Membranes for desalination and dye separation: Are 2D materials better than polymers? A critical comparison

According to the World Water Development report released at the UN 2023 Water Conference, there is an imminent risk of global water crisis. 2 billion people (26%) lack access to safe drinking water globally. 2–3 billion people suffer life risks due to water shortages experienced at least once yearly. Nine hundred thirty million global urban population facing water scarcity in 2016 is projected to double to 1.7–2.4 billion in 2050 [1]. Seawater and wastewater have long been considered potential sources of fresh water. Desalination or industrial wastewater purification technologies based on polymeric reverse osmosis (RO) and nanofiltration (NF) membranes can provide solutions to some extent, but achieving high water/ion (or dye) separation efficiency is still a challenge. Moreover, membrane fouling over a long period of operation is a significant bottleneck, making these systems less economically favorable. Two-dimensional (2D) materials-based membranes have emerged as attractive alternatives over polymeric membranes for desalination and dye-water separation due to their tunable surface properties and ability to form thin structures. The family of 2D materials can be configured in various forms, like pores, tubes, laminates, and channels. However, better control on pore size, thickness, and surface charge is necessary to achieve the desired membrane efficiencies. This review summarizes the existing desalination and dye separation technologies, their shortcomings, and how 2D materials can offer certain advantages over polymeric membranes. The mechanism of permeation through polymers and 2D materials is discussed in detail. We examine the conventional polymeric membranes and some popular 2D materials-based membranes from a critical perspective. We highlight their performances, structures, and potential strategies to fabricate highly selective, permeable, and fouling-resistant membranes. Finally, we put forward our insights based on the current challenges for future research direction. We believe this comprehensive review will help advance research in the rapid development of 2D materials-based membranes for solving critical issues that humanity is facing.