Composition-Based Separation of Pt–Fe₃O₄ Hybrid Nanoparticles by Thermal Field-Flow Fractionation

Abstract

Colloidal hybrid nanoparticles integrate two or more material domains into a single construct to achieve multifunctionality and synergistic properties. The synthesis of these complex multicomponent hybrid nanoparticles often yields size and composition distributions that subsequently impact observed properties and complicate structure–function studies. Analyses of nanoparticle systems such as these that contain multiple simultaneously occurring distributions are highly challenging. In this work, we introduce thermal field-flow fractionation (ThFFF) as an analytical method to separate and characterize iron oxide (Fe3O4), platinum (Pt), and multicomponent platinum–iron oxide (Pt–Fe3O4) hybrid nanoparticles by composition. The transport of matter by a temperature gradient or thermal diffusion is exploited in the ThFFF separation and characterization of inorganic nanoparticles. Thermal diffusion coefficient (DT ) values are determined from measured ThFFF retention times and translational diffusion coefficients. The DT for pure Fe3O4 and pure Pt are found to bracket those determined for hybrid Pt–Fe3O4 nanoparticles, demonstrating a proportionality between DT and composition. Furthermore, composition distributions can be determined since measured DT values vary as a function of retention time. The correlation of DT -derived cumulative distribution plots with TEM-EDS results confirmed the compositional polydispersity within hybrid nanoparticle populations. This composition-based fractionation of multicomponent inorganic nanoparticles provides insights into the fundamental forces governing thermal diffusion and highlights the ability of this technique for complex nanoparticle separations and analyses.

Ligand-mediated formation of Cu/metal oxide hybrid nanocrystals with tunable number of interfaces

“…the faceted morphology of the Cu domain in Fig. 8d, which might stem from some effects induced by the crystallinity of ZrO 2 seeds 3,6,16,17,[22][23][24][25]33,34 ), the results suggest that the method is indeed general.…”

“…Congurations of HNCs similar to Cu/(CeO 2 ) 2 and Cu/(CeO 2 ) 6 have been previously reported in the literature and were oen referred to as oweror clover-like structures. 3,6,16,17,[22][23][24][25] However, in these examples, the HNC core always consists of the NC seeds. Oppositely, in Cu/(CeO 2 ) 2 and Cu/(CeO 2 ) 6 , the core is the nucleating Cu domain while the "petals" are the ceria seeds, which is both unique and surprising.…”

“…As for the mechanism, the formation of abovementioned oweror cloverlike structures has been correlated to the polarity of the solvent, the change of seed size or structure (single crystal vs. multitwinned) and the reaction time. 3,6,16,17,[22][23][24][25] In our system, the solvent and the seeds are the same for all of the HNCs so their inuence on the heterojunction formation can be ruled out. Instead, the chemical nature of the ligands clearly plays a signicant role.…”

“…9,[13][14][15] One of the challenges in these systems is the tendency of the non-noble metal domain to easily oxidize, which limits the reaction environment to organic solvent, and precludes the possibility of using the metal as a seed for the growth of the oxide domain, which is a common approach for HNCs. 6,[16][17][18] In this work, we choose Cu/CeO 2 HNCs as one example of this class of materials because of the relevance of this interface for various applications, including thermal and electrochemical CO 2 conversion. 9,19,20 We report a ligand-mediated synthesis to access Cu/(CeO 2 ) n , with n ¼ 1, 2, 6 representing the average number of Cu/CeO 2 heterojunctions in each particle.…”

Field‐flow fractionation for nanoparticle characterization

“…Thus, the diversity of both NPs and their applications is highlighted. More and more manufactured NPs are structured with a complex fine architecture such as core-shells with single or double layer [14], hybrid nanoflowers [15], multiblock copolymer arrangements, or nanosheets [16], and /or with shapes far from the sphere, typically nanosheets, nanoplatelets, nanofibers, and nanotubes [13,[16][17][18][19][20][21][22][23][24]. Advanced characterization is, therefore, necessary to determine and /or confirm the arrangement of the NP assembly, as well as its properties.…”