Fe3O4/multi-walled carbon nanotubes as an efficient catalyst for catalytic ozonation of p-hydroxybenzoic acid

Fe3O4/multi-walled carbon nanotubes were prepared, characterized and used as a nanocatalyst for ozonation of p-hydroxybenzoic acid. The stability and reusability of the catalyst was evaluated. Characterization techniques including X-ray diffraction, Fourier transform infrared absorption spectroscopy, scanning electron microscope, high-resolution transmission electron microscopy and physical property measurement were used to analyze the reason for the decrease in catalyst activity. The addition of t-butanol and bicarbonate were used to explore the different process between hydroxyl radicals and ozone. The experimental results showed that the catalytic ozonation could significantly increase the degradation and mineralization of p-hydroxybenzoic acid. The initial pH value was a crucial factor influencing ozone decomposition and the surface property of catalyst or organic pollutant. The degradation of p-hydroxybenzoic acid increased by 32 % in catalyzed ozonation compared to single ozonation after 5 min reaction with unadjusted pH (about 5.4). In batch experiments, the removal efficiency of p-hydroxybenzoic acid and total organic carbon decreased 36.1 and 6.8 % after six run times. Bicarbonate significantly inhibited the mineralization of p-HBA, but it had almost no influence on the catalytic degradation of p-hydroxybenzoic acid. A possible pathway for p-hydroxybenzoic acid degradation was tentatively proposed.