Conjugated organic ligand enhancing chelating iron-based deep eutectic solvents for catalytic oxidation of hydrogen sulfide

Abstract

In recent years, non-aqueous iron-based ionic liquid (Fe-IL) desulfurization technology has garnered widespread attention for its avoidance of the excessive oxidation of hydrogen sulfide in aqueous systems. However, the hydrogen bond network in ionic liquids restricts molecular motion, resulting in poor reactivity of Fe-IL. In this work, the chelated Fe-ILs (BmimFeEDTA and BZKFeEDTA) were synthesized and dissolved in PEG200 to construct chelated iron-based deep eutectic solvents (Bm-Fe-DES, BZK-Fe-DES). 1,3-Dimethyl-2-imidazolidinone (DMI), as a conjugated active ligand, was introduced to enhance the catalytic oxidation of H2S by the two Fe-DESs. After five cycles, both Fe-DES/DMI systems exhibited excellent desulfurization and regeneration performance. POM and FT-IR analyses revealed that BZKFeEDTA with a long carbon chain exhibited a more ordered spatial structure, which was more conducive to the cycling of Fe(III) and Fe(II). CV, Py-IR, bond length analysis, and LUMO-HOMO energy gap indicated that DMI weakens the limitation of EDTA to Fe(III) by coordinating with Fe(III), which significantly enhances the catalytic activity of Fe-DES. UV–vis and CPA analysis demonstrated the transfer of π electrons from DMI to the EDTA ligand, facilitating the loss of electrons from [Fe(II)EDTA]2-. Therefore, the two types of chelated iron-based deep eutectic solvents prepared in this work have great application potential in the field of hydrogen sulfide catalytic oxidation.