Ternary Alloy Incorporated Janus Hydrogel Photothermal Film for Solar-Driven Water Evaporation, Desalination, and Wastewater Purification

Solar-driven interfacial evaporation is considered a promising solution to water pollution and water shortages, potentially reducing heat loss and improving energy conversion efficiency. However, the current photothermal films used for solar-driven interfacial water evaporation have some issues that need to be solved, including low light-to-heat conversion efficiency ( η ), high cost, the mismatch between optical absorption and solar spectrum, excessive heat loss, and poor photothermal stability. Here, we developed a ternary alloy (Cu-Ni-W) incorporated Janus hydrogel photothermal film for solar-driven water evaporation. We first prepared copper-doped nickel tungstate, then obtained the Cu-Ni-W using the hydrogen reduction method and applied it as the photothermal conversion material for the upper layer of the Janus photothermal film (Janus-1). Cu-Ni-W had low cost, perfect solar spectrum matching (full-spectrum absorption in the wavelength range of 200-2500 nm), and excellent thermal stability (0.2% weight loss at 30-800 °C). A composite hydrogel composed of gelatin and agar was used to prepare Janus photothermal film. They were cross-linked through hydrogen bonding to form complex three-dimensional water transport channels. Janus-1 had good hydrophilicity (water contact angle = 15°) and thermal insulation. Additionally, it showed an excellent solar evaporation rate of 1.72 kg m -2 h -1 and a high η value of 107% under one-sun irradiation. Besides, Janus-1 possessed the ability of desalination, salt inhibition, and purification of wastewater containing organic dyes and heavy metal ions