Effective and structure-controlled adsorption of tetracycline hydrochloride from aqueous solution by using Fe-based metal-organic frameworks

Abstract Removal of tetracycline hydrochloride (TCH) is vital to the environment yet challenging. Here, three Fe-based MOFs (metal-organic frameworks) with significantly different porous properties and open metal sites were applied as adsorbents to remove TCH, and the adsorption mechanism was investigated using experiments and computations. The experimental results showed structure-controlled TCH adsorption. The adsorption ability of the three MOFs was in the order MIL-101(Fe)> MIL-88A(Fe) > MIL-53(Fe); these results were closely related to the BET surface area, pore volume and open metal sites. Among these MOFs, MIL-101(Fe), with a high pore volume, high BET surface area, large number of open metal sites and high binding energy (Ebind), exhibited excellent TCH adsorption performance (qm= 420.6 mg g-1). The Ebind of MIL-53(Fe) is higher than that of MIL-88A(Fe), but the lower BET surface areas and porosity might limit its adsorption capacity. Zeta potential and XPS results showed that TCH adsorption was driven by electrostatic interactions and coordination between TCH and unsaturated Fe sites. The π-π interactions (TCH benzene ring and the MOF’s ligand) and pore fillings may be important for TCH removal. The results obtained will help in understanding surface interactions between MOFs and TCH and fabricating efficient MOFs-based adsorbents for pollutant removal.