Octahedron Nanoparticles Research Articles

Superbending (0-180°) and High-Voltage Operating Metal-Oxide-Based Flexible Supercapacitor.

Among various energy storage devices, flexible supercapacitors having high mechanical stability with extreme bending and foldable features are highly attractive for a large number of emerging portable lightweight consumer devices. Here, we report the fabrication of such a superflexible supercapacitor by using novel octahedron-shaped NiCo2O4 nanoparticles as the electrode material for the first time. A new, low-cost hydrothermal method was used to synthesize 50-60 nm monodispersed perfect octahedron nanoparticles without any structural deformation. An all-solid-state symmetric flexible supercapacitor was fabricated by sandwiching the octahedron nanoparticles and [EMIM][BF4] ionic liquid electrolyte between two sheets of newly developed superflexible current collector substrate. The calculated specific capacity and specific capacitance values are found to be 97.9 mAh g-1 and 117.3 F g-1, respectively, at 0.625 A g-1 current density and 3.0 V applied potential. It also offered a high energy density value of 33.54 Wh kg-1 and 10 000 measured cycling stability. The supercapacitor is so flexible that it can be bent or fold up to 180° without any mechanical deformation, and the measured capacitance and energy and power densities remain almost constant at any angle of twisting. For instance, calculated values of capacitances obtained by bending the cell at angles of 180, 150, 135, 90, and 45° are found to be 62, 63.3, 63.73, 64, and 66 F g-1 respectively, in comparison to 67 F g-1 for a nonbending or flat (0°) cell. A faster ion switching between electrode/electrolyte interface, [EMIM][BF4] electrolyte, and octahedron shape of the nanoparticle electrode material is found to be responsible for the outstanding charge storage behavior.

Development of Highly Efficient and Durable Three-Dimensional Octahedron NiCo2O4 Spinel Nanoparticles toward the Selective Oxidation of Styrene

Herewith, we have prepared poly(vinylpyrrolidone)-assisted water-based synthesis of the nanocrystalline spinel NiCo2O4 nanocatalyst by a one-pot hydrothermal route. The formation of the synthesized spinel NiCo2O4 nanoparticle has been confirmed by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure (EXAFS) analyses. The SEM results confirmed the formation of the three-dimensional octahedron structure with an average size of 20–30 nm. The EXAFS results further confirmed that the spinel NiCo2O4 nanoparticles exist in a pure phase. The catalytic activity of the synthesized spinel NiCo2O4 octahedron nanoparticles was evaluated for the conversion of styrene to styrene oxide by the oxidation reaction. It was found that the conversion of styrene was 78% with 67% of styrene oxide selectivity in the presence of hydrogen peroxide as an oxidant. The catalyst has also pro...

Effect of betaine in the successful synthesis of CoFe2O4 containing octahedron nanoparticles for electrocatalytic water oxidation

The development of robust catalysts that oxidize water is necessary for their application in artificial photosynthesis cells. Here we report the synthesis and characterization of octahedral CoFe2O4 nanoparticles obtained through a novel aqueous method that employs betaine, (CH3)3+NCH2COO−, as the stabilizer agent. The synthetic conditions are modified changing the betaine content and the metal precursor ratios. These conditions modify the shape of CoFe2O4 finding both, octahedral and semi-spherical nanoparticles. Linear voltammetry measurements show the octahedral CoFe2O4 lead to an overpotential of ∼390mV at the onset potential for water oxidation at alkaline conditions. Among the as-synthesized cobalt-ferrite nanomaterials, the CoFe(1:2)-C in the form of tiny nanoparticles performed a superior electrocatalytic water oxidation in alkaline conditions, showing an overpotential of ∼335mV, which is lower than other similar catalysts in literature.

Charge optimized many body (COMB) potentials for Pt and Au

Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress–strain behaviour is investigated and the primary slip systems {1 1 1}〈1 0〉 are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of eV for Pt and eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.

Gram scale synthesis of single crystalline nano-octahedron of NiFe2O4: Magnetic and optical properties

Gram scales Ni ferrite nano-octahedrons are prepared by cost effective and facile hydrothermal method. The mass of as-synthesized Ni ferrite nano-octahedron is about 1.37g. Nano-octahedron of Ni ferrite are highly uniform and the edge length of octahedron is 80nm. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) pattern confirm that octahedron nanoparticles are single crystalline. The direct and indirect band gaps are acquired to be 1.55eV and 1.7eV respectively. The saturation magnetization, coercivity, and remanent magnetization are obtained to be 55.1emu/g, 69Oe, and 9.8emu/g respectively. This method is useful to synthesize the Ni ferrite nanostructure for commercial and industrial scale.

Shape-controlled synthesis of Pt particles and their catalytic performances in the n-hexadecane hydroconversion

The platinum nanocrystals with truncated octahedral, spherical and cubic morphologies were synthesized and well dispersed onto the ZSM-22 support, in order to investigate the shape effect of Pt crystals on n-hexadecane hydroconversion. It is found that the crystal facets of Pt nanoparticles play more profound roles in determining the catalytic properties. The reaction test shows that both the conversion of n-hexadecane and selectivity of iso-hydrocarbons are higher for the catalysts with octahedron nanoparticles of Pt that are predominantly enclosed by Pt {111} crystal facets than those with spherical and cubic morphologies of Pt, whose surfaces consist of more Pt {100} facets. Combined with the results of CO-IR and TPHD, it is suggested that the activity and selectivity of the reaction are well correlated to the fractions of exposed Pt {111} crystal facets, which possess more activated surface defect sites and higher amounts of activated hydrogens either on the Pt surface or in the Pt phase. Meanwhile, the catalyst activity and selectivity are found to be highly sensitive to the Pt particle size. Smaller Pt particles have higher activity and lower isomerization selectivity.

Shape-controlled octahedral cobalt disulfide nanoparticles supported on nitrogen and sulfur-doped graphene/carbon nanotube composites for oxygen reduction in acidic electrolyte

Shape controlled cobalt disulfide octahedron nanoparticles are grown on nitrogen/sulfur-doped carbon nanotube-graphene composites as active non-precious oxygen reduction catalysts.

Graphene oxide and shape-controlled silver nanoparticle hybrids for ultrasensitive single-particle surface-enhanced Raman scattering (SERS) sensing

Graphene oxide (GO) is an emerging material for surface-enhanced Raman scattering (SERS) due to its strong chemical enhancement. Studying the SERS performance of plasmonic nanoparticle/GO hybrid materials at the single particle level is crucial for direct probing of the chemical effect of GO on plasmonic nanoparticles. In this work, we integrate GO and shape-controlled Ag nanoparticles to create hybrid nanomaterials, and the chemical enhancement arising from GO is investigated using single-particle SERS measurements. Ag nanoparticle@GO hybrid nanostructures are prepared by assembling Ag nanoparticles, including spheres, cubes and octahedra with GO sheets. The SERS behaviors of the hybrid nanostructures are characterized, and 2-3 times enhanced SERS intensities are detected from the Ag nanoparticle@GO hybrid nanostructures as compared to pure Ag nanoparticles. Furthermore, we probe the mechanism of SERS enhancement in the hybrid nanostructures by changing the surface coverage of GO on Ag octahedra, by using reduced GO in place of GO as well as by using probe molecules of different electronegativities. This hybrid system is an excellent candidate for single-particle SERS sensors. Sub-nanomolar levels of aromatic molecules are detected using a single Ag/GO hybrid nanomaterial. This as-prepared GO and shape-controlled Ag nanoparticle hybrid is capable of serving as a high performance SERS platform, providing new opportunities for efficient chemical and biological sensing applications.

Surface segregation of Au–Ag bimetallic nanowires

Monte Carlo simulation has been performed to study the size, shape, composition and temperature dependent surface segregation behaviors and atomic-scale structure of Au–Ag nanowires (NWs). Segregation of Ag to the surface is observed in all the NWs considered. The surface segregation of prism-like nanowires with tetragonal cross-section (T-NWs) is enhanced by the increasing of the particle sizes (or Ag compositions) and the decreasing of temperatures. For Au3Ag T-NWs, variation range of surface Ag fraction is smaller than that of truncated octahedron nanoparticles (TO-NPs) with the same diameter, however, AuAg and AuAg3 T-NWs show the opposite character. The surface Ag fraction of T-NWs is higher than that of cylindrical nanowires (C-NWs) and hexagonal cross-section nanowires (H-NWs) due to T-NWs’ owning more low-coordination sites while surface Ag fraction of C-NWs and H-NWs are close to each other under every composition, size and temperature. It is found that the most stable mixing configuration of NWs is Ag-rich-surface, Au-rich-subsurface and alloyed-core structures. Accordingly, the calculated alloying extents for NWs are consistent with those of Au–Ag NPs. The possible effects of size and shape distribution of surface Au atoms on tuning the catalytic activity and selectivity of bimetallic NWs are also discussed.

Observation of surface structural changes of Pt octahedron nanoparticles and its effect in electrocatalysis oxidation of methanol

The Pt octahedron nanoparticles closed by 8 {1 1 1} facets are synthesized as catalyst for methanol oxidation. The catalytic activity of the Pt octahedron nanoparticles is enhanced significantly after applying a number of potential cycles. Such enhancement is due to the formation of the defect and step sites introduced by the potential cycles, which is directly confirmed by transmission electron micrograph. Accumulation of the defect and step sites result in a formation of Pt(1 0 0) terraces, arising from more potential cycles. The poisoning of Pt(1 0 0) terraces leads to a rapid decay in the long-term performance.

Synthesis of In2O3 nanocrystal chains and annealing effect on their optical properties

The authors reported the synthesis of indium oxide nanocrystal chains on silicon substrates using gold nanoparticles as catalyst on native silicon dioxide. Scanning electron microscopy investigations showed that In2O3 nanocrystal chains were formed. The nanocrystal chains comprised many well shaped octahedron nanoparticles with their size ranging from 20to100nm connected with each other to form a network. Both high resolution transmission electron microscopy and diffraction pattern revealed that the In2O3 nanocrystal chains were single crystalline grown along the [111] direction. Photoluminescence study of In2O3 nanocrystal chains exhibited main photoemission at 544nm due to the recombination between electrons in localized state induced by oxygen vacancies and holes in valence band. After the annealing treatment, the main photoluminescence peak not only slightly redshifted to 558nm but also became narrower, which was attributed to the total localized state away from the conduction band caused by less defect distribution.