Synthesis and Adsorptive Performance of Zn/Al Dually doped Brassica oleracea var. italica Stem Nanocomposite: Insights from RSM Optimization

Abstract

In this study, a sustainable nanocomposite was synthesized using stem waste of Brassica oleracea var. italica, dually doped with zinc and aluminum (Zn/Al@BOI), through a chemical co-precipitation method. The material was designed for the efficient adsorptive treatment of wastewater to remove Malachite Green (MG). Structural and surface features were analyzed using approaches such as SEM, BET, EDX, XRD, FTIR, XPS, and TGA. The presence of Zn and Al was confirmed by EDX and XPS, while BET surface area analysis confirmed a notably high value of 80.53 m²/g, suggesting the material's strong capability for adsorption. To investigate its adsorption behavior, a set of batch tests were carried out, focusing on the influence of time, pH, adsorbent dose, MG dye concentration, and temperature. Using RSM with a CCD, the ideal operational conditions were determined to be approximately 29.64 minutes of contact time, 0.29 g/L dosage, pH 7.96, and 20 ppm dye concentration, resulting in a greater efficiency of 97.31%. Equilibrium data best fit the Freundlich isotherm (R² = 0.9957), while the Langmuir model analysis revealed a monolayer capacity of 476 mg. g^-1. The adsorption kinetics were effectively represented by the pseudo-2^nd-order model and thermodynamic findings revealed a spontaneous, endothermic, and, physisorption-driven process.