Preparation And Dye Desalination Performance Of Tannic Acid Modified MOFs Loose Composite Membrane

Billions of tons of printing and dyeing wastewater are produced in China every year,which is characterized by complex components,high salt content,variable water quality and high toxicity,but also contains a large number of reusable inorganic salts and dyes.The conventional treatment process can only remove the dye in the printing and dyeing wastewater,and cannot achieve dye concentration and inorganic salt recovery.Membrane separation technology has a great development prospect in the treatment of printing and dyeing wastewater,but the traditional nanofiltration membrane has a high retention rate of bivalent salts,which not only limits the effective separation of dye molecules and inorganic salts.This not only limits the effective separation of dye molecules and inorganic salts,resulting in waste of resources,but also causes the continuous accumulation of inorganic salts on the membrane surface,resulting in membrane pollution,thus reducing the service life of the membrane.In view of the above problems,this paper uses natural polyphenol tannic acid（TA）as modifier to prepare surface functionalized metal-organic framework（MOF）,and adds modified MOF to the separation layer to prepare loose composite membrane to realize dye desalination.The main research contents are as follows:Using TA as modifier,hydrophilic core-shell type was synthesized by simple and rapid method ZIF-8 Nanoparticles（TA@ZIF-8）.The physicochemical properties of the powder were analyzed by means of SEM,XRD and FT-IR characterization.The results showed that the ortho-phenol hydroxyl group of TA coordinated with Zn²⁺successfully and formed hydrophilic metal/polyphenol film outside the framework of ZIF-8,which is helpful to solve the problem of agglomeration of nanoparticles on the surface of the film.In addition,the weak acidity of TA further opens the pore channel of MOF,providing a preferential channel for water molecules,thus helping to improve the permeability of the membrane.Hydrophilicity to be synthesized TA@ZIF-8 After being dispersed in PEI solution,polyethylene imine（PEI）and pyromellitic acid（TMA）are amidated to form a dense separation layer at a certain temperature.Detailed study TA@ZIF-8 Effect of loading on surface morphology,chemical structure and separation performance of composite membrane.The results show that compared with ZIF-8,TA@ZIF-8 Addition does not reduce the crosslinking degree of the separation layer,which indicates that TA@ZIF-8 The surface TA enhances the coordination with PEI,thus improving the stability of the separation layer.The best condition is TA@ZIF-8 The content is 0.02 wt%,and the retention rates for MB and TB are 98.7%and 89.7%respectively.TA@ZIF-8-2The composite membrane maintained a high permeability(71 L·m^-2·h^-1·bar^-1),a 98%removal rate of MB and a high salt permeability during the 20 h long-term stability test.In addition,the composite membrane has good antifouling performance.The FRR of the composite membrane is 98.5%,99.4%and 99.4%respectively under three cycles of MB dye.MIL-53（Fe）nanoparticles with hydrophilic and photocatalytic properties were synthesized by solvothermal method using tannic acid as modifier（TA@MIL-53（Fe））.The structure and properties of TA@MIL-53（Fe）nanoparticles were systematically studied.Then piperazine（PIP）was used as the water phase monomer and trimethylene chloride（TMC）as the oil phase monomer TA@MIL-53（Fe）nanoparticles were embedded in the PA layer to prepare a porous composite film.Effect of TA@MIL-53（Fe）loading on morphology,chemical structure and separation performance of composite membrane was detailed analyzed.The best condition is TA@MIL-53 The content is 0.02wt%,the flux is about 55 L·m^-2·h^-1·bar^-1,and the retention rates for MBA,MO,TB and MB are 90.8%,93.1%,98.1%and 99.1%,respectively.MPTA-0.02 composite membrane maintains high permeability flux(47.8-52 L·m^-2·h^-1·bar^-1),high dye retention（MB:99%and TB:98.2%）and high salt permeability in the 20 h long-term stability test.In addition,the composite membrane has good antifouling performance.Driven by low pressure,the porous composite membrane prepared based on TA hydrophilic modified MOF has high permeability,excellent dye desalting effect,good antifouling performance and stability,which is expected to provide reference for the preparation of MOFs porous composite membrane and realize the harmless and resourceful treatment of printing and dyeing wastewater.