Solar water purification is a promising technology with a strong potential for producing fresh water without effluent discharge. For energy-intensive interfacial vapor generation, energy loss to air via heat radiation and convection occurs commonly but is normally ignored, which severely limits the energy efficiency. Therefore, it is necessary to precisely regulate the interfacial thermal energy for interfacial vapor generation. Here, we developed a hierarchically porous radiation-absorbing hydrogel film (hp-RAH) through an in situ gelation strategy and employed this hp-RAH on various existing solar evaporator surfaces. The hydrogel film efficiently absorbs and reutilizes the thermal radiation energy emitted by the photothermal layer and eradicates thermal convection of the photothermal layer into air. In this way, an evaporation efficiency up to 95% is obtained, and the heat radiation and convection losses are reduced from 6.6% to 0.39% under 1 sun. This strategy demonstrates a promising membrane evaporation prototype based on the evaporation surface thermal utilization.
Keywords: hierarchical nanostructure; hydrogel; radiation-absorbing; solar water purification; thermal management.