Individual effect of charge balance defects on the photocatalytic activity of Cr3+-modified TiO2

Loss in the photocatalytic activity of Cr3+: TiO2 powders upon hydrogen annealing shows that charge-compensating oxygen vacancies VO and Cr6+ ions can have opposite effects on the kinetics of photocatalytic decolorization of methyl orange solution. The former ones inhibit this reaction acting as electron–hole recombination centers, and the latter ones promote it playing the role of active sites. This conclusion is verified by an XPS technique for a Cr3+-doped TiO2 sample and by 121Sb Mössbauer spectroscopy for a co-doped (Cr3+,Sb5+): TiO2 sample.