High-Performance Silicone Sponge Evaporators with Low Thermal Conductivity for Long-Term Solar Interfacial Evaporation and Freshwater Harvesting

Solar interfacial evaporation (SIE) has emerged as a highly promising approach for sustainable freshwater harvesting. However, maintaining a stable evaporation rate and achieving a high freshwater yield in high-salinity brines remain a significant challenge. In this study, we present the development of silicone sponge-based evaporators with a "free-salt" structure, designed to enhance the efficiency of SIE and freshwater collection. These evaporators, designated as PSS@Fe₃O₄/CNTs, were fabricated by grafting durable silicone onto a silicone sponge framework, followed by the incorporation of Fe₃O₄ nanoparticles and carbon nanotubes. The unique combination of exceptional photothermal properties and a controlled yolk-shell structure with low thermal conductivity enabled the PSS@Fe₃O₄/CNT evaporators to sustain a stable evaporation rate of 1.87 kg m^-2 h^-1 in real seawater over 200 h of continuous operation under 1 sun illumination. Importantly, no salt accumulation was observed on the evaporator surfaces, even when exposed to highly concentrated brines. In a closed system equipped with a condenser, these evaporators achieved freshwater production rates of 14.5 and 11.8 kg m^-2 over 10 h from 10 and 20 wt % NaCl solutions, respectively, under 1 sun illumination. These values correspond to normalized production rates of 1.45 and 1.18 kg m^-2 h^-1, showcasing the consistent and efficient performance of the evaporators across varying salinity levels. Beyond salt rejection, the PSS@Fe₃O₄/CNT evaporators also demonstrated the ability to effectively remove various heavy metal ions (e.g., Cu²⁺ and Zn²⁺) and organic pollutants from contaminated water. This work provides valuable insights into innovative evaporator designs for efficient freshwater production from seawater and wastewater.