Synthesis of heterogeneous nanocatalysts comprising polyoxometalate ionic liquid-based magnetic nanocomposites for oxidation of thiobenzoic acid and 2,2′-dinitro-5,5′-dithiodibenzoic acid†

Abstract

Human health and the environment have been greatly impacted by fuels with sulphur-containing compounds used in vehicles. These sulphur-containing compounds cause serious problems, e.g., environmental pollution and acid rain. In the present study, two polyoxometalate ionic liquid-based magnetic nanocomposites (MoVPOM-IL@Fe₃O₄@SiO₂ and WPOM-IL@Fe₃O₄@SiO₂) were employed for desulfurization of thiobenzoic acid and 2,2′-dinitro-5,5′-dithiodibenzoic acid. MoVPOM-IL@Fe₃O₄@SiO₂ and WPOM-IL@Fe₃O₄@SiO₂ were prepared by encapsulating POM-ILs into Fe₃O₄@SiO₂ and were characterized using Fourier transform infrared spectroscopy (FT-IR), UV/vis spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). Initially, the desulfurization reaction was observed using TLC, and the final analysis was confirmed through reverse-phase high-performance liquid chromatography. Different factors were analysed that can affect desulfurization of thiobenzoic acid and 2,2′-dinitro-5,5′-dithiodibenzoic acid using MoVPOM-IL@Fe₃O₄@SiO₂ and WPOM-IL@Fe₃O₄@SiO₂ as a catalyst. Moreover, the oxidative product of thiobenzoic acid was confirmed via GC-MS and (¹H and ¹³C)NMR. These catalysts proved to be efficient in oxidation of thio compounds as the sulphur content in these thio compounds was successfully reduced. Using MoVPOM-IL@Fe₃O₄@SiO₂ and WPOM-IL@Fe₃O₄@SiO₂ as a catalyst, the sulphur level in thiobenzoic acid and 2,2′-dinitro-5,5′-dithiodibenzoic acid was decreased up to 99.32% and 99.56%, respectively. As both catalysts were magnetic, they were easily separated and reused 5 times without losing any oxidative properties.