Esra Altintig, Onur Kabadayi
This study aims to evaluate the adsorption performance of ZnO- and TiO2-coated clinoptilolite composites for the removal of methylene blue (MB) from aqueous solutions and to clarify the governing adsorption mechanisms. Batch adsorption experiments were systematically conducted to investigate the effects of initial pH (3–10), MB concentration (50–200 mg/L), adsorbent dosage (0.05–1.00 g/100 mL), contact time (5–300 min), and temperature (298–313 K). Equilibrium, kinetic, and thermodynamic analyses were employed to comprehensively describe the adsorption behavior. The results demonstrated that MB adsorption onto both composites followed the Langmuir isotherm model, indicating monolayer adsorption on homogeneous surfaces. The maximum adsorption capacities were determined as 56 mg/g for ZnO-coated clinoptilolite and 106 mg/g for TiO2-coated clinoptilolite, confirming the superior adsorption affinity of the TiO2-modified composite. Thermodynamic parameters further indicated that the adsorption process was spontaneous, feasible, and thermodynamically favorable within the investigated temperature range. Physicochemical characterization by FTIR, SEM, BET, and XRD confirmed the successful surface modification of clinoptilolite and the enhancement of its structural and textural properties. Overall, the findings suggest that ZnO- and TiO2-coated clinoptilolite composites are efficient and sustainable adsorbents with strong potential for wastewater treatment applications.