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Catalytic activity is primarily a surface phenomenon, however, little is known about Co₃O₄ nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co₃O₄ nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co²⁺ ions, whereas the surface Co³⁺ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts.

Two-dimensional silica nanoparticle assemblies were obtained by deposition of bubble made from a surfactant solution containing nanoparticles onto hydrophobic silicon substrate. The morphologies of the nanoparticle assemblies can be finely controlled by several experimental parameters, including surfactant concentration, nanoparticle concentration, and deposition time. Monolayer of nanoparticles with surface coverage of about 100% can be obtained under appropriate conditions. The method can also be applied to another hydrophobic substrate, HMDS (hexamethyldisilazane)-modified silicon substrate. Furthermore, it can be applied directly to lithography patterned substrates, meaning a high compatibility with the well-developed conventional top-down approaches to nanodevices. This bubble deposition technique is expected to be a promising method in the field of nano-object assembly and organization and has great application potentials.

Nitrogen-doped CoO (N-CoO) nanoparticles with high electrocatalytic activity for the oxygen-reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl2 in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen-doped Co nanoparticles were readily oxidized to N-CoO nanoparticles in air. In contrast to their N-free counterparts (CoO or Co3O4), N-CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The CoN x active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen-doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering of p-aminothiophenol and p-nitrothiophenol were obtained on the surface of Cu2O nanoparticles, showing novel spectral changes with morphology-dependent and time-dependent characteristics. The measured Raman signals were believed to partly originate from the newly produced surface species p,p′-dimercaptoazobenzene. The nature of surface chemisorption status during Raman measurement was investigated experimentally and theoretically via combined surface-enhanced Raman scattering and density functional theory study, indicating that surface catalytic reaction of p-aminothiophenol and p-nitrothiophenol could take place on the surface of oxide nanostructures as well as coinage metal material. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The discovery of the giant electrorheological (GER) effect poses a challenge to the theorists for an explanation of its physical underpinnings. This is particularly the case as the GER effect breaks the yield stress upper bound predicted on the basis of induced polarization mechanism. The GER effect was observed in suspensions of coated nanoparticles, each consisting of a core particle of barium titanyl oxalate (20-50 nm), coated with a 5-7 nm layer of urea. The suspending oil is also very important, as the "wrong" oil can mean no electrorheological effect at all. Our prior work has shown the GER data, on the field dependence of yield stress, to be quantitatively accountable by the formation of aligned molecular dipolar layers in the region of particle-particle contact. Here we justify this picture through microscopic statistical mechanic considerations. We present a model of hydrogen bonding which can give rise to both electrowetting between the particles and the oil, as well as inducing the formation of aligned surface molecular dipolar layers. Monte Carlo simulation is used to account for both the entropy and energetic effects. It is shown that the formation of aligned surface dipolar layers can indeed be a robust phenomenon. [ABSTRACT FROM AUTHOR]

A morphology-conserved transformation yields Sn@C nanowires (UTP@CW, ∼21 wt% carbon and ∼77 wt% tin) with a high encapsulation density of ultrafine tin nanoparticles in porous carbon nanowires, which exhibit excellent reversible capacities and cycling performance for lithium ion batteries, especially at high current rates. [ABSTRACT FROM AUTHOR]

We report the preparation of highly monodisperse ZnO nanoparticles using poly(vinyl pyrrolidone) (PVP) as the capping molecules. The surface-modified ZnO nanoparticles were found to be remarkably stable. The optical absorption shows distinct excitonic features. Markedly enhanced near-band-edge ultraviolet photoluminescence and significantly reduced defect-related green emission were also observed. We attribute this observation to the nearly perfect surface passivation of the ZnO nanoparticles by the PVP molecules. The third-order nonlinear optical response of these PVP-capped ZnO nanoparticles in a dilute solution was found to be significantly larger (by at least two orders of magnitude) than that of the bulk ZnO. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intrinsically low electric conductivity and self-aggregation of MFe2O4 during charge/discharge affect their lithium storage performance and electrocatalytic activity. To mitigate these problems, it is shown that N-doped graphene sheets (NGS), as a highly conductive platform, finely disperse the MFe2O4 nanoparticles and rapidly shuttle electrons to and from the MFe2O4 nanoparticles. Moreover, by forming a metal@oxide core-shell nanostructure, fast electron transfer from the exterior oxide layer to NGS is achieved. Introducing NGS into MFe2O4 allows the composites to exhibit the comparable specific capacity (based on the total mass) to MFe2O4, although over 10 wt% of NGS contributes a low specific capacity of around 320-400 mAh g−1. More importantly, introducing NGS significantly increases the cycling stability performance: 97.5% (CoFe2O4/NGS) and ≈100% (NiFe2O4/NGS) of the specific capacities have been retained after 80 cycles, far higher than the capacity retentions of CoFe2O4 (35.3%) and NiFe2O4 (43.7%) tested under otherwise identical conditions. Also demonstrated are the excellent rate capabilities of the composites. For catalyzing the oxygen reduction reaction, the activity is significantly improved when the MFe2O4 nanoparticles are transformed into metal@oxide core-shell nanostructure, mainly because the core-shell nanostructure exhibits lower charge transfer resistance. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides mechanistic insight into the self-assembly involved in the controlled synthesis of mesoporous TiO2 microspheres with tunable sizes (200nm, 400nm and 600nm on average). The salient features of these microspheres, when used as building blocks of photoanode films in lieu of traditional small nanoparticles, have been systematically studied for the first time in highly viscous gel-electrolyte-based dye-sensitized solar cells. The light scattering property, electron transport and interface recombination kinetics have been critically compared with respect to the morphology and the size of the building blocks. A >6.78% power conversion efficiency was achieved with the 400nm microspheres due to the balanced combination of light scattering, electrolyte permeation and charge collection advantages. This accentuates the performance limiting factor of the small nanoparticles and the 600nm microsphere photoanodes as the difficulty for the quasi-solid electrolyte to fill in their long, narrow mesoscopic pore channels, a scenario supported by their short electron lifetimes as measured by intensity modulated photovoltage spectroscopy (IMVS). [Copyright &y& Elsevier]

Abstract: A one step polyol process has been used to synthesize linear assemblies of Pd nanoparticles (NPs). TEM images show that highly linearly ordered Pd NP chains (about 8.5nm in diameter) have been formed, and the inter-particle distance is about 1.4±0.6nm. The Pd NP chains can be obtained by adding NH3·H2O and prolonging the heating time. A scaffolding mechanism is proposed to understand the short-ranged order of the Pd NP chains. The as-obtained Pd nanochains at Pd NCh/MWCNTs/GCE displayed high activity in the electrocatalytic oxidation of NO. [Copyright &y& Elsevier]

Abstract: An electrochemical method was developed to deposit platinum (Pt) and nickel (Ni) nanoparticles on multi-walled carbon nanotubes (MWCNTs) through a three-step process. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) show the alloy formation for Pt and Ni with a ratio of 1:1. The presence of Pt(0), Ni(0), Ni(OH)2, NiOOH and slight NiO was deduced from XPS data. Electrocatalytic properties of the resulting PtNi/MWCNT electrode for methanol oxidation reaction were investigated. Compared with Pt/MWCNT, an appreciably improved resistance to CO poisoning was observed for the PtNi/MWCNT electrode, which was interpreted by a mechanism based on the bifunctional catalysis. The successful preparation of PtNi/MWCNT nanocomposites opens a new path for an efficient dispersion of the promising electrocatalysts in the direct methanol fuel cells. [Copyright &y& Elsevier]

Abstract: The development of different morphologies is desired in the field of nano-materials research. Gold is an interesting material for electronic nanodevice among many other potential applications and lots of morphologies have been prepared. However, hollow gold tetrapod has not been reported. In this paper, hollow gold tetrapods were prepared for the first time by using ZnO tetrapods as a template, HAuCl4 as a gold source and ascorbic acid as a reducing reagent. The structure and growth mechanism were investigated and the results show that the hollow gold tetrapods are composed of gold nanoparticles with a mean diameter of about 7.0nm. [Copyright &y& Elsevier]