抄録
Oxygen and ferric ions were used as electron scavengers in the photocatalytic degradation of a pyrimidine derivative (2-isopropyl-6-methyl-4-pyrimidinol, IMP) in order to elucidate the difference in activity with respect to the crystal structure. Commercial catalyst P-25 was used as-purchased (P-25) and as-calcined at 800°C (calcined P-25). The main crystal structure of P-25 was anatase and that of calcined P-25 was rutile. When oxygen was employed as an electron scavenger, IMP was decomposed easily over P-25 whereas very slowly over calcined P-25. On the contrary, calcined P-25 showed better activity than P-25 when using ferric ion as an electron scavenger. It suggests that rutile can also have good photocatalytic activity under a certain condition. The formation rate of ferrous ions, which are converted from ferric ions along with the reaction, decreased over P-25 with reaction time, but it remained constant over calcined P-25. The result was explained in terms of the adsorption ability of ferrous ions on the catalyst. The CO2 formation rate was slower with the addition of ferrous ion in the degradation of IMP, and anatase adsorbed more ferrous ions than rutile. Ceria impregnation on P-25 lowered the conduction band position to be more positive according to electron energy. Ceria-impregnated P-25 lost its photocatalytic activity in the case of using oxygen as an electron scavenger. However, it showed the same activity as P-25 when ferric ions replaced oxygen. The results proposed that the conduction band position is mainly responsible for the different activities of the crystal structures.
