Self-Assembled Faceted Mesocrystals: Advances in Optimization of Growth Conditions

One aspect of the research on mesocrystals nowadays focuses on applications, whereby such applications demand mesocrystals with a tunable size. To achieve this task, more effort needs to be undertaken to understand how mesocrystals form, which parameters influence mesocrystal formation, and which kind of structure results from the nanoparticle assembly. Within this communication, we demonstrate for faceted mesocrystals assembled from iron oxide nanocubes stabilized by oleic acid that the proper choice of crystallization conditions in the gas phase diffusion setup is essential to achieve this task. The appropriate choice of substrate, dispersion and destabilizing agents, additive, nanocrystal concentration, crystallization kinetics, and duration allows growing faceted iron oxide mesocrystals with sizes ranging from a few micrometers up to almost a millimeter. By these findings supported by light and scanning electron microscopy, we show that in this system, heterogeneous nucleation is the predominant mechanism for mesocrystal formation on a solid substrate. Additionally, other surfactants than oleic acid can also act as molecular additives to support mesocrystal growth. These findings should be transferable to tune the size and quality of other self-assembled mesocrystals.