REVERSIBILITY OF PHOTOELECTROCHROMISM AT THE TIO2 METHYLENE BLUE INTERFACE/

This paper describes the photoelectrochromic bleaching and recoloratio n of methylene blue in aqueous or methanolic slurry suspensions of TiO 2. Using simple modification of a W-visible diode-array spectrometer s etup, the spectral changes undergone by the dye in these solutions wer e monitored in situ during irradiation of the TiO2 particles and in th e dark. A particular focus of this study was a systematic investigatio n of factors underpinning the chemical and electrochemical (kinetic) r eversibility of the dye bleaching-recoloration sequence. Thus, choice of solution pH and hole capture agents is shown to be crucial to the s uppression of parasitic chemical and photochemical reactions involving the dye. On the other hand, dye adsorption on the TiO2 surface, the s olvent medium itself, and its O-2 content are all important factors in dictating the kinetic reversibility of the photoelectrochromic proces s. Finally, the practical implications of the findings are presented.