Deqian Zeng

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.

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.

Hierarchical ZnO-Ag-C composite porous microspheres with superior electrochemical properties as anode materials for lithium ion batteries

Hierarchical ZnO-Ag-C composite porous microspheres are successfully synthesized by calcination of the preproduced zinc-silver citrate porous microspheres in argon. The carbon derives from the in situ carbonization of carboxylic acid groups in zinc-silver citrate during annealing treatment. The average particle size of ZnO-Ag-C composite porous microspheres is approximate 1.5 μm. When adopted as the electrode materials in lithium ion batteries, the obtained composite porous microspheres display high specific capacity, excellent cyclability, and good rate capability. A discharge capacity as high as 729 mA h g(-1) can be retained after 200 cycles at 100 mA g(-1). The excellent electrochemical properties of ZnO-Ag-C are ascribed to its unique hierarchical porous configuration as well as the modification of silver and carbon.

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.

Hierarchical ZnIn2S4/MoSe2 Nanoarchitectures for Efficient Noble-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light

A highly efficient visible-light-driven photocatalyst is urgently necessary for photocatalytic hydrogen generation through water splitting. Herein, ZnIn2 S4 hierarchical architectures assembled as ultrathin nanosheets were synthesized by a facile one-pot polyol approach. Subsequently, the two-dimensional-network-like MoSe2 was successfully hybridized with ZnIn2 S4 by taking advantage of their analogous intrinsic layered morphologies. The noble-metal-free ZnIn2 S4 /MoSe2 heterostructures show enhanced photocatalytic H2 evolution compared to pure ZnIn2 S4 . It is noteworthy that the optimum nanocomposite of ZnIn2 S4 /2 % MoSe2 photocatalyst displays a high H2 generation rate of 2228 μmol g-1  h-1 and an apparent quantum yield (AQY) of 21.39 % at 420 nm. This study presents an unprecedented ZnIn2 S4 /MoSe2 metal-sulfide-metal-selenide hybrid system for H2 evolution. Importantly, the present efficient hybridization strategy reveals the potential of hierarchical nanoarchitectures for a multitude of energy storage and solar energy conversion applications.

Facile fabrication of various zinc-nickel citrate microspheres and their transformation to ZnO-NiO hybrid microspheres with excellent lithium storage properties

Zinc-nickel citrate microspheres are prepared by a simple aging process of zinc citrate solid microspheres in nickel nitrate solution. As the concentration of nickel nitrate solution increases, the morphology of the produced zinc-nickel citrate evolves from solid, yolk-shell to hollow microspheres. The formation mechanism of different zinc-nickel citrate microspheres is discussed. After annealing treatment of the corresponding zinc-nickel citrate microspheres in air, three different ZnO-NiO hybrid architectures including solid, yolk-shell and hollow microspheres can be successfully fabricated. When applied as the anode materials for lithium ion batteries, ZnO-NiO hybrid yolk-shell microspheres demonstrate the best electrochemical properties than solid and hollow counterparts. After 200th cycles, ZnO-NiO hybrid yolk-shell microspheres deliver a high reversible capacity of 1176 mA h g−1. The unique yolk-shell configuration, the synergetic effect between ZnO and NiO and the catalytic effect of metal Ni generated by the reduction of NiO during discharging process are responsible for the excellent lithium storage properties of ZnO-NiO hybrid yolk-shell microspheres.

Shape-related optical and catalytic properties of wurtzite-type CoO nanoplates and nanorods

In this paper, we report the anisotropic optical and catalytic properties of wurtzite-type hexagonal CoO (h-CoO) nanocrystals, an unusual nanosized indirect semiconductor material. h-CoO nanoplates and nanorods with a divided morphology have been synthesized via facile solution methods. The employment of flash-heating and surfactant tri-n-octylphosphine favors the formation of plate-like morphology, whereas the utilization of cobalt stearate as a precursor is critical for the synthesis of nanorods. Structural analyses indicate that the basal plane of the nanoplates is (001) face and the growth direction of the nanorods is along the c axis. Moreover, the UV–vis absorption spectra, the corresponding energy gap and the catalytic properties are found to vary with the crystal shape and the dimensions of the as-prepared h-CoO nanocrystals. Furthermore, remarkable catalytic activities for H2 generation from the hydrolysis of alkaline NaBH4 solutions have been observed for the as-prepared h-CoO nanocrystals. The calculated Arrhenius activation energies show a decreasing trend with increasing extension degree along the <001> direction, which is in agreement with the variation of the charge-transfer energy gap. Finally the maximum hydrogen generation rate of the h-CoO nanoplates exceeds most of the reported values of transition metal or noble metal containing catalysts performing in the same reaction system, which makes them a low-cost alternative to commonly used noble metal catalysts in H2 generation from the hydrolysis of borohydrides, and might find potential applications in the field of green energy.

A facile approach to fabrication of well-dispersed NiO–ZnO composite hollow microspheres

A novel, facile and template-free approach was developed for the fabrication of amorphous zinc-nickel citrate hollow microspheres and crystalline well-dispersed NiO–ZnO composite hollow microspheres. In this approach, amorphous zinc-nickel citrate hollow microspheres were prepared through a simple chemical reaction and with room temperature ageing at nickel nitrate solution. The zinc-nickel citrate hollow microspheres have an average size of about 1.4 μm. The average thickness of the shell is about 300 nm. The content of Ni in the zinc-nickel citrate can be simply adjusted by changing the ageing time. The well-dispersed NiO–ZnO composite hollow microspheres can be prepared via the perfect morphology inheritance of the zinc-nickel citrate hollow microspheres, by calcination at 500 °C for 2 h. The optical absorption of the samples can extend into the visible region after the loading of NiO. The NiO–ZnO composite hollow microspheres with the high content of NiO exhibit the highest photocatalytic activity for the degradation of different organic dyes including Rhodamine-B, methylene blue and methyl orange under UV irradiation, which might be ascribed to their highest separation efficiency of photogenerated electron–hole pairs. In addition, these NiO–ZnO composite photocatalysts can be used repeatedly without a significant decrease of the photocatalytic activity under UV irradiation.

Phase-controlled synthesis and magnetic properties of cubic and hexagonal CoO nanocrystals

We report facile solution approaches for the phase-controlled synthesis of rock-salt cubic CoO (c-CoO) and wurtzite-type hexagonal CoO (h-CoO) nanocrystals. In the syntheses, the cobalt precursor cobalt (II) stearate is decomposed in 1-octadecene at 320 °C, and the crystalline phase of synthesized products depend critically on the amounts of H2O. While the presence of small amounts of H2O promotes the generation of c-CoO, h-CoO is obtained in the absence of H2O. The as-prepared c-CoO nanocrystals exhibit a multi-branched morphology with several short rods growing on the 〈100〉 direction interlaced together whereas the h-CoO nanocrystals show a multi-rod structure with several rods growing on the same base facet along the c-axis. The formation mechanisms are discussed on the basis of FTIR spectrometry data and color changes of the reaction mixture. Finally the magnetic properties of as-prepared CoO nanocrystals are measured and the results show that c-CoO nanocrystals are intrinsically antiferromagnetic with a Néel temperature of about 300 K but the antiferromagnetic ordering is not distinct for the h-CoO nanocrystals. Weak ferromagnetic contributions are also observed for both c-CoO and h-CoO nanocrystals with obvious magnetic hysteresis at 5 and 300 K. The uncompensated spins that can be induced by crystalline defects such as cation-vacancy may account for the observed weak ferromagnetism.

Solution synthesis of triangular and hexagonal nickel nanosheets with the aid of tungsten hexacarbonyl

The preparation of magnetic metal nanocrystals with strong shape-anisotropy has attracted great research interest in recent years due to their unique applications in fields such as magnetic materials and catalysis. This paper explores a non-aqueous one-pot route to synthesizing triangular and hexagonal Ni nanosheets with an average edge length that can be reduced to 15 nm. In the synthesis, a widely used Ni precursor, nickel(II)acetylacetonate, is reduced by oleylamine in the presence of tungsten hexacarbonyl. An important aspect of such a synthetic strategy is that the nucleation temperature of the Ni nanocrystals can be as low as 150 °C. In the meantime, a shape-anisotropic nanostructure can be achieved. By increasing the reaction temperature and aging time, nanosheets with larger sizes are obtained. A possible formation mechanism is proposed for the as-prepared Ni nanosheets. Magnetic measurements show that all the prepared Ni nanosheets exhibit ferromagnetic characteristics at room temperature and larger magnetic anisotropy compared to spherical nanoparticles is evident.