A method on the induction of piezoelectricity of PVDF by NaOH: Induced PVDF as ultrafiltration base membrane in interfacial polymerization to enhance the rejection of NaCl

Nanofiltration technology has garnered significant attention due to its potential to address global water scarcity. However, the low rejection rates of monovalent salts, such as NaCl, have limited the broader application of nanofiltration membranes. In this study, polyvinylidene fluoride (PVDF) powder was chemically modified by a saturated sodium hydroxide solution to the formation of a phase transition from the non-polar α-phase to the polar β-phase. The NaOH treatment promoted this phase transition by disrupting the crystal structure and enhancing molecular polarity, thereby inducing piezoelectric properties in the membrane. The modified PVDF was then formed as ultrafiltration substrate to fabricate a nanofiltration membrane with a dual-layer charge structure through surface charge-regulated interfacial polymerization. The NaOH-induced chemical modifications significantly improved both piezoelectric effect and ion rejection performance. The Piezo-PVDF nanofiltration membrane exhibited a 60 % rejection rate for 1 g/L NaCl, with an optimal water flux of 13.5 L m 2  h −1  bar −1 . This study demonstrates how NaOH-induced phase transition and piezoelectric activation optimize charge distribution across the membrane, leading to enhanced desalination performance. These findings provide new insights into the chemical mechanisms driving PVDF membrane modification and offer a strong theoretical and experimental foundation for the development of efficient and cost-effective desalination technologies.