pH-tailored activated water reservoir for rapid solar water purification via dual-layer hydrogel architecture

Solar vapor generation is a facile and effective approach to harvest pure water from seawater and polluted water, and diverse of materials or microstructure tuning methods have been reported to promote the evaporation rate. Nevertheless, the vapor yield via current solar water purification technology is limited due to high water evaporation enthalpy arising from the strong intermolecular hydrogen bonds. In this study, we advanced the solar evaporator architecture by adding another activated water reservoir beneath it. As such, the bottom poly (acrylic acid-co-acrylamide) (PAA-AM) layer could supply ample activated water (reduced evaporation enthalpy) to the top layer for solar water evaporation due to the increased intermediate water. By tuning the microstructure of PAA-AM bottom-layer with pH, the optimal dual-layer hydrogel evaporator presents a superior water evaporation rate of 2.79 kg m−2h−1 under one sun, 62.2 % enhancement compared with the single-layer PPy@PAA-AM solar evaporator (formed by in situ polymerization of pyrrole in the PAA-AM hydrogel). We demonstrated the strategy was applicable to other single-layer evaporators. The fabricated flexible dual-layer hydrogel evaporator was employed for real seawater desalination and water purification from polluted solutions, manifesting great possibility for the deployment to alleviate the water scarcity crisis, particularly for the economically stressed communities.