Ag/CoFe ₂ O ₄ @Biochar for Interfacial Solar Steam Generation and Heavy Metal Removal

Abstract The deterioration of marine ecosystems and the growing scarcity of clean water have become critical global challenges, which can be alleviated through interfacial solar steam generation (ISSG) to produce clean water vapor by harnessing renewable solar energy. Herein, a bifunctional, self‐floating water purification system is developed based on wood‐derived biochar (WB), functionalized with plasmonic Ag and magnetic CoFe ₂ O ₄ nanoparticles to yield Ag/CoFe ₂ O ₄ @WB composite capable of simultaneous solar‐driven evaporation and heavy metal removal. Under 1‐sun illumination, the system achieves a high evaporation rate of 1.70 kg m ⁻² h ⁻¹ and energy conversion efficiency of up to 97.2%, along with outstanding sorption toward Cr(VI) with a capacity of 89.85 mg g ⁻¹ and toward Cd(II) with a capacity of 100.48 mg g ⁻¹ . The Ag/CoFe ₂ O ₄ @WB composite is capable of producing potable freshwater from non‐potable wastewater sources, with maintained high evaporation performance under harsh conditions, such as organic and heavy‐metal wastewater and strongly acidic/alkaline solutions. The outstanding anti‐salt deposition and self‐cleaning capabilities of Ag/CoFe ₂ O ₄ @WB also endow it with superior desalination for both synthetic seawater with varying salinities and real seawater. All collected distillates consistently maintain high quality. This work demonstrates the potential of Ag/CoFe ₂ O ₄ @WB composite for sustainable water purification.