Parallel additions of molybdenum and copper particles for boosted peroxydisulfate activation process: Performance, mechanism, and application

Molybdenum (Mo) has been certified as a benign cocatalyst in homogenous Fenton/Fenton-like reactions. To improve zero-valent copper (Cu) induced peroxydisulfate (PDS) reaction, Mo and Cu were parallelly added to enhance the activation of (PDS for metronidazole (MTZ) degradation in this work. The efficient MTZ elimination (96.01 %) was reached after 20 min by Cu/Mo/PDS process in terms of 0.10 g⋅L−1 PDS, 0.08 g⋅L−1 Cu, 0.30 g⋅L−1 Mo, and initial pH 6.5. This ternary system presented a broad pH adaptive capacity (pH 3.5–9.5) and well cycling effect (above 80 % after three cycles). The addition of Mo enhanced Cu(II)/Cu(I) circulation and PDS decomposition, and electrochemical test testified that could be attributed to the electron migration between Cu and Mo. The cycle of Cu(II)/Cu(I) triggered by the conversion of Mo0 and Mo4+ was further proved by X-ray photoelectron spectroscopy result. Singlet oxygen and sulfate radicals were identified as the dominant reactive substances by scavenger test, probe measurement, and electron paramagnetic resonance spectroscopy. By density functional theory calculation and mass spectrometry analyses, two possible decomposed pathways of MTZ were raised. At last, Mo and Cu powders were immobilized together by a simple physical mixing with methacrylate, which also showed the integrated catalytic property and good reusability. This work could advance the development of Cu-catalyzed Fenton-like reaction with inorganic co-catalysis in water purification.