Investigation of the aging effect of electrolyte on the morphology and photocatalytic properties of TiO.sub.2NTs synthesized using the anodization route

In this study, TiO.sub.2 nanotube (TiO.sub.2NT) arrays were successfully synthesized via two-step anodization in organic electrolyte solutions composed of ethylene glycol, 0.5 wt% NH.sub.4F, and 3.0 wt% H.sub.2O. The effect of aged electrolytes on the morphological and photocatalytic properties of the obtained TiO.sub.2NTs was investigated. Field-emission scanning electron microscopy, X-ray diffractometry, UV-Vis absorption spectrometry, and photoluminescence measurements were also conducted to evaluate the physicochemical properties of the TiO.sub.2NTs synthesized with electrolytes of various ages. The photocatalytic activity of the TiO.sub.2NTs was characterized by photocurrent measurements and phenol degradation assay. The results confirmed the strong dependence of the morphology of the NTs on the aged electrolyte. Anodization of Ti foil with aged electrolytes led to not only reductions in morphological defects but also enhancement of the order of the TiO.sub.2NTs. The longer the aging time, the thicker the NT wall and the shorter the tube length obtained. Prolonged aging of the electrolyte resulted in the formation of TiO.sub.2NTs with a nanoporous surface, which could be attributed to the deposition of Ti(OH).sub.4. The results collectively indicate that improvements in the photocatalytic property of the TiO.sub.2NT samples could be obtained when synthesis is conducted with aged electrolytes. The aging process of the electrolytes was clearly demonstrated to promote the structural integrity and photocatalytic ability of the obtained TiO.sub.2NTs.