Hydroxylation Induced Alignment of Metal Oxide Nanocubes

Abstract

Water vapor is ubiquitous under ambient conditions and may alter the shape of nanoparticles. How to utilize water adsorption for nanomaterial functionality and structure formation, however, is a yet unexplored field. Herein, we report the use of water vapor to induce the self-organization of MgO nanocubes into regularly staggered one-dimensional structures. This transformation evolves via an initial alignment of the MgO cubes, the formation of intermediate elongated Mg(OH) structures, and their reconversion into MgO cubes arranged in staggered structures. Ab initio DFT modelling identifies surface-energy changes associated with the cube surface hydration and hydroxylation to promote the uncommon staggered stacked assembly of the cubes. This first observation of metal oxide nanoparticle self-organization occurring outside a bulk solution may pave novel routes for inducing texture in ceramics and represents a great test-bed for new surface-science concepts.

Thin water films and particle morphology evolution in nanocrystalline MgO

“…A TEM analysis reveals that the underlying particle size and shape is uniform throughout all the samples (Figure ). This rules out that the shape of the particles results from an oriented attachment process of the different cubes which would lead to staggered structures and multiple edges at regions of original particle contact and coalescence . Such features and morphological characteristics have not been observed in the course of the TEM investigations of this study (Figure ).…”

“…The properties of related water layers depend on the surface properties of the substrate and are typically very different from those of macroscopically thick films. In such a form, water does not only contribute to the conversion of oxide surface layers into hydroxides, it can also act as a two‐dimensional solvent, which drives the alignment of oxide particles and enables the spontaneous structural and microstructural transformation of particle systems under ambient conditions …”

Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites

“…The respective fields of application range from catalysis, to photoactive sensing devices and solid‐state white light emitters . Moreover, CVS represents a promising route toward ensembles of surface functionalized nanocubes which can be employed as model systems for surface chemistry, to study the formation and transformation of minerals as well as building blocks for the construction of hierarchical structures . As will be shown below, thermal annealing of these metastable nanoparticles provides a playground for the stepwise materials disproportionation and controlled emergence of optical, electronic, or magnetic properties …”

Morphology dependent interaction between Co(ii)-tetraphenylporphyrin and the MgO(100) surface

“…We believe the presence of hydroxyl groups at the MgO steps in the experimental measurements to be a plausible explanation. Hydroxyl groups are not stable on the terraces of MgO(100) at 300 K, but they are readily created at steps through the adsorption and dissociation of residual water from the background of the vacuum chamber 79,88 . It would not be unreasonable for hydroxyl groups to partially passivate the steps and weaken the adsorption at kink-Mg sites to where entropy makes terrace and kink-Mg adsorption equally favourable.…”