Sustainable Synthesis of Zn/Al-Doped Nanocomposite from Bio- Waste: Characterization and RSM-Guided Brilliant Blue Dye Adsorption Optimization

In this study, a sustainable zinc and aluminum dually doped nanocomposite (Zn/Al@BOB) was synthesized from stem bio-waste of Brassica oleracea var. botrytis via a chemical co-precipitation method for the remediation of Brilliant Blue (BB) dye from pollutant-bearing 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 manifested an exposed surface of 43.686 m²g ^− 1 . Batch-mode equilibrium studies assessed the effects of contact time (35 min), dosage (0.28 g/L), pH (6), temperature (318K), and dye concentration (20 ppm). Optimization via RSM and CCD identified ideal constraints: 34.83 min agitation, 0.289 g/L nanocomposite dose, pH 5.958, and 20 ppm dye concentration, achieving 95.11% removal efficiency. Equilibrium data best fit the Freundlich model (R² = 0.9970), 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 = 0.9929), and thermodynamic analysis confirmed the adsorption was spontaneous, endothermic, and physical in nature.