Fabrication, activity and mechanism studies of transition metal molybdate/molybdenum trioxide hybrids as novel CWAO catalysts

Abstract

Abstract We report for the first time the synthesis of a series of novel hybrid catalysts consisting α-MoO3 and MMoO4 (M = Cr, Mn, Fe, Co, Ni, Cu, or Zn) and their significantly enhanced catalytic activities for the degradation of cationic dyes at room temperature and atmosphere pressure. All obtained hybrid materials were thoroughly characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy-energy dispersive spectroscopy, and X-ray photoelectron spectroscopy, etc. The influence of divalent cations, calcination temperature, testing temperature, volume of dye and different kinds of cationic dyes were systematically investigated. Among all hybrid catalysts, MnMoO4/α-MoO3 and NiMoO4/α-MoO3 resulted in much better performance than all the others. We also demonstrated that such high activity can be not attained with either pure transition metal molybdates, pure α-MoO3 or the physical mixture of these two bulks. And only the hybrid catalysts prepared in this work containing both metal molybdates and α-MoO3 can deliver high catalytic activity for the CWAO of dye. The reaction kinetics and degradation mechanism were also explored. Electron spin resonance analysis suggests that the co-existence of transition metal molybdates and α-MoO3 promotes the formation of· OH radicals, which are crucial for their excellent catalytic activity. The intermediates produced during the catalytic degradation process was monitored using electrospray ionization-mass spectrometry analysis, based on which the degradation pathway was also proposed.