Organizations & People
Pure Appl. Chem.,
Vol. 71, No. 2, pp.321-335, 1999
COMMISSION ON PHOTOCHEMISTRY
Terminology, relative photonic efficiencies
and quantum yields in heterogeneous photocatalysis. Part II: Experimental
determination of quantum yields
Angela Salinaro, Alexei V. Emeline,
Jincai Zhao, Hisao Hidaka, Vladimir K. Ryabchuk, and Nick
Abstract: In the preceding article [Serpone
and Salinaro, Pure Appl. Chem., 71(2), 303-320 (1999)] we
examined two principal features of heterogeneous photocatalysis that
demanded scrutiny: (i) description of photocatalysis and (ii)
description of process efficiencies. For the latter we proposed a protocol
relative photonic efficiency which could subsequently be converted
to quantum yields. A difficulty in expressing a quantum yield in heterogeneous
photochemistry is the very nature of the system, either solid/liquid
or solid/gas, which places severe restrictions on measurement of the
photon flow absorbed by the light harvesting component, herein the photocatalyst
TiO2, owing to non-negligible scattering by the particulates. It was
imperative therefore to examine the extent of this problem. Extinction
and absorption spectra of TiO2 dispersions were determined
at low titania loadings by normal absorption spectroscopy and by an
integrated sphere method, respectively, to assess the extent of light
scattering. The method is compared to the one reported by Grela et
al. [J. Phys. Chem., 100, 16940 (1996)] who used a polynomial
extrapolation of the light scattered in the visible region into the
UV region where TiO2 absorbs significantly. This extrapolation
underestimates the scattering component present in the extinction spectra,
and will no doubt affect the accuracy of the quantum yield data. Further,
we report additional details in assessing limiting photonic efficiencies
and quantum yields in heterogeneous photocatalysis.
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