Surface functional group chemistry and interfacial energetics governing cationic dye adsorption onto raw Pinus pinea cone scale particles

초록

The valorization of abundant forestry residues into ready-to-use biosorbents offers a low-cost, sustainable route to dye-laden wastewater treatment. This study presents the first use of size-selected raw (unmodified) Pinus pinea cone scales (PCS) for the simultaneous removal of two structurally distinct cationic dyes - Malachite Green (MG, triphenylmethane) and Methylene Blue (MB, thiazine) - and links their surface chemistry to dye-specific interfacial energetics. Characterization by FTIR, XRD, TGA, SEM/EDX, and XRF revealed a largely amorphous, almost entirely organic lignocellulosic matrix (inorganic oxides 0.63%) rich in hydroxyl, carboxyl, and aromatic groups. Batch experiments identified pH 6 as optimal, with maximum Langmuir capacities of 588.64 mg/g (MG) and 171.49 mg/g (MB) - competitive with the best raw lignocellulosic biosorbents. Uptake followed pseudo-second-order kinetics (R2 > 0.99) for both dyes, and equilibrium data were best described by the Freundlich isotherm (R2 = 0.980 for MG), indicating adsorption onto an energetically heterogeneous surface. Thermodynamic analysis showed spontaneous adsorption (ΔG° < 0) that was endothermic for MG (ΔH° = +15.09 kJ/mol) but exothermic for MB (ΔH° = −8.19 kJ/mol); the low enthalpies and a desolvation–binding balance dictated by each dye's molecular size and hydration explain this contrast and point to a physisorption-dominant mechanism combining electrostatic attraction, hydrogen bonding, and π–π stacking. PCS retained over 84% efficiency across three regeneration cycles and tolerated competing Fe3+, Cd2+, and NH4+ ions. These results establish raw PCS as a mechanistically characterized, reusable, and economically attractive biosorbent that links functional-group chemistry to dye-specific adsorption behavior. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

키워드