Modeling and optimization of Acid Orange 7 adsorption process using magnetite/carbon nanocomposite

Abstract

The efficiency of a new magnetite/carbon nanocomposite (MCN), applied as adsorbent for the removal of Acid orange 7 (AO7) dye from aqueous solutions was investigated. The MCN was synthesized by combustion, and characterized using modern and relevant techniques. A full factorial design experiment was conducted to identify the optimum conditions for adsorption. The main effect of four process parameters: pH, dye concentration, adsorbent dose and temperature, and their interactions on the removal efficiency were established. A highly significant (p < 0.001) second-order polynomial model (R2 and R2adj of 0.99) provided great removal rates using: pH of 6–7, adsorbent dose of 1–1.5 g/L and initial dye concentration of 50–100 mg/L. The significance of the independent variables as well as their interactions was tested by ANOVA which revealed that the regression is statistically significant at 95% confidence level. Predicted data obtained for the removal efficiency were in good agreement with the experimental determinations (98%). The adsorption isotherms study demonstrated that the Sips model had the best fit with the experimental data (R2 0.9810) and a maximum adsorption capacity of 180.04 mg/g was obtained. The negative values obtained for Gibbs free energy and for enthalpy indicate that the adsorption process is spontaneous and has an exothermic character. After four consecutive cycles of adsorption/desorption, the removal efficiency of AO7 using MCN was yet 83.60%. The results demonstrated that MCN is a promising adsorbent, and response surface optimization could be successfully used to optimize the adsorption process parameters.