Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis
Initial quantum yields φ for the formation of DMPO-OH adducts in clear, aerated, unbuffered TiO2 sols irradiated at 295 nm were determined by kinetic electron paramagnetic resonance spectrometry as function of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap concentration, photon irradiance Io,...
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todo:paper_00223654_v100_n42_p16940_Grela2023-10-03T14:32:05Z Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis Grela, M.A. Coronel, M.E.J. Colussi, A.J. Initial quantum yields φ for the formation of DMPO-OH adducts in clear, aerated, unbuffered TiO2 sols irradiated at 295 nm were determined by kinetic electron paramagnetic resonance spectrometry as function of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap concentration, photon irradiance Io, and added dichlorobenzene DCB, at 298 K. φ steadily increases with [DMPO] in the range 0.3 mM to 0.3 M, extrapolating to φ[DMPO]→∞ = 0.54 ± 0.10, in contrast with the constant yields obtained for the homogeneous generation of OH radicals in the photodissociation of H2O2 at 254 nm under similar conditions. In TiO2 sols at [DMPO] = 0.6 mM, φ (≈0.002) remains constant over a 20-fold variation of Io, but decreases upon addition of comparable DCB concentrations. These observations prove that (1) DMPO reacts with photogenerated holes and/or OH radicals on the surface of TiO2 particles rather than in the solution bulk, (2) it is possible to approach quantitative carrier trapping, (3) DCB is as reactive as DMPO toward some of the photogenerated carriers and (4) the recombination of a single carrier pair - the usual event in small particles at moderate photon fluxes - is a pseudo-first-order process. Photocatalysis in semiconductor sols is a stochastic process not amenable to conventional kinetic analysis based on rate expressions involving continuous concentration variables. Quantum yields are largely controlled by the anodic (h + D → D+), rather than by the slower (e + O2 → O2•-) cathodic charge transfer reaction. © 1996 American Chemical Society. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00223654_v100_n42_p16940_Grela |
| institution |
Universidad de Buenos Aires |
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I-28 |
| repository_str |
R-134 |
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| description |
Initial quantum yields φ for the formation of DMPO-OH adducts in clear, aerated, unbuffered TiO2 sols irradiated at 295 nm were determined by kinetic electron paramagnetic resonance spectrometry as function of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap concentration, photon irradiance Io, and added dichlorobenzene DCB, at 298 K. φ steadily increases with [DMPO] in the range 0.3 mM to 0.3 M, extrapolating to φ[DMPO]→∞ = 0.54 ± 0.10, in contrast with the constant yields obtained for the homogeneous generation of OH radicals in the photodissociation of H2O2 at 254 nm under similar conditions. In TiO2 sols at [DMPO] = 0.6 mM, φ (≈0.002) remains constant over a 20-fold variation of Io, but decreases upon addition of comparable DCB concentrations. These observations prove that (1) DMPO reacts with photogenerated holes and/or OH radicals on the surface of TiO2 particles rather than in the solution bulk, (2) it is possible to approach quantitative carrier trapping, (3) DCB is as reactive as DMPO toward some of the photogenerated carriers and (4) the recombination of a single carrier pair - the usual event in small particles at moderate photon fluxes - is a pseudo-first-order process. Photocatalysis in semiconductor sols is a stochastic process not amenable to conventional kinetic analysis based on rate expressions involving continuous concentration variables. Quantum yields are largely controlled by the anodic (h + D → D+), rather than by the slower (e + O2 → O2•-) cathodic charge transfer reaction. © 1996 American Chemical Society. |
| format |
JOUR |
| author |
Grela, M.A. Coronel, M.E.J. Colussi, A.J. |
| spellingShingle |
Grela, M.A. Coronel, M.E.J. Colussi, A.J. Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| author_facet |
Grela, M.A. Coronel, M.E.J. Colussi, A.J. |
| author_sort |
Grela, M.A. |
| title |
Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| title_short |
Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| title_full |
Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| title_fullStr |
Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| title_full_unstemmed |
Quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. Implications for the mechanism of photocatalysis |
| title_sort |
quantitative spin-trapping studies of weakly illuminated titanium dioxide sols. implications for the mechanism of photocatalysis |
| url |
http://hdl.handle.net/20.500.12110/paper_00223654_v100_n42_p16940_Grela |
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