Polymer hydrogels as smart draw agents in forward osmosis processes

This chapter discusses thermosensitive polymer hydrogels as a new class of draw agent for forward osmosis (FO) desalination. The effect of hydrogel chemistry is reviewed, including the effect of incorporating ionic chemical moieties and light-absorbing carbon particles and reduced graphene oxide nanosheets on FO desalination performance. The presence of ionic groups in the hydrogel networks provides a unique capacity for hydrogels to attract more water. The pure ionic and composite ionic hydrogels show higher flux than nonionic hydrogels do. In any FO desalination process, the separation of permeated water from the draw agent is also very important. The dewatering process of hydrogel needs the deswelling of the swollen hydrogels to release the water. Solar energy is also used to release water from graphene-incorporated hydrogel. The chapter also focuses on further optimization of hydrogel properties and structures of membranes to enhance the performance of the hydrogel-driven FO process.