Chlorine tolerant, multilayer reverse-osmosis membranes with high permeate flux and high salt rejectionThis paper is part of a Journal of Materials Chemistry themed issue on advanced materials in water treatments. Guest editors: Dongyuan Zhao, Benjamin S. Hsiao and Mietek Jaroniec

A new class of high molecular weight polyethersulfone ionomers is described in which the ionic content can be varied, at will, over a very wide and fully controllable range. A novel type of coating process enables these materials to be deposited from alcohol-type solvents as cohesive but very thin (50-250 nm) films on porous support membranes, giving high-flux membranes (3.3-5.0 L m −2 h −1 bar −1 ) with very good, though not outstanding, salt rejection (typically 92-96%). A secondary layer of formaldehyde-cross-linked polyvinyl alcohol can be deposited from aqueous solution on the surface of the ionomer membrane, and this layer increases salt rejection to greater than 99% without serious loss of water permeability. The final multilayer membrane shows excellent chlorine tolerance in reverse-osmosis operation. A new type of polyethersulfone ionomer forms thin (99% salt rejection.