(569c) Zwitterion-Ag Complexes That Simultaneously Enhance Biofouling Resistance and Silver Binding Capability of Thin Film Composite Membranes

Biofouling can be overcome with zwitterion grafts and anti-microbial, metallic nanoparticles. However, the mechanism underpinning this effective approach remains unclear. To elucidate the role of each component in this system whilst maximizing membrane anti-fouling and anti-microbial properties, here we performed a comparative study to investigate the impact of zwitterion type and their interactions with Ag of various states. Two different zwitterions (SO₃^--based and COO^--based) were employed to modify polyamide (PA) thin film composite (TFC) membranes, and the metallized and mineralized membranes were developed via in-situ formation of silver (Ag) nanoparticles and deposition of silver chloride (AgCl) particles on the zwitterion-modified TFC membranes. The presence of zwitterions was key to enhancing Ag content, resulting in significantly improved anti-microbial and anti-fouling properties without compromising the nanofiltration separation performance. COO^--based zwitterions were found more favourable towards Ag metallization and mineralization compared to SO₃^--based zwitterions. The underlying mechanisms underpinning this discovery were further revealed using the Density Functional Theory (DFT) to reveal Gibbs free energy of the binding between zwitterions and Ag⁺ ions. This fundamental knowledge is crucial for designing next-generation anti-biofouling strategies.