Molecular engineering of biomass-derived hybrid hydrogels for solar water purification

Solar evaporation which ultilizes the sustainable solar energy for freshwater production from waste or saline water is one of the most attractive technologies to simultaneously address energy and freshwater crisis. Nevertheless, high energy consumption of water-vapor transformation greatly restricts the practical applications of solar-driven water purification. Herein, we report hybrid hydrogels formed by introducing biomass, starch, and carbon nanotube into hydrophilic polyvinyl alcohol in a cost-effective route, used as multifunctional evaporators. The interpenetrating network has good hydrophilicity, fast water transport and adjustable state of water molecules, which reduces the enthalpy of water vaporization to promote the evaporation process. Thus, the obtained hydrogel evaporator possesses an evaporation rate of 2.44 kg m^-2h^-1 with 95% efficiency under one-sun, and is capable of producing clean water from various types of wastewater, including salty, acidic, alkaline and organic polluted water, with long-term durability and stability. It also presents excellent antibacterial, salt resistance and self-cleaning capabilities, suitable for practical applications. More notably, with abundant OH groups from starch, the hybrid hydrogel can effectively adsorb heavy metal ions and organic dyes via formation of chelating and hydrogen bonds. Therefore, this work provides a new approach for portable and cost-effective solar-driven wastewater purification.