In the Space Between: Interlayer Alkali Metal-Dependent Exfoliation of ACrO2 (A = Li, Na, K)

Abstract

Two-dimensional (2D) materials exhibit tunable properties, high surface-to-volume ratios, and high mechanical strength, making them attractive for applications in electronics, catalysis, and energy storage. However, conventional methods like mechanical exfoliation or high-temperature synthesis are limited in scalability and restrict the range of accessible 2D materials, motivating the development of alternative synthetic approaches. Among these, chemical deintercalation of layered compounds containing interlayer alkali ions offers a potential method of producing tunable, high quality, and ultrathin sheets. Still, the role of the intercalated cation in determining exfoliation outcomes remains incompletely understood. Here, ACrO2 (A = Li, Na, K) is investigated as a model system and undergoes three chemical deintercalation and exfoliation methods: solvent reaction, proton exchange, and oxidative extraction with acid treatment. Powder X-ray diffraction was used to characterize the structural changes of products located at the bottom of the vial after chemical processing, alongside transmission electron microscopy to track the structural and morphological changes of the exfoliated nanosheets found in the supernatant. It is shown that all alkali metals allow the formation of exfoliated nanosheets that adopt a crystalline Cr2O3 structure. Still, bulk LiCrO2 remains largely unchanged, while NaCrO2 and KCrO2 undergo significant deintercalation and structural transformations following various chemical treatments to form crystalline CrOOH. These findings highlight the crucial role of interlayer cations in determining exfoliation outcomes and could potentially pave the path for controlled nanosheet synthesis in layered oxides for scalable 2D material production.