A biomimetic-inspired cross-scale hydrogel evaporator with synergetic light–heat–water–salt management for highly efficient and stable brine evaporation

Hydrogel-based solar-driven interfacial vapor generation is considered an effective method for freshwater production. However, traditional hydrogel evaporators suffer from weak mechanical strength and the trade-off between high evaporation rates and salt resistance, which limits their practical applications. Inspired by the unique water transport mechanism of natural reed, we construct a cellulose nanofiber-enhanced hydrogel evaporator with a hierarchical gradient pore structure. Microscale surface roughening design in hydrogel emulates leaf stomatal transpiration, enhancing light absorption while maintaining high vapor escape efficiency. Its bottom-to-top gradient pores enable rapid capillary-driven water transport and sustained interfacial supply, achieving efficient thermal-mass balanced evaporation. More importantly, the bilayered gradient hierarchical structure enables directional salt diffusion back to bulk water, effectively preventing salt crystallization. As a result, the hydrogel evaporator achieves an optimal evaporation rate of 2.61 kg m^-2 h^-1 under 1 sun. In a 20 wt% NaCl solution, a stable evaporation rate can be maintained without salt deposition. Moreover, the hydrogel evaporator is able to remove more than 99% of the primary metal ions from seawater and almost completely remove the dye ions from the dye solution. This work demonstrates a promising application in seawater desalination and dyeing wastewater treatment.