New insights into the catalyzed ozonation mechanism of a hydroxyl riched goethite: Contributions of H2O2 and surface Fe2+

Fe-based catalysts have been widely used to catalyze ozonation during water treatment. Among these catalysts, goethite (alpha-FeOOH) is of concern for the properties of low cost, easy availability, and excellent performance. In general, the surface hydroxyl groups of goethite are believed to be crucial catalytic sites. However, the contributions of Fe2+ on the goethite surface and H2O2 produced from pollutant degradation have rarely been mentioned. In this study, a goethite with rich surface hydroxyl was fabricated to remove aromatics by O3 catalysis. Probe and quenching experiments together proved that although the center dot OH was produced less than the O2 center dot- and 1O2 in the catalytic system, it contributed about 95 % of the target removal. EDTA complexation and heating experiments suggested that when the surface Fe2+ of the catalyst was destroyed, although the Fe-site hydroxyl or the vacancy hydroxyl of the catalyst was retained, its catalytic activity was reduced greatly. The outcomes of degradation kinetics of acetic acid further confirmed that, in the catalytic process, most of center dot OH originated from the reaction of Fe2+ reducing HO2 center dot and Fe2+ ozonation, while the surface hydroxyl contributed less than 44.7 %. Moreover, as the main source of HO2 center dot, the role of H2O2 produced from aromatics degradation cannot be ignored. The detection of H2O2 precursors in the degradation byproducts further confirmed this opinion. Finally, an efficient circular route for center dot OH production was proposed. This may be beneficial for the development of efficient Fe-based catalysts.