posted on 2021-07-02, 20:04authored byDaniel Thomele, Stefan O. Baumann, Johannes Schneider, Andreas K. Sternig, Sarah Shulda, Ryan M. Richards, Thomas Schwab, Gregor A. Zickler, Gilles R. Bourret, Oliver Diwald
Developing simple,
inexpensive, and environmentally benign approaches
to integrate morphologically well-defined nanoscale building blocks
into larger high surface area materials is a key challenge in materials
design and processing. In this work, we investigate the fundamental
surface phenomena between MgO and water (both adsorption and desorption)
with particles prepared via a vapor-phase process (MgO nanocubes)
and a modified aerogel process (MgO(111) nanosheets). Through these
studies, we unravel a strategy to assemble individual MgO nanoparticles
into extended faceted single-crystalline MgO nanosheets and nanorods
with well-defined exposed surfaces and edges. This reorganization
can be triggered by the presence of H2O vapor or bulk liquid
water. Water adsorption and the progressive conversion of vapor-phase
grown oxide particles into hydroxides give rise to either one-dimensional
or two-dimensional (1D or 2D) structures of high dispersion and surface
area. The resulting Mg(OH)2 lamella with a predominant
(001) surface termination are well-suited precursor structures for
their topotactic conversion into laterally extended and uniform MgO(111)
grain surface configurations. To understand the potential of polar
(111) surfaces for faceting and surface reconstruction effects associated
with water desorption, we investigated the stability of MgO(111) nanosheets
during vacuum annealing and electron beam exposure. The significant
surface reconstruction of the MgO(111) surfaces observed shows that
adsorbate-free (111)-terminated surfaces of unsupported MgO nanostructures
reconstruct rather than remain as charged planes of either three-fold
coordinated O2– ion or Mg2+ ions. Thus,
here we demonstrate the role water can play in surface formation and
reconstruction by bridging wet chemical and surface science inspired
approaches.