Polyelectrolyte-based photothermal hydrogel with low evaporation enthalpy for solar-driven salt-tolerant desalination

Photothermal membranes have been widely developed for solar seawater desalination, but their practical applications are limited by high evaporation enthalpy and solid-salt crystallization. To solve this problem, we prepared an anionic polyelectrolyte-based hydrogel (APH) as an “all-in-one” evaporator, possessing both photothermal property (to evaporate seawater) and electrostatic repulsion (to avoid solid-salt crystallization). The APH was prepared by freeze-thaw method, and it was composed of poly(vinyl alcohol) as framework and poly(3,4-ethylenedioxythiophene): poly(sodium-p-styrenesulfonate) as solar absorber. The fabricated material showed porous structure with solar absorption efficiency of 95.5% in 380–2500 nm. After soaking by water, the APH exhibited an evaporation enthalpy as low as 1624.14 kJ kg −1 with a high intermediate/free water ratio of 2.27:1, deriving from the interfacial electrostatic effect of SO 3 − and large amount of OH – from poly(vinyl alcohol) frame. Under the irradiation of simulated sunlight (1.0 kW m −2 ), the APH showed a high evaporation rate of 2.5 kg m −2 h −1 and its solar evaporation efficiency reached 90.7%. Importantly, the SO 3 − groups can efficiently separate anions (such as Cl − ) from cations (such as Na + and Mg 2+ ) in the evaporator, avoiding the formation of solid-salt crystals. The excellent evaporation performance and salt tolerance of APH confer broad practical prospects for solar-driven seawater desalination.