The photocatalytic degradation of rhodamine B (RhB) over NaBiO3 under visible light irradiation was investigated in this study. RhB (20 mg/L) was almost completely decolorized in 30 min in given conditions. It was found that catalyst heating temperature significantly influenced the photocatalytic activity of the catalyst in which crystal water may played an important role, and the original sample exhibited higher activity than the heated samples did. To scrutinize the mechanistic details of the dye photodegradation, several critical analytical methods including UV-vis spectroscopy, HPLC, LC/MS/MS, and GC/MS were utilized to monitor the temporal course of the reaction. All N-deethylation intermediates and several small molecular products were separated and identified. The yield distinctness between two isomer intermediates (DR and EER) was considered to be correlated with the changes in the electron density of the dye molecule. Then two possible competitive photodegradation pathways of RhB over NaBiO3 were proposed: Chromophore cleavage and N-deethylation. Yet, cleavage of dye chromophore structure predominated over the N-deethylation.

Titanium oxide nanotubes were successfully grown from a titanium plate by direct anodic oxidation with 0.2 wt % hydrofluoric acid being the supporting electrolyte. These nanotubes are of uniform size and are well-aligned into high-density arrays. They look like honeywell with the structure similar to that of porous alumina obtained by the same technique. TiO2 anatase phase was identified by X-ray diffraction. Significant blue-shift in the spectrum of UV- vis absorption was observed. The mechanism of the novel, simple, and direct growth of the nanotubes was postulated. To investigate their potentials in environmental applications, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photoelectrocatalytic (PEC) processes, comparing with electrochemical process (EP) and photocatalytic (PC). A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using TiO2 nanotubes electrode was 86.5% higher than that using TiO2 film electrode. In degrading PCP, 70% of TOC was removed using the TiO2 nanotubes electrode against 50% removed using TiO2 film electrode formed by sol-gel method in 4 h under similar conditions.

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