Superior cross-linking assisted layer by layer modification of forward osmosis membranes for brackish water desalination

In this work, a novel surface modification strategy was developed to modify polyethersulfone membrane substrate to create membranes for forward osmosis applications. A novel poly(ethylenimine) crosslinked Hexadecafluorodecanedioic acid polyelectrolyte was synthesized, followed by layer deposition on the surface of an ultrafiltration membrane substrate. While the unmodified membrane was negatively charged, this procedure reversed the surface charge, leading to a positively charged forward osmosis-nanofiltration membrane. Interestingly, at pH 7, the zeta potential approached 6.9 mV for membrane coated 4.5 as compared to the pristine membrane with a zeta potential value of approximately −11.0 mV. Extensive characterization and chemical analyses were carried out to ensure the effectiveness of the developed separation layer. The results revealed that the poly(ethylenimine) crosslinked Hexadecafluorodecanedioic acid was successfully deposited on the polyethersulfone membrane substrate. Preparation conditions, such as curing temperature and time were optimized. It was found out that membrane coated with 3.5 bilayers and cured at 60 °C for one hour exhibited optimal water permeability of 21.9 L m⁻² h⁻¹ bar‐1 of and solute permeability of 1.66 L m⁻² h⁻¹ as compared to the neat membrane.