Heteropoly acid-loaded ionic liquid@metal-organic frameworks: Effective and reusable adsorbents for the desulfurization of a liquid model fuel

An ionic liquid (IL) and a heteropoly acid (HPA) were sequentially incorporated to highly porous metal-organic frameworks (MOFs, ZIF-8 and MIL-100(Fe)) under mild conditions. The IL was synthesized from 1-methylimidazole and 1-bromobutane inside the pore structure of the MOFs via the ship-in-bottle (SIB) technique. Then, the HPA (here, phosphotungstic acid) was incorporated to IL@MOF, where the imidazolium cations play an essential role in anchoring the PA anions to form stable MOF adsorbents bearing IL and HPA. The efficiency of the tri-component adsorbents was evaluated for the adsorptive removal of thiophenics (benzothiophene (BT) and dibenzothiophene (DBT)) from liquid fuel. The BT or DBT adsorption capacity (Q₀) of the modified MOFs was 1.3–1.6 and 2.0–2.5 times to that of the pristine MOFs based on the unit weight and unit surface area of the adsorbents, respectively. The increased Q₀ could be explained by the synergistic affinity of IL and HPA species toward thiophenics. Moreover, the adsorbent could be reused for up to four cycles with little loss of BT adsorption capacity, indicating the stability (no leaching) of the HPA and IL within the porous MOFs. From this study, it can be concluded that HPA can be supported on IL@MOF via chemical interactions, affording stable tri-component adsorbents that can be applied to a variety of liquid phase adsorption processes.