Protic Ionic Liquid‐Mediated Liquid‐Phase Exfoliation of Titanium Disulfide for Photocatalytic CO 2 Reduction Reaction

ABSTRACT The titanium disulfide (TiS 2 ) nanosheets with single or few‐layer structures have attracted major attention due to the unique photoelectrochemical properties. However, the lack of efficient, green, and scalable methods for preparing TiS 2 nanosheets has severely limited their practical applications. Herein, four kinds of protic ionic liquids ([C 6 H 8 N][CH 3 O 3 S], [C 6 H 8 N][CH 4 NO 3 S], [C 6 H 8 N][C 6 H 12 O 5 P], and [C 6 H 8 N][C 4 H 2 NO 2 ]) were designed and synthesized as intercalation reagents. Combined with the green solvent γ ‐valerolactone, the TiS 2 nanosheets with single‐layer and few‐layers were successfully prepared via the liquid‐phase exfoliation strategy. This strategy achieved a high exfoliation yield of 35.5%, with the resulting nanosheets exhibiting a thickness of 1–2 nm and lateral dimension of about 4 μm. The alkalinity of anions in ionic liquids had a significant impact on the stripping yield. The exfoliation mechanism indicated that the strong Lewis acid–base interaction of NH 2 groups of cations and the C=O or C‐N bonds of anions in ionic liquids with TiS 2 weakened the interlayer forces of TiS 2 to successfully achieve the exfoliation of TiS 2 nanosheets at the assistance of ultrasound. In addition, as a photocatalyst, the TiS 2 nanosheets demonstrated a CO production rate of 103.3 μmol·g −1 h −1 with a selectivity exceeding 90%, which was over 35 times higher than that of bulk TiS 2 powder (2.9 μmol·g −1 h −1 ). These nanosheets also show the exceptional photocatalytic stability.