Design of morphology and light-absorbing tunable FexOy@SiO₂@C nanoparticles for solar-driven water evaporation and purification.

Solar desalination driven by interfacial heating is regarded as a promising technique to mitigate the freshwater shortage crisis. Significant efforts have been dedicated to developing innovative photothermal materials and optimizing thermal management to enhance system evaporation rates. Carbon-based photothermal materials typically exhibit superior broadband light absorption due to their unique energy band structures. However, the fabrication of solvent-processable carbon materials demonstrating both high light absorption and broadband spectral coverage remains a significant challenge. Microstructural engineering of these materials presents a promising approach for enhancing their optical absorption characteristics and resultant photothermal conversion efficiency. In this study, a carbon shell with adjustable light absorption capacity was fabricated on the outer layer of Fe x O y @silicon cores. Adjustable light absorption is achieved through a critical fabrication process comprising templated co-condensation of silica and resorcinol-formaldehyde resin and subsequent carbonization. The rough and nanoporous carbon layers introduce randomness that disrupts spherical symmetry and eliminates light scattering-induced reflection peaks, thus enhancing solar energy absorption and utilization. After establishing the nanoparticle preparation process with optimal light absorption capability, nanoparticles are coated onto the surface of wood sponge to fabricate anti-pollution solar evaporators. These solar evaporators combine excellent light absorption with salt resistance, yielding a solar evaporation rate of 1.32 kg m −2  h −1 and an outstanding photothermal conversion efficiency of 91.8 % under 1 sun irradiation. The evaporator demonstrated exceptional practical applicability by effectively purifying real-world water matrices, including seawater, domestic sewage, and industrial wastewater. It achieved high ion removal rates (>97 % for major seawater ions), efficient heavy metal rejection (e.g., 99.09 % for Cu 2+ , 99.79 % for Ag + ), and significant reduction in organic pollutants and total dissolved solids, with the purified water meeting stringent WHO and EPA standards for drinking and discharge. Owing to its exceptional salt resistance and self-cleaning properties, the sponge@coating interfacial evaporator enabled continuous desalination operation with minimal fouling. Ultimately, a multifunctional device for sustainable freshwater production (encompassing desalination, purification, and harvesting) was developed and demonstrated in an operational solar interfacial evaporation platform.