Confinement Capillarity of Thin Coating for Boosting Solar-Driven Water Evaporation

Realizing ultrathin water and generating an abundant water/air interface in the interconnected pores of photothermal materials is an effective way to boost the solar-driven water evaporation rate, but still a great challenge. Herein, confinement capillarity (CC) of photothermal thin coating on porous sponge for significantly enhancing the solar-driven water evaporation is proposed. The thin coating is composed of abundant agminated black/hydrophilic nanoparticles (BHNPs), and the channels among the BHNPs can generate strong capillarity for water transportation. Water can be spontaneously limited and transported among the agminated nanoparticles, rather than fill in the interconnected pores of the sponge. Thus, ultrathin water layer can be realized on the outer/inner surface of the sponge skeleton, without precisely controlling water supply. The thin water layer can not only expose as much evaporation area as possible by increasing the vapor escape channel, but also prevent solar energy to heat excess water. Thanks to the CC, the rate of solar steam generation can be greatly improved. Moreover, the photothermal material with CC can maintain its high evaporation rate during the whole day, and can remove the salt during night time, highlighting its recyclability and anti-salt-accumulation property. Moreover, the CC can be readily scaled up for practical applications.