Self-contained Janus Aerogel with Antifouling and Salt-Rejecting Properties for Stable Solar Evaporation.

Janus structural interfacial vaporization by separating the solar absorber from the bulk working fluid has attracted tremendous attention due to its low heat losses and high solar conversion efficiency for desalination, water purification, energy generation, etc. However, a totally separated double-deck structure with a discontinuous interfacial transition and inefficient photothermic materials undermines its long-term use and large-scale practical exploitation. Herein, a low-cost Janus monolithic chitosan aerogel with continuous aligned run-through microchannels has been demonstrated to have a highly efficient photothermic effect on seawater desalination and wastewater purification. The top solar absorber layer enhances broadband light absorption and photothermal conversion efficiency via the multiple internal reflection of incident light in the aligned microchannels. Moreover, the insulating/hydrophilic bottom layer promotes water transportation and heat localization, and simultaneously prevents salt/fouling accumulation. As a result, a long-term solar vaporization rate of ∼1.76 kg m-2 h-1 is achieved, corresponding to a light-to-vapor efficiency of ∼91% under 1 sun irradiation. Notably, the large-vessel microchannels throughout the aerogel and favorable swelling property provide sufficient water replenishment and storage for completely isolating self-contained evaporation, illustrating an enhanced and time-extended self-contained solar steam generation. Such a low-cost bilayer aerogel with remarkable cycling stability in various fluids offers potential opportunities for freshwater production in remote rural areas.