Study On The Synthesis Of 3d Transition Metal-Organic Framework Materials And Their Performance For Photocatalalytic And Electriccatalytic CO₂ Reduction

The rapid consumption of fossil fuels has been leading to the increase of CO₂content in the atmosphere,which causes a series of energy and environmental problems.Looking for renewable energy and reducing the CO₂ concentration are two major challenges that need to be solved urgently.In recent years,electric or photo-driven CO₂reduction can not only convert CO₂ into valuable chemical fuels such as CO,CH₄,C₂H₅OH,etc.,but also reduce the concentration of CO₂ which eases the greenhouse effect.These reactions can be carried out in mildly condition without secondary pollution,and they were expected to be promising ways to solve the current energy and environmental problems.During the process of CO₂ reduction reaction,the catalysts play an important role,which determine the energy conversion efficiency and product selectivity.As a porous material,metal organic framework?MOFs?materials were developed and widely applied in photocatalytic and electrocatalytic CO₂ reduction system due to their outstanding performance,such as facile preparation,large specific surface area,high porosity,easy functionalization and highly selectivity adsorption of CO₂.However,the low electrical conductivity,poor photoresponse and unsatisfactory stability significantly limited their practical application.Thus,it is still a challenge for developing MOF-based catalysts with high activity and stability.Herein,we were devoted to adjusting the composition and coordination environoment of MOFs to improve their performance for electrocatalytic and photocatalytic CO₂ reduction.The main content of the paper is as follows:1.Metal nanoclusters have excellent electrochemical performance and are widely used as catalysts for energy conversion and storage,but the poor stability limits their application.In this section,we selected Cu-BTC with high adsorption and activation performance for CO₂ as the research object.Then,Au₂₅?p-MBA?₁₈ nanoclusters were introduced on the surface and inside of Cu-BTC by self-assembly method and in-situ growth method respectively,to prepare surface-loaded Au₂₅?p-MBA?₁₈/Cu-BTC and encapsulated Au₂₅?p-MBA?₁₈@Cu-BTC.The as-prepared samples were characterized by powder X-ray diffraction,infrared spectroscopy and transmission electron microscopy etc.,which confirmed the successful preparation of Cu-BTC,Au₂₅?p-MBA?₁₈/Cu-BTC and encapsulated Au₂₅?p-MBA?₁₈@Cu-BTC.These as-prepared samples were used as electrocatalysts to reduce CO₂.The activity test demonstrated that composite materials showed a significant improvement compared to pure Cu-BTC.Among them,the encapsulated Au₂₅?p-MBA?₁₈@Cu-BTC shows higher electrocatalytic efficiency than the loaded one.It may be attributed to more tight contact between Au₂₅?p-MBA?₁₈ and Cu-BTC resulting in efficient electron migration.Meanwhile,the confined effect of Cu-BTC effectively inhibited the agglomeration of gold clusters,which given Au₂₅?p-MBA?₁₈@Cu-BTC better catalytic stability.2.Introducing transition metal complexes with good photocatalytic performace into MOFs as ligands was demonstrated an effective strategy to improve the cycle stability of homogeneous molecular complexes.In this section,a series of metal terpyridine complexs?M?cbtpy?₂,M=Co,Ni,Cu?were served as organic ligands to construct water-stable Fe-based MOF.The as-prepared compounds were characterized by X-ray single crystal diffarctometer,powder X-ray diffractometer and inductively coupled plasma spectroscopy etc.These characterized results showed that M?cbtpy?₂undergone two structural transformations under the action of FeCl₃.During Co?cbtpy?₂system,the metal center Co was replaced by Fe and formed a Fe-MOF with new coordination mode.However,Cu?cbtpy?₂ and Ni?cbtpy?₂ transformed into two new molecular complexes?Cu-CP and Ni-CP?under same condition.The metal center and content of Cu-CP and Ni-CP were not changed compared with pristine Cu?cbtpy?₂ and Ni?cbtpy?₂.However,their spatial structure has changed,which in turn leads to changes in cell parameters and/or crystal form.The activity test showed that these two structural changes have achieved an order of magnitude improvement performance in photocatalytic CO₂ reduction.