Few-Layer Materials in Porous Membranes for Advanced Water Desalination

The constant growth of the human population, together with drastic climate change, is compromising the availability of an essential natural resource, water, which is needed for drinking and domestic use, agriculture, industry, and the safety of biodiversity. Saline water represents more than 97% of the water on the planet, but only 2.5% is used as freshwater. The main obstacle is the costs, including energy, required for process implementation enabling a sustainable large access to water. Seawater desalination is a reliable method for water supply and since the post-war period, it has been practiced successfully with classic distillation techniques such as multistage flashing (MSF) and multi-effects distillation (MED), and then membrane operations such as nanofiltration (NF) and reverse osmosis (RO) and derived processes. In recent decades, increasingly efficient desalination techniques have been proposed through the development of new membrane-based technologies such as Membrane Distillation (MD). However, the scalability of this kind of operation requires more fruitful productivity-efficiency trade-offs and lower energy consumption to be within the framework of green and circular economies. In the case of membrane operations, desalination procedures have been optimized through the design of progressively high-performing membranes, which are regarded to work as the engine for each separation process. This has solicited the exploration of different classes of materials, taking the chance to drive their specific properties towards the design of next-generation membranes needed to make desalination competitive on a large scale. Among others, the portfolio of 2D materials has grown exponentially for different uses, but more recently has been oriented to water desalination. Few-layer materials have been proposed to fill polymeric porous membranes for assisted productivity and durability or to generate additional nanochannels through which ions bringing different charges can be filtered. This chapter gives an overview of the attractive use of few-layer materials confined in membranes for water desalination. After an introduction on the most used and promising membrane operation dedicated to water desalination and a brief discussion about environmental issues, a wide section is dedicated to the production of few-layer materials and their related use in water desalination. Specifically, exfoliation strategies are discussed together with the use of 2D materials as nanofillers in composite membranes and intercalated channels in layered membranes. Effects on productivity, resistance to wetting and fouling, thermal efficiency, and capability to discriminate from mono-and divalent ions, as well as the recovery of reusable crystals from brine, are analyzed and discussed. An assessment of the role of few-layer materials within the framework of circular economy is provided.