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

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 °C. 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 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.