Development of eco-friendly coating for the fabrication of high performing loose nanofiltration membranes for dye-contaminated wastewater treatment

This study introduces highly efficient loose nanofiltration (LNF) membranes developed through a green synergistic combination of tannic acid (TA) and polyvinyl alcohol (PVA), aimed at addressing the complex challenge of dye/salt fractionation in wastewater treatment. Utilizing a one-step co-deposition technique onto a polysulfone (PSF) substrate, the integration of TA and PVA has produced membranes with excellent functional capabilities. Comprehensive chemical analyses, including FTIR and XPS, confirm the successful integration and chemical modification of TA, leading to enhanced membrane functionality. This is further evidenced by SEM, MWCO, and contact angle measurements, which reveal decreased pore size and increased hydrophilicity. The TA/PVA-coated membranes demonstrated high water permeability up to 138 LMH/bar and excellent dye/salt selectivity, achieving ~99 % Congo Red (CR) rejection with <10 % salt rejection in both single-component and dye/salt mixture filtrations. Notably, these membranes exhibited remarkable fouling resistance, with Flux Recovery Ratios (FRR) up to 99 % against dye/salt mixtures. This eco-friendly approach, leveraging the green chemistry of TA and PVA, offers a cost-effective solution to one of the most challenging wastewaters in membrane technology.