Unveiling the challenge of evaporator design in clean water production promoted by superabsorbent hydrogels and sunlight

Abstract

Climate change is affecting water availability and the supply. This situation is particularly worrying in Mediterranean area countries, where droughts are becoming increasingly long and severe. Herein, a superabsorbent porous hydrogel composed of thermoresponsive hydrogel (TSH) poly(<em>N</em>-isopropylacrylamide) (PNIPAAm), copolymerized with poly(acrylamide) (PAAm) and modified with poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT/PSS), as a solar absorber, is presented. This superabsorbent hydrogel optimizes water uptake and provides long life stability through a continuous supply of water to the evaporation surface, promoted by its thermosensitivity property and light absorption efficiency with a very low amount of photothermal material (1 wt %). The fine-tuning of both the hydrogel composition and the solar vapor generator (SVG), assisted by a metallic reflector, results in an impressive evaporation rate (ER) of 6.34 kg·m^–2·h^–1. This configuration minimizes the heat losses and allows maintaining the ER high, if compared to other SVG architectures. The hydrogel also exhibits strong removal capacity for monovalent cations and transition metals as well as reusability properties under stable multiple evaporation-swelling cycles, thanks to its good covalent interpenetrating network and its mechanical integrity. This superlative performance significantly expands the potential applications of porous hydrogels in clean water production, which are moved by sunlight irradiation and seawater, two abundant natural resources.