Regulation of polyamide reverse osmosis membrane structure by nanobubbles: Unraveling the mystery of structure-property relationships

The development of nanofoaming strategies presents a new avenue for designing polyamide (PA) thin film composite reverse osmosis membrane structures. However, the precise mechanism by which nanobubbles regulate the overall structure of the PA layer and the relationship between the influence on membrane structures and properties remain unclear. In this study, the PA layer structure was precisely regulated with H 2 nanobubbles based on free interfacial polymerization, and the impact of H 2 nanobubbles on the backside opening properties, internal nanovoids, and surface morphology of membranes was comprehensively analyzed. Furthermore, this strategy has been successfully extended to CO 2 and O 2 nanobubble systems. Through analyzing the robust correlation between nanovoid size and PA layer thickness in all membranes, an innovative “volcano” relationship between membrane structure and water permeance was proposed. Upon this basis, a model of nanovoid size ratio was developed and revealed that the water permeance of PA membranes increased with the increase of nanovoid size ratio. Remarkably, the H 2 -0.05 % membrane, located at the apex of the “volcano” with the highest nanovoid size ratio (0.56), exhibited outstanding water permeance (2.61 L·m −2 ·h −1 ·bar −1 ) and reasonable salt rejection (97.9 %). This study provides valuable insights into the intricate relationship between the structure and property of PA membranes.