Biomass-Based Ferric Tannate Hydrogel with a Photothermal Conversion Function for Solar Water Evaporation

Solar water evaporation is an effective solution for water desalination without the energy use of secondary energy or fossil fuels. A ferric tannate (TA-Fe3+)/sodium alginate (SA-Fe3+)/polyacrylamide (TFSFP) hydrogel was synthesized and constructed as a solar water evaporator (SWE). Tannic acid (TA) and Fe3+ was chelated in situ through a convenient method combined with the cross-linking of SA. Along with an ion cross-linked SA-Fe3+ network, a porous hydrogel with a hydrophilic water transportation network maintained continuous water supply to an evaporation interface. Additionally, the water molecules in the evaporation interface could be activated effectively by the hydrophilic network and TA, which is of benefit to reduce water evaporation enthalpy. A 0.8 TFSFP hydrogel had reduced evaporation enthalpy and broad light absorption with an evaporation rate of 1.53 kg·m–1·h–1 under 1 sun and a photothermal conversion efficiency of 83.34%. With salt resistance and solar light intensity adaption, a 0.8 TFSFP hydrogel SWE could keep evaporating in five cycles and has excellent water desalination ability, which displays potential application in freshwater acquisition.