Chromium Carbide Nanosheets Prepared by Selective Etching of Aluminum from Cr₂AlC for Hydrazine Detection

We report on the chemical exfoliation of bulk Cr2AlC to two-dimensional (2D) chromium carbide (Cr2C) nanosheets and its characterization and application for hydrazine sensing. MXenes are a swiftly expanding family of ultrathin 2D nanomaterials with tailorable surface chemistry. MXenes with mixed surface terminations such as oxygen, hydroxyl, and fluorine are mainly synthesized from MAX phase precursors via selective etching of “A” element using fluoride-based etchants. However, etching of Al from Cr2AlC remains challenging due to the similar reactivity of Cr and Al toward the fluoride-based etchants. Herein, a combination of ferric chloride and tartaric acid was employed as an etchant for the first time to exfoliate Cr2AlC. The difference in redox potential and metal-complex-forming ability of the etchant combination were exploited for selective removal of Al from Cr2AlC. Application of the synthesized Cr2C nanosheets with oxygen and hydroxyl surface termination is demonstrated for hydrazine sensing. The proof of concept for utilizing MXene as a receptor in a microresonator is investigated for the first time by coating the cantilever with Cr2CTx nanosheets to detect hydrazine in the ppm level.