Selective Dye Adsorption by Zeolitic Imidazolate Framework-8 Loaded UiO-66-NH2

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 pi-pi stacking interactions.