Mesocrystals from Platinum Nanocubes

Abstract

Platinum nanoparticles are widely known for their numerous electrochemical and catalytic applications. Enhanced or novel properties that may arise when ordering such particles in a highly defined manner, however, are still subject to ongoing research, as superstructure formation on the mesoscale is still a major challenge to be overcome. In this work, we therefore established a reproducible method to fabricate micrometer-sized superstructures from platinum nanocubes. Through small-angle X-ray scattering and electron diffraction methods we demonstrate that the obtained superstructures have a high degree of ordering up to the atomic scale and, therefore, fulfill all criteria of a mesocrystal. By changing the solvent and stabilizer in which the platinum nanocubes were dispersed, we were able to control the resulting crystal habit of the mesocrystals. Aside from mesocrystal fabrication, this method can be further utilized to purify nanoparticle dispersions by recrystallization with respect to narrowing down the particle size distribution and removing contaminations.

3D Binary Mesocrystals from Anisotropic Nanoparticles

“…This method has already been reported for cubic iron oxide as well as platinum nanoparticles. [32,44] Ar ecrystallized particle sample is shown in Figure 1a.I no rder to gain insight into the specific mesocrystal structure of our samples with regards to applicable characteristics,w hich can be exploited for ab inary mesocrystal formation, further in-depth experiments were conducted. Recrystallized IONCs have been assembled from hexane into tetragonal-shaped 10-30 mms ized mesocrystals by using the gas-phase diffusion technique (Figure 1b)a nd subsequently broken apart with amicromanipulator to reveal their inner bulk structure.F ield-Emission Scanning Electron Microscopy (FE-SEM) imaging at very high resolutions displayed that our IONC particles preferably self-assemble into stacked layers of hexagonally ordered particles (Figure 1b-d).…”

“…Thec oncentration of the particle mixture had to be significantly reduced by af actor of 5, to avoid mono-phase formation of pure IONC-and pure PtNC-based mesocrystals separately.W eh ypothesize here that the reason behind the impossibility to form reverse binary mesocrystals at high particle concentrations lies in the formation kinetic discrepancy between PtNC and IONC as reported in our preceding research. [32,44] While the formation of aP tNC host lattice takes 10-14 days in hexane,t he development of IONC-based mesocrystals usually occurs in less than 7days.T his results in the consumption of the majority of the IONCs before the PtNC host lattice can form. We assume that areduced particle concentration prevents the IONCs from reaching acritical particle concentration (CPC) during the gas-phase diffusion process within the set crystallization period of 14 days,w hich would otherwise trigger IONC cluster formation and ultimately result in am onophase mesocrystal formation.…”

“…[29,30] These findings are not exclusive to iron oxide nanoparticles,a sasimilar behavior could be further demonstrated on the example of platinum nanocubes. [31,32] When it comes to the growth of multicomponent superlattices however,t he assembly process is far more sophisticated due to the distinct pairwise interactions alongside the space-filling rules that often drive self-assembly and potential particle fusion in the first place. [33][34][35] So-called binary nanocrystal superlattices (BNSLs) have been investigated intensively in recent years,asthe resulting metamaterials promise to show exciting new properties because of their structuredependent collective properties and self-organization.…”

Titelbild: Binäre 3D‐Mesokristalle aus anisotropen Nanopartikeln (Angew. Chem. 2/2022)

“…This method has already been reported for cubic iron oxide as well as platinum nanoparticles. [32,44] A recrystallized particle sample is shown in Figure 1 a. In order to gain insight into the specific mesocrystal structure of our samples with regards to applicable characteristics, which can be exploited for a binary mesocrystal formation, further in-depth experiments were conducted.…”

“…[29,30] These findings are not exclusive to iron oxide nanoparticles, as a similar behavior could be further demonstrated on the example of platinum nanocubes. [31,32] When it comes to the growth of multicomponent superlattices however, the assembly process is far more sophisticated due to the distinct pairwise interactions alongside the space-filling rules that often drive self-assembly and potential particle fusion in the first place. [33][34][35] So-called binary nanocrystal superlattices (BNSLs) have been investigated intensively in recent years, as the resulting metamaterials promise to show exciting new properties because of their structuredependent collective properties and self-organization.…”