Comparison of the Photocatalytic and Photoelectrocatalytic Decolorization of Methyl Orange on Sputtered TiO2 Thin Films

Abstract

Correlations between the photocatalytic and photoelectrocatalytic decolorization of methyl orange, using TiO2 thin films sputtered under various conditions, were made. Three types of systems, namely: two photocatalytic systems, one with and one without a Pt counter electrode, and a third with a Pt counter electrode having an applied potential, were used to evaluate photocatalytic activity.The crystal structure, morphology, bandgap energy, flatband potential, and the resistances of the TiO2 films were characterized by X-ray diffraction, scanning electron microscopy, UV/vis spectroscopy, a photocurrent method, and electrochemical impedance spectroscopy, respectively. The results showed that the decolorization of methyl orange only occurred on the anode of the TiO2/Ti electrode and that the decolorization rate increased 67% when the photocatalyst was coupled to a Pt electrode (0 V applied potential), and 275% when connected with the Pt cathode and 1 V vs. Ag/AgCl applied potential. The benefits of high crystallinity, a high quantity of the anatase, and a more negative flatband potential were found in the photocatalytic reaction, whereas the resistance of the film was the main factor affecting the photoelectrocatalytic activity.