A facile, reliable, general, and robust synthetic method for preparation of high-quality, (100)-terminated Pt(3)M nanocubes (M = Pt or 3d-transition metals Co, Fe, and Ni) has been developed. It was identified that addition of W(CO)(6) is crucial for control of the nucleation process when the metallic precursors are reduced, whereas an optimized ratio of the solvent pair, oleylamine and oleic acid, is the key to enabling the lowest total surface energy on {100} facets in order to develop cubic nanocrystals in the present system. The resultant monodisperse nanocubes, in which Pt is partially substituted, are expected to exhibit unusual electrocatalytic characteristics, providing an alternative for developing high-performance electrocatalysts for use in fuel cells.
Shape-controlled catalysis: High-quality Pt-Cu nanocubes with an average size of about 8 nm (see picture, scale bar = 20 nm) were synthesized from a high-temperature organic solution system in the presence of various capping ligands. These cubic Pt-Cu nanocrystals terminated with {100} facets demonstrated a superior catalytic activity towards methanol oxidation compared to similar sized Pt-Cu and Pt nanospheres.
High-quality ZnS, ZnS:Mn2+, and ZnS:Mn2+/ZnS (core/shell) nanocrystals (NCs) were synthesized via a high-boiling solvent process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The monodisperse ZnS NCs (size = 8 nm), which self-assembled into several micrometer-sized domains, were achieved by adopting poly(ethylene glycol) (PEG) in the reaction process (without using a size-selection process). The obtained ZnS:Mn2+ and ZnS:Mn2+/ZnS core/shell NCs are highly crystalline and quasimonodisperse with an average particle size of 6.1 and 8.4 nm, respectively. All of the as-formed NCs can be well dispersed in hexane to form stable and clear colloidal solutions, which show strong visible emission (blue for ZnS and red-orange for ZnS:Mn2+ and ZnS:Mn2+/ZnS) under UV excitation. The growth of a ZnS shell on ZnS:Mn2+ NCs, that is, the formation of ZnS:Mn2+/ZnS core/shell NCs, resulted in a 30% enhancement in the PL intensity with respect to that of bare ZnS:Mn2+ NCs due to the elimination of the surface defects.
Bimetallic convex and concave nanocrystals are an ideal platform that is intriguing for Surface-Enhanced Raman Scattering performance and for various catalytic applications, due to the existence of "hot spots" and high-indexed lattice planes on these unique nanostructures. These unique features can be further tuned by facilitating their surface "roughness," selecting surface facet, and utilizing lattice strain through shape-control and composition-control manipulations. This chapter focuses on this nano-architecture family, and covers their synthetic strategies, structural characterization and various selected properties. In each section, case studies are provided to discuss the topics in depth.
SnO2 has successfully been doped into octahedral In2O3 nanoparticles using a high-temperature nonaqueous reaction. The resultant ITO nanoparticles exhibit a particle/crystal decrease in size, sphericity in morphology, and enhancement in photoluminescence.
Yttrium oxide (Y2O3) microprisms with interesting trilobal cross section were synthesized through a large-scale and facile hydrothermal method followed by a subsequent heat treatment. The size of the Y2O3 trilobal prisms could be modulated from micro- to submicroscale with the increase of pH value. The as-formed products via the hydrothermal process, monoclinic yttrium oxide hydroxide nitrate, Y4O(OH)9(NO3), could transform to cubic Y2O3 with the same morphology after annealing at high temperatures. The formation mechanism for the Y4O(OH)9(NO3) trilobal prisms has been proposed. Under hydrothermal conditions, the synergistic effect of Y-type aggregates of primary Y4O(OH)9(NO3) nanorods and sequent preferential of different crystal planes resulted in the formation of trilobal prisms.
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