Molecular Design And Synthesis Of The Organic-inorganic Hybrid Nanoparticles/Nanostrands And Study On The Polymerr-Based Composite Membranes

As a new and highly efficient separation technology, membrane technology is considered as one of universal technique to solve important problems in the fields of resources and environments. Actully, membrane process has been widely used in wastewater treatments, seawater desalination, food and beverage purification, biomedical separation, chemical filtration etc. Basically, membrane material is thought the core of membrane technology. Nowadays, organic polymer membranes play a dominating role in most membrane technologies. Compared with neat polymeric or inorganic membranes, polymer-based organic-inorganic composite membranes often combine the advantages of both polymeric and inorganic membranes, and show more excellent separation performance and antifouling ability. The organic-inorganic composite membranes are attracting increasing attention in the field of membrane technologies. However, some problems and disadvanatages are still exisited for available organic-inorganic composite membranes. The inorganic nanomaterials are often difficult to disperse homogenously in polymer matrix, resulting in the occurance of defects in membrane. Moreover, the inorganic nanomaterials are easy to leach out during membrane application due to the poor miscibility and interaction between organic and inorganic phases. As a result, membrane performance might gradually degrade in membrane use. These problems have becoming the major obstacles of furture development and popularity of organic-inorganic composite membranes.In this thesis, we present two strategies to solve the above-mentioned problems. In the first strategy, a filtration and deposition route was used to prepare organic-inorganic composite membranes. The hybrid nanostrands well dispersed in water were filtrated and deposited onto polymer membrane and formed a hybrid separation layer. In this route, the nanostrands only contacted with the surfaces of polymer membranes. So the agglomeration of the nanostrands in the polymer matrix and the miscibility between two phases can be avoided. In the second strategy, polymer brushes were grafted from inorganic nanoparticle surfaces via surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization and obtained the organic-inorganic hybrid NPs. Then the organic-inorganic composite membranes were prepared from the blending solutions of polymer and the synthesized hybrid nanoparticles. The agglomeration of the nanoparticles in the polymer matrix can be effectively suppressed and the interaction between these two phases and the stability of the nanoparticles can be remarkably improved.First, the monodisperse positively charged Cu(OH)2nanostrands were prepared in a weakly alkaline copper nitrate solution in the presence of2-aminoethanol. Then a certain amount of negatively charged heparin (Hep) solution was added into the solution of nanostrands. The Hep was immobilized onto the surface of Cu(OH)2nanostrands by electrostatic interaction forming organic-inorganic hybrid Hep@Cu(OH)2nanostrands. The PSf/Hep@Cu(OH)2organic-inorganic composite membranes were prepared by filtration and deposition of the Hep@Cu(OH)2hybrid nanostrands onto a polysulfone (PSf) porous membrane surface. The results showed that the properties of the prepared composite membranes were highly affected by the amount of immobilized Hep on Cu(OH)2nanostrands. When the amount of immobilized Hep was about65.9μg/cm2, the water contact angles of the composite membrane indicated that the hydrophilicity of the composite membranes was best. When the amount of immobilized Hep was about212.0μg/cm2, the water flux of the composite membrane was more than that of the pure PSf membrane. Furthermore, when the amount of immobilized Hep was about408.4μg/cm2, the water flux of the composite membrane reached the maximum value. It was about517.2Lm-2h-1. The platelet adhesion resistant properties of the composite membranes were significantly improved by immobilizing Hep on membrane surface. In addition, the composite membranes exhibited very good antibacterial activities against Escherichia coli (E.coli) and Staphyloccocus aureus Rosenbach (5. aureus).In order to improve the dispersity and stability of silica nanoparticles (SiO2NPs) in PES and the interation between these two phases, the shell core SiO2-g-PHEMA organic-inorganic hybrid NPs were prepared by grafting poly(2-hydroxyethyl methacrylate)(PHEMA) brushes from SiO2NPs surfaces via RAFT polymerization. Then the PES/SiO2-g-PHEMA organic-inorganic composite membranes were fabricated from the blending solutions of polyethersulfone (PES) and the additive of SiO2-g-PHEMA hybrid NPs via the non-solvent induced phase separation (NIPS) process. The effects of SiO2-g-PHEMA hybrid NPs concentration on the structures and properties of the prepared composite membranes were mainly discussed. The results showed that the obtained SiO2-g-PHEMA hybrid NPs well dispersed in casting solution. The well dispersed SiO2-g-PHEMA hybrid NPs tended to migrate toward the membrane top surfaces under the driving force of minimization of interfacial energy between membrane and coagulation bath. The membrane hydrophilicity, antifouling and platelet adhesion resistant properties were significant improved caused by the enriched SiO2-g-PHEMA hybrid NPs on the membrane surface. When the concentration of SiO2-g-PHEMA hybrid NPs was increased from0to6wt%, the water permeability and the BSA rejection of the corresponding composite membranes increased simultaneously. The phenomenon indicated that the trade-off between permeability and selectivity of traditional ultrafiltration membranes was broken. The SiO2-g-PHEMA hybrid NPs had good stability in/on PES membrane due to the intertwisting and hydrogen bonds of polymer chains between PHEMA and PES.In order to achieve further functionalization of the organic-inorganic composite membranes, based on the molecular design, the shell core SiO2-g-PDMAEMA organic-inorganic hybrid NPs were prepared by grafting reactive poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) brushes from SiO2NPs surface via RAFT polymerization. Then the PES/SiO2-g-PDMAEMA organic-inorganic composite membranes were fabricated from the blending solutions of PES and the additive of the obtained SiO2-g-PDMAEMA hybrid NPs via the NIPS process. The results showed that well dispersed SiO2-g-PDMAEMA hybrid NPs tended to migrate toward the membrane top surfaces. Therefore, the contributions of SiO2-g-PDMAEMA hybrid NPs to the hydrophilicity and water permeability of the membrane were significantly improved. The efficiencies of the SiO2-g-PDMAEMA hybrid NPs were increased. In addation, the SiO2-g-PDMAEMA hybrid NPs showed well stability in/on PES membrane due to the intertwisting of polymer chains between PDMAEMA and PES. More importantly, the reactive PDMAEMA chains enriched on membrane surface provided a strategy to further surface modification. On one hand, the composite membranes were transformed into surface-zwitterionic composite membranes by quaternization between7,3-propane sultone (7,3-PS) and PDMAEMA. On the other hand, the composite membranes were transformed into cationic composite membranes by quaternization between methyl iodide (CH3I) and PDMAEMA. These membranes exhibited better hydrophilicity. It was confirmed that the surface-zwitterionic composite membranes had well antifouling abilities and the cationic composite membranes exhibited high antibacterial activities against E.coli and S. aureus.In order to further improve the dispersity and the stability of SiO2NPs in/on poly(vinylidene fluoride)(PVDF) matrix and the interaction between these two phases, based on the molecular design, poly(methyl methacrylate)(PMMA) and PDMAEMA brushes were serially grafted from SiO2NPs surface via RAFT polymerization forming the shell core SiO2-g-(PMMA-b-PDMAEMA) organic-inorganic hybrid NPs. Then the PVDF/SiO2-g-(PMMA-b-PDMAEMA) organic-inorganic composite membranes were fabricated from the blending solutions of PVDF and the additive of the obtained SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs via the NIPS process. The results showed that the SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs well dispersed in the PVDF matrix and significantly enhanced the formation and the development of membrane pores and the hydrophilicity. When the concentration of SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs was lower (2.5wt%), the tensile strength was higher than that of the pure PVDF membrane. Moreover, the SiO2-g-(PMMA-b-PDMAEMA) hybrid NPs had better stability in/on PVDF membrane than that of SiO2-g-PDMAEMA hybrid NPs. The composite membranes were transformed into surface-zwitterionic composite membranes by quaternization between1,3-PS and PDMAEMA. It was confirmed that the surface hydrophilicity, antifouling ability and BSA rejection of the PVDF membranes were significantly enhanced after surface zwitterionicalization.In summary, the comprehensive properties of the polymer-based organic-inorganic composite separation membranes were significantly improved by molecular design of organic-inorganic hybrid nanoparticles/nanostrands used in membrane fabrication. The present work provides us with some useful academic and technological information on the modification and functionalization of commonly-used polymer separation membranes.