Black Titanium Dioxide/Calcium Alginate Composite Hydrogel for Efficient Solar-Driven Interfacial Evaporation

Solar-driven interface evaporation (SDIE) technology is considered an effective way to alleviate the world's water resources scarcity problem, and the development of structurally stable and high-performance photothermal materials is the key to SDIE technology. Black titanium dioxide (TiO₂) has excellent light absorption capacity and good chemical stability, rendering it a desirable candidate for SDIE technology. Herein, a black TiO₂ nanoparticle was prepared by calcining a colloidal titanium dioxide precursor, and then a black TiO₂/calcium alginate composite hydrogel (PUCA-TiO₂) was obtained by an impregnation cross-linking technique using a polyurethane sponge as a backbone. The PUCA-TiO₂ evaporator exhibited excellent evaporation performance at one solar light intensity (1 kW m^-2) with an evaporation rate of 3.331 kg m^-2 h^-1 and a photothermal conversion efficiency of 92.79%. Notably, the material was able to maintain an efficient evaporation rate of 2.876 kg m^-2 h^-1 even in a high brine concentration of 25 wt%. Real seawater desalination tests further confirmed its excellent seawater desalination capacity and long-term salt stability. The developed PUCA-TiO₂ composite hydrogel breaks through the bottleneck of traditional TiO₂ photothermal applications and has great potential in solar interface evaporation applications.