The experimental design methodology was used to model and optimize the operational parameters of the photocatalytic degradation of Acid Red 73 using immobilized TiO 2 nanoparticles. Four experimental parameters were chosen as independent variables: pH, initial dye concentration, H 2 O 2 concentration, and anion concentration. A multivariate experimental design was used to establish a quadratic model as a functional relationship between the efficiency of Acid Red 73 degradation (response) and four independent variables. The degradation efficiency was significantly affected by the initial dye concentration and the pH. The optimal values of the parameters were found to be a pH of 3, an initial dye concentration of 25 mg/L, an H 2 O 2 concentration of 0.5 mg/L, and an anion concentration of 0.69 mg/L. The degradation efficiency approached 92.24% under optimal conditions. Regression analysis with an R 2 value of 0.9785 indicated a satisfactory correlation between the experimental data and predicted values.

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Polyaniline (PANI) as an excellent conducting polymer was used to prepare an organic-inorganic hybrid nanocomposite based on nitrogen (N)-doped titanium dioxide (TiO 2 ) under different synthesis conditions. Based on the DRS, XRD, FESEM, BET, XPS, and FT-IR results, the optical and structural properties of the asprepared composites were found to be affected by N-TiO 2 to aniline (ANI) molar ratio, reaction time, and initial pH of solution, which in turn influence the photocatalytic performance of nanocomposites. The experimental design methodology was used to study the simultaneous effect of these synthesis parameters on the Vis activity performance of N-TiO 2 /PANI nanocomposites for degradation of Acid Red 73. The degradation efficiency was significantly affected by the reaction time of polymerization, initial pH of solution, and interaction between the reaction time and N-TiO 2 / ANI molar ratio. The optimal synthesis conditions for maximum Acid Red 73 degradation efficiency (58.25%) were found to be a molar ratio of N-TiO 2 /ANI of 106.13 M, the reaction time of 487.42 min, and pH of 3.37. TEM images, N 2 adsorption-desorption isotherms and BET analysis of the as-prepared nanocomposites show the increase in surface area and porosity and decrease in agglomeration formation by adding nitrogen and PANI. The N-TiO 2 /PANI nanocomposites prepared at optimal synthesis conditions show higher visible activity compared to those modified with nitrogen or PANI only due to the synergistic effect between PANI and N doping. The mineralization studies of Acid Red 73 using the as-prepared nanocomposites show their ability to decompose approximately all organic compounds present in the solution. POLYM. COMPOS., 00:000-000,