Chemically grafted di-quaternized polyphenylene oxide-based anti-fouling and anti-bacterial membranes

For large-scale operations, membrane flux and fouling present a critical barrier to the economic sustainability of the water treatment process. To achieve high permeability, anti-fouling and anti-bacterial properties, we report a novel scalable and simple approach for the membrane preparation involving functionalization of polyphenylene oxide by di-quaternization and chemical grafting of aliphatic carbon chain spacer for fine-tuned hydrophobic-hydrophilic balance and comb-shaped morphology. Five aliphatic carbon chains (three, four, six, eight, and ten carbon atoms) were chemically grafted on the di-quaternized polyphenylene oxide (QPPO) to comprehensively study the impact of functional groups on membrane surface properties, water flux, anti-fouling and anti-bacterial characteristics. 3C-SUL-g-QPPO membrane showed high pure water flux (875 ± 10.02 L m−2 h−1) and bovine serum albumin rejection (98.04 ± 1.02 %), attributed to hydration between water and zwitterionic surface and well-architected porous structure. The surface roughness and water contact angle for the 3C-SUL-g-QPPO membrane were minimal. The 3C-SUL-g-QPPO membrane showed good anti-fouling characteristics, as confirmed by the flux recovery and decline ratio data. The anti-bacterial activity against Gram-negative E. coli and Gram-positive S. aureus was attributed to the di-quaternized nitrogen of grafted polymer. The present work suggests quaternization of PPO for improved hydrophilicity and enhanced membrane permeability, while chemical grafting of aliphatic carbon chain balanced hydrophobic-hydrophilic character, improving the membrane anti-fouling properties.