Fabrication And Separation Properties Of Graphene Oxide-based Novel Nanofiltration Membranes

Interfacial polymerization with the merit of simple operation and easy control has been the most method to fabricate composite nanofiltration membranes. The as-prepared membrane surface has a tight polymer layer, namely separation layer. The separation layer can be effective to retain divalent or multivalent salt ions, so the membrane has been applied in these fields such as industrial wastewater treatment,drug separation or refining as well as food concentration. However, traditional nanofiltration membrane fabricated by interfacial polymerization often has the drawback of low water flux and weak anti-pollution ability, resulting in increasing energy consumption and short life expectancy of membrane use. Therefore, the paper aims to introduce graphene oxide(GO) composite materials into polymer layer fabricated by interfacial polymerization to modify composite nanofiltrations. The main research contents and results in this work are as follows:(1) Preparation of EHT/GO composite material and EHT/GO hybrid positively charged nanofiltration membranesGO was prepared by improved Hummer method. Mg/Al hydrotalcite(HT) with high degree of crystallinity was prepared using a “urea” method and subsequently the interlayer anions were exchanged as NO3-, then NO3--HT was obtained. EHT/GO composite was synthesized under electrostatic interaction by mixing HT dispersed in formamide and GO dispersed in water. The EHT/GO organic-inorganic hybrid positively charged nanofiltration membrane was developed through interfacial polymerization on the surface of polyethersulfone(PES) UF membrane substrate by using Mg/Al HT/GO composites as additives in the PEI aqueous phase and TMC in the organic phase. The results indicated that PEI could disintegrate flocculent EHT/GO to form small aggregates. The disintegrated EHT/GO was able to be dispersed well in PEI aqueous solution. The addition of EHT/GO composites could be effective to improve the water flux of composite nanofiltrations. The water flux reached 26 L/(m2h) under the pressure of 0.8 MPa. The as-prepared nanofiltration membrane showed obvious positively charged property and the rejection order for all the membranes was Mg Cl2> Na Cl >Mg SO4>Na2SO4. The rejection rate of Mg Cl2 salt reached 97%, which showed strong water softening ability.(2) Preparation of GO-Ti O2 composite material and GO-Ti O2 hybrid negatively charged nanofiltration membranesWith GO as a template and Ti(SO4)2 hydrolyzable in the condition of heat, Ti O2 nanoparticles were generated on the surface of GO by in-situ generation method. TheGO-Ti O2 organic-inorganic hybrid negatively charged nanofiltration membrane was developed through interfacial polymerization on the surface of polyethersulfone(PES)UF membrane substrate by using GO-Ti O2 composites as additives in the piperazine(PIP) aqueous phase and TMC in the organic phase. The results indicated that when the addition content of GO-Ti O2 composites was 0.2 wt%, the water flux reached42.71 L/(m2h) under the pressure of 0.8MPa. The as-prepared nanofiltration membrane showed obvious negatively charged property and the rejection rate of Na2SO4 exceeded 98.5%, while the rejection rate of Mg Cl2 was below 20%.Meanwhile, the anti-pollution ability was improved. When the as-prepared negatively charged nanofiltration membrane with a 0.2 wt% Ti O2 addition content was polluted by bovine serum albumin(BSA), the once recovery rate of water flux after being polluted exceeded 70%.(3) Preparation of GO-ZIF composite material and GO-ZIF hybrid antibacterial nanofiltration membranesWith GO as a template and the coordination of Zn2+ and oxygen atoms on the surface of GO, zeolitic imidazolate frameworks materials(ZIF-8) were generated on the surface of GO by in-situ generation method and GO-ZIF composites were obtained. GO-ZIF organic-inorganic hybrid antibacterial nanofiltration membranes were prepared by interfacial polymerization and GO-ZIF composites were dispersed in the piperazine(PIP) aqueous phase. The results indicated that although ZIF owned a good antibacterial effect with a minimum inhibitory concentration(MIC) of 256μg/ml, GO-ZIF exhibited a stronger antibacterial ability and MIC reached 128 μg/ml.When the addition content of GO-ZIF was 3 wt%, the bacteriostasis rate exceeded80%.GO existing as different forms into polymer layer has a significant effect on membrane permeation flux. And the combination of GO and inorganic nanoparticles can create more delivery passages to improve permeation flux. Meanwhile, the composite membrane with the good properties of both GO and inorganic materials can further improve separation and anti-pollution performance of nanofiltraion membranes.