Selective photo-degradation of Rhodamine B over zirconia incorporated titaniananoparticles: a quantitative approach

Abstract

This study attempts to elucidate the selectivity of photo-degradation of Rhodamine B (Rh–B) over zirconia-incorporated TiO₂ (ZIT) by UV light, through a comparison of the photocatalytic activities of pure TiO₂ (Degussa P25) and ZIT nanoparticles. The incorporated atomic ratio of Zr/Ti in ZIT is chosen at three levels: i.e. Zr/Ti = 68.01% (maximum, denoted as ZIT-1), Zr/Ti = 15.94% (medium, denoted as ZIT-3), and Zr/Ti = 1.88% (minimum, denoted as ZIT-4). The selective photo-degradation of Rh–B over ZIT occurs in two routes. They are N-de-ethylation and de-carboxylation. The photo-degradation N-de-ethylation of Rh–B is generally observed in an anatase-structured titania domain. However, the photo-catalytic de-carboxylation of Rh–B has not been reported for the titania-based photocatalysts. The spectra deconvolution data of solid state FT-IR suggest that the ZrO₂–TiO₂ matrix is responsible for the photo-catalytic de-carboxylation of Rh–B. The typical photocatalytic rate constants (k_cat) of Rh–B over P25 (0.389 min⁻¹), ZIT-1 (0.945 min⁻¹), ZIT-3 (1.755 min⁻¹), and ZIT-4 (1.197 min⁻¹) are in the ratio 0.22 : 0.51 : 1.00 : 0.68. The k_cat of ZIT is 2.78 to 4.89 times that of P25. The highest catalytic efficiency is not achieved by the sample having the highest zirconia doping. Based on the experimental data, the optimal incorporation amount of ZrO₂ in ZIT for photo-degradation of Rh–B is Zr/Ti = 15.94%.