Hydrophilic Modification Of Poly(Ether Sulfone) Membranes And Their Applications

With the development of human society,the shortage of water resources is becoming more and more obvious.The key to solve this problem is to increase the reuse of water resources.In recent years,membrane separation technology has developed rapidly due to the advantages of simple operation,safety,low pollution,low energy consumption and high separation efficiency.It is found that hydrophilic membranes contribute to better separation performance,worse membrane fouling and longer membrane life.Therefore,the development of membranes with high hydrophilicity,high separation performance and high antifouling property will bring ineffable benefits to the application development of membranes in the field of water treatment.Therefore,in this dissertation,the hydrophilicity of membrane was improved by utilizing the hydrophilic characteristics of sulfonic acid groups through bulk modification,blending modification or both.Flat ultrafiltration membranes and nanofiltration membranes were prepared,the permeability,antifouling and separation performance of the prepared membrane were evaluated comprehensively.Poly(ether sulfone)is a kind of polymer material with high acid and alkali resistance,solvent resistance and thermal stability.The membranes prepared by PES is widely used in the field of water treatment.However,the hydrophobic characteristics of PES can easily lead to membrane fouling,degradation of separation performance and shortening of service life.Based on the strategy of bulk hydrophilic modification,sulfonated poly(aryl ether sulfone)s(SPAES)with sulfonic acid content of 0?40%were synthesized by high temperature polycondensation.A series of SPAES flat homogeneous membranes were prepared by immersion precipitation phase transformation method.Scanning electron microscope(SEM)was used to observe the morphology of the membrane.The results showed that the compactness of the membrane increased rapidly with the increase of sulfonic acid content,and the pore size decreased sharply,while the membrane structure changed from ultrafiltration membrane to nanofiltration membrane.With the increase of sulfonic acid content,the water flux and salt rejection rate of SPAES membrane changed significantly.For example,the pure water flux decreased sharply from 169.31 kg·m^-2·h^-1 for the SPAES(0/10)membrane to 11.89 kg·m^-2·h^-1 for the SPAES(4/6)membrane(0.4 MPa).The rejection rates of the SPAES(1/9)and SPAES(4/6)membranes to sodium sulfate(magnesium sulfate)were 38.6%(18.6%)and 75.7%(50.0%),respectively,while the rejection rate of the SPAES(0/10)membrane to both were nearly 0.The treatment of phenol,1,3-m-dinitrobenzene(m-DNB)and DNP simulated wastewater by SPAES membrane was investigated.The results showed that the order of the rejection rate of the three compounds was DNP>m-DNB>phenol,and the SPAES membrane with higher sulfonic acid content was more favorable for these three compounds.Among them,the rejection rate of SPAES(4/6)membrane to DNP simulated wastewater(1 mmol·L^-1)was close to 60%.The structure of the SPAES membranes were deeply affected by the sulfonic acid content,the SPAES membrane with high sulfonic acid content was prone to swelling in water and possessed low mechanical strength.Therefore,based on the same strategy of bulk modification,a series of flat PES/SPAES/n Cu blend ultrafiltration membranes were prepared with immersion precipitation phase inversion method by blending SPAES(4/6)(1wt%),copper nanoparticles(n Cu,0?0.4wt%)and PES.SEM results showed that the prepared ultrafiltration membranes had typical asymmetric structures with dense skin top layer,porous sublayer and macroporous bottom layer,and n Cu particles were helpful to improve membrane porosity and inhibit macropore formation.The effect of PES/SPAES/n Cu on the treatment of simulated wastewater containing single alginate,bovine serum albumin(BSA)or humic acid was investigated.The results showed that the hydrophilicity,antifouling and antibacterial properties of the PES/SPAES/n Cu blend ultrafiltration membranes were significantly improved.Among them,the pure water flux of the PES/SPAES/n Cu(0.4)membrane reached 193.0 kg·m^-2·h^-1 at 0.1 MPa,the static water contact angle was 52°,the flux recovery rate arrived at 79%,and the bacteriostatic rate was 78.9%.In addition,the interaction of SPAES polymer with n Cu particles significantly inhibited the loss of n Cu particles in the membrane matrix,and the content of n Cu particles in the effluent was lower than 30?g·L^-1.Finally,considering the toxicity of nanoparticles,and to further improve the dispersion and stability of nanoparticles,sulfonated nano carbon onion(SCNO)was synthesized by directly introducing high content of sulfonated phenyls on the surface of nano carbon onion,and the blending system of PES and SCNO(0?1.5wt%)was constructed.A series of flat PES/SCNO blend ultrafiltration membranes were prepared by immersion precipitation phase transformation.SCNO had good dispersion,stability and compatibility with polymer in the casting solution.The SEM results showed that this series of ultrafiltration membranes also showed a typical asymmetric structure with dense top-layer,porous sublayer and macroporous bottom layer.SCNO also helped to improve porosity and inhibit the formation of macropores.BSA was used as a representative pollutant to investigate the water flux,rejection and antifouling performance of the blend membranes.The results showed that the introduction of SCNO greatly improved the water flux,rejection and antifouling properties of the blend membranes.Among them,the pure water flux of the PES/SCNO(1.0)membrane was 163.64kg·m^-2·h^-1 at 0.1 MPa,which was 3.4 times as high as that of PES membrane(48.73 kg·m^-2·h^-1).The rejection rate of BSA was close to 90%,and the flux recovery rate reached 93.4%.