Dynamic biosorption of Basic Fuchsin by Pinus brutia cones: A comparison of the effects of different pretreatment conditions analysis of kinetics and thermodynamics

This study evaluates the adsorption performance of raw Pinus brutia cone powder (PCB) and its modified forms—calcined (PCB-Cal) and chemically activated with phosphoric acid (PCB-0.5 M)—for the removal of Basic Fuchsin (BF) dye from aqueous solutions. Batch adsorption experiments were conducted to investigate the effects of contact time, pH, initial dye concentration, and temperature. All biosorbents reached equilibrium within 30 min, with maximum dye removal (>95 %) obtained at acidic conditions (pH 2–4). Kinetic analysis showed that the pseudo-second-order model best fitted the data (R² > 0.99), indicating that adsorption was mainly controlled by available binding sites. Equilibrium studies revealed that PCB-Raw followed the Freundlich isotherm, suggesting multilayer adsorption on heterogeneous surfaces, while PCB-Cal and PCB-0.5 M fitted better to the Langmuir model, indicating monolayer coverage. Thermodynamic parameters (ΔH° = –15.8 to –22.4 kJ·mol⁻¹; ΔG° = –4.3 to –7.1 kJ·mol⁻¹) confirmed that the process is spontaneous, exothermic, and primarily physical in nature. BET analysis further demonstrated that chemical activation increased surface area from 0.16 to 100.9 m²/g, significantly enhancing adsorption capacity. These findings highlight Pinus brutia cones as efficient, low-cost, and eco-friendly biosorbents for dye-contaminated wastewater treatment.