Triple network zwitterionic polyelectrolyte hydrogel evaporators based on anti-salt-ion hydration effect for...

Solar-driven interfacial evaporation technology is widely regarded as a cost-effective and sustainable method for freshwater production. However, conventional evaporators are confined to two-dimensional (2D) structures to ensure sufficient water supply when treating high-salinity brine, which suffer from limited evaporation rates and poor sustained evaporation due to the adverse effects of salt ions. This work introduces a novel three-dimensional (3D) evaporator composed of poly(vinyl alcohol) (PVA) sponge, zwitterionic polyelectrolyte hydrogel, and multi-walled carbon nanotubes (MWCNTs). The porous PVA sponge enhances water transport and mechanical robustness, while the anti-polyelectrolyte effect of the zwitterionic polyelectrolyte hydrogel further improves water transport performance in brine. Additionally, the anti-salt-ion hydration effect of the zwitterionic polyelectrolyte hydrogel activates water molecules in brine to promote evaporation. Under 1 kW m^-2 solar irradiance, the 7-cm-high evaporator reaches a stable evaporation rate of 3.35 kg m^-2 h^-1 in 10 wt% brine during a continuous 9-h operation, with no observable salt deposition or structural degradation on its surface. Furthermore, the zwitterionic polyelectrolyte hydrogel exhibits excellent antibacterial properties, providing additional reliability for practical desalination applications. In outdoor experiments using turbid seawater under natural winter conditions, a simple device incorporating the 3D evaporator gets a freshwater collection rate of 1.37 kg m^-2 h^-1, with the ion concentration in collected freshwater reduces by 3-4 orders of magnitude compared to raw seawater, meeting the World Health Organization drinking water standards. This work provides a new pathway and design principles for developing next-generation solar evaporation systems applicable to both seawater desalination and wastewater treatment.