A novel route for the facile synthesis of NH₂-MIL-53(Fe) and its highly efficient and selective adsorption of congo red

Metal-organic frameworks (MOFs) have shown attractive advantages in adsorbing dyes from wastewater. However, their complex synthesis processes and poor stability have limited their applications. Herein, we proposed a novel two-step route to prepare NH2-MIL-53(Fe) at room temperature and investigated its dye adsorption performance. The prepared NH2-MIL-53(Fe) displayed high water stability in the pH range of 3-11. Moreover, NH2-MIL-53(Fe) showed a significantly higher adsorption capacity and faster adsorption rate towards congo red (CR) than the other selected dyes, with more than 99 % of CR being removed by NH2-MIL-53(Fe) within 20 min. The maximum adsorption capacity of NH2-MIL-53(Fe) for CR was 1877 mg center dot g(-1). Besides, the removal efficiency of CR could maintain higher than 80 % within the tested pH range (3 to 11), and removal efficiency was consistently higher than 95 % at different NaCl concentrations (0 to 0.4 M). The dynamic CR adsorption process matched the pseudo-second-order kinetic model and fitted well using the Langmuir model, suggesting that the adsorption of CR onto NH2-MIL-53(Fe) was a monomolecular-layer chemical adsorption process. More importantly, NH2-MIL-53(Fe) showed high removal efficiency and good reusability towards CR in both synthetic and model wastewater. Mechanistic studies suggested that the removal of CR was attributed to the synergistic effects of the pi-pi stacking interactions, hydrogen bonds and electrostatic interactions between CR and NH2-MIL-53(Fe). Overall, the present study provides a novel strategy for the facile synthesis of NH2-MIL-53(Fe), highlights the excellent adsorption performance and reusability towards CR and underlies the adsorption mechanisms involved.