Advances in forward osmosis membranes: Altering the sub-layer structure via recent fabrication and chemical modification approaches

The forward osmosis process has obtained renewed interest nowadays and it might become an alternative solution for many industrial applications to meet the current and future requirements for potable water. The FO process depends on the osmotic pressure gradient between a high salinity draw solute and low salinity feed solution across a semi-permeable membrane to extract pure water. Despite the potential advantages of FO, there are some technical drawbacks that hinder FO application for water desalination. One of the most significant critical challenges is the need for membrane compatible with the FO process. To improve FO desalination feasibility, membrane development is required to obtain maximum water permeability and minimum reverse solute flux over long-term operations. Therefore, this review starts by demonstrating the fundamentals and membrane development over the years. Fabrication modifications for the support layer of FO membranes and the crucial challenges of the FO process are summarized. Recent trends of the chemical modifications of the bulk and substrate are discussed. The advantages and disadvantages of the modifications on the FO membrane productivity are also addressed. Finally, concluding with future perspectives.