Insights into the Exfoliation Process of VO·HO Nanosheet Formation Using Real-Time V NMR.

Nanostructured hydrated vanadium oxides (VO·HO) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating VO·HO nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of VO·HO nanosheets from the VO and VO precursors in real time using solution- and solid-state V NMR. Solution-state V NMR showed that the aqueous solution contained mostly the decavanadate anion [HVO] and the hydrated dioxovanadate cation [VO·4HO], and during the exfoliation process, decavanadate was formed, while the amount of [VO·4HO] remained constant. The conversion of the solid precursor VO, which was monitored with solid-state V NMR, was initiated when VO was in its monoclinic forms. The dried VO·HO nanosheets were weakly paramagnetic because of a minor content of isolated V. Its solid-state V signal was less than 20% of VO and arose from diamagnetic V or V.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.