Chiang Mai Journal of Science

The improvement of photocatalytic activity of TiO₂  was studied by heat treating the mixtures of silver nitrate solution and three different sizes of TiO₂ ; commercial-grade C02 (71 nm), P25 (24 nm) and homemade precipitated TiO₂  (pTiO₂ , 11 nm). The activity toward nitrite degradation of large particles (C02) can be improved to be equal to small particles (P25) by optimum Ag loading. The optimum loading for pTiO₂ , P25 and C02 were 2.0, 0.75 and 0.75% which corresponded to the Ag contents of  1.35, 0.74 and 0.66%, respectively. Small particles tended to have high, while large particles tended to have low Ag contents as optimum levels. The agglomeration, dispersion and coverage of  Ag on each TiO₂  type were different and able to change the activity order. The Ag agglomerates on C02 were large and not well diffused while those on P25 were small and diffused homogeneously. As a result, the critical content (minimum Ag content creating measurable Ag agglomerates) of  large TiO₂ particles was relatively low (C02 = 0.66%) compared to that of the small ones (P25 = 1.24%).