Photo-oxidation of water sensitized by TiO2 and WO3 in presence of different electron acceptors
A. Mills and M.A. Valenzuela*
Department of Pure & Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, G11XL, UK.
Recibido el 17 de septiembre de 2003; ]]> Aceptado el 7 de octubre de 2003.
Abstract
The photo-oxidation of water is studied in presence of UV-light (λ < 400 nm) using titanium dioxide (TiO2) and tungsten oxide (WO3,micro-and nano-crystalline) semiconductors in presence of different sacrificial electron acceptors (SEA): Fe(NO3)2, Na2S2O8, Ce(SO4)2, Co[(NH3)5Cl]Cl2, AgNO3, HgCl2 and Cu(NO3)2. TiO2 is 5 to 10 times more photoactive than WO3 with reference to oxygen evolution. Ag ions are the best of the SEAs, for all the semiconductors tested in the photo-redox process. No oxygen evolution is observed when Hg2+ or Cu2+ ions are used as SEAs. The effect of high (10-2 mol dm-3) and low (10-3 mol dm-3) SEA concentrations is also studied but no common trend is observed. Instead, each system (i.e., SEA+H2O+Semiconductor) exhibits a different behaviour and the results are rationalised in terms of the spectral and redox potential features of the system.
Keywords: Semiconductor photosynthesis; TiO2; WO3; water oxidation; electron acceptor.
Resumen
Se estudió la foto-oxidación del agua en presencia de luz UV (λ < 400nm) empleando óxido de titanio (TiO2) y óxido de tungsteno (WO3, polvo y nanocristalino) con diferentes aceptores de electrones (AE): Fe(NO3)2, Na2S2O8, Ce(SO4)2, Co[(NH3)5 Cl] Cl2, AgNO3, HgCl2 y Cu(NO3)2.. En general, el TiO2 presentó la mayor fotoactividad, produciendo entre 5 y 10 veces más oxígeno que el WO3. En cuanto a las especies iónicas utilizadas en el proceso redox, los iones Ag+ fueron los más efectivos con los tres semiconductores. No se detectó la evolución de oxígeno cuando se utilizaron los iones Hg2+ y Cu2+. El efecto de la concentración de los AE no mostró una tendencia definida, si no que cada sistema (AE+H2O+Semiconductor) tuvo un comportamiento distinto y los resultados se discutieron en función de sus características espectrales.
Descriptores: Semiconductores; TiO2; WO3; fotodescomposición del agua; aceptor de electrones.
]]> PACS: 81.05.Hd; 82.50.Fv; 82.30.Lp; 82.65.Jv
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References
* Corresponding Author. Permanent address: Laboratorio de Catalisis y Materiales, ESIQIE-Instituto Politecnico Nacional, Edificio 8, tercer piso, Zacatenco, 07738, Mex, D.F. México., mavalenz@ipn.mx.
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