Xina Wang

Double-shelled ZnO/CdSe/CdTe nanocable arrays for photovoltaic applications: microstructure evolution and interfacial energy alignment

A series of high-density double- and single-shelled ZnO/CdSe/CdTe, ZnO/CdTe/CdSe, ZnO/CdTe and ZnO/CdSe nanocable arrays were synthesized as photoanodes by an electrodeposition method using ZnO nanorod arrays as cores. For ZnO/CdSe/CdTe nanocable arrays, the uniform CdSe and CdTe nanoshells were composed of zinc-blende phase nanocrystals with a respective average size range of 10–20 nm and 7–15 nm, and formed a compact and continuous interface in between. Based on the band offset of the bulk material before contact and the interfacial Fermi level shift after contact, the energy level alignments at the CdSe/CdTe and CdTe/CdSe interface were deduced for the double-shelled nanocable arrays. The CdTe/CdSe interface of the ZnO/CdTe/CdSe nanocables has a negative band offset of −0.16 eV whilst for ZnO/CdSe/CdTe nanocables, the band edge of CdTe lies above CdSe with a conduction band offset of 0.16 eV at the CdSe/CdTe interface. Such a stepwise band alignment, together with the compact interface, fewer grain boundaries along the radial direction, and the fast transfer rate along the axial direction of the nanocables, makes the ZnO/CdSe/CdTe nanocable arrays photoanode have a saturated photocurrent of ∼14.3 mA cm−2. This is under the irradiation of AM1.5G simulated sunlight at 45 mW cm−2, which is greatly higher than ZnO/CdTe/CdSe, ZnO/CdSe or ZnO/CdTe nanocable arrays.

Synthesis and photoelectrochemical response of CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes

A continuous and compact CdS quantum dot-sensitive layer was synthesized on TiO2 nanorods by successive ionic layer adsorption and reaction (SILAR) and subsequent thermal annealing. The thickness of the CdS quantum dot layer was tuned by SILAR cycles, which was found to be closely related to light absorption and carrier transformation. The CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet–visible absorption spectroscopy, and photoelectrochemical property measurement. The optimum sample was fabricated by SILAR in 70 cycles and then annealed at 400°C for 1 h in air atmosphere. A TiO2/CdS core-shell structure was formed with a diameter of 35 nm, which presented an improvement in light harvesting. Finally, a saturated photocurrent of 3.6 mA/cm2 was produced under the irradiation of AM1.5G simulated sunlight at 100 mW/cm2. In particular, the saturated current density maintained a fixed value of approximately 3 mA/cm2 without decadence as time passed under the light conditions, indicating the steady photoelectronic property of the photoanode.

Surface Roughening of Nickel Cobalt Phosphide Nanowire Arrays/Ni Foam for Enhanced Hydrogen Evolution Activity

Development of earth-abundant, efficient, and stable electrocatalysts for hydrogen evolution reactions (HER) in alkaline or even neutral pH electrolyte is very important for hydrogen production from water splitting. Construction of bimetal phosphides via tuning the bonding strength to hydrogen and increasing effective active sites through nanostructuring and surface engineering should lead to high HER activity. Here, ternary NiCoP nanowires (NWs) decorated by homogeneous nanoparticles have been obtained on Ni foam for a highly efficient HER property via long-term cyclic voltammetric (CV) sweeping. The electron density transfer between the positively charged Ni and Co and negatively charged P atoms, one-dimensional electron transfer channel of the NWs, and abundant active sites supplied by the nanoparticles and NWs endow the catalyst with low overpotentials of 43 and 118 mV to achieve the respective current densities of 10 and 100 mA cm-2 together with long durability for at least 33 h in 1 M KOH. A cycled anodic dissolution-redeposition mechanism is disclosed for the formation of the NiCoP nanoparticles during the CV sweeping process. Such a surface roughening method is found to be adaptable to enhance the HER property of other phosphides, including Ni2P nanoplates/NF, NiCoP nanoparticles/NF, and CoP NW/NF.

Selective Growth of Vertical-aligned ZnO Nanorod Arrays on Si Substrate by Catalyst-free Thermal Evaporation

By thermal evaporation of pure ZnO powders, high-density vertical-aligned ZnO nanorod arrays with diameter ranged in 80–250 nm were successfully synthesized on Si substrates covered with ZnO seed layers. It was revealed that the morphology, orientation, crystal, and optical quality of the ZnO nanorod arrays highly depend on the crystal quality of ZnO seed layers, which was confirmed by the characterizations of field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence measurements. For ZnO seed layer with wurtzite structure, the ZnO nanorods grew exactly normal to the substrate with perfect wurtzite structure, strong near-band-edge emission, and neglectable deep-level emission. The nanorods synthesized on the polycrystalline ZnO seed layer presented random orientation, wide diameter, and weak deep-level emission. This article provides a C-free and Au-free method for large-scale synthesis of vertical-aligned ZnO nanorod arrays by controlling the crystal quality of the seed layer.

Two novel cytochrome P450 genes CYP6CS1 and CYP6CW1 from Nilaparvata lugens (Hemiptera: Delphacidae): cDNA cloning and induction by host resistant rice.

Two novel full-length P450 cDNAs, CYP6CS1 and CYP6CW1, were cloned from the fourth instar nymphs of brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae) reared on its susceptible rice variety Taichung Native 1 (TN1) plants. The deduced proteins are typical microsomal P450s sharing conserved structural and functional domains with other insect CYP6 members. Temporal expression analysis by northern blot hybridization indicated pre-exposure to N. lugens moderately resistant rice Minghui 63 (MH63) seedlings caused a time course-dependent induction of CYP6CS1 which peaked after 24 h of treatment; in contrast, CYP6CW1 was induced and remained at a constant time course from 0-72 h. CYP6CS1 and CYP6CW1 are dramatically induced in gut tissues and, slightly upregulated in carcass and fat bodies as revealed in spatial gene expression analysis. Whole mount in situ hybridizaion revealed that the two genes are expressed at a basal level in gut tissue and Malpighian tubules in nymphs fed with TN1 rice. After exposure to MH63, the expression of CYP6CW1 was found to be high in the whole gut, including Malpighian tubules. Expression of CYP6CS1 was significantly increased in midgut, and slightly increased in foregut, hindgut and Malpighian tubules. These data suggest a potential role of the two P450s in determining patterns of N. lugens-rice relationships through allelochemical detoxification.

Loading Cd0.5Zn0.5S Quantum Dots onto Onion-Like Carbon Nanoparticles to Boost Photocatalytic Hydrogen Generation

Carbon dots (C dots, size < 10 nm) have been conventionally decorated onto semiconductor matrixes for photocatalytic H2 evolution, but the efficiency is largely limited by the low loading ratio of the C dots on the photocatalyst. Here, we propose an inverse structure of Cd0.5Zn0.5S quantum dots (QDs) loaded onto the onionlike carbon (OLC) matrix for noble metal-free photocatalytic H2 evolution. Cd0.5Zn0.5S QDs (6.9 nm) were uniformly distributed on an OLC (30 nm) matrix with both upconverted and downconverted photoluminescence property. Such an inverse structure allows the full optimization of the QD/OLC interfaces for effective energy transfer and charge separation, both of which contribute to efficient H2 generation. An optimized H2 generation rate of 2018 μmol/h/g (under the irradiation of visible light) and 58.6 μmol/h/g (under the irradiation of 550-900 nm light) was achieved in the Cd0.5Zn0.5S/OLC composite samples. The present work shows that using the OLC matrix in such a reverse construction is a promising strategy for noble metal-free solar hydrogen production.

Cobalt Oxide Porous Nanofibers Directly Grown on Conductive Substrate as a Binder/Additive-Free Lithium-Ion Battery Anode with High Capacity

In order to reduce the amount of inactive materials, such as binders and carbon additives in battery electrode, porous cobalt monoxide nanofibers were directly grown on conductive substrate as a binder/additive-free lithium-ion battery anode. This electrode exhibited very high specific discharging/charging capacities at various rates and good cycling stability. It was promising as high capacity anode materials for lithium-ion battery.

Structural and photocatalytic properties of Cd1-xZnxS nanocrystals via organic solution method

Uniform CdxZn1−xS nanocrystals with size between 4nm and 9nm were fabricated by an organic chemical method. The structural, morphology as well as optical properties of the samples were investigated by X-ray diffraction (XRD), TEM, and UV–Vis absorbance techniques. The XRD patterns of CdxZn1−xS nanocrystals indicated that the solid solution possesses cubic zinc-blende structure. By tuning the composition of Zn ions in the alloy, the band gap of CdxZn1−xS can be modulated from 2.10eV to 3.17eV. Photocatalytic hydrogen evolution was investigated under visible-light (λ≥420nm) irradiation with Na2S/Na2SO3 as the electron donor. It is found that Cd0.5Zn0.5S nanocrystals have the highest photoactivity with a H2 evolution rate of 1.52mmol/h⋅g. The CdxZn1−xS nanoparticles exhibit stable activity in a cycled hydrogen evolution experiment.

Analysis on properties of magnetised water and its application in sprayed concrete

Abstract Substantial research results show that the magnetised water can make the cement hydration reaction more completely, so the properties of magnetised water are studied in the thesis. The research starts with the chemical properties of magnetised water such as the conductivity, viscosity, pH value. On the basis of the study of magnetised water by the predecessors, a test about the application of magnetised water on sprayed concrete has been taken based on the selected magnetised parameters. The magnetised water which is used to mix concrete can improve the performance of concrete. This paper presents the effect of magnetised water on performance of sprayed concrete in laboratory. The results indicate that the early strength of concrete mixed with magnetised water has been obviously improved.

ZnO nanorod multilayer film prepared by hydrothermal growth and its application in dye sensitised solar cells

Abstract ZnO nanorod multilayer film was hydrothermal fabricated on fluorine-doped SnO2-coated glass (FTO) substrate using the sol–gel method from a ZnO seed layer. Such a multilayer film has micrometre scale arms linking with ZnO nanorod arrays vertical to the FTO substrate. It provides a large surface area for dye adsorption and a rapid pathway for electron transport along the nanorod channel. The sensitised solar cell based on the optimised ZnO nanorod multilayer film with thickness of 56.7 μm reaches a power conversion efficiency (PCE) of 1.8%.