Mechanism, interfacial interactions and thermodynamics of the monolayer adsorption of trace geogenic pollutants from water using mil metal-organic frameworks: Fluorides and arsenates

Abstract

This paper analyzes the thermodynamics and interfacial interactions of the adsorption of fluorides and arsenates on pristine MIL-100(Fe) and MIL-101(Fe) structures. Experimental equilibrium studies showed that the fluoride adsorption was exothermic on both MOFs at 20–40 °C and pH 7, while the arsenate adsorption was endothermic at the same operating conditions. Density functional theory calculations indicated that the arsenate adsorption was governed by an ion exchange mechanism where Fe centers from MOFs were involved, while electrostatic interactions affected the ion exchange during the fluoride adsorption on these metal-organic structures. The adsorption properties of MIL-101(Fe) were better than those of MIL-100(Fe) for both fluoride and arsenate. Particularly, MIL-101(Fe) showed an outstanding performance for the arsenate removal with adsorption capacities up to 4.57 mmol/g (i.e., 342 mg/g) and it can be regenerated using NaOH. This MOF outperformed several adsorbents reported in the literature for the arsenate removal including other MOFs with higher surface areas. This crystalline material is attractive and promising to be applied in the intensification of treatment technologies to depollute aquifers contaminated by geogenic pollutants. These results contribute to the understanding of the adsorption properties of MIL-family MOFs, with the aim of consolidating their utilization in water purification.