High-performance zwitterionic membranes via an adhesive prebiotic chemistry-inspired coating strategy: A demonstration in dye/salt fractionation

Built upon the recently developed prebiotic chemistry-inspired aminomalononitrile (AMN) coating strategy, a new class of loose nanofiltration membranes (LNMs) immobilized with zwitterionic functionality was prepared, and their capacity in dye/salt fractionation was explored. The immobilization of a zwitterionic copolymer poly(sulfobetaine methacrylate-co-2-aminoethyl methacrylate hydrochloride) (PSBAE) assisted by the AMN chemistry was proven successful. The resulting membrane exhibited a dense selective layer with a more hydrophilic and nearly electroneutral surface. Although increasing the AMN/PSBAE ratio led to an enhanced membrane performance, only limited improvement was observed beyond 1:7. Comprehensive investigations of the optimal membrane M_A1P7 with various feeds demonstrated that size sieving was the dominant separation mechanism, and the electrostatic interaction was minimized due to the zwitterionic nature. With a competitive water permeance of 75.3 L m⁻² h⁻¹ bar⁻¹, the as-developed membrane shows consistently high rejection of both negative and positively charged dyes (up to 99.9%) and consistently lower rejection of salts (<10%) at different salinity levels, which means that the membrane developed here exhibited more versatility in terms of its resilience to compositional changes of the wastewater. Overall, this work explored the versatility of the AMN-based modification method in producing efficient membranes with superior molecular fractionation ability in water applications.