ADSORPTION OF CAFFEINE ONTO TiO2-ZrO2 AND EVALUATION OF PHOTOCATALYTIC BEHAVIOUR

Adsorption of caffeine on the TiO2-ZrO2 photocatalyst prepared via sol gel impregnation method was investigated. The adsorption kinetics was evaluated by three models including the pseudo-first-order, pseudo-second-order and intra-particle diffusion, and the result showed that the pseudo-second-order model fitted best based on the correlation coefficient (R-2>0.99). A highest removal percentage (18.8%) and a maximum capacity (0.41 mg/g) were acquired at pH 9.0 in the study of pH effect, and a best agreement (R-2>0.993) was achieved by the Langmuir model compared to the Freulidch one, indicating that the active sites distributed homogeneously on the surface of the TiO2-ZrO2 photocatalyst. In the photocatalytic degradation of caffeine with TiO2-ZrO2, the optimum condition of influential parameters were 5 mg/l, 5, 0.5 g/l and 40 degrees C for initial concentration, pH, photocatalyst dose and temperature, respectively. The effect on degradation of caffeine in the presence of tert-butyl alcohol (TBA) and inorganic anions presented that hydroxyl radical (*OH) was the main active species in the photocatalytic process; the order of the influence of anions on degradation suppression was: sulphite > carbonates > phosphate > sulphate > chloride.