Design of dual-layer Janus polyelectrolyte hydrogel via dynamic covalent bonds for highly efficient solar desalination

Abstract

Solar-driven evaporation offers a promising solution for water scarcity and efficient desalination with low energy requirements. Recently, polyelectrolyte hydrogels have attracted considerable attention in the field of salt resistance owing to their electrostatic effect between the charged groups within the skeleton of hydrogel. The conventional polyelectrolyte hydrogels mostly use single-charged groups, limiting their ability to resist salt accumulation during prolonged operation. For solving this problem, we herein demonstrated self-healing as an effective method for binding anionic–cationic polyelectrolyte dual-layer hydrogels using dynamic covalent bonds of borax. Such design have minimized the amount of Na⁺ and Cl⁻ ions diffusion into the hydrogel matrix and achieved exceptional salt-resistance, benefiting from electrostatic interaction between functional groups of the evaporator and salt ions. Additionally, the dual layers provided excellent thermal insulation, reducing the heat loss to surrounding water. Hereby the hydrogel evaporator achieved stable long-term performance with an evaporation rate of 2.43 kg m⁻²h⁻¹ under 1sun irradiation. More importantly, no salt precipitation occurred on the solar absorber surface, even with varying salinities over more than seven days. All in all, the integration of anionic and cationic hydrogel layers achieved through the self-healing feature, significantly enhances the performance of interfacial steam generators used in seawater desalination applications.