Suppressing Polyamide Crystallization Unlocks Ultrapermeable and Highly Selective Nanofiltration Membranes

Nanofiltration (NF) membranes are essential for water purification. However, their performance is still largely optimized through empirical methods, as polyamide crystallinity remain difficult to control in scalable interfacial polymerization processes. In this study, we introduce an ultra-low-temperature interfacial polymerization strategy at -20 °C that enables direct polyamide chain assembly, suppresses crystallization, and forms a smooth, defect-free, fully amorphous selective layer. Comprehensive characterization confirms the formation of a homogeneous amorphous network, enabling a fourfold increase in water permeability and a threefold improvement in Cl^-/SO₄^2- selectivity compared with room-temperature controls, surpassing high-performance NF membranes. The smooth surface further improves the antifouling performance of the NF membrane. Life cycle assessment based on experiments with real industrial wastewater, demonstrate that using the fabricated membrane can reduce treatment costs by 79.1%. This work establishes temperature-controlled chain assembly as a scalable lever for NF design and provides a practical pathway toward next-generation membranes for water treatment.