Alternative materials for interfacial polymerization: recent approaches for greener membranes

Thin-film selective layers fabricated via interfacial polymerization (IP) form the core of membrane-based water purification and desalination, as well as other molecular separations. The monomers and organic solvents used in the reaction are for the most part toxic chemicals, likely to be banned in the near future, for environmental protection. There is, therefore, a growing need to find alternative, sustainable, materials that can produce adequate membranes for industrial applications, fabricated via IP. The present work summarizes recent studies on fabricating RO/NF/OSN membranes via IP using sustainable solvents and/or monomers, in comparison to the toxic chemicals used to fabricate polyamide, the chosen polymeric material for the commercial selective membrane layer. The properties of these 'green' materials are described, as well as the properties of the resultant membranes, discussing possible limitations in the fabrication techniques and the benefits of the process. Furthermore, an eco-scale score is calculated for representative membranes, demonstrating the utility of this tool for assessing the 'greenness' of the fabricated membranes. Overall, the presented literature shows that there is a great potential for fabricating more sustainable and scalable membranes. However, studies exhibit various limitations, for example, no standardization for performance tests and performance criteria for every membrane type, which prevents accurate and true comparisons among different membranes. Suggestions are made, where applicable, for future work to add aspects that assess the potential of fabricated membranes to future industrial applications. Finally, and most importantly, there is still a need for improved fundamental understanding of IP, with which to facilitate the search of alternative sustainable materials for membrane fabrication with desired properties. A critical overview is provided, on use of green monomers and solvents for fabrication of selective thin-films via interfacial polymerization used inseparation processes.