Removal of reactive dye with metal-organic framework: New insight into the adsorption mechanism

Synthetic dyes, especially reactive dyes, present considerable ecological and environmental challenges due to their extensive use in the textile industry and discharge into wastewater. Among the various methods for dye removal, adsorption is considered the most effective, with metal-organic frameworks (MOFs) emerging as promising adsorbents. However, there is still a limited understanding of the adsorption mechanisms for reactive dyes. These mechanisms are affected by factors such as the bigger molecular size of dyes, higher charge, and the presence of functional groups. Herein, we investigate the adsorption of toxic Reactive Blue 4 (RB4) dye on MIL-101(Fe). The influence of MOF dosage, initial dye concentration, pH level, temperature, and contact time are discussed. The pH level has no significant influence on adsorption. Thermodynamic study shows that the adsorption is spontaneous and endothermic. The adsorption behavior aligns well with the Temkin isotherm model and follows pseudo-second-order kinetic pattern. Findings suggest that adsorption is primarily due to the robust covalent bond formation between the dye’s triazine moiety and ferric oxygen sites of the framework. The desorption is poor in all used substances, indicating the strong attachment of dye molecules on MOF’s surface.