Study On Preparation And Separation Of Covalent Reaction Multilayer Organic-inorganic Composite Membrane

Currently, the good performance of polyelectrolyte multilayers can be preparedby using the electrostatic adsorption between the polyanion and polycation. However,the stability of these electrostatically assembled membranes is usually weak inextreme environment. This seriously limits practical separation applications so it isvery important to improve the structural stability of such multilayers. Covalentassembly of multilayer films can show greater stability in salt swelling. Thecovalently assembled multilayer membranes showed much higher stabilitiescompared with those prepared by electrostatically LbL assembly methods, and offermany opportunities for practical applications. In this paper, based on the previousstudies on dynamic LbL technique. First, tubular ceramic substrates have beenpre-treated using dynasylan ameo silane coupling agents. Then poly(acrylicacid)(PAA)/poly(vinyl alcohol)(PVA)/glutaraldehyde(GA) was dynamicallyassembled on to the inner surfaces of tubular ceramic substrates by LbL technique.Subsequently, the composite membranes were thermally cross-linked to form covalentbonds. The covalently crosslinked multilayers are stable. This study was firstlyprepared good performance of organic-inorganic composite membranes based oncovalent assembly, which can be used for pervaporation and nanofiltration fields,achieving good separation effect.The formation mechanism of organic-inorganic composite membranes wasstudied. Zeta potential demonstrated that PAA、PVA and GA can be successfullyassembled on to the inner surfaces of tubular ceramic substrates by LbL technique.The infrared spectroscopy confirmed that the formation of the covalent bond betweenthe carboxyl group and hydroxyl. Some nanoscale pores were disappeared and thesurface of membrane looked very smooth after assembling multilayers by means ofthe SEM analyzer. It can be further determined that multilayers had indeed beenassembled on to the tubular ceramic substrate from the thickness of the organicseparation layers. The effect of layers on morphology and hydrophilic performancewere investigated by AFM and the contact angle by assembling PAA/PVA/GAmultilayers onto quartz slides. The results show that the roughness of membranesurface and the contact angle was decreased, hydrophilic was increased with theincreasing number of layers.The separation applications of organic-inorganic composite membranes was studied. It was demonstrated that the composite membranes exhibited highdehydration performance with respect to different solvent-water mixtures. Forexample, in the case of separating95.0wt%ethanol-water mixture, the water contentcould be enriched from5.0wt%(in the feed) to99.5%(in the permeate), whereas thepermeate flux was102g/m2h (at75°C). The feasibility of separation of dye/saltmixture using composite membranes was explored. The results suggest that the dyeretention and salt rejection rate to aqueous solution containing100mg/l congo red and1000mg/l NaCl were97%and lower than3.0%, respectively. It means the multilayermembranes possessed nanofiltration functions. The rejection of dye and salt wassubstantially constant after water washing and HCl washing，so the covalentlycrosslinked multilayers are more stable. Therefore, it is believed that thisorganic-inorganic multilayer membrane based on covalent assembly has greatpotential for separation applications.