Engineered nanomaterials for water desalination: Trends and challenges

Abstract

It is ironic that the world suffers from water scarcity even with more than 70% of Earth being covered by water. This has majorly been attributed to the lack of cost-effective and less energy intensive desalination technologies that would enable easy conversion of seawater to freshwater for safe consumption. Several strides have been made in the desalination front that have led to the emergence of new nanomaterials with higher salt rejection efficiency. This review discusses the design considerations for these materials along with different classes of nanomaterials synthesized for effective water desalination. The type of material used (organic/inorganic), method of preparation, pore size and surface chemistry, mechanical strength and biodegradability were identified as important considerations for the synthesis of such nanomaterials. Among the preparation methods, sol–gel and chemical vapor deposition techniques were found to be the most cost-effective so far. Pore size and surface chemistry have been reported as crucial considerations for selective removal of salt ions and controlling the fouling tendency. The developed materials are also expected to exhibit good durability and stability that can be achieved through surface modification, crosslinking and blending. Carbon-based materials (CNTs, graphene), aquaporin, zeolites and clays and, metal oxide nanoparticles have been used as membrane materials with promising desalination potential. However, the recyclability of nanomaterials used for desalination and their environmental impact remains a challenge and relatively unexplored that could be investigated using integrated bioprocessing approaches.