Nonclassical Recrystallization

Abstract

Applications in the fields of materialss ciencea nd nanotechnology increasingly demand monodisperse nanoparticles in size and shape. Up to now,n og eneral purification procedure exists to thoroughly narrow the size and shape distributions of nanoparticles.H ere, we show by analytical ultracentrifugation (AUC)a sa na bsolute and quantitative high-resolutionm ethod that multiple recrystallizations of nanocrystals to mesocrystalsi savery efficient tool to generate nanocrystals with an excellent and so-far unsurpassed size-distribution(PDI c = 1.0001)a nd shape. Similart o the crystallization of molecular building blocks, nonclassical recrystallization removes "colloidal" impurities(i.e.,n anoparticles,w hich are different in shape and size from the majority) by assembling them into am esocrystal. In the case of nanocrystals, this assembly can be size-and shape-selective, since mesocrystals show both long-range packing ordering and preferable crystallographic orientation of nanocrystals. Besides the generation of highly monodisperse nanoparticles, these findings provide highly relevant insights into the crystallization of mesocrystals.

Mesocrystals from Platinum Nanocubes

“…So far, we were able to demonstrate the feasibility of the gas-phase diffusion technique to synthesize platinum-nanocube-based mesocrystals analogous to iron oxide nanocubes. In a complementary study, our group further reported on the utilization of this method for recrystallization of a stable particle dispersion to narrow down its size distribution [ 41 ]. Similar to recrystallization, as it is commonly used in organic and inorganic preparative chemistry, a batch of crude nanoparticles can slowly crystallize from solution as described above.…”

Morphogenesis of Magnetite Mesocrystals: Interplay Between Nanoparticle Morphology and Solvation Shell

“…The more this value deviates from 1, the higher is the degree of truncation of the cubic particles: batch I: 0.927; batch II: 0.942; batch III: 0.940; batch IV: 0.931.These nanocrystals were assembled to mesocrystals using either an adapted approach of the "gas phase diffusion technique" (to form faceted 3D mesocrystals) or evaporation induced self-assembly (to form mesocrystalline 2D/3D films). 13,64,68,69 A simplified illustration of the experimental setups of the different techniques is presented in Figure 1. In the case of the gas phase diffusion technique (Figure 1 a), the destabilizing diffusion phase infiltrates the nanoparticle dispersion via the gas phase.…”

Advances of Non-Classical Crystallization Towards Self-Purification of Precious Metal Nanoparticles Mixtures

“…1,2 Particle-mediated crystallization (i.e., "non-classical crystallization") offers a principial different approach to achieve the same task. 3,4 Nanoparticle self-assembly to ordered structures and classical crystallization by ions and molecules share some similarities, which makes it possible to use some common techniques and principles to control crystallization processes. One of the easiest methods to purify nanoparticles by self-assembly is a drying-mediated approach where a drop of NC dispersion is placed on top of a substrate and dried.…”

“…11 In our recent work on cubic iron oxide nanocrystals, we showed that repeated recrystallization of mesocrystals could be successfully used to remove the colloidal impurities and overall tremendously narrow the particle size and shape distribution and achieve a PDIc up to 1.0001. 3 All above mentioned methods were mainly used for either big colloidal particles with sizes more than 100 nm or relatively small ones with sizes well below 20 nm. Precious metal nanoparticles can be easily synthesized in quite good quality also with sizes between 30 and 100 nm.…”

“…24 Misshaped particles with no defined packing behavior are excluded to the rim of both phases following self-assembly behavior reported previously for magnetite and Pt NCs. 3,4,11 A more thorough exclusion of misshaped particles occurs for batches with smaller particles size, indicating that a successful particle separation benefits from a higher mobility in solution and a partially reversible attachment to the growing crystalline domains. This is highly influenced by the particle size and strengthens the argument of a partially entropic pathway.…”