Terminal conversion of polyamide membranes by homologous monomer vapors for chlorine-resistant desalination

Abstract

Water scarcity is a global challenge and severely threatens human development. Membrane desalination shows great potential for producing freshwater from saltwater to alleviate this crisis. However, the dominating polyamide membranes suffer from the issue of poor chlorine resistance, which cause performance deterioration and shortens membrane lifespan. In this study, we report a concept of terminal conversion to design high-performance, antifouling, and especially chlorine-resistant polyamide desalination membranes. This amino-to-carboxyl conversion of commercial membranes can be simply performed by controllable and scalable chemical vapor deposition through exposure in homologous monomer vapor and hydrolysis of unreacted acyl chloride groups. We demonstrate that this conversion not only adjust the electronegativity and hydrophilicity of membranes to boost fouling resistance and reverse osmosis performance, but also tune the reactivity and electron cloud distribution of polyamide networks to restrain chlorine accessibility and substantially improve anti-chlorination property. After extreme chlorination for 240000 ppm h, the resultant membranes show limited rejection decline of only 7.2 %. For high-salinity (35000 ppm) and high-pressure (38 bar) desalination, the modified membranes before and after chlorination for 144000 ppm h still exhibit rejection of 94.5 % and 90.0 % and flux of 75.2 and 71.4 L m−2 h−1, respectively, which are much better than those of the pristine membranes (89.6 % and 63.5 %, and 64.2 and 57.5 L m−2 h−1). Our findings pave an alternative mechanism and strategy to reconstruct polyamide membranes for efficient water desalination.