Architecting highly hydratable polymer networks to tune the water state for solar water purification.

Water purification by solar distillation is a promising technology to produce fresh water. However, solar vapor generation, is energy intensive, leading to a low water yield under natural sunlight. Therefore, developing new materials that can reduce the energy requirement of water vaporization and speed up solar water purification is highly desirable. Here, we introduce a highly hydratable light-absorbing hydrogel (h-LAH) consisting of polyvinyl alcohol and chitosan as the hydratable skeleton and polypyrrole as the light absorber, which can use less energy (<50% of bulk water) for water evaporation. We demonstrate that enhancing the hydrability of the h-LAH could change the water state and partially activate the water, hence facilitating water evaporation. The h-LAH raises the solar vapor generation to a record rate of ~3.6 kg m-2 hour-1 under 1 sun. The h-LAH-based solar still also exhibits long-term durability and antifouling functionality toward complex ionic contaminants.

Synergistic Energy Nanoconfinement and Water Activation in Hydrogels for Efficient Solar Water Desalination.

Precisely controlled distribution of energy in solar-to-thermal energy conversion systems could allow for enhanced energy utilization. Light-absorbing hydrogels provide a means for evaporating water by using solar energy, yet targeted delivery of solar thermal energy to power the water evaporation process remains challenging. Here, we report a light-absorbing sponge-like hydrogel (LASH) that is created by in situ gelation of a light-absorbing nanoparticle-modified polymer, leading to synergistic energy nanoconfinement and water activation. By experimental demonstration and theoretical simulation, the LASH presents record high vapor generation rates up to ∼3.6 kg m-2 h-1 and stable long-term performance under 1 sun (1 kW m-2) irradiation. We investigate the energy confinement at the polymer-nanoparticle interphases and the water activation enabled by polymer-water interaction to reveal the significance of such effects for high-rate solar vapor generation. The water vaporization enabled by LASHs can remove over 99.9% of salt ions in seawater through solar water desalination. The fundamental design principle, scalable fabrication route, and superior performance offer possibilities for portable solar water purification, industrial solar-powered water treatment, and other advanced solar thermal applications.