Guanidineacetic acid dual-regulated interfacial polymerization towards highly permeable and ultraselective nanofiltration membranes

Nanofiltration (NF) membranes hold promise for energyefficient liquid separation, but achieving high permeance and precise separation membrane via a facile approach remains a great challenge. Herein, we introduce guanidinoacetic acid (GAA) as an economical additive to modify interfacial polymerization (IP) for high-performance NF membranes. Comprehensive characterizations and simulations revealed that GAA regulates the IP process through two mechanisms: (1) modulation of piperazine (PIP) diffusion kinetics at the aqueous–organic interface and (2) covalent incorporation of GAA that triggers in situ modification within the polyamide (PA) layer. This controlled diffusion and reaction kinetics produced a thinner, more electronegativity PA layer with an optimized microstructure. Benefiting from these optimized physicochemical properties, the GAA-functionalized membranes exhibit a 2.3-fold increase in water permeance compared to conventional NF membranes, while maintaining high Na 2 SO 4 rejection (>98.5 %) and excellent removal efficiency for organic micropollutants. Moreover, the modified membranes achieve superior ion selectivity, particularly for the separation of Ca 2+ /SO 4 2− , surpassing the state-of-the-art PA-based NF membranes. The incorporation of GAA presents a rational design paradigm for engineering selective layers in NF membranes, thereby advancing the prospects of NF technology for sustainable water purification.