Highly-efficient H2S capture by deep eutectic solvents based on ionic liquid hybridized polyoxometalate: Insights into conformational transitions and structure-activity relationships

Abstract

While the combination of polyoxometalates (POM) with green solvents has attracted considerable interest, the application of desulfurization in non-aqueous solvents remains a challenge, and a systematic understanding of the reaction mechanism and the conformational contributions is still lacking. Herein, the long-chain ionic liquids hybrid polyoxometalates deep eutectic solvents (PCDES) system was designed and constructed by combining two materials possessing the background of ionic liquid (ILs), alkyl long-chain ionic liquids hybrid polyoxometalates (POM-ILs) and ILs-based deep eutectic solvents (DES), to realize the liquid-phase desulfurization application of POM-ILs hybrid materials. Guided by density functional theory (DFT) calculations and characterization analyses, the “cloverleaf” conformational transition theory was firstly proposed to explain the desulfurization mechanism of PCDES. The exposure of the desulfurization active site, the expansion of the hydrogen sulfide (H₂S) capturing range, and the charge chain transfer behavior are the critical success factors for the enhancement of the PCDES desulfurization performance. The optimal desulfurizer PCDES@3C₁₄-2Im can be maintained at 100% desulfurization efficiency for nearly 150 min over a wide temperature range of 25-200 ^oC. Furthermore, the complete regeneration of the desulfurizer can be realized by adding hydrogen peroxide (H₂O₂), and more than 98% desulfurization efficiency can still be maintained after multiple cycles. The final desulfurization product is sulphate, which satisfies the harmless treatment of H₂S under the framework of green engineering. This work facilitates the deep fusion applications of polyoxometalate chemistry with green solvents and opens a fresh perspective for the investigation of structure-performance relationships of polyoxometalate non-aqueous liquid-phase desulfurizers.

Environmental Implication

Considering the current urgent demand for environmental protection, the treatment of H₂S holds significant practical importance. The PCDES system proposed in this study achieves efficient H₂S capture and conversion in a wide temperature range through a unique “core-shell” to “cloverleaf” conformational transition. H₂S is converted into stable and environmentally friendly sulfate, realizing the green closed-loop treatment of H₂S. It reduces the use of chemical reagents, resource consumption and environmental burden. This proposal offers a new perspective on efficient air pollution control technology and is expected to overcome the technical bottlenecks of traditional wet oxidation desulfurization.