Reaction kinetics of dye decomposition processes monitored inside a photocatalytic microreactor

• Published in: Physical chemistry chemical physics : PCCP 2012-01, Vol.14 (14), p.4734-4741
• Main Authors: Tsuchiya, Naomi, Kuwabara, Kenta, Hidaka, Asuna, Oda, Kazuyo, Katayama, Kenji
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Decomposition reactions; Dyes; Exact sciences and technology; Fluorescence; General and physical chemistry; Photocatalysis; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Reaction kinetics; Reaction mechanisms; Spectra; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium dioxide
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp23979e

The photocatalytic decomposition processes of several kinds of dyes were monitored in real-time, in a TiO 2 -immobilized microcapillary. Their fluorescence spectra were measured directly from the UV-irradiated area. The photocatalytic reactions proceeded two orders of magnitude faster in the microcapillary than in a bulk reaction, and intermediate species were easily observed, due to their high concentrations compared with those of the reactants. Even for molecules that were not originally fluorescent, fluorescence was detected for the reactants or intermediate species of all the molecules studied. Photocatalytic reactions are typically analyzed in terms of pseudo-first-order or LangmuirHinshelwood reaction mechanisms, but it was ascertained that all of the dyes investigated in this study decomposed via a multi-step reaction such as a simple multi-step reaction, a self-catalytic reaction, and further, a more complicated reaction, depending on the molecular structure. These reactions were simulated using models based on the reaction kinetics, and reaction mechanisms were assigned to each type of dye. The fact that intermediate species (which are difficult to observe using conventional analytical methods) were successfully detected meant that mechanisms for different dyes could be further clarified. Monitoring the photocatalytic degradation processes in real-time in a TiO 2 microcapillary.