Hydrogel-regulated synthesis of thin film composite membranes for antibiotic/salt separation: piperazine diffusion and distribution constraint

Nanofiltration (NF) membranes present environmentally sustainable potential in the separation and purification of antibiotic. However, targeted enhancement of antibiotic separation efficiency while maintaining high permeability remains a significant challenge for conventional NF membranes. Precise regulation of the interfacial polymerization (IP) process at the monomer molecular level shows promises for achieving tailored control over thin-film composite (TFC) membrane properties and performance. Here, a novel TFC membrane synthesis strategy was developed with hydrogel assisted. The aqueous-phase-free IP was conducted at the interface between the hydrogel doped with piperazine (PIP) monomers and the organic solution, achieving precise regulation of PIP diffusion. Molecular dynamics simulations were employed to analyze the monomer diffusion behaviour and the effects on the membrane properties during regulated IP. The diffusion rate and distribution range of the amine monomers were effectively constrained, thereby reducing the thickness of the polyamide layer, which was beneficial for mass transfer. PIP monomers were enriched at the interface during the regulated IP process, which enhanced the consumption of the organic phase monomer while limiting hydrolysis of unreacted acyl chloride groups and reducing membrane electronegativity, specifically improving the permeation of monovalent salt ions. Furthermore, the hydrogel layer promoted the “gutter effect” and contributed to an increase in the TFC membrane permeability. The TFC membrane constructed via AFIP demonstrated excellent performance characteristics, including a permeability of 18.5 LMH/bar and a high erythromycin/NaCl selectivity of 44.3. This research provides new insights into customizing the performance of TFC membranes and their applications in antibiotic purification.