Adsorption performance and kinetic study of hierarchical porous Fe-based MOFs for toluene removal

In light of the promising merits of large surface area, uniform pore size, and tunable functional groups, metal-organic frameworks (MOFs) have great potential to be utilized for adsorbing volatile organic compounds (VOCs). In this study, three Fe-based MOFs, MIL-100(Fe), MIL-101(Fe), and MIL-53(Fe), were synthesized systematically and used to adsorb a typical VOC, toluene. Static adsorption, dynamic breakthrough curves, and adsorption kinetics were conducted to assess the adsorption performance. Additionally, the surface functional groups, pore structure, and morphology were systematically characterized by means of XRD, SEM, XPS, FTIR and N2 adsorption-desorption analyses to reveal the cause of the difference in adsorption of these Fe-based MOFs. The results revealed that the maximum equilibrium adsorption capacity of 663 mg/g was achieved by MIL-100(Fe) with the highest specific surface area and pore volume. The dynamic adsorption of toluene on MIL-100(Fe) was in accordance with the pseudo-first order kinetic model and the Langmuir isothermal model. The formed π-π stacking interaction between organic ligands and the benzene ring in the MIL-100(Fe) cluster is the primary adsorption mechanism based on XPS analysis. Moreover, MIL-100(Fe) was easily regenerated via microwave irradiation with a negligible adsorption capacity decrease after three cycles. This work highlights the feasibility of hierarchical porous Fe-based MOFs as toluene adsorbents and promotes the application of MOFs in the field of pollution control.