Simultaneous elimination of Rhodamine B and Malachite Green dyes from the aqueous sample with magnetic reduced graphene oxide nanocomposite: Optimization using experimental design

Many industrial effluents contain various cationic pollutants, including organic dyes with infrangible and stable structures, and are often toxic, posing a severe threat to public health and the environment. In this study, magnetic reduced graphene oxide nanocomposite (RGO/Fe3O4-NC) was used to simultaneously adsorption the mixture of cationic dyes Rhodamine B (Rh B) and Malachite Green (MG) from the aqueous solution. The synthesized adsorbent was characterized by XRD, FTIR, SEM, TEM, VSM, BET-BJH, and zeta potential analyses. In this study, the effect of essential variables such as initial dye concentration, adsorbent dose, contact time, and pH of the solution was optimized using the response surface methodology (RSM) based on central composite design (CCD). The optimum conditions for the adsorption of dyes were pH = 8.0, mixture concentration of each dye 16 mg L−1, contact time 20 min, and adsorbent mass of 0.028 g. The results showed that the equilibrium constant data follow the Langmuir isotherm model with R = 0.99 for both dyes. Adsorption kinetics showed that the adsorption process of the mixture of both dyes was of the second-order type. Also, the thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. The adsorbent recycling results showed that the adsorbent could be reused for up to 4 cycles with good efficiency. Finally, the prepared magnetic nanocomposite was a promising adsorbent for effective water purification with good adsorption efficiency, magnetically separability, and good recyclability, which can simultaneously eliminate the mixture of dyes.