Self-cycled photocatalytic Fenton system and rapid degradation of organic pollutants over magnetic 3D MnS nanosheet/iron–nickel foam

Abstract

Photocatalytic self-Fenton systems by coupling photocatalysis and Fenton technology overcome the limitations of conventional Fenton reactions by in situ generation and activation of H₂O₂. However, a considerable amount of iron sludge is still produced. In this study, we developed a novel self-cycled photocatalytic Fenton process for the degradation of organic pollutants via an iron–nickel foam-supported MnS nanosheet (MnS/INF). Without the external addition of both H₂O₂ and ferrous ions, the MnS/INF 3D Z-scheme heterojunction exhibited an extremely high H₂O₂ production rate of 25.4 mM h⁻¹ g⁻¹ under visible light irradiation, which is 2–119 times higher than those of the reported photocatalytic self-Fenton systems in the literature. The photogenerated electrons of MnS/INF can participate in the Fe²⁺/Fe³⁺ cycle process to promote H₂O₂ activation, significantly enhancing the catalytic performance owing to the formation of a 3D Z-scheme heterojunction. DFT calculations indicate that MnS/INF can lower the energy barrier of *OOH formation and result in an enhanced photocatalytic activity of H₂O₂ production. Magnetic MnS/INF was easily recycled, remained very stable, and mitigated the extra undesirable Fe-containing sludge and only little iron sludge (0.43 mmol L⁻¹) was produced after nine cycles of reuse. Furthermore, large (100 cm²) MnS/INF was used for an unassisted solar-driven in situ photocatalytic H₂O₂ production and rapid degradation of RhB with requirements of only water, oxygen and sunlight. In addition, MnS/INF also exhibited good performance in real wastewater containing fluoronitrobenzene from a factory (initial COD 2310 mg L⁻¹) and wastewater from a sewage treatment station (initial COD 106 mg L⁻¹). This work may provide leverage to minimize iron sludge from the Fenton reaction's source.