Sunflower-inspired hydrogel evaporator with mutual reinforcement of evaporation and photodegradation for integrated water management

Solar interface photothermal evaporation is a promising strategy to ensure affordable water production. However, obtaining freshwater from wastewater containing highly concentrated volatile organic compounds (VOCs) is still a high hanker. Here, a polyvinyl alcohol (PVA)-based hydrogel evaporator was developed to mutually reinforce photothermal evaporation and photocatalytic degradation. The vertical structure promoted the rapid transfer of water molecules between the microchannels. Moreover, the solar absorption efficiency can be improved through multiple reflections. Furthermore, introducing polypyrrole (PPy) and MXene@TiO2@g-C3N4 (MTG) heterojunction can not only regulate the interaction force between the polymer network and water molecules to reduce the evaporation enthalpy, but also endow the PVA/PPy@MTG hydrogel with excellent photocatalytic degradation performance. Besides, the first principles simulation indicated that this hydrogel displayed higher binding energy for contaminants than water molecules. Therefore, it can achieve an evaporation rate of ∼3.0 kg m−2 h−1 and energy efficiency of ∼97.2 % under 1-sun, higher than the structure-disordered PVA/PPy@MTG hydrogel. In addition, it can degrade different complex components, especially for highly concentrated VOCs (100 ppm) with an efficiency of >94.2 %, exceeding most of the reported integrated evaporators. This work will pave a potential pathway to design novel evaporation for sustainable water remediation.