Biopolymer based composite nanofiltration membranes resistant to strong acids, alkalis and chlorine for Cr(VI) removal

Nanofiltration (NF) membranes play a crucial role in wastewater treatment based on their unique separation mechanism. However, conventional polyamide nanofiltration membranes are susceptible to degradation in extreme pH or chlorine environments, resulting in a limited range of applications. In this study, hydrophilic functional coatings were constructed on polyethersulfone (PES) support using the biopolymer materials, κ-carrageenan (κ-CGN) and sodium carboxymethyl cellulose (CMC). The coatings were cross-linked with glutaraldehyde (GA) to form a dense three-dimensional network structure insoluble in water, enabling structural stability in harsh environments. The Na 2 SO 4 retention of the κ-CGN/CMC/PES composite membranes was maintained at 92.1 and 91.4 % after 38 days of immersion in 20 wt% H 2 SO 4 and 2 M NaOH aqueous solutions, respectively. Meanwhile, κ-CGN/CMC/PES maintained a good salt retention (Na 2 SO 4 , ∼90.0 %) after chlorine treatment (72,000 ppm h). The excellent separation performance of the κ-CGN/CMC/PES composite membranes at different pH and concentration of Cr (VI) indicated its wide application for Cr(VI) removal at harsh conditions.