Effective Enhancement of the Degradation of Oxalic Acid by Catalytic Ozonation with TiO₂ by Exposure of {001} Facets and Surface Fluorination

Abstract

Heterogeneous catalytic ozonation is a promising advanced oxidation technology for water treatment. In the present work, the surface fluorination of TiO2 catalysts with a high percentage of exposed {001} facets (F-TiO2) were synthesized through a hydrothermal method using tetrabutyl titanate as the precursor and HF as the shape controlling agent. The structural properties of the catalysts were characterized by X-ray diffraction, the Brunauer–Emmett–Teller method, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The sheetlike TiO2 is pure anatase, with ∼75% of highly reactive {001} facets. The surface fluoride of the F-TiO2 nanosheets can be removed by washing with dilute NaOH solution (abbreviated here as OH-TiO2), resulting in a decrease of Ti3+ content and an increase of the specific surface area. The catalytic activity of the samples was evaluated by degradation of oxalic acid in aqueous solution in the presence of ozone. It was found that F-TiO2 facilitated the catalytic ozonation process by comparison with OH-TiO2 and pure TiO2 nanoparticles prepared in pure water. We conclude that the high surface energies of {001} facets and the increased concentration of oxygen vacancies contributed to the enhancement of the ozonation activity of fluorinated TiO2 with dominant {001} facets.