Photoreduction of methyl orange sensitized by colloidal titanium dioxide
- 1 January 1984
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 80 (6) , 1631-1643
- https://doi.org/10.1039/f19848001631
Abstract
Colloidal TiO2 can sensitize the photoreduction of Methyl Orange to a hydrazine derivative. In steady-state experiments the maximum rate occurs at pH 4.7 in the absence of O2, but shifts to pH 3.0 when O2 is present. Similar behaviour is observed with Methyl Red despite the difference in pKa values for the two dyes. This suggests that the maximum rate results from changes in the surface composition of TiO2. Flash-photolysis experiments show that electron transfer from TiO2 to Methyl Orange depends on the concentration of protonated dye (DH) and the potential of an electron in the conduction band (eCB) of TiO2, so the rate of electron transfer = 8.3 × 107[DH][eCB]/[H+]0.38(mol dm–3)–0.62 s–1. Electron transfer to O2 was also measured indirectly in this work and showed a similar logarithmic dependence on pH, rate = 5.5 × 103[O2][eCB]/[H+]0.42(mol dm–3)–0.58 s–1. These results can be described by a Taffel relationship when the overvoltage is controlled by the pH of the solution.Keywords
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