Two-step Surface Modification Method To Prepare Amphiphilic Anti-pollution Nanofiltration Membrane And Its Performance Research

Nanofiltration membrane technology is widely used as an emerging water treatment technology.However,the membrane fouling problem is the bottleneck that restricts the practical application of nanofiltration membrane.It is necessary to fabricate the nanofiltration membrane with improved antifouling performance.In this study,an amphiphilic nanofiltration membrane with improved antifouling properties in a variety of pollutants was developed,to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism.The polyamide nanofiltration membrane was fabricated by interfacial polymerization of piperazine and trimesoyl chloride on the polysulfone ultrafiltration membrane.The pure water flux of NF membrane prepared under optimum process conditions was 80.1 L·m^-2·h^-1,and the rejection of 1 g/L Na₂SO₄ was 82.1%.An amphiphilic nanofiltration membrane with enhanced antifouling properties was prepared on the polyamide NF membrane by two-step surface modification method.Firstly,triethanolamine with many hydrophilic functional groups was grafted to the surface by reacting with the residual acyl chloride group of nanofiltration membrane;secondly,the 1H,1H,2H,2H-Perfluorodecyltrichlorosilane which is usually known as a low surface energy material was covalently grafted on hydroxyl functional groups through hydrogen bonding.The membranes were characterized by X-ray photoelectron spectroscopy,attenuated total reflectance Fourier transform infrared spectroscopy and etc.Experiments with model foulants?bovine serum albumin protein solution,humic acid solution and sodium alginate solution?were performed to estimate the antifouling property of the newly developed nanofiltration membranes.The results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed the successful preparation of hydrophilic modified membranes and amphiphilic membranes.Scanning electron micrographs and atomic force microscopy figures showed that the membrane surface after surface modification present some nodular structures,and the roughness increased slightly,the modification process had no big influence on the morphology of membrane structure.Hydrophilic modified membrane had higher hydrophilicity and lower surface negative charge.On the contrary,the surface hydrophilicity of amphiphilic modified membrane decreased and the negative charge increased.The separation performance of the unmodified and modified membranes was measured by the Na2SO4 and NaCl rejection as well as molecular weight cut off?polyethylene glycol?,the results showed that the separation performance of the unmodified and modified membranes was good.The rejection of Na₂SO₄ was about80%,and the rejection of NaCl was about 30%.The molecular weight cut off of PA/PSF,H₄-PA/PSF and F₁-PA/PSF was 305 Da,290 Da and 290 Da,respectively.The pore size of the membrane before and after modification did not change.The amphiphilic modified membrane had better fouling resistance to the model foulants of bovine serum albumin protein solution,humic acid solution and sodium alginate solution than the hydrophilic modified membrane and unmodified membrane under the same conditions,showing the flux recovery ratio FRR was highest,96.9%,97.5%and 96.8%,respectively,total flux decline ratio DRt was lowest,12.5%,14.6%and 12.5%,respectively.