Box-Behnken Modeling and Optimization of Visible-Light Photocatalytic Removal of Methylene Blue by ZnO-BiFeO3 Composite

Abstract

Box-Behnken experimental design was utilized to model and optimize the photocatalytic removal of methylene blue (MB) using ZnO-BiFeO3 composite under visible light (LED). Three catalysts with different ZnO: BiFeO3 molar ratios (2:1, 1:2, and 1:1) were synthesized successfully using hydrothermal method. The synthesized photocatalysts were characterized by XRD, FESEM, EDX, PL, FTIR, and UV-vis. FESEM showed the uniform distribution of ZnO particles over the surface of bigger BiFeO3 particles. The best photocatalytic activity was obtained by ZnO-BiFeO3 with 2:1 molar ratio. In order to optimize the experimental conditions, four factors of initial MB concentration (5 to 20 mg/L), pH (3 to 12), catalyst dosage (0.5 to 1.25 mg/L) and light intensity (4 to 18 W) were selected as independent input variables. BBD suggested a quadratic polynomial equation to fit the experimental data. Results of ANOVA confirmed the goodness of fit for the suggested model (predicted- and adjusted-R2 0.99). The optimum conditions for maximizing the photocatalytic MB degradation were found to be initial MB concentration of 11 mg/L, pH of 11.7, catalyst dosage of 0.716 mg/L, and light intensity of 11.4 W. Under the optimum conditions, the highest photocatalytic MB degradation of 62.9% was obtained which is in reasonable agreement with the predicted value of 69%.