The Structural Control And Selective Molecular/ion Separation Mechanism Of Polyethersulfone Based Inorganic Nanohybrid Composite Membrane With High Permeability

How to effectively control the microstructure of polymeric membrane and reveal the relationship between membrane structure and separation efficiency as well as improve the permeability flux are the key issues for the research and development of high-performance membrane.The aim of current study is to control the structure of polyethersulfone(PES)/sulfonated polysulfone(SPSf)blend membrane with the enhancement permeation and antifouling properties by incorporating graphene oxide(GO).Further,the PES/SPSf/GO membrane was employed as the base membrane to prepare the high-performance polyamide composite nanofiltration membrane with the construction of the interlayer by polydopamine-piperazine-halloysite(PDP-HNTs)nanomaterials using vacuum filtration assisted interfacial polymerization(VFIP).Simultaneously,the membrane formation mechanism and selective separation of molecules/ions were explored to lay the foundation for the development of a high-performance membrane and its application in dye wastewater treatment.PES and SPSf as polymers,N,N-dimethylacetamide(DMAc)as solvent and non-solvent water as additive were used to form the casting solution system.The PES/SPSf blend ultrafiltration membranes were prepared by non-solvent induced phase separation(NIPS).The effects of polymer concentration,PES/SPSf blend ratio and non-solvent water concentration on the structure and properties of the blend membrane were investigated.Results showed that the resultant membrane displayed a sponge-like structure when the polymer concentration,PES/SPSf blend ratio and non-solvent water concentration were 28 wt.%,84:16 and 7 wt.%,respectively.Simultaneously,the pure water permeance and PEG 20 k Da rejection of this membrane was up to 110.4 L/m² h bar and 96.9%,respectively.The thermodynamic behavior and phase separation kinetics of PES/DMAc,PES/H₂O/DMAc,PES/SPSf/DMAc and PES/SPSf/H₂O/DMAc casting solution systems were studied to further explore the membrane formation mechanism during phase inversion process and reveal the synergistic effect of SPSf and water on membrane structure and performance.Results showed that the resultant PES/SPSf tight ultrafiltration membrane possessed superior pure water permeance(110.4 L/m² h bar)compared to the pristine PES membrane(0.13 L/m² h bar).The improvement in water permeance was ascribed to the synergy of SPSf and water,which enhanced the surface pore size,top surface porosity and hydrophilicity of PES membrane.In addition,the results of molecular dynamic(MD)simulations revealed that H₂O can weaken the interaction between PES and SPSf chains and in favour of the ordered arrangement of chains and gelation of the casting solution system.Additionally,the rejection of Evans blue,Coomassie brilliant blue,Congo red and Acid fuchsin dye solution by the membrane obtained from PES/SPSf/H₂O/DMAc casting solution system were 99.0%,99.9%,99.2%and 90.1%,respectively,whereas the rejection of Na₂SO₄ was less than5.0%.It exhibited a good selectivity for dye and salt mixtures.Furthermore,aqueous dispersion of GO was employed as an additive in the PES/SPSf/DMAc casting solution system to fabricate antifouling and antibacterial PES/SPSf/GO mixed matrix membranes(MMMs)by the NIPS method.The effect of different amounts of GO on the morphology and performance of MMMs was studied.The results showed that pure water permeance of the MMMs with GO content of 0.012wt.%was up to 816.9 L/m² h bar and the rejection of bovine serum albumin was 99.2%.Additionally,the fouling recovery and antibacterial rate against Escherichia coli of MMMs was 94.2%and 90.0%,respectively.Polydopamine-piperazine(PDP)nanoparticles were first synthesized by the reaction of piperazine(PIP)and dopamine(DA),and then PDP was deposited on the surface of halloysite(HNTs)nanotubes to prepare the PDP-HNTs nanomaterials.The PES/SPSf/GO MMMs was employed as the base membrane to prepare the high-performance polyamide composite nanofiltration membrane using VFIP and construction of the interlayer with PDP-HNTs nanomaterials.The results showed that the polyamide composite nanofiltration membrane displayed an ultrahigh water permeance of 45.3 L/m² h bar under Na₂SO₄ rejection of 97.1%.