Fluoride-free Anodization of Titanium and the Photocatalytic Behaviour the Produced TiO2 Nanostructures

Current methods for anodizing titania to produce immobilized titanium dioxide (TiO2) photocatalyst require the use of hazardous fluoride electrolytes. A fluoride-free electrolyte anodization method was developed. The electrolytes tested in this study were both bromide- and chloride-based and contained ethylene glycol as an additive. Under optimised anodization times and temperature conditions the alternative electrolytes led to growth of stable immobilized TiO2 layers. Crystal phases and topography of the produced TiO2 layers were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoelectron spectroscopy (XPS). Photocatalytic experiments showed that differences in the crystal phases had a strong effect on the degradation of the model aquatic contaminants carbamazepine and phenol. Nitrogen doping using urea made the photocatalyst more efficient by red shifting light absorption from UV into the visible region. The photocatalytic ability of fluoride-free anodized immobilized TiO2 photocatalysts has previously not been investigated. Using electrolytes without fluorine can be a more sustainable and a safer way to produce immobilized TiO2.