posted on 2019-06-24, 08:13authored byAhmed
S. Etman, Andrew J. Pell, Peter Svedlindh, Niklas Hedin, Xiaodong Zou, Junliang Sun, Diana Bernin
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.