Bifunctional Hydrogel Membranes for All-Day Freshwater Collection

Freshwater crisis is a global problem and seeking more sources of fresh water is the key to solving this problem. Solar water purification and fog collection are two separate ways to obtain fresh water. However, neither of these methods could operate 24/7 when used alone. Herein, we report a hydrogel membrane that can achieve both solar water purification and fog collection, thus enabling all-day freshwater collection. The hydrogel membrane with microstructured patterns inspired by the structure on the back of the Namib Desert beetle consists of poly(vinyl alcohol) (PVA), chlorine-reinforced polypyrrole (PPy-Cl), and silicon dioxide nanoparticles (SiO2NPs), which is capable of harvesting up to 25 L of fresh water per square meter per day under the outdoor conditions. The excellent freshwater collection capacity is realized based on the synergetic interaction among the hydrophilicity of PVA, the photothermal conversion capacity of PPy-Cl, and the biomimetic microstructures. Furthermore, due to the improved mechanical properties brought by SiO2NPs, the hydrogel-based evaporator reported in the current study has better water resistance as well as mechanical properties, which allows it to be used outdoors for long periods of time and facilitates its practical application.