Yuanzhi Chen

Copper Nanowires as Fully Transparent Conductive Electrodes

In pondering of new promising transparent conductors to replace the cost rising tin-doped indium oxide (ITO), metal nanowires have been widely concerned. Herein, we demonstrate an approach for successful synthesis of long and fine Cu nanowires (NWs) through a novel catalytic scheme involving nickel ions. Such Cu NWs in high aspect ratio (diameter of 16.2 ± 2 nm and length up to 40 μm) provide long distance for electron transport and, meanwhile, large space for light transmission. Transparent electrodes fabricated using the Cu NW ink achieve a low sheet resistance of 1.4 Ohm/sq at 14% transmittance and a high transparency of 93.1% at 51.5 Ohm/sq. The flexibility and stability were tested with 100-timebending by 180°and no resistance change occurred. Ohmic contact was achieved to the p- and n-GaN on blue light emitting diode chip and bright electroluminescence from the front face confirmed the excellent transparency.

Preparation and magnetic properties of nickel nanoparticles via the thermal decomposition of nickel organometallic precursor in alkylamines

Nickel nanoparticles were prepared from the thermal decomposition of nickel(II) acetylacetonate in alkylamines and characterized by powder x-ray diffraction, transmission electron microscopy and magnetic measurement. The reaction temperature, heating rate and solvent type play an important role in the control over the crystalline phase. Depending on the reaction conditions, face-centered cubic (fcc) or hexagonal close-packed (hcp) nickel nanoparticles can be obtained. Monodisperse nickel nanoparticles were also obtained by introducing surfactants. The results of magnetic characterization showed that the magnetic properties of the hcp nickel nanoparticles are quite different from those of the fcc nickel nanoparticles.

Template-Free Synthesis of Amorphous Double-Shelled Zinc-Cobalt Citrate Hollow Microspheres and Their Transformation to Crystalline ZnCo2O4 Microspheres

A novel and facile approach was developed for the fabrication of amorphous double-shelled zinc-cobalt citrate hollow microspheres and crystalline double-shelled ZnCo2O4 hollow microspheres. In this approach, amorphous double-shelled zinc-cobalt citrate hollow microspheres were prepared through a simple route and with an aging process at 70 °C. The combining inward and outward Ostwald ripening processes are adopted to account for the formation of these double-shelled architectures. The double-shelled ZnCo2O4 hollow microspheres can be prepared via the perfect morphology inheritance of the double-shelled zinc-cobalt citrate hollow microspheres, by calcination at 500 °C for 2 h. The resultant double-shelled ZnCo2O4 hollow microspheres manifest a large reversible capacity, superior cycling stability, and good rate capability.

First application of core-shell Ag@Ni magnetic nanocatalyst for transfer hydrogenation reactions of aromatic nitro and carbonyl compounds

A magnetically separable core-shell Ag@Ni nanocatalyst was prepared by a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as surfactant. The synthesized nanoparticles were characterized by several techniques such as X-ray diffraction pattern (XRD), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) pattern, and energy dispersive X-ray spectroscopy (EDS). The core-shell Ag@Ni nanocatalyst was found to have very excellent activity for the transfer hydrogenation reactions of aromatic nitro and carbonyl compounds under mild conditions using isopropyl alcohol as hydrogen donor. Excellent chemoselectivity and regioselectivity for the nitro group reduction was demonstrated.

Facile synthesis of near-monodisperse Ag@Ni core-shell nanoparticles and their application for catalytic generation of hydrogen.

Magnetically recyclable Ag-Ni core-shell nanoparticles have been fabricated via a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as a surfactant. As characterized by transmission electron microscopy (TEM), the as-synthesized Ag-Ni core-shell nanoparticles exhibit a very narrow size distribution with a typical size of 14.9 ± 1.2 nm and a tunable shell thickness. UV-vis absorption spectroscopy study shows that the formation of a Ni shell on Ag core can damp the surface plasmon resonance (SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magnetic measurement indicates that all the as-synthesized Ag-Ni core-shell nanoparticles are superparamagnetic at room temperature, and their blocking temperatures can be controlled by modulating the shell thickness. The as-synthesized Ag-Ni core-shell nanoparticles exhibit excellent catalytic properties for the generation of H(2) from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogen generation rate of Ag-Ni core-shell nanoparticles is found to be much higher than that of Ag and Ni nanoparticles of a similar size, and the calculated activation energy for hydrogen generation is lower than that of many bimetallic catalysts. The strategy employed here can also be extended to other noble-magnetic metal systems.

Ni12P5 nanoparticles embedded into porous g-C3N4 nanosheets as a noble-metal-free hetero-structure photocatalyst for efficient H2 production under visible light

Transition metal phosphides (TMPs) have recently been thrust into the limelight as promising substitutes for precious noble metal-based cocatalysts for photocatalytic H2 evolution. Herein, colloidally synthesized Ni12P5 nanoparticles were successfully embedded into porous g-C3N4 nanosheets through a facile solution-phase approach under sonication. The as-prepared photocatalysts with an optimum 5 wt% anchoring of Ni12P5 (5NP-CN) displayed an excellent H2 production activity of 535.7 μmol g−1 h−1 under visible light irradiation. The high apparent quantum yield (AQY) of 4.67% at 420 nm was achieved in the 5NP-CN system for the production of H2, exceeding a large scientific spectrum of literature studies on the TMP-based catalysts. The superior photocatalytic H2 evolution of Ni12P5/g-C3N4 was predominantly attributed to the formation of intimate contact interfaces, in which Ni12P5 nanoparticles with high purity and good crystallinity were homogeneously embedded into the porous g-C3N4 nanosheets, thus facilitating the separation and transfer of photogenerated charge carriers. Meanwhile, a possible photocatalytic mechanism of Ni12P5/g-C3N4 hybrid nanocomposites was proposed and corroborated by photoluminescence (PL) spectroscopy and photoelectrochemical (PEC) results. As such, the present reported synthetic route to the g-C3N4-based photocatalysts incorporating Ni12P5 paves a new way for the advancement of g-C3N4 and a cornucopia of colloidal nanocrystals, which will be auspicious toward the nanoarchitecture engineering of noble-metal-free heterojunction interfaces for application in renewable energy production.

Structure, optical and magnetic properties of Ni@Au and Au@Ni nanoparticles synthesized via non-aqueous approaches

Although the combination of magnetic and noble metals in core-shell nanoparticles is very useful in many applications, the preparation of magnetic-noble bimetallic core-shell nanoparticles with uniform shells remains a great challenge due to large mismatch of crystal lattices between magnetic and noble metals. Herein we present non-aqueous methods for combing Au and Ni in nanoscale to form a core-shell structure. Ni@Au nanoparticles were prepared via an injection-quenching process in which Au precursors decomposed and formed closed shells on pre-formed Ni seeds synthesized in oleylamine, whereas Au@Ni nanoparticles were obtained in a one-step reaction involving a seed-catalyzed mechanism. The formed core-shell structure was confirmed by high-angle annular dark-field imaging along with the analyses of energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. UV-Visible absorption spectroscopy and superconducting quantum interference device magnetometer were used to characterize the optical and magnetic properties of the as-prepared bimetallic core-shell nanoparticles. Through the adjustment of growth conditions, Ni@Au and Au@Ni nanoparticles with different core or shell dimensions and morphologies were obtained, which offers an important means to tailor their optical and magnetic properties for multiple practical applications.

Characterization and Optical Properties of the Single Crystalline SnS Nanowire Arrays

The SnS nanowire arrays have been successfully synthesized by the template-assisted pulsed electrochemical deposition in the porous anodized aluminum oxide template. The investigation results showed that the as-synthesized nanowires are single crystalline structures and they have a highly preferential orientation. The ordered SnS nanowire arrays are uniform with a diameter of 50 nm and a length up to several tens of micrometers. The synthesized SnS nanowires exhibit strong absorption in visible and near-infrared spectral region and the direct energy gapEgof SnS nanowires is 1.59 eV.

One-pot synthesis of hexagonal and triangular nickel–copper alloy nanoplates and their magnetic and catalytic properties

A facile one-pot route has been developed for the synthesis of hexagonal and triangular Ni–Cu alloy nanoplates. The synthesis was conducted using nickel(II) acetylacetonate and copper(II) chloride dihydrate as metal precursors, trioctylphosphine as a capping agent, and oleylamine as a solvent and reducing agent. Structural analyses from X-ray diffraction and transmission electron microscopy indicate that the as-synthesized nanoplates have an fcc crystalline structure and their side faces are bound by a mixture of {100} and {111} facets, while their top and bottom faces are bound by {111} facets. The oxidative etching effect of Cu(II) on Ni(0) in the presence of Cl ions plays an important role in the generation of the anisotropic nanoplates. The results of magnetic measurements revealed differences between the hexagonal and triangular nanoplates in their ability to undergo the transition from the ferromagnetic to the superparamagnetic state with increasing temperature. The magnetic properties of the as-synthesized Ni–Cu alloy nanoplates can also be tuned by adjusting the Ni content which correlates closely with reaction temperature. Excellent catalytic properties for the catalytic reduction of methylene blue by NaBH4 in aqueous solution were observed for the as-synthesized nanoplates.

Seed‐Induced Growth of Flower‐Like Au–Ni–ZnO Metal–Semiconductor Hybrid Nanocrystals for Photocatalytic Applications

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.