Designing tubular composite membranes of polyelectrolyte multilayer on ceramic supports with nanofiltration and reverse osmosis transport properties

Abstract

Ceramic membranes are relevant for applications, which require mechanical robustness and chemical stability. The preparation of purely ceramic membranes for nanofiltration (NF) and reverse osmosis (RO) is a demanding process. Composite membranes comprise a mechanically stable ceramic support and a functional polymeric separation layer, combining the advantages of both worlds. In this work, we present a molecular strategy to fabricate polyelectrolyte multilayer membranes (PEMM) ranging from dense nanofiltration into the region of reverse osmosis deposited on tubular ceramic supports. A dynamic coating of PAH/PSS on a α-Al2O3 support membrane with pore sizes of 150 nm (MF) and 50 nm (UF) leads to a dense separation layer on the lumen side, with NaCl rejections above 90%. Coating solutions with increased ionic strength, as well as a subsequent covalent crosslinking of the amine groups of the PAH improve long term stability. The substitution of the polyanion PSS by PVSA, having a higher charge density, results in a remarkably low MWCO of 115 Da. This work indicates that balancing the charge density of polymers with the ionic matrix can result in reverse osmosis type selective layers on ceramic support with pore size even as large as 150 nm.