Optimization of the photocatalytic activity of N-doped TiO2 for the degradation of methyl orange

Methyl orange, a well-known detrimental azo dye, is treated by N-doped TiO2 photocatalyst synthesized by the simple and effective annealing method. In this study, the effects of light intensity in terms of irradiance by the number of lamps, photon energy and radiation sources, the initial concentration of total organic carbon (TOC), and pH on the degradation efficiency of methyl orange are investigated. A four-factor Box-Behnken design along with response surface methodology is used to maximize the removal of TOC and color. Statistical models are developed to predict both color and TOC removals as response variables. In all cases, the light intensity and TOC concentration cross-factor interaction with the light wavelength is intensified when the latter is at the lowest range value while pH does not require adjustments. Maximum TOC and color removals of 96.11% and 98.18%, respectively, were achieved at the optimum operating conditions of light intensity in terms of five lamps, light wavelength of 418 nm (visible light range), initial TOC concentration of 10.54 mg/L, and pH of 6.66. The model was validated by an additional experiment at the optimal operating conditions. The agreement between experimental values and model predictions demonstrate the proposed models could effectively describe the degradation of azo dyes by photocatalysis using the N-doped TiO2 composite under visible light.