Integrating photo-Fenton-like Fe3O4/CdS-O modules into sponge-based gel solar evaporator for synergistic water regeneration and pollutant degradation

Abstract

Addressing the dual challenges of freshwater scarcity and pollution elimination requires innovative technologies that rationally integrate multiple functions. This study developed a representative dual-functional solar evaporator by coupling photothermal Fe₃O₄ nanospheres with oxygen-doped CdS (CdS-O) within a sponge-based hydrogel matrix, achieving concurrent high-efficiency solar-driven water regeneration and pollutant degradation. The design leverages the unique roles of two unique components, wherein, Fe₃O₄ endows the evaporator with broadband solar absorption (300–800 nm) and an superior photothermal conversion efficiency of 80 %, while oxygen doping CdS-O narrows its bandgap (from 2.31 eV to 2.29 eV), enhancing visible-light harvesting and charge separation. Crucially, the synergistic interplay between Fe₃O₄ and CdS-O establishes a self-sustained photo-Fenton-like mechanism. CdS-O generates H₂O₂ via photogenerated electron reduction of O₂, and Fe₃O₄ acts as an electron acceptor to accelerate Fe^3 +/Fe²⁺ cycling, Fe²⁺ ions react with H₂O₂ via a Fenton-like process to produce ·OH radicals for pollutant mineralization. Simultaneously, the hydrogel-sponge architecture ensures rapid water transport and localized heat confinement, enabling an evaporation rate of 1.55 kg·m⁻²·h⁻¹ under 1 sun irradiation. The system demonstrates remarkable dual-functionality: 86.9 % tetracycline degradation in lake water within 240 minutes and 89 % photocatalytic activity retention after six cycles. This work overcomes the limitations of conventional single-function systems by unifying photothermal evaporation and photocatalytic oxidation into a scalable platform, offering a sustainable solution for simultaneous water production and purification through material synergy and energy-efficient design.