Response surface methodology (RSM) and central composite design have been applied to describe and optimize photocatalytic degradation of azo pyridone dye using TiO₂, H₂O₂, and simulated sun light. The mutual interactions between three independent variables, viz. H₂O₂ concentration, irradiation time, and TiO₂ content were obtained. The results revealed that the most influential variables under selected reaction conditions were irradiation time and TiO₂ content. The optimized conditions for the photocatalytic degradation of azo pyridone dye were as follows: H₂O₂ concentration: 130.5 mg/L, irradiation time: 54.8 min, and TiO₂ content: 2.48 g/L. Under these conditions, the maximum decolorization efficiency of 96.43% was achieved. This experimental value was in good agreement with the predicted one, which proved the validity of the model. Operation cost analysis indicated that irradiation time had the major influence on total process cost. The RSM based on the central composite design was shown to be a successful technique for the optimization of the decolorization efficiency of azo pyridone dye and can be very helpful in improving the process economic feasibility. TOC analysis showed that the dye could be effectively mineralized during photocatalytic degradation.

Photocatalytic degradation of synthesized azo pyridone dye (5-(4-sulpho phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone), in aqueous solutions by simulated sunlight in the presence of commercial TiO₂, Aeroxide P25, was studied. The reaction kinetics analysis showed that photodegradation exhibits pseudo first-order kinetics according to Langmuir-Hinshelwood model. The effects of various process parameters on the photocatalytic degradation were investigated. The optimal catalyst content and pH were determined. A decrease in the reaction rate was observed upon the increase of the initial dye concentration. Degradation of the dye was enhanced by hydrogen peroxide, but it was inhibited by ethanol. The influence of temperature was studied, and the energy of activation was determined. According to total organic carbon (TOC) analysis, 54% of TOC remained when 100% of the dye was decolorized. Although the intermediates were not determined in this study, the TOC results clearly indicate their presence during the reaction. In addition, photocatalytic degradation of simulated dyehouse effluents, containing tested azo pyridone dye and associated auxiliary chemicals was investigated.