Salting-Out Effect-Induced Fabrication of Biomass-Based Porous Sponge: Efficient Seawater Desalination Enabled by Tea Polyphenol-Fe3+ Photothermal Conversion

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Solar-driven interface evaporation technology offers a green and sustainable solution to alleviate the global freshwater crisis. However, traditional hydrogel evaporators generally have problems such as small pore diameters, limited water transmission, complex preparation processes, and the high cost of photothermal materials. In this study, a green and low-cost soybean protein isolate (SPI)/poly(vinyl alcohol) (PVA)/tea leaf residue (SPT) biomass porous sponge solar evaporator was developed based on the salting-out effect-induced phase separation strategy and the tea polyphenol (TP)-Fe3+ complex blackening strategy. The whole preparation process of SPT has low energy consumption and high efficiency. The mechanical properties, microscopic pore structure, hydrophilicity, and photothermal behavior of the SPT sponge were measured. The results show that SPT has excellent light absorption performance, achieving an absorption rate of 92.6% in full-spectrum sunlight. DSC results showed that SPT has a low evaporation enthalpy of 1478 J/g. SPT achieves a pure water evaporation rate of 3.30 kg m–2 h–1 and an evaporation efficiency of 94.88% under 1 sun. Meanwhile, SPT also demonstrated outstanding salt resistance and stability and exhibited excellent purification performance for real seawater. This work has developed an environmentally friendly and cost-effective strategy to fabricate an efficient biomass material-based solar evaporator, which can be used for long-term sustainable seawater desalination.