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Time Scales and pH Dependences of the Redox Processes Determining the Photocatalytic Efficiency of TiO_2 Nanoparticles from Periodic Illumination Experiments in the Stochastic Regime

Cornu, C. J. G. and Colussi, A. J. and Hoffmann, M. R. (2003) Time Scales and pH Dependences of the Redox Processes Determining the Photocatalytic Efficiency of TiO_2 Nanoparticles from Periodic Illumination Experiments in the Stochastic Regime. Journal of Physical Chemistry B, 107 (14). pp. 3156-3160. ISSN 1520-6106. https://resolver.caltech.edu/CaltechAUTHORS:20150623-154756868

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Abstract

The quantum yield, φ, of methyl orange photocatalytic oxidation on TiO_2 nanoparticles under periodic illumination drops from φ_(τ_L)→0 to φ_(τ_L)→∞ in two well-resolved steps at increasingly longer bright intervals, τ_L, when they are separated by sufficiently long dark periods, τ_D. The {τ_(L1) < τ_(L2)} values at which the inflections occur depend exponentially, but with opposite trends, on the solution pH. The condition τ_D ≫ τ_L ensures charge sparsity, leads to a stochastic kinetics regime in which carrier recombination is minimized, and lets carriers manifest their dissimilar redox reactivities. The more reactive intermediates in acid (basic) media are ascribed to the photogenerated holes (electrons), the crossover occurring ca. pH 8. We found that φ_(τ_L)→0 and φ_(τ_L)→∞ coincide with the φ values measured under steady illumination at (γI_a) and I_a photon absorption rates, respectively, γ = τ_L/(τ_L + τ_D) being the duty cycle. The similar φ vs τ_L behaviors observed for methyl orange and formate are traceable to the dynamics of interfacial species. The photochemically relevant intermediates persist longer than a few milliseconds under typical conditions, i.e., several orders of magnitude longer that the plethora of transient spectroscopy signals (half-lives down to <1 ps) previously associated with these species.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jp027568+DOIArticle
http://pubs.acs.org/doi/abs/10.1021/jp027568%2BPublisherArticle
ORCID:
AuthorORCID
Colussi, A. J.0000-0002-3400-4101
Hoffmann, M. R.0000-0001-6495-1946
Additional Information:© 2003 American Chemical Society. Received: November 26, 2002; In Final Form: January 10, 2003.
Issue or Number:14
Record Number:CaltechAUTHORS:20150623-154756868
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150623-154756868
Official Citation:Time Scales and pH Dependences of the Redox Processes Determining the Photocatalytic Efficiency of TiO2 Nanoparticles from Periodic Illumination Experiments in the Stochastic Regime C. J. G. Cornu, A. J. Colussi, and M. R. Hoffmann The Journal of Physical Chemistry B 2003 107 (14), 3156-3160 DOI: 10.1021/jp027568+
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58480
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:28 Jul 2015 20:47
Last Modified:03 Mar 2020 13:01

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