Insights into the Exfoliation Process of V₂O₅·nH₂O Nanosheet Formation Using Real-Time ⁵¹V NMR

Nanostructured hydrated vanadium oxides (V₂O₅·nH₂O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V₂O₅·nH₂O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V₂O₅·nH₂O nanosheets from the V₂O₅ and VO₂ precursors in real time using solution- and solid-state ⁵¹V NMR. Solution-state ⁵¹V NMR showed that the aqueous solution contained mostly the decavanadate anion [H₂V₁₀O₂₈]^4- and the hydrated dioxovanadate cation [VO₂·4H₂O]⁺, and during the exfoliation process, decavanadate was formed, while the amount of [VO₂·4H₂O]⁺ remained constant. The conversion of the solid precursor V₂O₅, which was monitored with solid-state ⁵¹V NMR, was initiated when VO₂ was in its monoclinic forms. The dried V₂O₅·nH₂O nanosheets were weakly paramagnetic because of a minor content of isolated V⁴⁺. Its solid-state ⁵¹V signal was less than 20% of V₂O₅ and arose from diamagnetic V⁴⁺ or V⁵⁺.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.