Enhancing nanofiltration performance via a transient interlayer during interfacial polymerization: improved rejection of representative antibiotics

The permeability–selectivity trade-off and the permanent hydraulic resistance introduced by conventional interlayers remain critical challenges for thin-film composite polyamide nanofiltration (NF) membranes. In this paper, we present a low-cost, transient polyester interlayer strategy that utilizes pyrogallol (PG) and trimesoyl chloride (TMC) to regulate interfacial polymerization (IP). A transient polyester interlayer strategy is presented, in which the PG-TMC layer serves as a temporary regulatory scaffold: it suppresses piperazine diffusion during interfacial polymerization and subsequently undergoes partial structural disintegration in aqueous environments, leaving behind a residual porous sublayer with tunable content, thereby avoiding the formation of dense, permanent mass-transfer barriers. This process of kinetic suppression resulted in the compression of the IP reaction zone, thereby yielding a significantly thinner (∼60 nm), smoother (Rq = 25.6 nm), and more uniformly porous polyamide selective layer in comparison to the pristine membrane (83 nm, Rq = 33.3 nm). Consequently, the optimized membrane achieved a ∼ 64% increase in pure water permeability (from 11.4 to 18.7 L m −2  h −1  bar −1 ) while maintaining high Na₂SO₄ rejection (95.0%). It is noteworthy that pharmaceutical rejection was significantly enhanced owing to the narrowed pore size distribution and reduced defect density, with cefalexin rejection rising from 82.6% to 95.0%. In the context of cyclic cross-flow fouling conditions, the modified membrane exhibited enhanced flux and favorable flux recovery, thereby substantiating that the observed permeability enhancement was not attained at the expense of antifouling efficacy. The stability of the separation selectivity was verified over a period of 32 h by conducting long-term cross-flow tests. In contrast to conventional permanent interlayers, the PG-TMC layer functions as a transient regulatory layer and undergoes partial structural disintegration in aqueous environments. This prevents the formation of dense permanent mass-transfer barriers. Utilizing commercially available reagents and a simple dip-coating process that is fully compatible with existing manufacturing lines, this strategy offers a scalable route toward high-performance NF membranes.