A self-floating Janus evaporator with high efficiency and salt tolerance for sustainable solar desalination

Solar-driven interfacial evaporation has emerged as a promising and sustainable strategy for freshwater production. Nevertheless, conventional evaporators are often limited by insufficient structural robustness and significant heat dissipation. While self-floating designs mitigate these limitations through simplified architectures, their water transport efficiency, thermal management, and salt tolerance remain suboptimal. Here, we report a self-floating Janus evaporator composed of a tannic acid-Fe³⁺ (TA-Fe³⁺)-modified agar-PVA hydrogel/cellulose fabric combined with a hydrogel-infused polystyrene (PS) sphere array substrate. This bilayer architecture promotes efficient photothermal conversion while enabling continuous water supply and effective thermal confinement. By rationally tuning the hydrogel composition and the thicknesses of porous substrate layers, the evaporator with a hierarchical porous structure exhibits a solar absorptance exceeding 91.1%. Under one-sun illumination (1 kW m⁻²), the optimized device achieves an evaporation rate as high as 2.92 kg m⁻² h⁻¹. It also exhibits remarkable salt resistance, maintaining stable performance over 100 h in 10 wt% saline solution without observable salt accumulation. Outdoor testing further demonstrates robust operation, yielding a sustained evaporation rate of 1.97 kg m⁻² h⁻¹ for simulated seawater under an average solar irradiance of 0.685 kW m⁻². Additionally, the components of the evaporator can be readily recovered via a thermally assisted dissolution process without compromising their integrity. These results establish an integrated design strategy that simultaneously enhances efficiency, durability, salt tolerance, and recyclability, providing a viable route towards practical solar desalination in high-salinity and resource-constrained environments.