Synthesis And Photo/electrocatalytic Properties Of Two-dimensional Co, Ni, Cd-based Metal Organic Frameworks And Their Fe-doped Materials

Metal-Organic Frameworks（MOFs）are crystalline porous materials with periodic network structure assembled by metal ions or metal clusters as nodes or secondary building units（SBUs）and multifunctional organic ligands as linkers through coordination bonds.MOFs materials have characteristics of high specific surface area,high porosity,adjustable framework structure,easy functionalization etc.which make them have broad application prospects in many fields such as energy,environmental pollution control,catalysis（photocatalysis,electrocatalysis,biocatalysis）,nanomaterials,photoelectric functional materials,chemical industry and so on.With the continuous development of the field of MOFs,how to construct MOFs materials with specific functions by rationally designing organic ligands and metal nodes is a research hotspot in the field of chemistry.When two or more organic ligands with different sizes,shapes and coordination characteristics are used,synergistic coordination of different ligands with the metal occurs,resulting in a versatile MOFs with a designable topology,adjustable porosity,adjustable functionality and variable surface environment.Among them,the mixed ligand strategy represented by nitrogen-containing heterocyclic and carboxylic acid ligands is widely used branch in the directional design of multifunctional MOFs.The two-dimensional metal-organic framework materials constructed by mixing ligands not only inherit the unique structural advantages of traditional MOFs,but also have many advantages of two-dimensional materials,such as abundant active sites,uniqueπ-πstacking andπ-d conjugation,and excellent electrical conductivity,which make them have potential application value in electrocatalysis,photocatalysis and other fields.In this thesis,a series of functional MOFs with novel structure were assembled by pyridine derivatives,carboxylic acids and transition metal ions,and their applications in photocatalytic degradation and electrocatalysis were studied.On the other hand,composite materials,doping materials and amorphous MOFs materials with heterogeneous structure can improve the inherent defects and give them more extensive application value.The difference of charge transfer ability of different metals and the cooperation between adjacent metals can significantly improve the charge capacity,electron transfer efficiency and electrocatalytic activity.Not only that,we also try to improve the electrocatalytic performance of the materials by doping modification.The main contents are as follows:（1）With 3,5-Bis-4-pyridyl-4H-1,2,4-triazole-4-amine（4,4’-abpt）and 3,6-dipyridine-3-yl-（1,2,4,5）-tetrazine（3,3’-bptz）as main ligands,2,5-furandicarboxylic acid,1,3-amantadecarboxylic acid and 4,4-dicarboxylic diphenyl ether as the auxiliary ligands,five novel two-dimensional MOFs[Ni（4,4’-abpt）（2,5-fdca）H₂O]_n（1）,[Co（4,4’-abpt）（2,5-fdca）H₂O]_n（2）,[Co（4,4’-abpt）（1,3-abc）]_n（3）,{[Co（3,3’-dptz）（4,4’-oba）]_n（DMF）₂}（4）and[Cd（3,3’-dptz）（4,4’-oba）]_n（5）,were constructed by self-assembly of transition metals under the solvothermal condition.Among them,complexes 1 and 2 have the same sql topology,and small molecule H₂O is involved in the coordination.Complex 3 is a binuclear two-dimensional fishnet structure with good thermal stability and suitable band gap.The secondary building units and topologies of complexes 4 and 5 are similar to those of complex 3,and DMF solvent molecules are present in the pore structure of complex 4.In addition,complex 5 also has some fluorescence properties,inheriting the properties of Cd metal ions.（2）In the catalytic performance experiments,complexes 1-3 exhibit both photocatalytic and electrocatalytic functions.In the absence of photosensitizers and co-catalysts,complexes 1-3 showed different degradation effects in the photocatalytic degradation of crystal violet,Methylene blue and Rhodamine B dyes driven by UV light.Complexes 1 and 2 showed good catalytic activity to crystal violet,and the catalytic activity of Co-based complex 2 was slightly better than that of Ni-based complex 1.Due to proper band gap and good light absorption ability,complex 3 can degrade more than 90%of the dyes in 30 minutes,and shows high catalytic effect on all three dyes,it has good universality and stability.The degradation mechanism of the three complexes shows that·OH radical is the main species causing photocatalytic reaction.Moreover,the complexes 1-3 have certain electrocatalytic properties,and the LSV curves combined with Tafel slope,C_dl and electrochemical impedance parameters showed that complex 1 had the best performance,followed by complex 2 and complex 3.（3）Using complex 4 as the substrate material,the electrocatalyst with high performance was prepared by crystal plane regulation of complex and Fe element doping during mechanical grinding.The effect of doping modification process on the catalytic performance of the material was analyzed from the aspects of microstructure,electronic structure and valence state.The results show that there is a crystal transformation in the substrate Co-MOFs during the doping process of Fe element.The integration of amorphous structures brings a large number of surface active sites to the material,which increases the electron transfer rate.It was found that the amount of Fe doping had a great influence on the catalytic performance,and the optimum amount of Fe doping was found by contrast experiments.The optimized Fe@Co-MOFs-3 catalyst has an amorphous structure and exhibits excellent OER and HER performance in alkaline solution.The optimal OER drive potential was up to 248 m V(50 m A·cm^-2),representing an improvement of nearly 150 m V compared with that before modification,while HER drive potential was 151 m V(10m A·cm^-2),which was 55 m V lower than the original MOFs.In addition,the optimized Fe@Co-MOFs-3 catalyst can work stably for more than 11 h at a current density of 50m A·cm^-2.