Weiwei Xia

Behind the change of the photoluminescence property of metal-coated ZnO nanowire arrays

The effect of metal coating on the photoluminescence (PL) properties of ZnO nanowire arrays has been investigated in detail in this letter. The Zn coating induces remarkable enhancement of the ultraviolet and green emissions of the nanowires, while the deposition of Ag leads to notable decrement of them. A model considering the type of contacts formed between metals and ZnO is proposed to interpret the change of the PL spectra. Also, this model is strongly supported by the PL variation of the nanowires after coating with other kinds of metals.

One-pot construction of three dimensional CoMoO4/Co3O4 hybrid nanostructures and their application in supercapacitors

A facile one-pot hydrothermal method was developed to synthesize a CoMoO4/Co3O4 hybrid nanostructure where CoMoO4 nanosheets were supported by a hierarchical framework assembled by Co3O4 nanorods. The morphology and structure of this three dimensional nanocomposite were characterized in detail and a rational growth mechanism was proposed based on them. The unique structural features of our CoMoO4/Co3O4 hierarchical nanohybrid allow for high specific surface and multiple faradaic redox reactions for electrode materials of supercapacitors. Consequently, a high specific capacitance (1062.5 F g−1 at the current density of 1 A g−1) and an excellent cyclic performance (90.38% of the initial capacitance retained after 2000 cycles at a current density of 20 A g−1) were obtained. In addition, an asymmetric supercapacitor with high energy density of 31.64 W h kg−1 was achieved at a power density of 7270 W kg−1. This work thus provides an excellent candidate for high-performance supercapacitor fabrication.

Nanoplate-Built ZnO Hollow Microspheres Decorated with Gold Nanoparticles and Their Enhanced Photocatalytic and Gas-Sensing Properties.

Hierarchical porous ZnO microspheres decorated with gold nanoparticles (AuNPs) were successfully synthesized by a facile solvothermal route. The hierarchical ZnO superstructure was constructed of interconnected nanoplates with numerous voids. Photoluminescence, X-ray photoelectron spectroscopy, and electron paramagnetic resonance measurements demonstrated that the main defects were oxygen vacancies (V(O)(•)) with minor interstitial oxygen (O(i)(-)) in the hierarchical ZnO hollow microspheres. The as-prepared hierarchical ZnO hollow microspheres and the AuNPs used to decorate them were examined for their photocatalytic degradation ability and as gas sensors. The photodegradation results demonstrated that the degradation rate constant on rhodamine B for undecorated ZnO microspheres was 0.43 min(-1), which increased to 1.76 min(-1) for AuNP-decorated ZnO microspheres. The AuNP-functionalized ZnO microspheres displayed superior sensing properties, with a 3-fold enhancement in their gas response to 1 ppb of dibutyl phthalate.

High-efficiency photocatalytic activity of type II SnO/Sn3O4 heterostructures via interfacial charge transfer

Flower-like hollow microspheres were synthesized on a large scale using a one-step hydrothermal route. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy. The results showed that the shells of the hollow microspheres were composed of numerous type II SnO/Sn3O4 heterostructures. A 500 °C annealing treatment changed the type II SnO/Sn3O4 heterostructures into type I SnO2/Sn3O4 heterostructures; at 700 °C, the products were pure SnO2 semiconductors. A photocatalytic degradation test showed that the highest efficiency degradation of rhodamine B (RhB) was obtained using type II SnO/Sn3O4 heterostructure semiconductors with a degradation rate constant of 2.3 × 10−3 min−1. This highly efficient activity was induced by enhanced charge separation in type II SnO/Sn3O4 heterostructure semiconductors.

Loss mechanism and microwave absorption properties of hierarchical NiCo2O4 nanomaterial

Understanding the loss mechanism of microwave absorption is of great significance for the design and fabrication of low-cost, high-efficient and light-weight microwave absorbing materials. In this study, the microwave absorption of a hierarchical NiCo2O4 nanomaterial synthesized via a hydrothermal method and a subsequent annealing process was investigated in detail. The effects of the annealing temperature on the phase evaluation and microwave absorption properties were also investigated to reveal the microwave loss mechanism of NiCo2O4 nanostructures. The results show that the Debye relaxation and superior electric conductivity of NiCo2O4 are beneficial to its excellent microwave absorption performance. This study will be useful for the fundamental understanding of microwave absorption in NiCo2O4 nanomaterial, and for the design of a novel microwave absorbent.

A 3D-SERS substrate with high stability: Silicon nanowire arrays decorated by silver nanoparticles

Stability is an important issue of surface-enhanced Raman scattering (SERS) substrates. In this paper, a highly stable three-dimensional (3D)-SERS substrate has been prepared by surface migration of silver on the surface of silicon nanowires (SiNWs). Along with the formation of silver nanoparticles (AgNPs), a thin layer of compact SiO2 caps is formed on AgNPs, protecting the silver from aggregation effectively and guaranteeing the stability of the SERS substrates. Their shelf life can be improved greatly. The thin SiO2 layer, which protects the silver from degradation, can be easily and quickly removed just prior to analysis of optimal SERS performance. This work introduces a creative technique to produce highly stable and efficient 3D-SERS substrates for trace detection of chemical and biological molecules.

Gold nanoparticles assembling on smooth silver spheres for surface-enhanced Raman spectroscopy.

A simple and cost-effective chemical method was introduced to assemble gold (Au) nanoparticles on smooth silver (Ag) spheres for realizing surface-enhanced Raman scattering (SERS) enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. We found that the Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.

Mesoporous multi-shelled ZnO microspheres for the scattering layer of dye sensitized solar cell with a high efficiency

Both light scattering and dye adsorbing are important for the power conversion efficiency PCE performance of dye sensitized solar cell (DSSC). Nanostructured scattering layers with a large specific surface area are regarded as an efficient way to improve the PCE by increasing dye adsorbing, but excess adsorbed dye will hinder light scattering and light penetration. Thus, how to balance the dye adsorbing and light penetration is a key problem to improve the PCE performance. Here, multiple-shelled ZnO microspheres with a mesoporous surface are fabricated by a hydrothermal method and are used as scattering layers on the TiO2 photoanode of the DSSC in the presence of N719 dye and iodine–based electrolyte, and the results reveal that the DSSCs based on triple shelled ZnO microsphere with a mesoporous surface exhibit an enhanced PCE of 7.66%, which is 13.0% higher than those without the scattering layers (6.78%), indicating that multiple-shelled microspheres with a mesoporous surface can ensure enough light sca...

Electrophoretic fabrication of silver nanostructure/zinc oxide nanorod heterogeneous arrays with excellent SERS performance

A simple and green strategy is presented to fabricate Ag-decorated ZnO nanorod arrays based on electrophoretic deposition in a Ag colloidal solution prepared by laser ablation in water. The edges or corners of each nanorods upper surface feature dendritic aggregates consisting of nanoparticles, and the other surfaces exhibit irregular particles of less than 200 nm in size. Overall, the created Ag nanostructure/ZnO nanorod is hierarchically micro/nanostructured and very rough at the nanoscale. The inter-particle spacings in the decoration layer are nanometers to tens of nanometers in scale. Further experiments have revealed that suitable electrophoretic potential and sufficient growth duration are crucial for obtaining complete coverage on every nanorod. The site-specific deposition of Ag nanoparticles on ZnO nanorods can be explained by the different distributions of the electric field and the colloidal concentration during electrophoresis. Such heterogeneous nanorod arrays are functionalized and exhibit excellent surface-enhanced Raman scattering performance. This study provides a new method for creating decorated nanorod arrays with novel nanostructures by using unstable colloidal nanoparticles as building blocks and deepens the understanding of the physical mechanisms of electrophoretic deposition.

Quantum dot-assembled mesoporous CuO nanospheres based on laser ablation in water

A simple and green strategy is presented to fabricate CuO quantum dot-assembled nanospheres based on laser ablation of Cu metal targets in water. The colloidal nanospheres are mesoporous, with an average size of approximately 200 nm. Furthermore, the quantum dots, as a building block, can be easily tuned in size by changing the laser power. Importantly, such mesoporous nanospheres exhibit good photocatalytic activity due to their unique structure.