Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO2 in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO2 was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO2 was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO2 was 39.5, 86.0, and 96.3 mg g(-1) for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO2 when compared with that of undoped TiO2. Moreover, the degradation of RY 84 on N-doped TiO2 in sunlight was faster than the commercial Aeroxide(A (R)) P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l(-1) Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO2. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l(-1), due to the strong absorption of photons in the wavelength range 200-400 nm by the dye solution. LC-MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO2.