Preparation And Performance Study Of Mixed Matrix Membranes Based On Several Different Structures Of MOFs

In recent years,metal organic frameworks（MOFs）materials have become one of the current research hotspots due to their novel structure,diverse pore sizes,and large specific surface area,which have broad application prospects in catalysis,fluorescence,molecular adsorption,proton conduction,chemical sensing,energy conversion and storage,and other fields.In numerous application reports,MOFs materials often exist in the solid powder state,but the presence of MOFs in the solid powder state can to some extent narrow their application range.At the same time,its own shortcomings of easy decomposition and deactivation will further reduce its practicality.Adding powdered MOFs to flexible and thermally stable polymers such as polyvinylidene fluoride（PVDF）and polycaprolactone（PCL）to form a metal organic framework composite membrane（MOFs mixed matrix membrane）is currently the most effective solution to this problem.This composite membrane material has toughness and stability,significantly improving the functionality and applicability of MOFs materials.At the same time,it also has the dual properties of polymers and MOFs,and can even exhibit other unexpected properties.Based on this,this thesis selected PVDF as the substrate to prepare MOFs based composite membranes based on two acid ligands,5-（（4-tetrazole）-5-benzyl）oxyisophthalic acid（H₃L）and oxalic acid.After that,the catalytic performance of composite membrane materials synthesized by the Institute in specific reactions was studied with a view to developing excellent catalytic materials and enhancing the practical application value of MOFs materials.The research content and results are as follows:1.Two structures of Mn MOFs,Mn（H₂L）₂（H₂O）₂（1）and Mn₄L₂（HL）（H₂O）₅（2）,were synthesized by solvothermal synthesis based on the ligand 5-（（4-tetrazole）-5-benzyl）oxyisophthalic acid（H₃L）.Because of their Lewis acid active sites,1 and 2exhibit excellent catalytic effects.1 and 2 were mixed with polyvinylidene fluoride（PVDF）to obtain 1@PVDF and 2@PVDF.Using crystal powder of 1,2,1@PVDF,2@PVDF materials were used as catalysts to study 9 binary and 9 ternary Strecker reactions.The results showed that the four materials had good catalytic performance and could be recycled.In addition,1@PVDF composed of 1 D chain structure 1 has better catalytic activity to Strecker reaction than 2@PVDF prepared by 3 D skeleton structure 2.At the same time,it has been shown that the reaction process can be accelerated by giving electron groups to the substrate.The binary reaction has no side reactions,so the product is more pure;Compared to the binary reaction,the ternary reaction saves the step of synthesizing the intermediate imine,saves time,and has more advantages.In the catalytic experiment,compounds 1 and 2 showed good solvent stability,while compounds 1 and 2 exhibited fluorescence properties.Therefore,their solvent sensing properties were investigated and their chemical sensing properties for different cations and anions were studied.The results showed that compounds 1 and 2 were not sensitive to common cations and anions,but showed varying degrees of fluorescence quenching in solutions of iron ions and dichromate ions at different concentrations,exhibiting excellent selectivity and can be used to detect iron ions and dichromate ions.2.Based on oxalic acid ligands,a two-dimensional scandium containing coordination polymer was synthesized by hydrothermal synthesis method.Sc-MOFs:Sc（ox）_1.5（H₂O）₂·H₂O（3）,Sc（Ⅲ）has a coordination number of 6,and has an unsaturated coordination site,which can be used as catalytic centers.Mixing 3 in polyvinyl fluoride（PVDF）obtained 3@PVDF.Catalytic studies have shown that Sc-MOFs and Sc-MOFs membranes can be used to catalyze the Knoevenagel condensation reaction.Fifteen kinds of substrates were selected for the substrate expansion experiment,and the influence of functional group push pull Electronic effect on the catalytic reaction was studied.The results indicate that when the substituent is an electron donating group,the reaction conversion rate will significantly decrease.Meanwhile,research has shown that 3@PVDF composite membrane has more excellent catalytic activity than the powder crystal sample,can be used repeatedly,stably and efficiently,and can be easily recycled.