Dong-Liang Peng

Core–shell nanoparticles: synthesis and applications in catalysis and electrocatalysis

Core-shell nanoparticles (CSNs) are a class of nanostructured materials that have recently received increased attention owing to their interesting properties and broad range of applications in catalysis, biology, materials chemistry and sensors. By rationally tuning the cores as well as the shells of such materials, a range of core-shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. Various synthetic methods for preparing different classes of CSNs, including the Stöber method, solvothermal method, one-pot synthetic method involving surfactants, etc., are briefly mentioned here. The roles of various classes of CSNs are exemplified for both catalytic and electrocatalytic applications, including oxidation, reduction, coupling reactions, etc.

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.

Structural and magnetic properties of Mn3O4 films grown on MgO(001) substrates by plasma-assisted MBE

Mn3O4 thin films with distorted spinel structure are grown on MgO(0 0 1) substrates by plasma-assisted molecular beam epitaxy (MBE) The films are (0 0 1) oriented and the lattice parameters are a = b approximate to 5.72 Angstrom, and c approximate to 9.5 Angstrom, with c/a = 1.66 slightly larger than the ratio of 1.64 for bulk single-crystal samples, if a body-center tetragonal unit cell is adopted for Mn3O4. It is found that the Curie temperature T-CF of the Mn3O4 film is 46 K higher than (T-CB = 42 K) for bulk single-crystal samples. The spontaneous magnetization reaches 1.73 mu(B)/molecule which is in between the reported results of 1.56 mu(B)/molecule for polycrystalline and 1.85 mu(B)/molecule for single-crystal sample. The temperature dependence of the inverse magnetic susceptibility in the paramagnetic range agrees well with the Curie-Weiss formula. The induced effective magnetic moment for Mn ion is about 3.59 mu(B), which is small compared with the 5.24 mu(B)/magnetic atom calculated based on electronic spins only

Electrostatic Assembly of Sandwich-like Ag-C@ZnO-C@Ag-C Hybrid Hollow Microspheres with Excellent High-Rate Lithium Storage Properties

Herein, we introduce a facile electrostatic attraction approach to produce zinc-silver citrate hollow microspheres, followed by thermal heating treatment in argon to ingeniously synthesize sandwich-like Ag-C@ZnO-C@Ag-C hybrid hollow microspheres. The 3D carbon conductive framework in the hybrids derives from the in situ carbonation of carboxylate acid groups in zinc-silver citrate hollow microspheres during heating treatment, and the continuous and homogeneous Ag nanoparticles on the outer and inner surfaces of hybrid hollow microspheres endow the shells with the sandwiched configuration (Ag-C@ZnO-C@Ag-C). When applied as the anode materials for lithium ion batteries, the fabricated hybrid hollow microspheres with sandwich-like shells reveal a very large reversible capacity of 1670 mAh g(-1) after 200 cycles at a current density of 0.2 A g(-1). Even at the very large current densities of 1.6 and 10.0 A g(-1), the high specific capacities of about 1063 and 526 mAh g(-1) can be retained, respectively. The greatly enhanced electrochemical properties of Ag-C@ZnO-C@Ag-C hybrid microspheres are attributed to their special structural features such as the hollow structures, the sandwich-like shells, and the nanometer-sized building blocks.

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.

Structural and magnetic characteristics of monodispersed Fe and oxide-coated Fe cluster assemblies

We systematically studied structural and magnetic characteristics of size- monodispersed Fe and oxide-coated Fe cluster assemblies with the mean cluster sizes of 7–16 nm. Transmission electron microscopy and scanning electron microscopy (SEM) observations show that the Fe clusters in the assemblies maintain their original size at room temperature. In the SEM images, a random stacking of the Fe clusters and a porous structure with a low cluster packing fraction of about 25% are observed. For the Fe cluster assemblies, magnetic coercivity (Hc) at room temperature increases from 4×101 to 4×102 Oe by increasing the mean cluster size from 7.3 to 16.3 nm. Using the experimental values of the coercivity at T⩾100 K and the fitting values of blocking temperature TB from Hc=Hc0[1−(T/TB)1/2], we estimated the values of magnetic anisotropy constant K of the order of 106 erg/cm3 from TB=KV/25kB, which is larger by an order of magnitude than the bulk Fe value (5×105 erg/cm3). Such a large effective anisotropy at T⩾100 ...