Pyramidal Polyvinyl Alcohol/MXene Hydrogel Evaporator for Seawater Desalination and Salt Recovery

Abstract

Global freshwater scarcity urgently demands sustainable, energy-efficient desalination technologies, and solar-driven interfacial evaporation is a highly promising solution. Hydrogels are attractive evaporator materials because they enable continuous water supply and flexible structural design. However, developing durable hydrogel evaporators combining excellent photothermal conversion, rapid multidirectional water−salt transport, and outstanding salt resistance remains a significant challenge. Herein, a pyramidal poly(vinyl alcohol) (PVA)/Ti3C2Tx MXene composite hydrogel evaporator is fabricated by directional freezing and low-temperature cross-linking. MXene provides excellent broadband solar absorption and photothermal conversion, while a uniquely designed anisotropic architecture combining honeycomb-like and lamellar channels enables rapid vertical and lateral water−salt transport. The pyramidal geometry enlarges the effective evaporation area, while siphon-assisted water supply directs salt crystallization toward the bottom of the evaporator. Under 1 sun irradiation, the evaporator achieves an excellent evaporation rate of 2.38 kg m−2 h−1, and during a 70 h long-term test with a 15 wt % NaCl solution, it maintains an average evaporation rate of 2.20 kg m−2 h−1 while enabling directional salt recovery. It also preserves its shape and evaporation performance upon dehydration-rehydration cycling, demonstrating good reusability. This work offers an effective strategy for high-performance seawater desalination and salt recovery.