Improved chemical compatibility of zeolite and organic polymer for salt rejection and fouling resistance performance of the asymmetric hybrid polyamide-based reverse osmosis membrane

Abstract

An asymmetric configuration of the reverse osmosis (RO) membrane was synthesised, consisting of a dense citrate-capped Ag⁰/LTA/PES layer (67.5±7.4 µm thick) sandwiched between a porous PES/PE substrate (26.7±4.8 µm thick) and a dense citrate- capped Ag⁰/LTA/PA layer (ca. 21.8±6.2 µm thick), constructed onto a bottom non-woven polyester layer (84.3±13.1 μm thick). Membrane permeability, salt rejection, and antifouling performance were attributed to superior hydrophilicity and the ion-sieving channels of microporous Al-rich Na-LTA (linde type A) zeolite, enhanced by the presence of extra-framework antimicrobial Ag⁰ species. Negatively charged citrate caps on the Ag0/LTA surface improved both stability and compatibility of the dispersed zeolite phase in the bulky polymer matrix. Under harsh operational conditions, characterised by high transmembrane pressure and feed solution heavily contaminated with NaCl and micro-organisms, a less severe trade-off between water permeability and salt rejection was observed as the citrate-capped Ag⁰/LTA load increased to 14%. After 30 days of exposure to the contaminated feed at a high transmembrane pressure of 140 psi, the RO membrane with 14 wt.% citrate-capped Ag⁰/LTA, containing negligible incompatible voids, produced a significantly high water flux (ca. 15.0 l.m^-2.h^-1), demonstrated improved fouling resistance, and maintained Cl^-rejection at 71%.