| Dense composite membrane has the ultrathin selective separation layer and a poroussupport layer. It can improve the separation performance and stability of the compositemembrane. Therefore, the dense composite membrane has board application prospects in thefield of membrane separation. The key factor for the industrial application of the compositemembrane was excellent performance and stable operation. One of the main approaches islayer-by-layer self-assembly technical. The organic-inorganic hybrid and compositemembrane can combine the advantages of both polymeric and ceramic membranes, whichposs great theoretical and practical sigificance. In this work, nanohybrid membrane wasdeposited onto the organic and inorganic substrate by dynamic self-assembly. Therelationship between the microstructure, morphology and separation performance of themultilayers was investigated by modern analytical tools. The composite membrane was usedon pervaporation and nanofiltration. The separation performance and stability of thecomposite membrane was investigated.Firstly, the organic-inorganic composite hollow fiber membrane was prepared bydynamic layer-by-layer self-assembly and heat cross-linking technology. Static electricitybetween the polyelectrolyte was converting to covalent bond. The composite membrane hasan excellent pervaporation performance with high stable. The formation of multilayers on thehollow fibers was characterized with an EDX, SEM and electrokinetic analyzer. Thecomposite membrane has an excellent separation performance on95wt.%ethanol/watermixtures. The effects of layer number, feed temperature and water content in the feed on thepervaporation performance have been investigated. The membrane obtained with fivebilayers had a permeate flux of1050g/m2h, while the water content in permeate was97.5wt.%. Compared with an organic polymer based membrane, the permeate flux wassignificantly improved while the selectivity still remained at a relatively high level whenusing the ceramic hollow fiber substrate. Furthermore, the mechanical, chemical and thermalstability of the composite membrane can be enhanced. The composite membrane wasoperated over30h for pervaporation separation of95wt.%ethanol/water mixtures and had arelatively good long-term stability.Secondly, a stable, well-dispersed graphene oxide/polyelectrolyte nanohybrid complexwas prepared by sonication and electrostatic dispersion. The size of graphene oxide sheetdecreased from micronmeters to nanometers, which could match the pore size of the substrate.The nanohybrid complex was assembled onto the surface of PAN membrane. The assemblyprocess was systemtically investigated by SEM, FTIR and an electrokinetic analyzer, anano-indenter and TGA. The nanoindentation and thermogravimetric experiments in particular indicated that the GO incorporation greatly improved the Young’s modulus,hardness and thermal stability of the membranes. The Young’s modulus and hardnessincreased from1.3GPa and0.16GPa to1.9GPa and0.24GPa, respectively. The nanohybridmembrane show comparable nanofiltration and pervaporation performances in the dyeremoval, separation of monovalent and divalent ions, and dehydration of solvent-watermixtures. The retention of nanohybrid membrane for congo red and methyl blue could reach99%. The retention for Mg2+and Na+was92.9%and44.1%, respectively. For separation ofethanol/water mixtures, the water content in permeate could reach98.1wt.%and thepermeate flux was156g/m2h. The results suggested that the nanohybrid multilayermembrane can be used on varies separation fields.Lastly, a poly(vinyl alchol)/graphene oxide nanohybrid complex was prepared bysonicated. The nanohybrid complex was assembled onto an asymmetric PAN ultrafiltrationmembrane to form “pore-filling†composite membrane by dynamic pressure-driven assembly.The nanoindentation and thermogravimetric experiments in particular indicated that the GOincorporation greatly improved the Young’s modulus, hardness and thermal stability of themembranes. The composite membrane was used on pervaporation of toluene/n-heptanemixtures. The effects of pressure, filtration time, polymer, and GO concentration onpervaporation performance were investigated. When the feed solution was50wt.%toluene/n-heptane mixtures, the separation factor of the composite membrane was12.9andthe permeate flux was27g/m2h。The composite membrane was immersed into50wt%toluene/n-heptane solution for480h. Results of the swelling experiment suggest thatassembly of the nanohybrid membrane by molecular-level dispersion of GO in PVA led toenhanced affinity of the membrane to aromatic compounds and thus improved thepervaporation performance. Meanwhile, the pore-filling structure could effectively reduceswelling of the nanohybrid membrane to make the composite stable. |
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