Thermally stable thin film composite polymeric membranes for water treatment: A review

Abstract

Demand for hot water treatment has opened up broad new areas of research for fabricating thermally stable polymer membranes. In multiple industrial applications, the contaminated process water must be treated at high temperatures to maintain a sustainable and energy-efficient water recycling process. The present article reviews recent efforts made to develop thermally stable thin film composite membranes and provides insights on polymer material selection rationale, characterization techniques, promising progresses, major challenges, and potential future trends. Thin film composite membranes are the most commonly used polymeric membranes for desalination and water treatment, primarily due to their outstanding permeation properties. However, commercially available thin film composite membranes suffer from limited thermal resilience at temperatures above 45 °C, resulting in a short working lifetime. This limitation has motivated researchers to improve the thermal stability of thin film composite membranes through three primary approaches: (i) tuning the chemistry of the selective layer, (ii) enhancing the thermal properties of the porous sublayer, and (iii) incorporating nanomaterials into both the selective and support layers of thin film nanocomposite membranes. Among different approaches, efforts on modifying the selective layer have gained momentum due to the critical role it plays on the overall separation performance. Synthesis parameters were modified to develop new polyamide layers with higher cross-linking degree and rigidity. Furthermore, employing other strategies, such as using novel sublayers or well-dispersed nanoparticles was also found to increase the thermal tolerance of thin film composite membranes. The major challenges for the development of robust thin film composite and nanocomposite membranes are yet to: (i) overcome the trade-off relation between thermal stability and permselectivity of membranes, primarily caused by low reactivity of new monomers with stabilized resonance structure and severe aggregation of nanoparticles, and (ii) explore reliable methods to characterize the individual layers of composite membranes. This review explains how to select appropriate materials and preparation methods to produce thermally stable thin film composite membranes. The possible future directions of research in this field also discussed.