A designed experiment for CdS-AgBr photocatalyst toward methylene blue.

A boosted photocatalytic activity was observed for the CdS-AgBr nanocomposite in the degradation of methylene blue (MB). The experimental design method based on the response surface methodology (RSM) approach used to study the simultaneous interaction effects between the influencing variables. Analysis of variance (ANOVA) of the results confirmed a significant model for processing the data because an F value of 32.34 for the suggested model was higher than that of the critical value of F = 2.55 at 95% confidence interval. This analysis also showed a non-significant lack of fit (LOF) (as a measure of the randomness of the deviations around the obtained data) because the LOF F value of 8.27 was smaller than that of the critical value of F = 8.79. R values near to unity were achieved (the multiple correlation coefficients R (R = 0.9627), adjusted R (adj-R = 0.9226), and predicted R (pred-R = 0.7423)). Six center points suggested by the model included the following conditions: pH, 6.1; C, 3.5 mg/L; a dose of the catalyst, 0.68 g/L; and irradiation time, 40.5 min. During the center point runs, the degradation efficiencies were obtained in the range of 38 to 43%. The optimal run included pH, 9; catalyst dosage, 1 g/L; irradiation time, 60 min; and C, 2 mg/L, and the best removal efficiency of 98% was achieved during these conditions.