Mechanism insight of pollutant degradation and bromate inhibition by Fe-Cu-MCM-41 catalyzed ozonation

A flexible catalyst, Fe-Cu-MCM-41, was employed to enhance diclofenac (DCF) mineralization and inhibit bromate formation in catalytic ozonation process. Greater TOC removal was achieved in Fe-Cu-MCM-41/O₃ process (78%) than those in Fe-MCM-41/O₃ (65%), Cu-MCM-41/O₃ (73%) and sole ozonation (42%). But it was interesting that both Cu-MCM-41/O₃ and Fe-MCM-41/O₃ achieved 93% bromate inhibition efficiency, only 71% inhibition efficiency was observed in Fe-Cu-MCM-41/O₃. Influence of pH, TBA/NaHSO₃ and detection of by-products were conducted to explore the mechanism. By Pyridine adsorption-IR and XPS, a relationship was found among activity of catalysts, Lewis acid sites and electron transfer effect between Fe (II/III) and Cu (I/II). Fe-Cu-MCM-41 promoted ozone decomposition to generate OH, which accounted for enhanced DCF mineralization. The consumption of aqueous O₃ also suppressed the oxidative of Br^- and HBrO/Br^-. More HBrO/BrO^- accumulated in catalytic ozonation process and less bromate generated. Bromate formation in Fe-Cu-MCM-41/O₃ process was sensitive with pH value, the acidic condition was not favor for bromate formation. Both DCF mineralization and bromate inhibition were influenced by surface reaction. Moreover, Fe-Cu-MCM-41 showed excellent catalytic performance in suppressing the accumulation of carboxylic acid, especially for oxalic acid. Nearly no oxalic acid was detected during Fe-Cu-MCM-41/O₃ process.