Da. Friesen et al., Factors influencing relative efficiency in photo-oxidations of organic molecules by Cs3PW12O40 and TiO2 colloidal photocatalysts, J PHOTOCH A, 133(3), 2000, pp. 213-220
Citations number
45
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY
This paper examines the factors influencing the efficiency of photo-oxidati
ve degradation of N-methylpyrrolidinone (NMP) and atrazine by TiO2 and Cs3P
W12O40 colloids, especially the roles of mechanism and substrate-photocatal
yst interaction at the colloid surface. For both photocatalysts, major prim
ary intermediates generated by the photo-oxidation of atrazine are the same
. However, cyanuric acid appears to be oxidized by the UV irradiation of PW
12O403- in deaerated solution as evidenced by the formation of the heteropo
ly blue PW12O404-, suggesting that tin contrast to TiO2) photo-oxidation is
not solely due to hydroxyl radicals. Picosecond spectroscopy in water and
simple alcohols indicates the importance of direct hydrogen abstraction by
the excited tungstate. Quantum yields for the photo-oxidation of NMP by TiO
2 fit a Langmuir-Hinshelwood model, with a limiting quantum yield at high s
urface coverage of 0.029+/-0.005 and an adsorption/desorption coefficient K
of 2900+/-600 M-1. For Cs3PW12O40 under the same conditions, the quantum y
ield is 0.004-0.009 over the concentration range 10(-5)-10(-2) M. In the ca
se of atrazine, an analogous treatment for (Cs3PW12O40 yields K=1.4(+/-0.1)
x 10(4) M-1 while the value for TiO2 is at least an order of magnitude les
s. The quantum yields indicate the importance of heterogeneity of the photo
catalyst surface for Cs3PW12O40. where the concentration dependence of the
quantum yields can be explained by substrate adsorption at a small number o
f reaction sites, analogous to preassociation of dissolved polyoxotungstate
s and organic molecules. (C) 2000 Elsevier Science S.A. All rights reserved
.