Abstract
UV illumination of aqueous TiO2 suspensions yields hydroxyl radicals which can be trapped by methanol yielding formaldehyde (HCHO). The photonic efficiency of HCHO formation (345 ± 35 nm cw illumination) in aqueous, oxygenated TiO2 suspensions (2.4 nm diameter TiO2 particles, Degussa P25 and Sachtleben Hombikat UV 100) containing methanol at pH ca. 1-12 has been determined as well as the respective quantum yield in case of 2.4 nm TiO2. Differences in the activity of the three photocatalysts have been found and are discussed. The photonic efficiency in the presence of P25 and Hombikat UV 100 depends on the catalyst loading (g1-1) and the pH. Below 2.5 g1-1 the photonic efficiency is higher for P25 than for Hombikat UV 100 and vice versa at above 2.5 g1-1. Optimum pH values for P25 and Hombikat UV 100 resulting in maximum photonic efficiencies (ca. 0.13 for P25 and 0.07 for Hombikat UV 100) are 7.7 and 10.4, respectively. Other than with P25 and Hombikat UV 100, which scatter light strongly, the quantum yield of HCHO formation in the colloidal 2.4 nm TiO2 suspension varies but little with the pH and virtually does not change with the photocatalyst loading (0.1-1.0 g/1). Employing these colloidal particles as photocatalysts the quantum yield varies as the inverse square root of light intensity. It increases from 0.02 to 0.08 when the absorbed photon flux decreases from 8.1 x 10-7 to 4.9 x 10-8 Einstein 1-1 s-1. A simple model is presented to explain this observation.
Original language | English |
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Pages (from-to) | 169-176 |
Number of pages | 8 |
Journal | Journal of Photochemistry and Photobiology A: Chemistry |
Volume | 148 |
Issue number | 1-3 |
DOIs | |
State | Published - 31 May 2002 |
Keywords
- Formaldehyde
- Methanol
- OH radical
- Photonic efficiency
- Quantum yield
- TiO photocatalysis