We report a facile method to fabricate CuNi nano-octahedra and nanocubes using a colloidal synthesis approach. The CuNi nanocrystals terminated with exclusive crystallographic facets were controlled and achieved by a group of synergetic capping ligands in a hot solution system. Specifically, the growth of {111}-bounded CuNi nano-octahedra is derived by a thermodynamic control, whereas the generation of {100}-terminated CuNi nanocubes is steered by a kinetic capping of chloride. Using a reduction of 4-nitrophenol with sodium borohydride as a model reaction, CuNi nano-octahedra and nanocubes demonstrated a strong facet-dependence due to their different surface energies although both exhibited remarkable catalytic activity with the high rate constant over mass (k/m). A kinetic study indicated that this is a pseudo first-order reaction with an excess of sodium borohydride. CuNi nanocubes as the catalysts showed better catalytic performance (k/m = 385 s-1•g-1) than the CuNi nano-octahedra (k/m = 120 s-1•g-1), indicating that 4-nitrophenol and hydrogen were adsorbed on the {100} facets with their molecules parallel to the surface much easier than those on {111} facets.

Ceria (CeO2) possesses a distinctive redox property due to a reversible conversion to its nonstoichiometric oxide and has been considered as a promising catalyst in the oxidative coupling of methane. Since a heterogeneously catalytic process usually takes place only on the surface of catalysts, it is reasonably expected that the performance of a catalyst, such as CeO2, highly relies on its size- and shape-dependent surface structure. We report our recent progress in achieving exclusive crystal facet-terminated CeO2 nanocrystals using a shape-controlled synthesis protocol in a one-pot colloidal system. We modified a two-phase solvothermal approach to fabricate cubic and truncated octahedral CeO2 nanocrystals with a size-control. During the two-phase solvothermal process, we propose that the Ce-precursors transfer from the aqueous layer to the interface of the organic phase, promoted by the capping ligands (as known as phase-transfer catalysts), for the oxidation and nucleation, and subsequently form CeO2 nanocrystals in the organic layer. As different capping ligands favor binding on diverse crystal facets, tuning the composition of the capping ligand with a precise control could generate nanocrystals that are dominated by a single type of facets with a relatively narrow size distribution.

In this work, we demonstrate a size-controlled synthesis of CuNi octahedral nanocrystals (NCs) using a hot colloidal solution approach. Two different sizes of CuNi nano-octahedra are chosen and investigated. It is determined that the reagent concentration remarkably plays a key role in the formation of the size-defined CuNi octahedral NCs. In terms of the reduction of 4-nitrophenol (4-NP), it uncovers that the obtained CuNi octahedral NCs (in both sizes) exhibit higher catalytic activity than those of CuNi spherical NCs reported previously. It further indicates that the catalytic performance is strongly size-dependent due to their devise specific surface areas of the exposed crystallographic planes.

In the synthesis of metallic nanocrystals (NCs) using a high-temperature colloidal approach, the competition between deposition and diffusion of “free atom (or clusters)” plays an important role as it can direct the morphology of NCs during their evolution. This competition is closely associated with some dynamic conditions such as heat and mass transfer. Stirring speed and ramp rate of heating are two factors that greatly impact the heat and mass transfer processes and consequently determine the morphology of the products but rarely discussed in most synthetic protocols. Herein, we study the syntheses of Pt-M (M = Ni, Fe) NCs as model reactions, showing that a low stirring speed and high ramp rate of heating result in ununiform pod-like NCs, whereas the inverse conditions promote NCs in a uniform shape. This observation can be plausibly explained using a competition mechanism between the deposition and diffusion of the newly reduced atoms during a stage of the NC’s growth.

Pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laser-excited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tuning of MAPbI3, enriching potentially the toolkit for engineering perovskites related photovoltaic devices.

Nanosized Platinum (Pt) nanocrystals (NCs) have been extensively investigated in catalytic fields because of their high reactivity due to the unique electron structure. However, the rarity and the high cost of Pt limit its applications in industry. To reduce the usage of Pt in catalytic industry, research interests have been extended to Pt-based nanoalloys. Among various nanostructures, nanoframes (NFs) showed promising catalytic performance even with a lower metallic loading dose. Herein, we report a facile and robust method to transfer the Pt-Ni tetrahexahedral (THH) NCs into THH NFs in which carbon monoxide (CO) plays a role of the “etching reagent”. The driving force of the etching is a formation of gaseous metallic complex, Ni(CO)4, known as Mond Process, preferentially dealloying nickel atoms along <100> directions of the Pt-Ni THH NCs. It is determined that the resultant Pt-Ni THH NFs possess an open, stable and high-index preserved nanostructure, in which the outside atomic layers are composed of only Pt atoms with surface strains. Compared to a solution-based etching process, this approach requires less etching time and generates a well-defined structure. The associated thermal annealing operation also releases extra internal stress, making the NFs more stable with fewer surface defects. Such Pt-Ni THH NFs show interesting potentials in the improvement of stability and activity as advanced catalysts.

Aluminum–silicon alloys are an important class of commercial casting materials having wide applications in automotive and aerospace industries. Etching the Al–Si eutectic leads to selective dissolution of Al, resulting in novel morphology – macroporous Si spheres with a three-dimensional nano network. Up to 5% Al is dissolved in Si, leading to an expansion of the crystal lattice. The resulting porous Si is electrochemically active with lithium and thus can be used as a high capacity anode for lithium-ion batteries. The etching of Al–Si provides a simple and low-cost method of producing nano-structured Si materials.

In recent years, platinum-based single crystalline nanoalloys as nanoscale catalysts, such as Pt-M (M = Ni, Co, Fe..etc.), have exhibited improved catalytic performance due to the increase in the surface-to-volume ratio. Some Pt-M nanopolyhedra such as nanocubes and nano-octahedra have been reported with enhanced activity when being used as electrocatalysts. In order to further establish a correlation between the exposed nanocrystal facets (shapes) and their corresponding activities, a pursuit of shape-controlled nanocatalyst synthesis is essential. Although PtPb nanoalloys have been prepared using solution-based methods, few studies have highlighted their catalytic activity as a function of the nanocrystal shape. This work focuses on a modified polyol synthesis technique and an adjustment of the Pb-metal precursor, which serves as a “buffer” in the nucleation stage of the shape-controlled nanoalloy development. Using this developed synthetic strategy, shape-controlled hexagonally close-packed PtPb nanoalloys can be prepared in a one-pot synthesis without additional post-treatment. The as-prepared PtPb nanocrystals demonstrate an improved anode electrocatalytic performance.

Electrocatalytic activity and stability of platinum nanocubes and nanospheres were comparatively investigated towards methanol oxidation reaction. The results indicate that the {100}-bounded Pt nanocubes exhibit not only higher catalytic activity but also higher stability compared with the mixed crystallographic facet-terminated Pt nanospheres.

High-quality Pt-Cu nanocubes were prepared through simultaneous reduction of platinum (II) acetylacetonate and copper II) acetylacetonate in 1-octadecene by 1,2–tetradecanediol in the presence of tetraoctylammonium bromide, oleylamine, and 1-dodecanethiol. The growth process of Pt-Cu nanocubes was explored based on the observation of intermediates. The electrocatalytic behavior indicates that cubic Pt-Cu nanocrystals are more active than spherical Pt-Cu nanocrystals and Pt nanocrystals towards methanol oxidation reaction.

Colloidal Europium-doped In2O3 nanocrystals were successfully prepared in a noncoordinating solvent using indium (III) and europium (III) acetates as precursors. The concentration of doped europium was varied up to 2.88 at%. Linear electrogyration induced by coherent circularly-polarized light was observed from samples in which europium-doped In2O3 nanocrystals were embedded in photopolymer oligoethracryalte matrices. The result on ˜2.5 at% europium-doped sample shows that the maximal linear electrogyration could reach to ˜12 deg./mm at an electric field of 120V/cm for He-Ne laser.

As a potential biological imaging probe with a long-wavelength of emission, InP quantum dots were prepared via a high-temperature organic solution approach, and successfully transferred into an aqueous system through a ligand-exchange process using various functional surfactants. Photoluminescence and X-ray characterizations confirmed the desired properties of the InP quantum dots. The cytotoxicity of the water-soluble InP quantum dots against phaeochromocytoma PC12 cells as evaluated by the MTS cell viability assay was low relative to a positive control, poly(ethyleneimine). This study suggests a bright potential for this new type of InP quantum dots in bioimaging applications.

This paper describes a co-reduction colloidal method for the synthesis of In-containing III-V nanocrystals (NCs) by using pnictogen halides (such as PCl3, AsCl3, and SbCl3) as the pnictogen-sources and superhydride (LiBH(C2H5)3) as the reducing agent. The syntheses were generally carried out in octadecene in the presence of fatty acids at ∼250 °C. The as-synthesized InP NCs were monodisperse in particle size and size distribution, whereas the InAs and InSb NCs showed relatively lower quality. The growth process of NCs was studied using InP as a model system.

Precursor-reduction method is employed to synthesize nanostructures of ZnTe. The shape of zinc blende ZnTe nanocrystals could be influenced by reaction temperature, concentration of the precursors as well as the use of stabilizing agent. By controlling the synthetic conditions, three types of nanoscaled ZnTe, quasi-spherical ZnTe nanocrystals, ZnTe nanobelts and ZnTe nanorods have been observed. Their crystalline structures are also discussed.

ZnTe quantum dots (QDs) have been very attractive because of their potential applications in optoelectronic devices operating in the blue-green region of the spectrum. This paper describes a convenient one-step synthesis of high-quality ZnTe QDs in high-temperature organic solution with high yield. Anhydrous zinc chloride was dissolved in phenyl ether under argon protection and oleic amine was used as coordinating agent. Complex solution of metal tellurium in trioctylphosphine (TOP) was injected into the hot reaction mixture as a source of tellurium. The reaction was complete in several minutes and the resulting QDs were isolated by centrifugation and re-dispersed in hexane. The produced spherical ZnTe QDs are monodispersed and their sizes could be controlled simply by varying the growth temperature. The morphology and phase structure were investigated using TEM and XRD. Photoluminescence (PL) spectra were also studied and quantum size effects were observed as well.

III-V semiconductor nanocrystals are of considerable interest due to their extensive applications in the optoelectronic and biomedical fields. In order to meet the practical use, the convenient and scalable production of III-V narrow-disperse nanocrystals is inspiring. We report an efficient and rapid method of preparing highly monodisperse InP nanocrystals using a wet-chemical redox synthetic approach with a noncoordinating solvent, employing organic reducing agent LiBH(CH2CH3)3 and yellow phosphor. As advantages of this approach, reaction temperature is relatively low (80°C-120°C) and reaction time is less than 2 hours. Our characterization shows that the photoluminescence properties of InP nanocrystals are highly dependent on the particle size.

In this presentation, we report the self-assembly of monolayer and multilayer nanorings of PbSe nanoparticles. PbSe nanoparticles were synthesized by using a high temperature precipitation method. The nanoparticles are about 5 nm and appeared as truncated octahedral enclosed by the {100} and {111} crystal facets of fcc structure. The large area monodisperse self-assembly nanoarrays were obtained by dropping the high concentration solution of PbSe nanoparticles on the carbon grid. The nanoparticles are hexagonal close packed and oriented randomly in the nanoarrays. By diluting the solution for large area self-assembly, self-assembly of monolayer and multilayer nanorings can be achieved. The nanoring formation is determined by hydrodynamics, surface effects, and interaction between the nanoparticles and carbon grid.

γ-Fe2O3@Au core-shell nanoparticles were prepared through a combined route, in which high temperature organic solution synthesis and colloidal microemulsion techniques were successively applied. High magnification of TEM reveals the core-shell structure. The presence of Au on the surface of as-prepared particles is also confirmed by UV-Vis absorption. The magnetic core-shell nanoparticles offer a promising application in bio- and medical systems.