Adsorptive removal of Basic Blue 41 dye from aqueous solution using quince (Cydonia oblonga) peel as a novel low-cost biosorbent: equilibrium, kinetics, and thermodynamic studies

Abstract

Coloured effluents from the textile sector are still one of the more awkward problems in water treatment, and Basic Blue 41 (BB41) a cationic azo dye used for dyeing acrylic fibres is a good example of a colourant that is both visually persistent and biologically troublesome. In the present work the peel of quince fruit (Cydonia oblonga), an agricultural by-product that is normally thrown away, was examined as a cheap biosorbent for taking BB41 out of water. The raw peel was simply washed, dried, milled and used without any chemical or thermal activation. FTIR, XRD and FESEM were combined into a single characterization step to follow the surface chemistry and morphology of the material before and after dye uptake. Batch experiments looked at the influence of solution pH (2–10), biosorbent dose (0.4–3.0 g L⁻¹), contact time, initial dye concentration (25–200 mg L⁻¹) and temperature (298–328 K). Removal improved sharply as the pH rose, which agrees with electrostatic attraction between the protonated dye and the deprotonated surface groups, and equilibrium was reached in roughly 60 min. The equilibrium data were described best by the Langmuir model, giving a monolayer capacity of about 113.6 mg g⁻¹ at 298 K that increased with temperature to nearly 126 mg g⁻¹ at 328 K, while the kinetics obeyed the pseudo-second-order equation. The thermodynamic functions showed the process to be spontaneous, endothermic and accompanied by a rise in randomness at the solid–liquid interface. Overall, the findings indicate that quince peel is a practical, inexpensive adsorbent for the decolourisation of dye-bearing wastewater.