Recyclable and efficient ocean biomass-derived hydrogel photothermal evaporator for thermally-localized solar desalination

Interfacial evaporation is gaining popularity as a facile and effective method for harvesting solar energy and yielding freshwater from sewage and seawater. However, challenges exist for achieving a balance among a plethora of performance metrics, e.g., low cost, high evaporation efficiency, off-grid deployment, and negligible environmental impact. In this study, a hydrogel evaporator is prepared by combining agar, naturally abundant ocean biomass, with titanium nitride nanoparticles. Due to the excellent photothermal conversion effect of titanium nitride nanoparticles, the evaporator shows a solar absorptance of 0.98. This evaporator has vertically aligned water channels and is fabricated by an ice template-induced self-assembly method, enabling the formation of a biomimetic wood structure. The rapid water transport and salt drainage within its aligned channels, effective water activation in hydrogel molecular meshes, and efficient heat localization allow this hydrogel evaporator to achieve an evaporation rate of 5.15 kg m−2 h−1 under the irradiance of one sun (1 kW m−2). The indirect water supply method using cotton wipe as the water transportation channels and polystyrene foam as the thermal barrier efficiently localize heat within the top small evaporation region, which ensures such a high evaporation rate. Moreover, this hydrogel evaporator is easy to be recycled without performance reduction to achieve an extended lifespan with the advantage of facile thermal recyclability after long-term utilization. The freeze-thawing fabrication of this hydrogel evaporator is feasible for scalable deployment. This work offers new possibilities for high-quality freshwater yields with cost-effective raw materials and deployable solar desalination systems for industrial implementations.