The performance and mechanism of a MIL-53(Fe)/ZnIn2S4 heterophase photo-Fenton system in degrading p-nitrophenol

Abstract

Among organic pollutants, p-nitrophenol (PNP) is one of the most widely used compounds, extensively utilized in the synthesis of pesticides, herbicides, pharmaceuticals, dyes, and pains. PNP possesses strong toxicity, with carcinogenic and bioaccumulative effects, leading to its classification as a priority pollutant in many countries. Therefore, MIL-53(Fe)/ZnIn₂S₄ composites were synthesized using a hydrothermal method for the degradation of PNP. The experimental results showed that MIL-53(Fe)/ZnIn₂S₄-20has the highest degradation rate with a rate constant of 0.24408 min⁻¹, which was 20.86 and 34.47 times those of MIL-53(Fe) (0.0117 min⁻¹) and ZnIn₂S₄ (0.00708 min⁻¹). Degradation efficiency reached 95.09% within 12 min. Photoelectrochemical characterization indicated that upon composite formation, MIL-53(Fe)/ZnIn₂S₄ was able to utilize a broader spectrum of visible light and exhibited enhanced electron–hole separation efficiency. This phenomenon facilitated the rapid Fe²⁺/Fe³⁺ cycle, efficiently utilizing H₂O₂ to produce a larger amount of ˙OH for the degradation process. Scavenger experiments and electron paramagnetic resonance tests confirmed that ˙OH, h⁺, and ˙O₂⁻ were the primary reactive species involved in the degradation process. Furthermore, based on the band structure of MIL-53(Fe) and ZnIn₂S₄, and the generation process of the reaction substances, a plausible heterogeneous photo-Fenton degradation mechanism was elucidated. The MIL-53(Fe)/ZnIn₂S₄/vis/H₂O₂ system exhibits broad application prospects in the treatment of organic wastewater.