Synthesis of hierarchical hollow MIL-53(Al)-NH as an adsorbent for removing fluoride: experimental and theoretical perspective.

The MIL-53(Al)-NH was designed to remove fluoride with hierarchical hollow morphology. It was used as an adsorbent for fluoride removal at a wide pH range (1-12) due to the positive zeta potential of MIL-53(Al)-NH. The pH did not significantly influence the fluoride adsorption into MIL-53(Al)-NH. However, the adsorbent indicated good adsorption capacity with maximum adsorption of 1070.6 mg g. Different adsorption kinetic and thermodynamic models were investigated for MIL-53(Al)-NH. The adsorption of fluoride into MIL-53(Al)-NH followed the pseudo-second-order model and a well-fitted Langmuir model indicating chemical and monolayer adsorption process. When mass transfer model was used at initial concentrations of 100 ppm and 1000 ppm, the rates of conversion were 8.4 × 10 and 4.7 × 10 m s. Moreover, anions such as [Formula: see text], [Formula: see text], [Formula: see text], Cl, and Br also had less effect on the adsorption of fluoride. Also, experimental and theoretical calculations on adsorption mechanism of MIL-53(Al)-NH revealed that the material had good stability and regenerative capacity using alum as regenerant. In a nutshell, the dominant crystal face (1 0 1) and adsorption sites Al, O, and N combined well with F, HF, and HF through density functional theory. It opens a good way of designing hollow MOFs for adsorbing contaminants in wastewater.