Photothermal coupling of low-grade waste heat to achieve high efficiency fresh water production via sponge-based evaporator

Solar interfacial evaporation (SIE) can provide solar energy for the production of clean freshwater without increasing energy consumption and carbon emissions. However, its low theoretical evaporation efficiency and the complexity preparation process of 3D solar interfacial evaporators hinder the efficient freshwater production and the large-scale application, which cannot meet practical living and industrial requirements. Inspired by the Earth's core-shell structure, we have designed a simple, easy-to-prepare, and scalable all-weather three-dimensional super-hydrophilic polydopamine modified polyvinyl alcohol sponge (PDA/PVA sponge) interfacial water evaporation system driven by coupled photothermal and low-grade waste heat (LGWH). Through adjusting the surface hydrophilicity of the polyvinyl alcohol sponge by covering polydopamine in-situ, the water evaporation enthalpy is reduced from 2130 to 1697 J g⁻¹. A copper tube is embedded into the PDA/PVA sponge to introduce waste heat of 90 °C, achieving water evaporation production rate exceeding 8.73 kg m⁻² h⁻¹ under 1 kW m⁻² h⁻¹ irradiation and demonstrating superior durability in brine. And it exhibits strong salt resistance attribute to its excellent water absorption, with almost no decline in evaporation rate in high-concentration brine of 20 wt%. Therefore, this system provides a promising and easily implementable solution for clean water production and salt resistance without imposing additional energy burdens on society.