Selective Dye Adsorption by Zeolitic Imidazolate Framework-8 Loaded UiO-66-NH(2)

In this study, Zeolitic Imidazolate Framework-8 (ZIF-8)-loaded UiO-66-NH(2) was synthesized, characterized, and analyzed for its potential to efficiently remove dyes. The selective adsorption on ZIF-8-loaded UiO-66-NH(2) or its parent MOFs (UiO-66-NH(2) 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-NH(2) displayed much better selectivity to MB than its parent MOFs. Adsorption capacity of ZIF-8-loaded UiO-66-NH(2) (173 mg/g) toward MB was found to be 215% higher than UiO-66-NH(2) (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-NH(2) 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-NH(2) and MB was mainly affected by the mechanism, for instance, electrostatic interaction as well as π–π stacking interactions.