Efficient removal of Congo red using adsorbents prepared via MOF-on-MOF strategy

Congo Red (CR) is a toxic compound posing serious health issues and to the aquatic ecosystem. To solve the problems of low efficiency of single MOF adsorbents and to improve adsorption capacity of this class of adsorbents, in this research a new strategy is adopted to prepare ZIF-67@Cu-MOF composite with a core-shell structure employing in situ growth strategy with carboxyl linkage wherein Co 2+ ions were anchored onto Cu-MOF surface to efficiently remove the Congo Red, a pollutant from wastewater sources via adsorption. Influence of solution pH, contact duration, initial concentration, temperature, and the presence of coexisting ions on adsorption performance of CR was investigated to remove the dye up to 98.9 % in 5 min. The Langmuir isotherm model suggested the maximum adsorption capacity of 3494.06 mg/g at 25 °C. Thermodynamic analysis confirmed adsorption was spontaneous and endothermic (ΔG ranging from −35.35 to −43.55 kJ/mol, ΔH = 85.82 kJ/mol). The CR removal efficiency remained at 94.8 % after 5 consecutive adsorption-desorption cycles confirmed that ZIF-67@Cu-MOF composite had the potential ability to remove CR molecules from wastewater sources.