Polyamide formation on a cellulose triacetate support for osmotic membranes: Effect of linking molecules on membrane performance

TFC membranes with a cellulose triacetate (CTA) support layer were prepared using a modified interfacial polymerization (IP) method. In this method, a linking molecule covalently binds the polyamide (PA) active layer to the CIA support. The effects of three linking molecules (trimesoyl chloride (TMC), succinyl chloride and malonyl chloride) on membrane performance were investigated. The membrane prepared using TMC as the linking molecule displayed a strong decrease in salt rejection as a function of time in reverse osmosis (RO) and a strong increase in reverse salt flux as a function of draw solute concentration in forward osmosis (FO). The membranes made with bifunctional succinyl and malonyl chloride displayed a more stable performance. Confocal laser scanning microscopy (CLSM) images of the membranes indicate changes in CTA support morphologies upon exposure to high salt concentrations, especially for the TMC membrane. The different behavior of the trifunctional TMC membrane could be attributed to the higher number of charged groups on the support membrane, which causes anisotropic swelling/deswelling in the polymer. Our results suggest that bifunctional linkers can be used to "fabricate membranes with performance characteristics less dependent upon salt concentration. The implications of the results for FO and pressure retarded osmosis are discussed. (C) 2012 Elsevier B.V. All rights reserved.