In situ photoacoustic spectroscopic analysis on photocatalytic decolorization of methylene blue over titanium(IV) oxide particles

Photoabsorption of an aqueous suspension containing methylene blue (MB) dye and titanium(IV) oxide (TiO2) powder was evaluated using photoacoustic spectroscopy (PAS). Simultaneous detection of photoabsorption of MB both in solution and adsorbed on TiO2 was performed using a corrosion-resistant cell with microphone detection. In addition, time-course PAS measurements were employed to observe the photocatalytic decolorization of MB in the aqueous suspension. The time-course data of the MB decolorization process attributed to the oxidation or reduction of MB was obtained at 20 s intervals. Moreover, the MB decolorization rate as a function of the initial pH of the suspension was different from that obtained by conventional evaluation methods. This discrepancy most likely stems from the advantages of PAS analysis, which enables the detection of all MB dye included in the aqueous suspension.