Black hydrophilic NPs 17 can also be used for water purification. A photothermal thin film confinement capillary phenomenon (CC) on a porous sponge is proposed. The thin coating is composed of richly aggregated black/hydrophilic nanoparticles (BHNPs) and channels between BHNPs can generate strong capillary action for water transport. Photothermal materials with CC can maintain high evaporation rates throughout the day and remove salts during the night, thus highlighting their recyclability and salt accumulation properties are emphasized.