EPR study of the radicals formed upon UV irradiation of ceria-based photocatalysts

Spanish National Research Council, Madrid, Madrid, Spain
Journal of Photochemistry and Photobiology A Chemistry (Impact Factor: 2.5). 07/2002; 150(1):213-221. DOI: 10.1016/S1010-6030(02)00092-8


EPR measurements reveal remarkable differences on the type of radicals produced after UV illumination of TiO2, CeO2 and 0.8% CeO2/TiO2 photocatalysts. Photoactivation of the TiO2 sample in vacuum results in the formation of Ti4+–O− species and a small amount of Ti3+ centers. In the presence of adsorbed oxygen, irradiation of this material also generates Ti4+–O3− radicals. In the case of the CeO2/TiO2 catalyst, the ceria component is present in a highly dispersed state, as indicated by XRD and UV–Vis diffuse reflectance spectra (DRS) results. Accordingly, the only type of Ce4+–O2− adducts generated on the CeO2/TiO2 sample are indicative of the presence of two-dimensional patches of ceria on the anatase surface. On the other hand, photoactivation of the CeO2/TiO2 sample in the presence of oxygen also leads to the formation of some Ti4+–O− and Ti3+ centers. In the case of the CeO2 sample, superoxide radicals are observed upon irradiation in vacuum and subsequent oxygen adsorption. Further irradiation of this material in the presence of oxygen increases the amount of Ce4+–O2− radicals and simultaneously generates new species, which are tentatively assigned to Ce4+–O2H radicals. Photocatalytic activity was tested for toluene oxidation, and the results obtained show that the photodegradation rate is slightly lower for CeO2/TiO2 than for the TiO2 sample. However, the selectivity towards benzaldehyde (6–13%) is comparable for both materials. In the case of CeO2, the photo-oxidation rate is an order of magnitude lower than for TiO2, although mineralization of toluene is almost complete. Photoactivity results are discussed in connection with the characteristics of the radicals observed.

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Available from: Javier Soria, Jan 15, 2014
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    • "This implies that there was an interaction between Ce and Zr in the mixed oxides, and the formation of Ce x Zr 1Àx O 2 solid solution is possible. On the other hand, the shifting of the adsorption band is the result of either the rearrangement in the electronic adsorption site [43] or the strain development [44], with respect to those of the pure phase. Other bands in the mixed oxides are attributed to the various charge transitions . "
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    • "), WO 3 (Waldner et al., 2007; Sayama et al., 2010; Saepurahmanet et al., 2010; Cao et al., 2011), WS 2 (Jing and Guo, 2007), Fe 2 O 3 (Chen et al., 2001; Bandara et al., 2001; Pal and Sharon, 1998), V 2 O 5 (Akbarzadeh et al., 2010; Teramura et al., 2004a,b), CeO 2 (Lin and Yu, 1998; Coronado et al., 2002; Ji et al., 2009; Song et al., 2007), CdS (Bessekhouad et al., 2004; Reuterġardh and Langphasuk, 1997; Tang and Huang, 1995), ZnS (Torres-Martínez et al., 2001), and CuO (Lim and Kim, 2004; Sathishkumar et al., 2011; Nezamzadeh-Ejheieg and Hushmandrad, 2010). "

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    • "\g[ = 1/3(g x + g y + g z ); g = 3(g y -g x )/(2g z -g y -g x ); b, in bulk; s, on surfaces. Reference 1, this study; 2, Hochstrasser et al. (1969); 3, Bernarek and Schlick (1991); 4, Kappers et al. (1978); 5, Coronado et al. (2002); 6, Murata et al. (2003); 7, Zhao et al. (2004); 8, Wang and Lunford (1971); 9, Priest et al. (1991) of the spin-orbit coupling for oxygen and the energy difference between the pp u and pr u * orbitals. Scaling the value of (g \ -g e ) observed for F 2 -by the ratio of the spinorbital coupling for F to O yields g \ & 2.014 and g || & g e = 2.0023 for the isolated O 2 3-ion. "
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