Structure And Properties Of MOFs Synthesized Based On Polycarboxylic Acids And Metal

Metal-Organic Frameworks（MOFs）are novel crystalline porous materials composed of metal ions and organic ligands through coordination bonds.They not only have a variety of spatial structures,but also have photocatalysis and gas adsorption.And separation,single-molecule magnetism,drug delivery and other fields have shown good application prospects.In addition,the serious deterioration of water quality caused by the random discharge of dye wastewater from the printing and dyeing industry has become a global water pollution problem.As a promising new material,MOFs have a good internal surface area and a certain degree of semiconductor characteristics,and can efficiently absorb and photochemically degrade organic dyes in printing and dyeing wastewater.The design and construction of novel and stable light-responsive MOFs,especially high visible-light-responsive MOFs,has become a research hotspot in the field of photodegradation of organic pollutants.Under solvothermal conditions,highly conjugated V-shaped bidentate carboxylic acid ligands H₂L[H₂L=2,6-bis（4-carboxylphenyl）-4-（trifluoromethoxy）benzenamine)]with transition metal Cu（II）and Cd（II）as central ions.Semi-rigid dicarboxylic acid ligand H₃L[（H₃L=4,4’-（hydroxymethanediyl）dibenzoic acid）]as the main ligand;phenylbisimidazole（BIB）,biphenyl Nine auxiliary ligands including imidazole（BIMB）were used to synthesize five novel MOFs,and their single crystal structure analysis,infrared spectroscopic characterization,thermogravimetric analysis,and X-ray powder diffraction were tested.The dye adsorption,photocatalytic degradation and other studies were conducted.The specific results are as follows:（1）Using Cu（NO₃）₂·3H₂O and H₂L as reactants,3D complex 1 with many Channel-type stacking channels was synthesized under solvothermal conditions:[CuL（DMF）]（solvent）_x（1）.In the 3D structure of complex 1,two Cu²⁺and four H₂L double tooth bridges form a paddle-shaped[Cu₂（O₂C-）₄]SBU unit,which further connects with H₂L to form a 2-cycle A-B-A-B Stacked 3D frame structure.In addition,we studied the physical adsorption and photochemical degradation of complex 1 on methylene blue（MB）and methyl orange（MO）.Adsorption experiments show that complex 1 can adsorb MB quickly and efficiently.Visible-light catalytic experiments show that complex 1 can degrade MB and MO dye solutions efficiently,and the degradation efficiency is above 95%.（2）We choose UV-Vis characteristic absorption band（380⁷80 nm）range basically covering the entire UV-vis light range methylene blue（MB,λ=450⁷50 nm）,cationic bright yellow 7GL（BY24,λ=380⁴80 nm）,cationic brilliant red 5GN（BR14,λ=390⁵80nm）The dye sensitized complex 1,further studied the photocatalytic degradation of phthalocyanine dye-RB21 by dye-sensitized three composites BY24@1,BR14@1 and MB@1.Experiments show that the degradation efficiency of the three composites is BY24@1（89.0%）<BR14@1（91.5%）<MB@1（97.3%）.（3）We use 4,4’-hydroxymethyl-dibenzoic acid（H₃L）as the main ligand and BIB,BIMB ligands containing N as auxiliary ligands.Under certain conditions of solvothermal reaction with Cd（II）and Co（II）metal salts,complexes 2-5 were constructed:[Cd₂（HL）₂]_n（2）,[（Co）₂（HL）（μ₃-O）（H₂O）₂]_n（3）,[（Cd）₂（HL）_1.5（BIB）_0.5（H₂O）]_n（4）,[（Cd）₂（HL）₂（BIMB）_0.5（DMF）]_n（5）.Among them,complex 2 is a 2D structure,and complexes 3-5 is a three-dimensional structure.In complex 2,Cd1 and Cd2 form a dinuclear secondary structural unit with an oxygen atom on the carboxyl group,and are further linked to the ligand H₃L to form a 2D structure.In the three-dimensional structure of complex 3,two Co1 and twoμ₃-O are connected to form a diamond-shaped binuclear SBU,and a 3-nuclear cluster is formed by connectingμ₃-O to Co2.This trinuclear cluster is along the a-axis.The orientation and H₃L connection form a 3D frame structure with a seat-like channel.There are two coordination modes of Cd（Ⅱ）in complex 4,and the coordination mode is that Cd1 is connected with the carboxyl oxygen atoms of the six monodentate bridges,forming a 6-coordinated octahedron.One oxygen atom and one N atom in the BIB ligand form a 6-coordinated distorted octahedral configuration.The structure of complex 5 is similar to that of complex 4,except that BIMB has only one benzene ring more than BMB,which results in BIMB only connecting two SBUs obliquely but not through BBM.Thermogravimetric analysis showed that complexes 2-5 had better stability in the temperature range of 30-350℃,PXRD showed that the sample we used for the test was consistent with that of single crystal diffraction.