Acetic acid mediated fabrication of highly exposed Fe(III)/Fe(II) sites in Fe2O3/MA for enhanced peroxymonosulfate activation

The design and synthesis of efficient heterogeneous catalysts with the accessible and mixed-valence metal centers for the activation of peroxymonosulfate (PMS) is an important research topic in water pollution control. In this work, the highly efficient catalysts Fe2O3/MA have been successfully synthesized with acetate acid as an important regulating agent. Methylene blue (MB) has been applied as the organic pollution for catalysis experiments and Fe2O3/MA-1.5 can achieve 98% catalytic degradation of MB at a concentration of 10 mg/L in 100 min, showing much higher catalytic efficiency than those of single MA (acetate modified MIL-53(Fe)) (60%) and Fe2O3 (57%). Electron paramagnetic resonance (EPR) spectroscopy and radical scavenging experiments have shown that hydroxyl radical (•OH), sulfate radical (•SO4ˉ), and singlet oxygen (1O2) all participate and contribute to the degradation process. The efficient catalytic mechanisms have been carefully studied. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and pyridine Fourier transformed infrared (py-FT-IR) have successfully proved the construction of highly exposed coordinatively unsaturated sites and the coexistence of Fe(III)/Fe(II) double catalytic centers in Fe2O3/MA-1.5, which function together with the high dispersion of Fe2O3 on MA to realize the final high activation activity for PMS. Further research shows that the initial coordination of acetic acid with Fe sites and the departure of acetic acid after vacuum treatment help construct highly exposed Fe(III)/Fe(II) double catalytic sites in Fe2O3/MA-1.5. Eventually, the intermediates produced in the reaction were analyzed by gas chromatography mass spectrometry (GC-MS), and the degradation pathway has been tentatively proposed. This study has proposed a new route to build active sites in catalysis, which shows high application potential for the effective degradation of organic pollutants in water.