Enhanced mineralization of dimethyl phthalate by heterogeneous ozonation over nanostructured Cu-Fe-O surfaces: Synergistic effect and radical chain reactions

Cu-Fe-O nanoparticles (CFO NPs), synthesized with zero-valent iron (ZVI) and Cu(NO3)(2) as the metal precursors, were used to enhance ozonation to degrade dimethyl phthalate (DMP). Great DMP degradation and mineralization rates were achieved in a wide range of the initial pH values (3-9); the amount of 'OH in catalytic ozonation was much higher than that of O-3 alone at the initial pH of 5.70. The generation of hydroxyl radicals ((OH)-O-center dot), methyl radicals ((CH3)-C-center dot) and superoxide radicals (O-3(center dot-)) were identified and (OH)-O-center dot mainly contributed to DMP removal. The potential of Fe(III)/ Fe(II) and Cu(II)/ Cu(I) cycles have largely been overlooked, which was found to be the key for producing more (OH)-O-center dot in CFO/O-3 system. The underlying mechanisms were probably initiated by a chain reaction: initiated O-3 reaction with Cu(I)/ Fe(II)-OH to form (OH)-O-center dot and O-2(center dot-), accelerated reaction between Cu(II)/ Fe(III) and the in situ generated O-2(center dot-) with a relatively high reaction constant, redox reaction between Cu(I) and Fe(III), (OH)-O-center dot oxidizing reaction with DMP to produce (CH3)-C-center dot. In addition, different degradation pathways of DMP were proposed based on the intermediates in the presence of (CH3)-C-center dot. This study sheds new light on the specific radical chain reaction mechanisms of catalytic ozonation.