Microscopic Investigation of Chemoselectivity in Ag–Pt–Fe₃O₄ Heterotrimer Formation: Mechanistic Insights and Implications for Controlling High-Order Hybrid Nanoparticle Morphology

Abstract

Three-component hybrid nanoparticle heterotrimers, which are important multifunctional constructs that underpin diverse applications, are commonly synthesized by growing a third domain off of a two-component heterodimer seed. However, because heterodimer seeds expose two distinct surfaces that often can both support nucleation and growth, selectively targeting one particular surface is critical for exclusively accessing a desired configuration. Understanding and controlling nucleation and growth therefore enables the rational formation of high-order hybrid nanoparticles. Here, we report an in-depth microscopic investigation that probes the chemoselective addition of Ag to Pt-Fe3O4 heterodimer seeds to form Ag-Pt-Fe3O4 heterotrimers. We find that the formation of the Ag-Pt-Fe3O4 heterotrimers initiates with indiscriminate Ag nucleation onto both the Pt and Fe3O4 surfaces of Pt-Fe3O4, followed by surface diffusion and coalescence of Ag onto the Pt surface to form the Ag-Pt-Fe3O4 product. Control experiments reveal that the size of the Ag domain of Ag-Pt-Fe3O4 correlates with the overall surface area of the Pt-Fe3O4 seeds, which is consistent with the coalescence of Ag through a surface-mediated process and can also be exploited to tune the size of the Ag domain. Additionally, we observe that small iron oxide islands on the Pt surface of the Pt-Fe3O4 seeds, deposited during the formation of Pt-Fe3O4, define the morphology of the Ag domain, which in turn influences its optical properties. These results provide unprecedented microscopic insights into the pathway by which Ag-Pt-Fe3O4 heterotrimer nanoparticles form and uncover new design guidelines for the synthesis of high-order hybrid nanoparticles with precisely targeted morphologies and properties.

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

“…On the basis of competently designed control experiments, the observed chemoselectivity was preliminarily assumed to correlate with an electron enrichment of the Pt domains in the Fe 3 O 4 -Pt hetero-dimer seeds due to charge transfer from the adjacent Fe 3 O 4 domain (a process not achievable in isolated Pt nanoparticles, in fact). Further microscopic investigations of chemoselectivity in the formation of Ag-Pt-Fe 3 O 4 hetero-trimer MHNCs (Hodges et al, 2015) (Hodges et al, 2015). In line with these results, further studies have been successfully extended to the case of ternary Au-Pt-Cu x S y HNCs synthesized upon chemoselective metal-sulfide deposition over preformed Pt-Au hetero-dimers (Bradley et al, 2015).…”

Metal/semiconductor interfaces in nanoscale objects: synthesis, emerging properties and applications of hybrid nanostructures

“…253 In Fig. 10, some possible heterotrimer morphologies are depicted resulting from deposition of material 'C' on 'A-B' dimers that were formed in a previous step, adapted from Hodges et al 253 The Schaak group has thoroughly investigated the depicted heterostructures, [253][254][255][256] and has even expanded the breadth of these methods, for example, by introduction of a solid-state protective group. Without a protective group (from A-B to C-A-B, marked with a green arrow in Fig.…”

Synthesis of Colloidal Molecules: Recent Advances and Perspectives

“…This chemoselectivity was initially assumed to correlate with the electron enrichment of the Pt crystals due to charge transfer from the adjacent Fe 3 O 4 crystal. But electron microscopy investigations on the Fe 3 O 4 ‐Pt‐Ag system showed that in the first moments Ag nucleate on both domains, and then surface diffuse and coalesce onto the Pt one . In order to promote the formation of the other isomer, namely Ag‐Fe 3 O 4 ‐Pt, the organic‐chemistry concept of protecting group was extended by creating a thin amorphous shell of iron oxide on the Pt domain of the Fe 3 O 4 ‐Pt seed to redirect successfully the Ag nucleation to the otherwise disfavored Fe 3 O 4 site .…”

“…But electron microscopy investigationso nt he Fe 3 O 4 -Pt-Ag system showed that in the first momentsA gn ucleate on both domains, and then surface diffuse and coalesce onto the Pt one. [30] In order to promote the formationo ft he other isomer,n amely Ag-Fe 3 O 4 -Pt, the organic-chemistryc oncept of protecting group was extended by creating at hin amorphous shell of iron oxide on the Pt domain of the Fe 3 O 4 -Pt seed to redirect successfully the Ag nucleation to the otherwise disfavored Fe 3 O 4 site. [31] It may be observed that the as-obtained AXY-type CMs are not systematically linear.…”