Biomimetic Zwitterionic Nanofiltration Membrane And Its Performance Study

Nanofiltration membrane separation technology has a good prospect in wastewater treatment.However,nanofiltration membranes are easily polluted during use,resulting in poor permeation and antifouling performance,which severely restricts the application and development of nanofiltration membranes.This paper focuses on the trade-off effect and poor antifouling performance of nanofiltration membranes.Inspired by the natural zwitterionic molecule trimethylamine nitroxide(TMAO)in saltwater fish,a new type of nitrogen oxide zwitterionic PEI(ZPEI)has been prepared.Nanofiltration membranes with high flux and antifouling were prepared through two methods,including biomimetic co-deposition and interfacial polymerization.The main research contents are as follows:(1)Using the hydrolyzed polyacrylonitrile ultrafiltration membrane(HPAN membrane)as the base membrane,a loose nanofiltration membrane for the desalination of dyes in textile wastewater was prepared using the strategy of biomimetic co-deposition of ZPEI and dopamine.Using ammonium persulfate(APS)as the initiator,the Schiff base reaction between ZPEI and dopamine,the Michael addition reaction,the role of cation-?and its covalent polymerization are used to form a separation layer with a network structure.The effects of ZPEI concentration and dopamine concentration on the performance of loose nanofiltration membranes were studied.X-ray photoelectron spectrometer(XPS),Field emission scanning electron microscope(SEM)and Atomic force microscope(AFM)were used to observe the surface structure and element composition of the membrane.The hydrophilic performance of the loose nanofiltration membrane prepared under the optimal ratio was significantly improved.Under the pressure of 0.6 MPa,the flux of pure water was as high as 163.3 L·m^-2·h^-1,which can reject acid fuchsin as high as 99.48%,and the rejection rate of Na Cl by this membrane is as low as 8.68%.When filtering 1 g/L BSA solution,the recovery rate of the loose nanofiltration membrane is as high as 90.44%,and it has good antifouling performance.In addition,when the dye-salt mixed solution is filtered for up to 40 h,it can maintain stable dye desalination performance.(2)Using HPAN membrane as the base membrane,ZPEI as the aqueous phase monomer,and benzoyl chloride(TMC)as the organic phase monomer,the polyamide composite nanofiltration membrane was prepared through the interfacial polymerization strategy,and the four membrane preparation conditions,including the concentration of aqueous phase monomer,the time of aqueous phase reaction,the concentration of organic phase monomer and the time of organic phase reaction,were optimized.The optimal conditions for preparation of nanofiltration membrane has a very smooth surface.Under the pressure of 0.6 MPa,the pure water flux is as high as80.77 L·m^-2·h^-1,the rejection of acid fuchsin rate is as high as 99.74%,for different inorganic salt also showed higher rejection rate(96.12%for Na₂SO₄,93.74%for Mg SO₄,92.98%for Mg Cl₂,93.15%for Ca Cl₂and 49.41%for Na Cl).When filtering BSA solution of 0.5 g/L,the recovery rate of nanofiltration membrane was up to 97%,indicating a good antifouling performance.In addition,the prepared nanofiltration membrane has stable permeability flux and Na₂SO₄rejection when filtering Na₂SO₄solution for up to 40 h.