Assembly of Colloidal Clusters Driven by the Polyhedral Shape of Metal–Organic Framework Particles

Abstract

Control of the assembly of colloidal particles into discrete or higher-dimensional architectures is important for the design of myriad materials, including plasmonic sensing systems and photonic crystals. Here, we report a new approach that uses the polyhedral shape of metal–organic-framework (MOF) particles to direct the assembly of colloidal clusters. This approach is based on controlling the attachment of a single spherical polystyrene particle on each face of a polyhedral particle via colloidal fusion synthesis, so that the polyhedral shape defines the final coordination number, which is equal to the number of faces, and geometry of the assembled colloidal cluster. As a proof of concept, we assembled six-coordinated (6-c) octahedral and 8-c cubic clusters using cubic ZIF-8 and octahedral UiO-66 core particles. Moreover, we extended this approach to synthesize a highly coordinated 12-c cuboctahedral cluster from a rhombic dodecahedral ZIF-8 particle. We anticipate that the synthesized colloidal clusters could be further evolved into spherical core–shell MOF@polystyrene particles under conditions that promote a higher fusion degree, thus expanding the methods available for the synthesis of MOF–polymer composites.

Exploiting anisotropic particle shape to electrostatically assemble colloidal molecules with high yield and purity

“…[22] The shape of the central particle may further limit the number of adsorbed spheres. [24] To test the effects of electrostatic interactions and shape of the central core, we exploited the predictive power of numerical simulations to investigate their combined influence on the size and yield of the assembled clusters for different size ratios. We run Monte Carlo simulations in which a repulsive and an attractive Yukawa pair potential account for the screened Coulomb interactions between spherical satellite particles of diameter σ s , and between the latter and the cubic core with edge length σ c , respectively.…”

“…The robustness of the resulting colloidal molecules towards variation in the size ratio also explains why colloidal molecules based on templating polyhedral particles could be achieved without an extensive search for optimal size ratios. [24] In the case of adsorption onto a cube, the available space for binding a second sphere to a facet is greatly reduced when a sphere is already attached to that facet. For α 1.2, the anisotropic shape of the central particle has no or little effect on the number and organization of bound particles.…”

“…Assembly can be driven by a manifold of approaches ranging from the hybridization of surface-bound [17] or surface-mobile DNA linkers, [18] hydrophobic [19] and depletion interactions, [20] to the assembly driven by opposite charges. [21,22,23,24] On the other hand, they also require strategies to limit the assembly to finite-sized clusters with a predetermined valence, [25,26,27,28] a mechanism to achieve a uniform arrangement of the constituent particles in the clusters, and separation of the resultant colloidal molecules by their size or type.…”

“…A straightforward self-assembly approach for producing colloidal molecules from binary mixtures of colloidal spheres is hetero-aggregation through electrostatic interactions. [17,29,23,22,24] In this procedure, two particle species with opposite surface charge are selected and mixed such that they aggregate in solution. This aggregation process can be considered irreversible, meaning that when the particles are linked they fluctuate at most near their contact position.…”

“…[29] In contrast, if polyhedral metal-organic framework particles were used as the center of the cluster, it was found that their geometry in principle sets the cluster size. [24] For sufficiently high number ratios, the polyhedral shape allows for adsorption of one sphere per facet if the adsorbing spheres are neither too large nor too small. However, how the size ratio is connected to the successful assembly of highly coordinated clusters and thus whether this strategy is robust to polydispersity was not investigated.…”