Incorporating controlled nanovoids into thin-film nanocomposite membranes to enhance boron rejection and improve desalination performance

The growing demand for energy-efficient desalination technologies necessitates the development of advanced membranes capable of addressing challenges for both boron rejection and water recovery in brackish water desalination. Conventional thin-film composite (TFC) reverse osmosis (RO) membranes, though highly selective for salt, often exhibit limited water permeability due to their dense polyamide layer. To address this, recent approaches have incorporated nanofillers to create additional transport pathways; however, many require post-synthetic treatments that risk damaging the membrane structure and reducing crosslinking density. In this study, we propose a sacrificial hybrid nanostructure-assisted strategy by integrating ZIF-67 with LDH to engineer nanovoids within TFN membranes, exploiting the aqueous instability of ZIF-67 and the interfacial interaction characteristics of LDH to enhance selective transport and boron removal. Membrane morphology, surface properties, and interfacial chemistry were systematically characterized using FESEM, AFM, XPS, zeta potential analysis and water contact angle. The optimized TFN membrane (M3) achieved a water permeance of 3.72 ± 0.2 LMH bar⁻¹, representing almost 69 % increament over the control membrane, while maintaining a high NaCl rejection of 99.52 % and an improved boron rejection of 81.92 % at pH 8. A long-term stability test conducted over 7 days showed no significant change in salt rejection, indicating that the nanovoid formation strategy does not introduce non-selective defects or compromise membrane integrity. In addition, M3 demonstrates effective boron rejection and water recovery from actual seawater permeate (collected from the Tuas Desalination Plant, Singapore). This work demonstrates that balancing the permeability–selectivity trade-off using hybrid nanofillers through nanovoid engineering provides a viable route for enhancing boron-selective desalination performance without additional post-treatment steps.