Robust and Antifouling Composite Hydrogels Enhanced by Directional Freeze-Casting and Salting-Out for Highly Efficient Solar Evaporation

Hydrogels have been identified as a promising material platform for solar-driven interfacial evaporation. However, designing durable hydrogel solar evaporators that can combine effective photothermal conversion, superior water transport, salt resistance, and robust mechanical properties to ensure stable and efficient evaporation remains a significant challenge. Herein, a robust and antifouling hydrogel-based solar evaporator composed of poly(vinyl alcohol), sodium alginate, and MXene is successfully constructed through directional freeze-casting and salting-out processes. The directional freeze-casting aids in forming vertically aligned, well-interconnected channels within the hydrogel that facilitate rapid upward water transfer and effective salt ion discharging, while the optimized salting-out process promotes the cross-linking of polymer chains, creating a sponge-like porous structure that enhances key mechanical properties such as high elasticity and exceptional flexibility. The developed hydrogel evaporator achieves an impressive evaporation rate of 2.53 kg m-2 h-1 with an energy efficiency of 93%, as well as excellent salt resistance and long-term evaporation stability even when desalinating high-concentration brines. These exceptional characteristics make this composite hydrogel evaporator highly suitable for practical applications in seawater desalination and wastewater purification.