Sustainable synthesis and characterization of Zn–Al doped nanocomposites for removal of brilliant blue dye: optimization using a response surface methodology

In this study, a sustainable zinc and aluminum dually doped nanocomposite (Zn/Al@BOB) was synthesized from Brassica oleracea var. botrytis stem waste via chemical co-precipitation method for the remediation of Brilliant Blue (BB) dye from water. The material was extensively explored via SEM, XPS, XRD, FT-IR, TGA, and BET techniques. XPS confirmed successful doping of Zn and Al while BET result revealed an exposed surface of 43.686 m²g^-1. Batch-mode equilibrium studies assessed the effects of contact time, nanocomposite dosage, pH, temperature, and dye concentration. Optimization via RSM and CCD identified ideal constraints: 35 min agitation time, 0.29 g/L nanocomposite dose, pH of 6.0, temperature of 318 K and dye concentration of 20 ppm, achieved 95% of removal efficiency. Equilibrium data best fit the Freundlich model (R² = 0.997), and the Langmuir model predicted a dye uptake of 400 mg. g^-1, consistent with the experimental 350 mg/g. Kinetics succeeded a pseudo-2nd -order approach (R² = 0.993), and thermodynamic analysis confirmed the adsorption was spontaneous, endothermic, and physical in nature.