Engineering

Polymer chemistry

Materials science

Evaporator

Enthalpy

Biochemistry

Chemical engineering

Heat exchanger

Geology

Oceanography

Polymer

Thermodynamics

Physics

Crystallization

Membrane

Desalination

Composite material

Evaporation

Chemistry

Polyelectrolyte

Seawater

Solar desalination

Vinyl alcohol

Chemical Engineering Journal

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 SO3− 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 SO3− groups can efficiently separate anions (such as Cl−) from cations (such as Na+ and Mg2+) 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.

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