Construction, Structural Characterization And Electro/photocatalytic Performance Of π-conjugated Cu, Co, Ni, Zn, Cd-based Metal Organic Framework Material

Metal-organic frameworks（MOFs）are a class of periodic crystal materials with potential voids assembled by metal nodes（metal ions or metal clusters）and organic linkers through a variety of interaction forces（coordination bonds,hydrogen bonds,π-πaccumulation,etc.）.Compared with traditional crystal materials,MOFs have the advantages of controllable structure,functionalization at the molecular level,stable structure,and abundant active sites.In particular,MOFs synthesized by introducingπ-conjugated ligands have excellent performance in the field of optoelectronics due to their attractive advantages such as well-defined framework structure and pore size,precisely defined active sites and structure-activity relationships,richer hydrogen bonding forces,overall enhanced frame stability,and higher charge transfer capacity.Therefore,variousπ-conjugated MOFs with semiconductor behavior are becoming the new favorite of materials researchers.In this thesis,13 complexes were synthesized through coordination self-assembly via solvothermal method by using Cu（Ⅱ）,Co（Ⅱ）,Ni（Ⅱ）,Zn（Ⅱ）,Cd（Ⅱ）as transition metal ions,and m-bix,dap,pbmd（m-bix=1,3-bis（（1H-imidazolyl）-methyl）benzene;DAP=4-dimethylaminopyridine;pbmd=2-（2-Pyridyl）-1H-benzimidazole）asπ-conjugated N-heterocyclic ligands,and 2,5-furandicarboxylic acid,5-nitroisophthalic acid,4-fluoroterephthalic acid,2,5-thiophene dicarboxylic acid and 1,4-terephthalic acid as dicarboxylic acid ligands.A detailed analysis of 13 crystal structures was carried out using Sc-XRD technology combined with a variety of computer software.IR（Infrared spectroscopy）,TG（Thermogravimetric analysis）,PXRD（Powder X-ray diffraction）,SEM（Scanning electron microscope）and other technical methods were used to further characterize the thermal stability,micromorphology and structural composition of materials.In addition,the semiconductor behavior and fluorescence characteristics of this series of complexes were studied by UV-Vis reflection spectroscopy and fluorescence spectroscopy.Finally,based on the characterization results,the OER（Electrocatalytic oxygen evolution reaction）electrocatalytic performance of Cu,Co and Ni-based complexes was studied by conventional electrochemical analysis methods.At the same time,the photocatalytic degradation of dyes by 13 complexes was investigated under the irradiation of sunlight using MO（Methyl orange）as template dye.The specific results of the study are as follows:（1）Two previously unreported complexes of{[Cu（m-bix）（FDC）（H₂O）]·H₂O}_n（1）;{[Cu₂（dap）₄（NIP）₂]·DMF}_n（2）were designed and constructed by using Cu（Ⅱ）ion as the metal source and mixed ligands of N-donor ligands（m-bix and dap）and dicarboxylic bridged ligands（2,5-furandicarboxylic acid and 5-nitroisophthalic acid）.Both Cu-based complexes have 1D chain-like structures.The band gap analysis shows that the optical band gap values of 1 and 2 are 2.51 e V and 2.77 e V,respectively.（2）Four novel complexes of{[Co（pbmd）（H₂O）]·0.5FBDC}_n（3）;{[Co（pbmd）（F DC）（H₂O）]}_n（4）;{[Co₂（m-bix）（BDC）₂（H₂O）₃]·2H₂O·CH₃OH}_n（5）;{[Ni₂（m-bix）（BD C）₂（H₂O）₃]·2H₂O·CH₃OH}_n（6）were constructed by solvothermal method using Co（Ⅱ）/Ni（Ⅱ）as the metal source,and mixed ligands of N-donor ligands（m-bix and pbmd）and dicarboxylic bridged ligands（4-fluoroterephthalic acid,2,5-thiophenedicarboxylic acid and 1,4-terephthalic acid）.Among them,3 is a 0D structure and 4 belongs to a 1D structure;5 and 6 are isomorphic,which relies entirely on coordination bonds to connect the binuclear metal clusters to form a 3D structure.The optical bandgap values of 3,4,5,and 6 were 2.68,2.85,3.01,and 3.69 e V,respectively.（3）Zn（Ⅱ）as the metal source,three novel complexes of{[Zn₂（pbmd）₂（FDC）₂（H₂O）₂]·H₂O}_n（7）;{[Zn₂（m-bix）（ATP）₂]·DMF]}_n（8）;{[Zn（m-bix）（CO₃）]}_n（9）were constructed by selecting pbmd and m-bix as N-donor ligands with conjugated structure,and dicarboxylic bridging ligands of 2,5-furandicarboxylic acid and2-aminoterephthalic acid as organic ligands.7 is linked by carboxylic acid ligands to form a 1D chain structure;The main frame of 8 and 9 belongs to a 2D structure,and the central metal is connected by a bidentate ligand to form a 2D sql network.The optical band gap values of 7,8,and 9 were 2.87,2.59,and 3.09 e V,respectively.In addition,three Zn-based complexes have certain fluorescence emission performance.（4）Four new complexes of{[Cd（m-bix）（ATP）]}_n（10）;{[Cd（m-bix）（BDC）（H₂O）]}_n（11）;{[Cd（m-bix）（Cl）]}_n（12）;{[Cd（FDC）（H₂O）₃]·2H₂O}_n（13）were designed and constructed by using Cd（Ⅱ）as the metal source,and using m-bix as N-donor ligand,and 2-aminoterephthalic acid,2,5-furandicarboxylic acid and 1,4-terephthalic acid as dicarboxylic bridged ligands.Both 10 and 11 are 2D structures,and the main frame can be further simplified to a 2D sql network.12 and 13 belong to two different 1D chain structures,12 is a 1D coordination chain with a six-membered ring structure,while 13is completely connected by carboxylic acid ligands to form a 1D chain structure.The bandgap analysis revealed that the optical bandgap values of 10,11,12,and 13 were2.86,3.91,3.19,and 3.09 e V,respectively.Fluorescence analysis found that all four Cd-based complexes exhibit certain fluorescence emission performance,which has the potential to further use them to develop fluorescent materials.In addition,abundant intermolecular hydrogen bonding forces further connect the 1D and 2D complexes here to form a 3D supramolecular structure.（5）The OER test analysis indicated that the Cu,Co and Ni-based complexes had obvious OER electrocatalytic performance,and the corresponding overpotentials of 1,2,3,4,5 and 6 at a current density of 1 m A cm^-2were 500,360,300,301,312 and 327m V,respectively.They can be used directly as OER electrocatalysts or as excellent precursors for further modification and synthesis of efficient complex-derived OER electrocatalysts.In addition,the photocatalytic degradation of MO illustrated that all13 complexes have a certain photocatalytic ability to degrade azo dyes,and their degradation efficiencies of 40 mg/L MO solution in 150 minutes under sunlight irradiation were 96.3,92.8,9.08,18.07,61.50,14.69,18.98,12.39,28.67,9.15,6.82,73.25,and 8.95%,respectively,which were higher than 5.40%in the absence of catalyst.Among them,1,2,5 and 12 can rapidly degrade MO under sunlight irradiation,and the catalyst is expected to photocatalyze the degradation of azo dyes in water under close to natural conditions.