High-Performance Silicone Sponge Evaporators with\nLow Thermal Conductivity for Long-Term Solar Interfacial Evaporation\nand Freshwater Harvesting

Solar\ninterfacial evaporation (SIE) has emerged as a highly promising\napproach for sustainable freshwater harvesting. However, maintaining\na stable evaporation rate and achieving a high freshwater yield in\nhigh-salinity brines remain a significant challenge. In this study,\nwe present the development of silicone sponge-based evaporators with\na “free-salt” structure, designed to enhance the efficiency\nof SIE and freshwater collection. These evaporators, designated as\nPSS@Fe<sub>3</sub>O<sub>4</sub>/CNTs, were fabricated by grafting\ndurable silicone onto a silicone sponge framework, followed by the\nincorporation of Fe<sub>3</sub>O<sub>4</sub> nanoparticles and carbon\nnanotubes. The unique combination of exceptional photothermal properties\nand a controlled yolk–shell structure with low thermal conductivity\nenabled the PSS@Fe<sub>3</sub>O<sub>4</sub>/CNT evaporators to sustain\na stable evaporation rate of 1.87 kg m<sup>–2</sup> h<sup>–1</sup> in real seawater over 200 h of continuous operation under 1 sun\nillumination. Importantly, no salt accumulation was observed on the\nevaporator surfaces, even when exposed to highly concentrated brines.\nIn a closed system equipped with a condenser, these evaporators achieved\nfreshwater production rates of 14.5 and 11.8 kg m<sup>–2</sup> over 10 h from 10 and 20 wt % NaCl solutions, respectively, under\n1 sun illumination. These values correspond to normalized production\nrates of 1.45 and 1.18 kg m<sup>–2</sup> h<sup>–1</sup>, showcasing the consistent and efficient performance of the evaporators\nacross varying salinity levels. Beyond salt rejection, the PSS@Fe<sub>3</sub>O<sub>4</sub>/CNT evaporators also demonstrated the ability\nto effectively remove various heavy metal ions (e.g., Cu<sup>2+</sup> and Zn<sup>2+</sup>) and organic pollutants from contaminated water.\nThis work provides valuable insights into innovative evaporator designs\nfor efficient freshwater production from seawater and wastewater.