Preparation Of Two-dimensional Copper-based Metal-organic Frameworks And The Performance For Photoelectrocatalytic Reduction Of CO₂

Consumption of fossil fuels leads to excessive emissions of carbon dioxide（CO₂）,and the energy crisis and global warming have increasingly become the greatest challenges facing mankind.Converting CO₂ into high value-added fuel is an effective way to solve the problems.Using clean electricity and solar energy,a photocatalyst is used to catalyze the reduction of CO₂ to produce high value-added products,thereby realizing a sustainable carbon cycle.The key core of photoelectrocatalytic reduction of CO₂ is the catalyst.Cu-based MOFs are regarded as a promising class of photoelectrocatalysts owing to their abundant porosity and tunable structure.In this thesis,Cu-based MOF was chosen as the starting point,and the reaction system was expanded by designing the catalyst for photoelectrocatalytic reduction of CO₂.（1）A series of CuBDC nanosheets with controllable thickness were constructed in-situ on copper foam（CF）by solvothermal method.The thickness of the nanosheets was adjusted by changing the volume ratio of the mixed solvent（N,N-dimethylformamide（DMF）,absolute ethanol（Et OH）,and deionized water（H₂O））.In the mixed solvent,DMF and Et OH were used as common solvents,and the nanosheets were grown perpendicular to the substrate.And H₂O participated in the coordination process.The thickness of the nanosheets increased because of the strong attraction of hydrogen bonds of water molecules.Using CuBDC/CF material as photocathode,the photorlectrocatalytic performance of CO₂reduction was evaluated.It has been demonstrated that CuBDC/CF prepared by using a mixed solvent(V_DMF∶V_{Et OH}∶V_H2O=16∶1∶1)exhibited high catalytic activity for CO₂reduction under photoelectrocatalytic conditions because of proper thickness,which gave C1 chemicals such as CO,CH₄ with a Faradaic efficiency（FE）of total products of 13%owing to good CO₂ adsorption capacity and effective electron transfer.（2）In order to solve the problem of low light absorption efficiency and photogenerated electron-hole separation efficiency,2-aminoterephthalic acid（NH₂BDC）was introduced,and dual-ligand Cu-based MOF（CuBDC-xNH₂/CF,x represents the molar ratio of NH₂BDC）was successfully constructed.The photoelectrocatalytic CO₂ reduction performance of all MOFs was explored.They were synthesized by two-ligand system with different molar ratios.The highest Faradaic efficiency of CO（49.7%）was achieved when the molar ratio of NH₂BDC was 10%.NH₂BDC can effectively improve the visible light absorption ability of MOFs.And both H₂BDC and NH₂BDC are coordinated with metal-oxygen clusters,which contribute to the generation and separation of charges.At the same time,the amino functional group can effectively adsorb the CO₂ molecules as a basic site.The synergistic effect improves the Faradaic efficiency of the reduction products.