Advances in draw solutes for forward osmosis: Hybrid organic-inorganic nanoparticles and conventional solutes

Forward osmosis (FO) is one of the emerging membrane technologies which has gained interest in the last decade for being a low energy desalination process. The most important factors controlling FO processes are performance, recyclability and cost of the draw solution (DS) used together with the FO membrane itself because they play a crucial role on the feasibility of this technology. Consequently, the selection of an appropriate DS is vital for the process efficiency, besides the required selectivity and permeance of the membrane and the efficient DS regeneration process. A wide variety of DS have been tested so far and this paper aims to review recent advances in the synthesis and selection of an appropriate DS. It provides valuable information on a new type of draw solutes based on hybrid organic-inorganic nanosystems which, at a certain extent, show synergistic properties that face some of the technology shortcomings. Magnetic nanoparticles (MNPs) are the most promising nanosystems intended for desalination because they can be readily recovered applying a magnetic field or by conventional membrane processes. This review also deals with the most important characteristics of DS based on nanoparticles (NPs) and how they affect the performance of the overall processes. Finally, this review also highlights future research directions, where nanosystems will mitigate inverse diffusion and concentration polarization phenomena widely reported as limiting factors in FO processes. (C) 2016 Elsevier B.V. All rights reserved.