Adsorptive and photo-Fenton properties of bimetallic MIL-100(Fe,Sn) and MIL-100(Fe,Ir) MOFs toward removal of tetracycline from aqueous solutions

Abstract

Bimetallic derivatives of MIL-100(Fe) are promising metal–organic frameworks (MOFs) that have caught increasing research and application attention in the last few years due to their superior potential com- pared to MIL-100(Fe) for treatment of wastewater. In this work, novel bimetallic MIL-100(Fe,Sn) and MIL-100(Fe,Ir) were synthesized using a facile synthesis method. The synthesized MOFs showed different activities toward removal of tetracycline (TC), a broad-spectrum antibiotic, from an aqueous solution under dark conditions, followed by photo-Fenton degradation. In this context, the best-performing Sn- doped MIL-100(Fe) MOFs, that is MIL-100(Fe,Sn-7.1), showed marginally increased adsorption and photo-Fenton activity compared to MIL-100(Fe), resulting in a TC removal efficiency of 76%. In contrast, the best-performing Ir-doped MIL-100(Fe), that is MIL-100(Fe,Ir-62.3), showed enhanced adsorption property by 34% compared to MIL-100(Fe), resulting in the best TC removal efficiency of 91% among the studied MOFs. The detailed analysis and characterization of the synthesized MOFs revealed that the average pore diameter of MIL-100(Fe,Ir-62.3) was approximately four times larger than that of MIL- 100(Fe) and MIL-100(Fe,Sn-7.1), though they possessed the lowest surface area. This observation demonstrated that the pore size is an essential parameter to be considered in the process of adsorptive removal of TC from an aqueous solution, which led to the significantly enhanced overall efficiency of bimetallic MIL-100(Fe) derived MOFs.