Optimizing adsorptive removal of malachite green and methyl orange dyes from simulated wastewater by Mn-doped CuO-Nanoparticles loaded on activated carbon using CCD-RSM: Mechanism, regeneration, isotherm, kinetic, and thermodynamic studies

In the present work, Mn-doped CuO-NPs-AC was prepared by a simple method, characterized using various techniques such as FESEM, EDX, XRD, PSD, and pH(pzc) and finally used for the adsorption of malachite green (MG) and methyl orange (MO) in a number of single and binary solutions. A series of adsorption experiments were conducted to investigate and optimize the influence of various factors (such as different pH, concentration of MG and MO, adsorbent mass, and sonication time) on the simultaneous adsorption of MG and MO using response surface methodology. Under optimal conditions of pH 10, adsorbent dose of 0.02 g, MG concentration of 30 mg L-1, MO concentration of 30 mg L-1, and sonication time of 4.5 min at room temperature, the maximum predicted adsorption was observed to be 100.0%, for both MG and MO, showing that there is a favorable harmony between the experimental data and model predictions. The adsorption isotherm of MO and MG by Mn-doped CuO-NPs-AC could be well clarified by the Langmuir model with maximum adsorption capacity of 320.69 mg g(-1) and 290.11 mg g(-1) in the single solution and 233.02 mg g(-1) and 205.53 mg g(-1) in the binary solution by 0.005 g of adsorbent mass for MG and MO, respectively. Kinetic studies also revealed that both MG and MO adsorption were better defined by the pseudo-second order model for both solutions. In addition, the thermodynamic constant studies disclosed that the adsorption of MG and MO was likely to be influenced by a physisorption mechanism. Eventually, the reusability of the Mn-doped CuO-NPs-AC after six times showed a reduction in the adsorption percentage of MG and MO.