Preparation And Study Of Graphene Oxide/Basic Aluminum Sulfate Doped Polyethersulfone/Polyamide Composite Nanofiltration Membrane

Nanofiltration(NF)is an advanced membrane separation technology which is widely applied in many fields,such as water softening,wastewater treatment,medicine and food processing.NF membrane is composite membrane which can be fabricated by tnterfacial polymerization method.Interfacial polymerization has become the most common membrane fabrication method taking advantages of its convenient and effectiveness.In this study,a novel material was used in NF membrane fabrication through interfacial polymerization to improve the composite membrane permeability while maintain its high salt rejection at low pressure operation condition.Firstly,graphene oxide(GO)was used as the starting material to synthesize the composite of graphene oxide/basic aluminum sulfate(GO-BAS).Then,the composite nanofiltration membrane was prepared by adding GO and GO-BAS respectively via interfacial polymerization.Finally,the optimum membrane fabrication parameters and the effects of the two additives on the structure and properties of the composite NF membrane were systematically investigated.In particular,GO was prepared via improved Hummers' method,and then washed and purified by tubular ceramic membrane.After freeze-drying,the structure and morphology of GO powders were observed and characterized by XRD,SEM and TEM.Then piperazine(PIP)solution and GO were blended as the aqueous phase,while the organic phase was formed by dissolving the trimesoyl chloride(TMC)in the hexane solution.The graphene oxide doped polyethersulfone/polyamide(PES-PA-GO)composite NF membrane was synthesized by interfacial polymerization method which forming a polyamide(PA)functional layer on the polyethersulfone(PES)ultrafiltration substrate membrane.The optimum film processing parameters were determined by single-factor variable method:the concentration of GO was 0.1 wt%,the concentration of PIP was 1.5 wt%,the time of water phase treatment was 10 min,the concentration of TMC was 1.5 wt%,polymerization time was 60 s,and heat treatment condition was 70 ?/20 min.In the following,GO-BAS composites were prepared by hydrothermal method and their structure and morphology were characterized and observed by XRD,SEM and STA.The contents of GO and BAS in GO-BAS-2 complexes was 72%and 28%respectively.For the first time,it is proposed to blend GO-BAS with PIP solution as the water phase,while the organic phase formed by dissolving the trimesoyl chloride(TMC)in the hexane solution.The graphene oxide/basic aluminum sulfate doped polyethersulfone/polyamide(PES-PA-GO-BAS)composite nanofiltration membranes were synthesized by interfacial polymerization method which forming a polyamide(PA)functional layer on the polyethersulfone(PES)ultrafiltration substrate membranes.Finally,the synthesized composite NF membranes were characterized and observed by ATR-FTIR,SEM,AFM and contact angle test.The study shows that the introduction of GO-BAS makes the point-liked bulge gradually reunite to form a larger lump-liked bulge on the surface of the composite NF membranes.The NF membrane hydrophilicity was improved with the increase of roughness,surface area and spacing between the peak and valley on membrane surface and the decreases of contact angle.Thus,it is more beneficial to the permeation of water molecules and the pure water flux gets improved..Under the operation pressure of 0.3 MPa,the pure water flux of PES-PA-GO-BAS-1 composite NF membrane is 24.19 L·h-1·m-2,while the rejection of four inorganic salt solutions are as follows:Na2SO4(91.08%)>MgS04(83.42%)>MgCl2(70.67%)>NaCl(17.7%),which conforms to the retention characteristics of the negatively charged NF membrane.The stability of the PES-PA-GO-BAS-1 composite NF membrane was tested after soaking NaOH for 12 h.The results show that the NF membrane has good alkali resistance and operation stability.