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 (KCa2+/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.