Magnetic activated carbon nanocomposite from Nigella sativa L. waste (MNSA) for the removal of Coomassie brilliant blue dye from aqueous solution: Statistical design of experiments for optimization of the adsorption conditions

The present work was carried out to evaluate the removal of Coomassie brilliant blue dye by adsorption onto a magnetized activated carbon nanocomposite (MNSA) prepared from Nigella sativa L. (NS) waste. Different techniques, including infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption/desorption, were used to characterize MNSA to investigate its adsorption properties. Adsorption experiments were carried out by simultaneously optimizing four variables that usually present a strong effect in adsorption studies. A full 2⁴ factorial design with 3 central points was used. The four independent variables were the initial pH of the dye solution (pH), the initial dye concentration (C_o), the adsorbent mass (m), and the contact time (t). The sorption capacity (q) of the adsorbent and the percentage of dye removal (% Rem) from an aqueous solution were used as the responses of the factorial design. The results indicated that pH, C_o, and m were essential factors for the overall optimization of both responses (q and % Rem) and that several interactions of two, three and four factors occurred. Based on the design of the experiments (DOE), the optimized conditions for adsorption were pH = 2.00, C_o = 40.0 mg L^-1, m = 30.0 mg, and t = 3.0 h. Under these conditions, both responses, q and % Rem, were maximized, with a desirability of 85.54%. The findings of this study could be useful for industrial wastewater treatment systems.