Research On Fabrication Of Nanofiltraition Membranes With Enhanced Structural Stability And Biomimic Coating

Nanofiltration which is a novel separation process between ultrafiltration and reverse osmosis has been applied in concentration, purification, waste water treatment etc. due to its energy saving, low operation pressure and high rejection ratio of divalent ion. However, the poor stability of interface, low rejection ratio and the use of organic solvent has already limited its further application. The objective of this paper was to improve the stability of the stucture and enhance the separation performance via modify the matrix material?blending membrane?, optimize the process for preparing membrane?constructing interfacial covalent bond?, develop a new method to fabricate membrane?novel composite membrane based on coordination? to obtain stable and effective nanofiltration.Composite nanofiltration membranes with enhanced structural stability were fabricated and used to concentrate oligomeric proanthocyanidins?OPC? in ethanol solution. The composite nanofiltration membranes were prepared by interfacial polymerization of piperazine?PIP? with trimesoyl chloride?TMC?, upon the porous supports of polyethersulfone?PES? and polyvinyl formal?PVF? blend membranes. The active layers of composite nanofiltration membranes were covalently linked to porous supports owing to hydroxyl groups of PVF upon support surface, which could participate in the interfacial polymerization reaction. The enhanced structural stability of the composite nanofiltration membranes were confirmed by long-term immersion experiment in ethanol. Water fluxes of PA/PES-PVF composite membranes could reach 34.9 L/m² h at operation press of 0.20 MPa, the rejection ratio of Na₂SO₄ was 92.7%, orange GII and congo red were more than 98.0%. Nanofiltration concentration process was considered as a potential alternative to conventional evaporation concentration process for OPC concentration in ethanol solution.Intrigued by bioadhesion phenomenon, in particular, the marine mussel's ironfortified adhesive system, a novel approach to composite nanofiltration membrane was developed utilizing TA and Fe^? as components for assembling active layer of composite nanofiltration membrane. The water flux of TA-Fe^?/PES composite nanofiltration membrane was 45.6 L/m² h, the rejection of Na₂SO₄ was 44.1%, the rejection of orange GII and congo red were 94.8% and 98.5%, respectively. Compared with interfacial interfacial polymerization, the new approach has the following advantages: green, single-phase reaction, easy to operate, easy to control the reaction process.A coordination multilayer was explored by the alternate deposition of TA and FeCl₃ solution on PES ultrafiltration membrane. The effect of monomer concentration and self-assembled layer number of composite membrane were investigated in the work. The water flux of?TA-Fe^??_n/PES composite membrane was 10.4 L/m² h, and the rejection of Na₂SO₄ was 81.8%, the rejection of orange GII and congo red were more than 99%. Metal-ligand coordination is a more stable force compared with the electrostatic interaction between polymer molecules, and has been regarded as a promising driving force to build multilayer membrane.