(183n) High-Yield Production of Boron-Based Nanosheets from Magnesium Diboride By Dissolution and Recrystallization in Water

Layered metal diborides
that contain metal atoms sandwiched in between boron honeycomb planes offer a rich
opportunity to access graphenic forms of boron. We have recently demonstrated
that Magnesium diboride (MgB2) can be exfoliated by ultrasonication in water to
yield boron-based nanosheets. However, the knowledge on the fate of metal
boride crystals in an aqueous phase is still in its incipient stages. This work
presents our preliminary findings on the discovery that MgB2 crystals can
undergo dissolution in water under ambient conditions to result in precursors
(pre-nucleation clusters), which upon aging, undergo a non-classical
crystallization preferentially growing in lateral directions by two-dimensional
(2D) oriented attachments. We show that this recrystallization can be utilized
as an avenue to obtain a high yield (~92%) of boron-based nanostructures, including
nanodots, nanodiscs, nanoflakes, and nanosheets/nanogarlands. These
nanostructures are found to comprise of boron honeycomb planes chemically
modified with hydride and oxy functional groups, resulting in overall negative
charge on their surfaces. This ability of MgB2 crystals to yield pre-nucleation
clusters, which can self-seed to form nanostructures comprising chemically
modified boron honeycomb planes, presents a new facet to the physicochemical
interaction of MgB2 with water. These findings also open newer avenues to
obtain boron-based nanostructures with tunable morphologies by varying the
chemical milieu during recrystallization.

Figure 1:
Dissolution and recrystallization of MgB_2­ crystals in water to
yield diverse morphologies of boron-based nanostructures analogous to graphene