Double Nanofoaming Enhanced Interfacial Polymerization toward Ultra-High-Performance Nanofiltration Membranes

Polyamide (PA) nanofiltration (NF) membranes represent a promising approach to safe drinking water production. Yet, selective removal of contaminants while retaining essential minerals remains a critical challenge for cost-effective water treatment processes. Here, we employed ammonia bicarbonate (AB) as an economical additive to modify interfacial polymerization (IP) for developing high-performance NF membranes suitable for drinking water applications. Comprehensive characterization coupled with molecular dynamics simulations demonstrate that AB modulates the IP process through three mechanisms: (1) controlling the diffusion kinetics of piperazine (PIP) at the aqueous-organic interface, (2) the reaction between HCO₃^- and H⁺ produced by IP achieves nanofoaming, and (3) the thermal decomposition of AB releases additional gaseous products (NH₃ and CO₂), enhancing the dual nanofoaming effect. This controlled reaction kinetics and increased nanobubble formation produced a thinner, more wrinkled PA selective layer with an optimized microstructure. The optimized NF-AB-8 membrane demonstrated enhanced permeance (28.5 LMH/bar) during actual surface water purification, while maintaining selective separation between minerals and dissolved organic matter (K_Ca2+/DOM = 34.5). In addition, the improved microstructure and separation performance enhanced the antiscaling and antifouling properties of the NF membrane. This study explored the application of dual-nanofoaming mechanisms in NF membranes, providing insights for designing NF membranes that simultaneously improve permeance and selectivity, which may promote the preparation of high-performance NF membranes and their application in drinking water production.