Abstract
In this study, Zeolitic Imidazolate Framework-8 (ZIF-8)-loaded UiO-66-NH2 was synthesized, characterized, and analyzed for its potential to efficiently remove dyes. The selective adsorption on ZIF-8-loaded UiO-66-NH2 or its parent MOFs (UiO-66-NH2 and ZIF-8) in the mixed dyes solution was explored, including anionic dye (methyl orange (MO)) and cationic dyes (methylene blue (MB) and rhodamine B (RhB)). ZIF-8-loaded UiO-66-NH2 displayed much better selectivity to MB than its parent MOFs. Adsorption capacity of ZIF-8-loaded UiO-66-NH2 (173 mg/g) toward MB was found to be 215% higher than UiO-66-NH2 (55 mg/g). A kinetics study based on adsorption data demonstrated that the adsorption process most closely matched with the model of pseudo-second-order kinetic and Langmuir isotherm. The adsorption was an exothermic and spontaneous physical process as revealed by the values of thermodynamic parameters. Furthermore, reusability of ZIF-8-loaded UiO-66-NH2 was investigated and revealed the significant regeneration efficiency in adsorption capacity for MB even after four adsorption cycles. Experimental results proved that the interaction between ZIF-8-loaded UiO-66-NH2 and MB was mainly affected by the mechanism, for instance, electrostatic interaction as well as π–π stacking interactions.
Highlights
Metal organic frameworks (MOFs) are three-dimensional porous crystal materials consisting of metal clusters or ions coordinated with organic ligands [1]
We demonstrated the isotherm, kinetics, and thermodynamics of the methyl blue (MB) adsorption on zeolitic imidazolate framework-8 (ZIF-8)-loaded UiO-66-NH2 and UiO-66-NH2 to understand the mechanisms behind the adsorption behavior
The diffraction peak of ZIF-8 did not emerge in the X-ray diffraction (XRD) pattern of ZIF-8-loaded UiO-66-NH2, which is due to the fact that the thickness of ZIF-8 shell was not good enough to form strong scattering crystalline peaks [21]
Summary
Metal organic frameworks (MOFs) are three-dimensional porous crystal materials consisting of metal clusters or ions coordinated with organic ligands [1]. It is essential to find desirable adsorption materials that can reduce pollutant organic dyestuff with high selectivity and adsorption capacity. ZIF-8 has pore size between 4–5 Å and possesses a large specific surface area and good water stability as well as it contains abundant acid-base groups. It is being used in various fields, especially for the separation of pollutants by adsorption [15,16,17,18,19]. The MB adsorption capacity of ZIF-8-loaded UiO-66-NH2 was found to be higher than its parent MOFs (UiO-66-NH2 or ZIF-8). We demonstrated the isotherm, kinetics, and thermodynamics of the MB adsorption on ZIF-8-loaded UiO-66-NH2 and UiO-66-NH2 to understand the mechanisms behind the adsorption behavior
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