Nanovoids Engineering for Enhancing Separation Performance and Compaction Resistance of Polyamide Reverse Osmosis Membranes.

Constructing nanovoids─rapid transport channels for water molecules─is an ideal approach to enhancing the water permeance of polyamide reverse osmosis (RO) membranes. However, their variable morphology and inconsistent size usually result in stress concentration and accelerate membrane compaction. In this study, a nanobubble-nanoparticle coupling strategy was utilized to confine the interfacial growth of nanobubbles, with sacrificial ZIF-8 nanoparticles serving as discrete pillars. This approach enabled the successful fabrication of the CO2-0.50/ZIF-8(32) membrane containing uniform, small-sized, and quasi-spherical nanovoids, which exhibited excellent water permeance (3.35 L·m-2·h-1·bar-1) and high salt rejection (99.13%) in brackish water. Compared to conventional RO membranes containing nonuniform, large-sized, and oblate spheroidal nanovoids, the CO2-0.50/ZIF-8(32) membrane demonstrated significantly enhanced compaction resistance. During accelerated compaction tests involving pressurization-depressurization cycles and long-term seawater RO experiments, its water permeance loss was only slightly higher than that of the void-free PA-pristine membrane. This study confirms that the multidimensionally finely designed nanovoids can serve as a unique zero-mass reinforcement "ingredient" to effectively disperse stresses and mitigate compaction effects in RO membranes. By enabling simultaneous improvements in permeance and physical structural stability without additional materials, this work offers an energy-efficient and sustainable membrane design strategy for desalination and freshwater production.