Preparation And Application Of High-Flux Nanofiltration Membrane Based On POSS Modification

Nanofiltration is a commonly used water treatment technology.However,in actual operation,the low permeability of the nanofiltration membrane and the high operating pressure lead to low water production efficiency,which increases the equipment operation investment and energy cost;the generation of membrane pollution also limits the further promotion of the nanofiltration membrane and application.Composite nanofiltration membranes composed of polymers and special fillers provide a new method for preparing high-performance separation membranes at low cost.Therefore,in this study,the nanofiltration membrane was modified by adding cage polysilsesquioxane(POSS)to prepare a high-throughput,pollution-resistant nanofiltration membrane.This paper mainly conducts the following research.First,using polyethersulfone(PES)as a polymer,the effects of two solvents and three additives and their concentrations on the performance of the ultrafiltration support layer were systematically analyzed.The results show that the optimal formula for the preparation of the ultrafiltration support layer is: 15% PES + 21% polyethylene glycol PEG2000 + 64% dimethylacetamide DMAc.At 0.1 MPa,the flux reaches 255.0 L/(m2·h),Which provides good support for subsequent preparation of polyamide nanofiltration membranes by interfacial polymerization.On this basis,piperazine(PIP)and trimesyl chloride(TMC)were selected as the reactive monomers for interfacial polymerization.The effects of the concentrations of the two monomers on the performance of the polyamide nanofiltration membrane were studied.When the concentrations were 0.5% and 0.1%,respectively,the properties of polyamide were comprehensively optimal,the flux reached 58.08 L/(m2·h),and the Na2SO4 rejection rate was 91.1%.Secondly,six kinds of POSS with different groups were used to modify the nanofiltration membrane during interfacial polymerization.By comparing flux and rejection rate,polyethylene glycol-based cage polysilsesquioxane(PEG-POSS)and octylamino cage-type polysilsesquioxane(OA-POSS)are preferred as aqueous phase additives.Effects of different concentrations of PEG-POSS and OA-POSS on the performance of nanofiltration membranes.At 0.5 MPa,when the concentration of PEGPOSS was 0.5%,the water flux of the modified membrane was 114.0 L/(m2·h),which was twice that of the unmodified membrane,and the Na2SO4 retention rate reached 95.8%;The concentration of OA-POSS was 0.05%(0.5% TEA was added),and the water flux of the modified membrane was 90.0 L/(m2·h),which was 1.4 times that before the modification,and the Na2SO4 rejection rate reached 98.78%.Fourier infrared and X-ray photon spectroscopy analysis proved that the POSS material was successfully added to the polyamide layer.Scanning electron microscope,contact angle meter and atomic force microscope were used to observe the structure of the membrane,study the hydrophilicity,roughness and surface morphology of the membrane,and analyze the reasons why POSS materials improve the water flux of nanofiltration membranes.Finally,in order to study the effectiveness of POSS modified nanofiltration membranes,the removal characteristics of environmental hormones and antibiotics,antipollution performance,and long-term operational stability of the modified membranes were investigated.The experimental results show that the removal rate of bisphenol A,levofloxacin,and roxithromycin by the POSS modified membrane can reach 70%,81% and 96%,respectively.The anti-pollution performance of the two POSS modified membranes also increased by 6%.The process of preparing nanofiltration membrane by POSS modification is simple and has application prospects in the field of water treatment.The obtained research results can provide theoretical and practical basis for the wide application of nanofiltration membranes.