Fabrication Of High Flux, Fouling Resistant Of Charged Nanofiltration Composite Membranes For Salts Permeation

In the procedure of dye synthesis, many mediates especially for inorganic salt would decrease dyes purity and stability. In addition, in the dyeing procedure, inorganic salts including sodium chloride(Na Cl, 6.0 wt. %) and sodium sulfate(Na2SO4, 5.6 wt. %) have been extensively used to enhance the dye uptake of the fabric. A mass of wastewater containing salts and dyes that endangers environment and people’s health need to be treated and separated with effective methods for dye desalination and reuse. However, traditional charged nanofiltration membrane(NFM) has a high retention for multi-valent salts, which can hardly realize the valid separation of salts from dyes. Therefore, we report the method including blending and in-situ growth to incorporate functional nanofillers to polymer matrix. Finally the loose nanofiltration membrane would be constructed via phase inversion. The loose membrane is used to realize the fractionation reactive dyes and salts.(1) Preparation of CS-MMT nanocomposites and fabrication of CS-MMT/PES negatively charged nanofiltration membraneWe improved a strategy to exfoliate MMT nanosheets in aqueous solution and collected them by trace amount of Chitosan solution to obtain CS-MMT nanocomposite, which was blended with polymer matrix to construct a novel "loose" nanofiltration membrane via phase inversion method. It was found that the hydrophilicity and water flux of hybrid membranes were greatly improved after adding CS-MMT nanosheets. In addition, the hybrid membranes exhibited a preferable antifouling property because the flux recovery ratio was as high as 95%.(2) Surface zwitterionization of graphene oxide and fabrication of GO-PSBMA/PES negatively nanofiltration membraneSurface zwitterionization of graphene oxide(GO) was firstly accomplished by grafting poly(sulfobetaine methacrylate)(PSBMA) via reverse atom transfer radical polymerization(RATRP), and then a novel antifouling nanofiltration(NF) membrane was fabricated by blending modified GO nanoplates via phase inversion method. The results showed that the hydrophilicity of hybrid membranes significantly enhanced in comparison with that of unfilled membrane. Zeta potential measurement indicated that the nanohybrid membranes were negatively charged. The water permeability of hybrid membrane achieved 119.8 L m-2 h-1 MPa-1. The antifouling tests revealed that GO-PSBMA embedded membranes exhibited a preferable antifouling property. The hybrid membranes exhibited a higher retention of Reactive Black 5(97.5%) and Reactive Red 49(92%), and lower rejection(10%) of bivalent salts under 0.4 MPa.(3) Fabrication of a Mixed Matrix Membrane with in Situ Synthesized Quaternized Polyethylenimine NanoparticlesA facile and novel method for the fabrication of mixed matrix membranes(MMMs) has been developed, i.e., in-situ synthesis of quaternized polyethyleneimine(QPEI) soft nanoparticles(SNPs) followed by quaternization with bromoethane(BE) in polyethersulfone(PES) casting solution. The resulting composite membranes were constructed via phase inversion method. The influences of SNPs on the morphology and performance of the hybrid membranes were systematically investigated by SEM, dynamic water contact angle, antifouling measurement, etc. Contact angle and water ratio measurements indicated that the hydrophilicity of hybrid membranes markedly improved in contrast with that of unfilled membrane. Meanwhile, the water flux of the membranes significantly enhanced due to the incorporation of SNPs. The ion-exchange capacity(IEC) value could achieve as high as 0.72 mmol g-1. The salts rejection of MMMs followed the order: Mg Cl2>Mg SO4>Na2SO4>Na Cl, confirming that the hybrid membranes were positively charged. Meanwhile, the fouling parameters demonstrated that the composite membranes exhibited a preferable antifouling property.The loose nanofiltration membrane showed higher rejection for reactive dyes and permeation for salts, demonstrating that it has a potential application in dye purification, desalination and recycling dye wastewater.