Unlocking the potential of thin-film composite reverse osmosis membrane performance: Insights from mass transfer modeling

Thin-film composite (TFC) reverse osmosis (RO) membranes have attracted considerable attention in water treatment and desalination processes due to their specific separation advantages. Nevertheless, the trade-off effect between water flux and salt rejection poses huge challenges to further improvement in TFC RO membrane performance. Numerous research works have been dedicated to optimizing membrane fabrication and modification for addressing this issue. In the meantime, several reviews summarized these approaches. However, the existing reviews seldom analyzed these methods from a theoretical perspective and thus failed to offer effective optimization directions for the RO process from the root cause. In this review, we first propose a mass transfer model to facilitate a better understanding of the entire process of how water and solute permeate through RO membranes in detail, namely the migration process outside the membrane, the dissolution process on the membrane surface, and the diffusion process within the membrane. Thereafter, the water and salt mass transfer behaviors obtained from model deduction are comprehensively analyzed to provide potential guidelines for alleviating the trade-off effect between water flux and salt rejection in the RO process. Finally, inspired by the theoretical analysis and the accurate identification of existing bottlenecks, several promising strategies for both regulating RO membranes and optimizing operational conditions are proposed to further exploit the potential of RO membrane performance. This review is expected to guide the development of high-performance RO membranes from a mass transfer theory standpoint.