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Quantum Yields of the Photocatalytic Oxidation of Formate in Aqueous TiO_2 Suspensions under Continuous and Periodic Illumination

Cornu, Catherine J. G. and Colussi, A. J. and Hoffmann, Michael R. (2001) Quantum Yields of the Photocatalytic Oxidation of Formate in Aqueous TiO_2 Suspensions under Continuous and Periodic Illumination. Journal of Physical Chemistry B, 105 (7). pp. 1351-1354. ISSN 1520-6106. doi:10.1021/jp003204a.

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Quantum yields φF for the oxidation of formate in periodically illuminated TiO_2 suspensions are always smaller than, but approach, at sufficiently high intermittence, the φ_F's measured under continuous exposure at equivalent average photon absorption rates 〈I_a〉. We find that φ_(F,cont) = (0.031 ± 0.003)×I_a^(-0.39±0.03) in the range 0.089 ≤ I_a/μeinstein L^(-1) s^(-1) ≤ 2.02. Under periodic illumination, φ_F begins to rise from its minimum value:  φ_(F,long τ) = φ_(F,cont)(I_(a,max)) = 0.021, for light periods τ_L ≤ 1 s, regardless of the duty cycle γ. Thereafter, φ_F climbs to its upper limit:  φ_(F,short τ) = φ_(F,cont) (〈I_a〉 = γI_(a,max)), after a single inflection at τ_L ∼ 200 ms for γ = 0.35, but only after a second inflection at τ_L ∼ 10 ms for γ = 0.05. Thus, the photocatalytic oxidation of formate in ∼10 nm TiO_2 nanoparticle suspensions under periodic illumination behaves kinetically as a homogeneous photochemical system; i.e., φ_F's are not limited by mass diffusion, or by adsorption/desorption, but by carrier recombination. The latter has a characteristic time of about 0.1 s under present conditions. Sparse carriers, such as those present in γ = 0.05 experiments at short τ_L's, are deactivated within ∼6 ms. Therefore, photocatalytic quantum yields on nanoparticle surfaces are actually insensitive to events in the sub-milliseconds domain.

Item Type:Article
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Colussi, A. J.0000-0002-3400-4101
Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 2001 American Chemical Society. Received: September 11, 2000; In Final Form: November 16, 2000. We are grateful to the National Science Foundation for its generous support of our research (NSF grant BES-9619885).
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Issue or Number:7
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Official Citation:Quantum Yields of the Photocatalytic Oxidation of Formate in Aqueous TiO2 Suspensions under Continuous and Periodic Illumination Catherine J. G. Cornu, A. J. Colussi, and Michael R. Hoffmann The Journal of Physical Chemistry B 2001 105 (7), 1351-1354 DOI: 10.1021/jp003204a
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58486
Deposited By: George Porter
Deposited On:28 Jul 2015 20:14
Last Modified:10 Nov 2021 22:05

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