Abstract
Metallic nanoparticles (NPs), either supported on a porous oxide framework or finely dispersed within an oxide matrix, find applications in catalysis, plasmonics, nanomagnetism and energy conversion, among others. The development of synthetic routes that enable to control the morphology, chemical composition, crystal structure and mutual interaction of metallic and oxide phases is necessary in order to tailor the properties of this class of nanomaterials. With this work, we aim at developing a novel method for the synthesis of metal/oxide nanocomposites based on the assembly of NPs formed by gas phase condensation of metal vapors in a He/O2 atmosphere. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies. Our goal is to show that the precursor with less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs. The selected case study for this work is the synthesis of a Fe-Co/TiOx nanocomposite, a system of great interest for its catalytic and magnetic properties. By exploiting the new concept, we achieve the desired target, i.e., a nanoscale dispersion of metallic alloy NPs within titanium oxide NPs, the structure of which can be tailored into TiO1-δ or TiO2 by controlling the synthesis and processing atmosphere. The proposed synthesis technique is versatile and scalable for the production of many NPs-assembled metal/oxide nanocomposites.
Highlights
Oxide-supported metal nanoparticles (NPs) are a class of functional materials that find innovative applications in many materials science fields such as catalysis for the production of synthetic hydrocarbons [1,2,3] and CO reduction [4], chemical synthesis [5,6], nanoplasmonics [7] for the development of higher efficiency photovoltaic cells [5,8], and magnetism [9]
We have presented a novel synthesis method for the preparation of metal/oxide nanocomposites based on the physical assembly of nanoparticles (NPs), which are formed by gas phase condensation in a He/O2 atmosphere
This approach goes beyond the simple post-synthesis partial oxidation of elemental [33,34] or alloy [39,40] NPs that can only yield a metal core-oxide shell morphology with obvious compositional restrictions
Summary
Oxide-supported metal nanoparticles (NPs) are a class of functional materials that find innovative applications in many materials science fields such as catalysis for the production of synthetic hydrocarbons [1,2,3] and CO reduction [4], chemical synthesis [5,6], nanoplasmonics [7] for the development of higher efficiency photovoltaic cells [5,8], and magnetism [9]. Much effort has been spent to develop novel and flexible synthesis routes for metal/oxide nanocomposites (NCs). Most of these techniques involve two-step processes, in which a porous oxide host (typically zeolites, Al2O3) or oxide NPs [15] are imbued with a colloidal suspension of metallic NPs produced via physical (e.g., pulsed laser ablation in liquid) or chemical methods (e.g., precipitation and nitride impregnation). Metallic NPs embedded in an oxide matrix can be prepared by a sol–gel method [19,20], again with some limitations on the independent control of the two phases. The deposition of metallic NPs on oxide surfaces is of great importance for fundamental studies on model systems [21], but cannot be used for the synthesis of 3D bulk materials
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