Studies On Synthesis And Properties Of Carboxylate Ligand Based Metal-organic Framework(MOFs) Materials

Metal organic frameworks(MOFs)are periodic infinite network frameworks formed by self-assembly of organic ligands and metal ions or metal clusters.MOFs possess characteristics of large specific surface,high porosity,adjustable pores,and modifiable frame.MOFs possess excellent performance in fluorescence sensing,catalysis,gas adsorption and separation.In this paper,three nicotinic acid-derived ligands(H₄BPTC,H₃DCPN,H₃BPT)with similar structures have been used to construct a series of two-dimensional(2D)and three-dimensional(3D)MOFs materials.The impact of position of carboxyl groups on the structure and function of MOFs have been studied in detial:1.Using H₄BPTC to react with 7 kinds of rare earth metal salts,a series of 2D rare earth MOFs materials(1-7)were synthesised.Based on the excellent fluorescence characteristics of 1 and 2,a relatively cheap Y³⁺is used to replace partial Eu³⁺and Tb³⁺in the crystal for doping.By adjusting the relative ratio of Eu³⁺/Y³⁺,Tb³⁺/Y³⁺,a series of 2D layered structure of bimetallic composite were obtained.Considering the cost and efficiency,8 and 9 with the longest fluorescence lifetime were selected as the research objects.8 and 9 were used to identify and detect metal ions:Ca²⁺,Co²⁺,Cu²⁺,K⁺,Mn²⁺,Ni²⁺,Fe²⁺,Cd²⁺,Hg²⁺,Al³⁺,Cr³⁺and Fe³⁺and solvent molecules:methanol(MT),ethanol(EA),acetone(CP),isopropanol(IPA),trichloromethane(TCM),ethyl acetate(EAC),tetrahydrofuran(THF),DMF and DMA.The luminescence mechanism was studied in detail.It was found that 1 and 2 can quickly and visually identify Fe³⁺,Cr³⁺and acetone(CP).Moreover,the material has good recyclability.In order to realize the practical application of the material,the method of“spraying”was adopted to make fluorescent test papers.The compounds 8 and 9 were ground respectively,dispersed in ethanol and sprayed on filter paper to make fluorescent test papers.The test papers were used to detect organic solvents.Under ultraviolet light,it can be obviously observed that the test paper dripped with acetone exhibits obvious fluorescence quenching,which realizes the real-time and convenient detection.2.The nicotinic acid ligand H₃DCPN with a similar structure was used to react with Zn and Cd metal salts.By regulating solvents and metal salts,three novel MOFs(10-12)were obtained.The catalytic performance of 12 supported ultrafine Pd nanoparticles(Pd NPs)was systematically studied:the synthesized Pd@12 catalyst was applied to the hydrogenation reduction of nitrophenol compounds[p-nitrophenol(4-NP),o-nitrophenol(2-NP),and p-nitrobenaniline(4-NA)],using UV spectroscopy to monitor the changes of concentration versus time,and use pseudo-first-order kinetic model for fitting.The conversion rate of Pd@12 to 4-NP can reach 90%,the rate constant k is 0.47min^-1,and the catalytic effect is superior to commercial catalyst Pd-C(wt.5%Pd)and various reported catalysts.Fluorescence properties of 10:Using 10 to detect metal ions(Ca²⁺,Co²⁺,Cu²⁺,K⁺,Mn²⁺,Ni²⁺,Fe²⁺,Cd²⁺,Hg²⁺,Al³⁺,Cr³⁺and Fe³⁺),anions(F^-,SO₄^2-,CO₃^2-,Cl^-,I^-,NO₃^-,Br^-,Cr O₄^2-and Cr₂O₇^2-)and antibiotics(nitrofurazone(NZF),chloramphenicol(CAP),florfenicol(FFC),sulfadiazine(SDZ),thiamphenicol(TAP),roxithromycin(RXM),norfloxacin(NFX)and ciprofloxacin(CPFX)).Iterestingly,10 shows different fluorescence signals for different substrates.It shows“enhanced fluorescence”for Cd²⁺,F^-ions and roxithromycin(RXM)while exhibits“fluorescence quenching”for Fe³⁺,Cr₂O₇^2-and nitrofural(NZF).3.A series of MOF-74 isomers(13-16)were synthesized by the reaction of H₃BPT with rare earth metal salts.This is the first time that rare earth metal salts have been used to synthesize a crystal with MOF-74 isomers.Based on the suitable pore size and a large number of hydroxyl groups extending into the cavity,we use it as supporter and homogenizers for Pd NPs for small molecules and dyes[p-nitrophenol(4-NP),o-nitrophenol(2-NP),rhodamine B(Rh B)]catalytic degradation experiment.The comparative experiment proves that the catalytic effect of Pd NPs@MOFs catalyst is superior to Pd-C and various catalysts that have been reported.13-16 are anionic skeleton structures with large pores(1.29 nm)and specific surface area(303.8m²/g).After the coordinated water molecules are removed,open metal sites(OMS)can be formed.Therefore,this series of crystals have the potential to adsorb and separate light hydrocarbon mixture gas molecules,C₂H₂/CO₂ mixture and dye mixture.This paper take 13 as an example.As most dyes are charged,and the channels of oppositely charged MOFs may tend to accommodate dye molecules.The 13-16 material has an anionic skeleton and appropriate pore size,so this material has the potential to adsorb cationic dyes.Experiments show that 13 can completely adsorb 20mg/L of cationic dye methylene blue(MB⁺)within 30 minutes.The static adsorption data shows that the adsorption capacity of 13 for C₂H₂ and C₂H₆ is much greater than that of C₂H₄.The separation ratio(IAST)and adsorption enthalpy(Qst)obtained by simulation calculations also prove that the adsorption capacity of the material for C₂H₂ and C₂H₆ is much greater than that of C₂H₄.It shows that the material has the potienal to adsorb C₂H₂ and C₂H₆ and purify C₂H₄.The“breakthrough experiment”further proved that 13 can not only realize the separation of C₂H₂/C₂H₄ and C₂H₄/C₂H₆ binary mixed gas,but also further realize the high-efficiency separation of C₂H₄/C₂H₆/C₂H₂.