posted on 2017-04-05, 00:00authored byMichal Wojcik, Yunqi Li, Wan Li, Ke Xu
The
potential of rising two-dimensional materials, such as graphene,
can be substantially expanded through chemistry. However, it has been
a challenge to study how chemical reactions of two-dimensional materials
progress. Existing techniques offer limited signal contrast and/or
spatial-temporal resolution and are difficult to apply to in situ studies. Here we employ an optical approach, namely
interference reflection microscopy, to quantitatively monitor the
redox reaction dynamics of graphene and graphene oxide (GO) in situ with diffraction-limited (∼300 nm) spatial
resolution and video-rate time resolution. Remarkably, we found that
the oxidation kinetics of graphene is characterized by a seeded, autocatalytic
process that gives rise to unique, wave-like propagation of reaction
in two dimensions. The reaction is initially slow and confined to
highly localized, nanoscale hot spots associated with structural defects,
but then self-accelerates while propagating outward, hence flower-like,
micrometer-sized reaction patterns over the entire sample. In contrast,
the reduction of GO is spatially homogeneous and temporally pseudo-first-order,
and through in situ data, we further identify pH
as a key reaction parameter.