We previously reported that nitrified Si-doped titanias exhibited relatively high photocatalytic activities under visible-light irradiation [1] and that the Fe addition to the N- and Si-co-doped titanias markedly improved the activities [2]. In this study, the effect of annealing on the photocatalytic activity of the N- and Si-co-doped titanias with and without Fe loading was studied.
Nanocrystalline Si-doped titanias were synthesized by a glycothermal method. The products were calcined in air at 500 ºC for 30 min, and treated in an NH₃ flow at 600 ºC for 1 h. Fe loading was conducted by an impregnation method, and the samples were annealed in air at various temperatures. Photocatalytic activity was evaluated by decomposition of acetaldehyde and Rhodamine B under visible-light irradiation with a xenon lamp and a UV cut-off filter.
Without annealing, the catalysts without Fe loading showed quite low activities. As the annealing temperature increased up to 500 ºC, the photocatalytic activity increased. The anneal treatment brought about a decrease in the population of the oxygen vacancies in the samples, which dominantly affected the activity. For the catalysts with Fe loading, on the other hand, increased annealing temperature decreased the activity as shown in Fig. 1. By the addition of Fe, the recombination of holes and electrons were efficiently suppressed. Therefore, the higher activities obtained with the catalysts annealed at lower temperatures are due to the higher amounts of nitrogen doped in the catalysts.