Solar steam generation is a promising technology for desalinating seawater for freshwater production. In this process, photothermal materials absorb sufficient solar radiation to drive evaporation systems, which yield potable water while leaving saline components and contaminants behind.

Materials tested to date include fabric and sponges that facilitate evaporation, but these don’t harness a) Chinese ink and writing brush, similar to those used for writing and drawing for over 2,000 years, b) digital and infrared images of the Chinese character “water” written in Chinese ink under simulated sunlight and c) a scheme of the fabrication process for ALD/Chinese-ink-coated materials. Source: Argonne National Laboratory.sufficient solar heat to be truly cost-effective. A dark liquid that can be applied to porous surfaces would be ideal, leading U.S. Argonne National Laboratory researchers to experiment with ink. Conventional ink found in pens did not uniformly coat desired surfaces, so the team turned to Chinese ink, a carbon‐based paint used in traditional painting and calligraphy.

This soot, glue and preservative-based ink adequately coats porous materials and absorbs solar light in the visible and infrared ranges. Its viscosity keeps it on the substrate’s surface, concentrating heating power where needed.

However, the water-soluble nature of Chinese ink limits its service life during solar steam generation. This constraint was overcome by atomic layer deposition (ALD) of a thin titanium dioxide layer to seal the ink in place, which forms a durable membrane that demonstrates excellent photothermal properties and superior evaporation performance under simulated sunlight.