Tunable, Thermoresponsive Hydrogel-Based Composites for Facile, Low-Energy Water Desalination and Recovery

As clean, conventional freshwater resources decrease, treating unconventional water is a global priority. While membrane technologies such as reverse osmosis enable the use of seawater and brackish waters, their relatively high energy demands, particularly the external pressure required to overcome osmotic gradients and infrastructure requirements, limit broader adoption. Among alternative technologies, stimuli-responsive hydrogels provide a promising approach to address such limitations. In particular, thermally responsive hydrogels that can effectively reject ions while saturating (swelling) with water and then dewatering (recovery) under low-energy, controlled conditions hold considerable promise. In this work, enhanced thermoresponsive hydrogels were developed, via graphene oxide addition, and a shell-core strategy whereby the modified hydrogel core drives flow in and out (i.e., pull-push) as a function of temperature, while a thin polymer shell enhances ion (salt) rejection. This multifunctional approach allows for system tunability and thus optimization for treated water recovery. Driven by near room-temperature swings (20-40 °C), composite materials described here desalinate water at 57-78% salt rejection for varying ionic strengths (17-550 mM) and types (NaCl, CaCl₂, MgCl₂) with ∼5 times swelling/recovery ratios consistently for five relatively rapid treatment cycles, with a water collection rate of 7.7 kg m^-2 h^-1.