Haihong Yin

Synthesis of Au-Decorated V2O5@ZnO Heteronanostructures and Enhanced Plasmonic Photocatalytic Activity

A ternary plasmonic photocatalyst consisting of Au-decorated V2O5@ZnO heteronanorods was successfully fabricated by an innovative four-step process: thermal evaporation of ZnO powders, CVD of intermediate on ZnO, solution deposition of Au NPs, and final thermal oxidization. SEM, TEM, EDX, XPS, and XRD analyses revealed that the interior cores and exterior shells of the as-prepared heteronanorods were single-crystal wurtzite-type ZnO and polycrystalline orthorhombic V2O5, respectively, with a large quantity of Au NPs inlaid in the V2O5 shell. The optical properties of the ternary photocatalyst were investigated in detail and compared with those of bare ZnO and V2O5@ZnO. UV-vis absorption spectra of ZnO, V2O5@ZnO, and Au-decorated V2O5@ZnO showed gradually enhanced absorption in the visible region. In addition, gradually decreased emission intensity was also observed in the photoluminescence (PL) spectra, revealing enhanced charge separation efficiency. Because of these excellent qualities, the photocatalytic behavior of the ternary photocatalyst was studied in the photodegradation of methylene blue under UV-vis irradiation, which showed an enhanced photodegradation rate nearly 7 times higher than that of bare ZnO and nearly 3 times higher than that of V2O5@ZnO, mainly owing to the enlarged light absorption region, the effective electron-hole separation at the V2O5-ZnO and V2O5-Au interfaces, and strong localization of plasmonic near-field effects.

The combinations of hollow MoS2 micro@nano-spheres: one-step synthesis, excellent photocatalytic and humidity sensing properties

The combinations of hollow MoS2 micro@nano-spheres were successfully fabricated through a one-step hydrothermal method. A possible growth mechanism was presented in detail based on time-dependent experimental facts. Besides, the photocatalytic activities of the samples were evaluated by monitoring the photodegradation of methylene blue (MB). The adsorption value of 150 mg g−1 shows a strong adsorption capability in the dark. After irradiation for only 30 min, the remaining MB in solution is about 9.7%. Moreover, the humidity sensing properties of the samples were measured for the first time. The results revealed high sensitivity at high RH, small humidity hysteresis, fast response and recovery times, and good stability. The greatest sensitivity is 32.19 nF/% RH and the maximum hysteresis is ∼6.3% RH. For humidity cycling of 17.2–89.5–17.2% RH, the response and recovery times are ∼140 s and ∼80 s, respectively. Capacitance fluctuations for one month are less than ±7% at various relative humidities (RHs).

Porous V2O5 micro/nano-tubes: Synthesis via a CVD route, single-tube-based humidity sensor and improved Li-ion storage properties

Porous V2O5 micro/nano-tubes were synthesized via a modified chemical vapor deposition process and a possible growth mechanism was proposed. The micro/nano-tubes have large surface area because of their tubular structure with a porous wall. A humidity sensor based on a single porous V2O5 micro/nano-tube was constructed, and humidity sensing measurements indicated fast response/recovery. Due to the large surface area, the porous V2O5 micro/nano-tubes were used as a cathode material for lithium-ion batteries that exhibited great improvement of the electrochemical performance such as a high lithium-storage capacity of ∼290 mA h g−1, excellent cycling stability and reversibility. Further cyclic voltammetry measurements under different scanning rates confirmed that the intercalation/de-intercalation is of high efficiency and the kinetic performance of the battery is significantly improved. These characteristics of porous V2O5 micro/nano-tubes make them promising materials for application in gas detection and lithium-ion batteries.

Highly efficient field emission properties of a novel layered VS2/ZnO nanocomposite and flexible VS2 nanosheet

Multi-layered VS2 nanosheets were synthesized via a facile hydrothermal process without using any additives or surfactants. Due to the large quantities of sharp edges, a VS2 nanosheet can serve as an efficient edge emitter for field emission (FE). The FE properties of VS2 nanosheets were investigated for the first time. The results indicated that the VS2 nanosheets had an excellent field emission performance with a turn-on field of ∼1.4 V μm−1 and a threshold field of ∼2.6 V μm−1 on a Si substrate. Moreover, the FE properties of ZnO-coated VS2 nanosheets were also investigated. The VS2/ZnO nanocomposite showed enhanced field emission properties with a turn-on field of ∼1.2 V μm−1 and a threshold field of ∼2.2 V μm−1, as well as an excellent emission stability without significant current degradation, which resulted from a well contacted metal–semiconductor junction and extra emission sites. In addition, the FE properties of the VS2 nanosheets were preserved on a highly flexible polyethylene terephthalate (PET) substrate. Approximately the same values of the turn-on field (∼1.8 V μm−1) and the threshold field (∼3.2 V μm−1) were measured on bent and unbent PET substrates.

Cu2S@ZnO hetero-nanostructures: facile synthesis, morphology-evolution and enhanced photocatalysis and field emission properties

A novel hierarchical three-dimensional (3D) Cu2S@ZnO heteroarchitecture was successfully synthesized by a facile three-step synthetic process. FESEM and TEM analyses revealed the formation of the hierarchical 3D structure of the as-prepared Cu2S@ZnO. The purity and crystalline phase of the individual component in the 3D Cu2S@ZnO were determined by a powder X-ray diffractogram. The formation of the hierarchical 3D structure of the as-prepared Cu2S@ZnO leads to multiple p–n junctions formed at p-Cu2S@n-ZnO interfaces, which promote the generation and separation of photoinduced electrons and holes and thus improves the photocatalytic efficiency tremendously. According to the data, after irradiation for 40 min, the remaining MB in solution is about 35% for Cu2S nanoflowers and 9% for Cu2S@ZnO binary nanoflowers. Also, the increases in the overall aspect ratio and the ZnO nanoparticles act as extra emission sites, which help to enhance the field emission properties. The turn-on fields and threshold fields for the Cu2S nanoflowers as well as the Cu2S@ZnO nanoflower hybrid emitters are 3.3 and 9.2 V μm−1, 2 and 6.3 V μm−1, respectively. Compared with the Cu2S nanoflowers, the Cu2S@ZnO hetero-nanoflowers show excellent improvements in both photocatalytic and field emission applications.

Fabrication and Temperature-Dependent Field-Emission Properties of Bundlelike VO2 Nanostructures

Bundlelike VO(2)(B) nanostructures were synthesized via a hydrothermal method, and VO(2)(M(1)/R) nanobundles were obtained after a heat-treatment process. Structural characterization shows that these nanobundles are self-assembled by VO(2) nanowires, and VO(2)(M(1)/R) nanobundles have better crystallinity. Temperature-dependent field-emission (FE) measurement indicates that FE properties of these two phases of nanobundles can both be improved by increasing the ambient temperature. Moreover, for the VO(2)(M(1)/R) nanobundles, their FE properties are also strongly dependent on the temperature-induced metal-insulator transitions process. Compared with poor FE properties found in the insulating phase, FE properties were significantly improved by increasing the temperature, and about a three-orders-of-magnitude increasing of the emission current density has been observed at a fixed field of 6 V/μm. Work function measurement and density-functional theory calculations indicated that the decrease of work function with temperature is the main reason that caused the improvement of FE properties. These characteristics make VO(2)(M(1)/R) a candidate material for application of new type of temperature-controlled field emitters, whose emission density can be adjusted by ambient temperature.

Synthesis of a MoS2@MWNT nanostructure with enhanced field emission and electrochemical properties

A polyol method was first employed to synthesize MoS2@MWNT nano-flower composites. Due to their high conductivity, large aspect ratio and sharp edges, an excellent field emission performance was obtained relative to pure MoS2 with the turn-on field decreasing from 5.3 V μm−1 to 2.7 V μm−1 and the threshold field decreasing from 8.0 V μm−1 to 5.3 V μm−1. When used as anode materials for Li-ion batteries in an aqueous electrolyte, the composites exhibit a highest specific capacity of 1217 mA h g−1 at a current of 100 mA g−1, excellent cycling stability and high-rate capability, and a high specific capacity of 851 mA h g−1, which was still retained at a high current density of 1600 mA g−1.

Facile synthesis, enhanced field emission and photocatalytic activities of Cu2O?TiO2?ZnO ternary hetero-nanostructures

Cu2O–TiO2–ZnO ternary nano-heteroarchitectures were designed and successfully fabricated using titanium (IV) oxideacetylacetonate (TiO(acac)2) as a precursor and polyethyleneimine (PEI) as a binding agent. Field emission and photocatalytic activities of pure Cu2O nanopines, Cu2O–TiO2 core–shell nanopines and Cu2O–TiO2–ZnO ternary composites were investigated and compared. The results revealed that the as-prepared nano-heterojunctions and nanoparticles at the surface remarkably enhanced the field emission and photocatalytic activities of pure Cu2O nanopines. The as-prepared nano-heterojunctions induced interfacial states and energy band differentials, which caused electron transition and the inhibition of photo-induced electron–hole pair recombination. The nanoparticles at the surface formed thousands of surface nano-protrusions and active sites for photocatalytic chemical reactions.

Fabrication of ZnO photonic amorphous diamond nanostructure from parrot feathers for modulated photoluminescence properties

A ZnO photonic amorphous diamond nanostructure was successfully synthesised using a feather barb of the Rosy-Faced Lovebird as supporting template via a facile sol-gel process. Different from ordered structures, an isotropic PBG around 500 nm was evidenced from reflectance spectra and an optical metallurgical microscopy image, which overlaps with the visible emission peak of ZnO. As a result, the inhibition of visible emission inside the PBG and the enhancement of UV emission at the PBG edges have both been observed, which is independent from the incident angle. Moreover, the rapid thermal annealing can also help improve the crystallinity of ZnO and raise the UV/visible emission ratio without affecting the structure. These results can be very useful for the study of the modification of the optical emission properties of ZnO and other semiconductor materials as well as research on ZnO random lasing.