOFs based composite photocatalysts.Construction of Z-scheme heterojunctions and Schottky junctions accelerates charge transfer rates,improves effective electron utilization,and increases active sites.In addition,in order to enrich the catalytic active sites,RGO was introduced on the basis of Zr-MOFs.Firstly,a kind of Ui O-66-NH₂/RGO covalent bond type photocatalyst was constructed to increase the electron concentration;Secondly,by changing the structure of RGO,we designed the DUT-67/RGO aerogel photocatalyst with macro pore structure and reaction sites;Further coupling the plasma resonance effect,RGO/Pd/Ui O-66-（SH）₂ aerogel photocatalyst with high charge utilization and active sites was constructed.Charge kinetics,interfacial mechanism and photocatalytic reduction of CO₂ reaction mechanism were discussed through systematic characterization.The main research work of this thesis are as follows:（1）Construction of heterojunction scheme Zr-MOFs composite photocatalyst and its photocatalytic reduction performance for CO₂a.In view of the contradiction between the excellent visible light absorption ability and the low charge transfer ability of Ui O-66-NH₂,we prepared a Z-scheme heterojunction by coupling Ui O-66-NH₂ with Cu₂O/Cu,and studied the photocatalytic reduction of CO₂ in the full spectrum of the Ui O-66-NH₂/Cu₂O/Cu（U/C/Cu）photocatalytic system.Without sacrificial agents,U/C/Cu can efficiently reduce CO₂ to CO.U/C/Cu-0.39 exhibits the best photocatalytic activity with a CO yield of 4.54μmol·g^-1·h^-1,37.8 times higher than Ui O-66-NH₂.The Z-scheme charge transfer mechanism enables U/C/Cu-0.39 not only to realize the effective separation of photogenerated charges,but also to maintain a high reduction capacity.Moreover,Cu as an electronic conductor of the Z-scheme heterojunction further accelerates the transport of charge carriers.b.Although the Z-scheme heterojunction improves the effective separation of charges and the photocatalytic reduction activity of CO₂,the CO yield still needs to be improved.A Schottky junction photocatalyst was constructed by modifying the surface of DUT-67 with Pd nanoparticles.Pd nanosheets can not only serve as electron libraries for rapid separation of photogenerated carriers from DUT-67 through Schottky barriers,but also serve as co-catalysts to provide more active sites for photocatalytic reduction of CO₂.Pd/DUT-67 could efficiently and stably reduced CO₂ to CO under simulated sunlight irradiation.Among these,the optimal modification ratio of 0.3-Pd/DUT-67 composite photocatalyst material for photoreduction of CO₂ to CO using pure water as a proton source has a yield of 12.15μmol·g^-1·h^-1.The effective structure of Schottky junctions increases the synergy between active sites and efficient charge separation and directional transport,further improving the efficiency of photocatalytic reduction of CO₂.（2）Construction of Zr-MOFs composite photocatalyst coupled with reduced graphene oxide and study on its photocatalytic reduction performance for CO₂a.The covalent bond type photocatalyst（66-NH₂/RGO）was constructed using the uncoordinated amino groups in Ui O-66-NH₂ and the oxidation groups at the edge of GO.Various comparative experiments have demonstrated the role of covalent bonds between the two components in hybrid materials.The greater charge driving force and the smaller interfacial charge transfer resistance of covalent bonds make the charge transfer process of 66-NH₂/RGO easier.And RGO can serve as an electron collector to promote the separation of photogenerated carriers and the transfer of active electrons.The rapid consumption of CO₂ also avoids the accumulation of charges at the active site.Therefore,under full spectrum,66-NH₂/RGO-3 showed a CO yield of 23.54μmol·g^-1.b.Three-dimensional porous DUT-67/RGO aerogel was prepared by hydrothermal co-assembly of DUT-67 and GO sheets.Under a mild gas-solid reaction system,the CO yield of 15D/R was 10.60μmol?g^-1?h^-1,with a selectivity of 99.6%.The enhanced photocatalytic activity and high selectivity are mainly attributed to the strong interaction between RGO and DUT-67,which enhances the electronic coupling effect.The three-dimensional RGO aerogel structure is conducive to light absorption and CO₂adsorption/activation.This study provides an idea for highly selective photocatalytic reduction of CO₂ in a gas-solid reaction model.c.In order to achieve the conversion of C1 products to C2 products,we designed RGO/Pd/U6S aerogel photocatalyst supported by three-dimensional RGO to achieve highly selective photoreduction of CO₂ to C₂H₄ in a gas-solid reaction system.30RGO/1.4Pd/U6S shows a C₂H₄ yield of 27.9μmol?g^-1,selectivity up to 73%.TRPL and photoelectrochemical experiments show that multiple charge transfer paths achieve efficient charge utilization.In situ Fourier transform infrared spectroscopy and CO-TPD reveal that*COCO is a key intermediate in C₂H₄ products.The limiting effect of30RGO/1.4Pd/U6S provides a suitable binding strength between*CO and the active site,so*CO is easily dimerized into*COCO,and ultimately*COCO is converted to C₂H₄under the action of electrons and protons.The adsorption of key intermediates in nanoreactors is the key to product selectivity changes.