Adsorption performance of chestnut cupule-derived carbon in olaparib removal from aquatic environments: kinetic, isotherm and thermodynamic evaluation

The occurrence of pharmaceutical contaminants in aquatic environments has become a critical environmental concern, necessitating effective and sustainable treatment technologies. This study investigates the adsorptive removal of olaparib (OLA), an anticancer pharmaceutical, from aqueous solutions using chestnut cupule-derived carbon (CCDC). Comprehensive characterization revealed that CCDC possesses a well-developed hierarchical porous structure with a specific surface area of 576.5 m²/g and a predominantly mesoporous character (75% of total surface area). Batch adsorption experiments were systematically conducted to evaluate the effects of adsorbent dosage, initial OLA concentration, solution pH, contact time, and temperature. Under optimized conditions (15 mg adsorbent/50 mL, pH 7, initial concentration ≤ 30 mg/L, 180 min), CCDC achieved up to 99.43% OLA removal. The adsorption process was remarkably robust against pH variations (2–12), maintaining removal efficiencies above 98%. Equilibrium data were best described by the Langmuir isotherm model (R² = 0.998), indicating homogeneous monolayer adsorption with a maximum capacity of 176.85 mg/g. Kinetic modeling indicated that the pseudo-second-order (PSO) model (R 2 = 0.947) effectively represented the adsorption rate and rate-controlling step, closely predicting the experimental equilibrium capacity (q e, cal = 148.36 mg/g vs. q e, exp = 147.43 mg/g). Concurrently, the superior mathematical fit of the Elovich model (R 2 = 0.981) confirmed that the adsorption occurs predominantly on an energetically heterogeneous surface governed by chemisorption mechanisms with varying activation energies. Thermodynamic analysis confirmed the spontaneous (ΔG° = -9.86 to -9.72 kJ/mol) and exothermic (ΔH° = -12.73 kJ/mol) nature of the process. The negative entropy change (ΔS° = -0.00964 kJ/mol·K) indicated decreased randomness at the solid-liquid interface. This study demonstrates that KOH-modified chestnut cupule-derived carbon (CCDC) is a promising, cost-effective, and sustainable adsorbent for the remediation of olaparib from aquatic environments, while promoting agro-industrial waste valorization within a circular economy framework.