Efficient removal of cytotoxic sunitinib from aqueous media using natural bentonite: Adsorption, kinetics, thermodynamics

This study investigates the use of natural bentonite as a low-cost, eco-friendly adsorbent for removing sunitinib, a cytotoxic anticancer drug, from aqueous solutions. XRF and XRD analyses confirmed the smectite structure of bentonite with typical aluminosilicate composition and exchangeable cations. FT-IR analysis indicated interactions between sunitinib and bentonite through shifts in –OH, C=O, and –CH vibrations. BET results showed a surface area of 67.93 m²/g and a Type II isotherm, suggesting a macroporous structure. SEM images revealed rough, heterogeneous surfaces in raw bentonite, which became partially covered after adsorption. EDX analysis confirmed the presence of key elements (Si, Al, O, Na, Mg) and showed increased surface carbon after drug loading, verifying organic adsorption. Under optimal conditions (pH 8, 35°C, 15 mg adsorbent, 75 ppm initial concentration), maximum removal efficiency reached 90%. Adsorption kinetics followed the pseudo-second-order model, indicating a combined physico-chemical mechanism, while intra-particle diffusion analysis revealed a multi-step process. Thermodynamic analysis (ΔH° = –4.52 kJ/mol; ΔG° < 0; ΔS° > 0) suggested the process was spontaneous and exothermic with increased disorder. Desorption studies showed high reusability in alkaline media. Overall, natural bentonite presents a promising, sustainable solution for the effective removal of hazardous pharmaceutical pollutants like sunitinib from water.