Jinghai Yang

Highly enhanced photocatalytic properties of ZnS nanowires–graphene nanocomposites

ZnS nanowires (NWs)–graphene (GR) nanocomposites were successfully synthesized via an easy electrostatic self-assembly method. The results showed that ZnS NWs were well dispersed on the surface of the graphene nanosheets, forming ZnS–GR nanocomposites. The photoluminescence intensity of the ZnS–GR nanocomposites exhibited a clear quenching in comparison with that of the ZnS NWs. The ZnS–GR nanocomposites were used as photocatalysts for the degradation of methylene blue (MB) under UV light irradiation. After irradiation for 1 h, the degradation efficiency was 21.69% for ZnS NWs, 31.52% for ZnS–0.5 wt% GR, 58.69% for ZnS–3 wt% GR, 88.33% for ZnS–5 wt% GR and 80.74% for ZnS–7 wt% GR, indicating that ZnS–5 wt% GR nanocomposites had the highest photocatalytic activity. The kinetic rate constant of the ZnS–5 wt% GR nanocomposites was about 16 times higher than that of the ZnS NWs. The mechanism of the highly enhanced photocatalytic properties was attributed to the efficient separation of the photogenerated electron–hole pairs and the high specific surface area of graphene.

Synthesis of urchin-like Fe3O4@SiO2@ZnO/CdS core–shell microspheres for the repeated photocatalytic degradation of rhodamine B under visible light

Herein, we developed the design and synthesis of urchin-like Fe3O4@SiO2@ZnO/CdS core–shell microspheres, in which the multiple functional components were integrated successfully into a single microcomposite. The morphology, composition, and optical and magnetic properties of those core–shell microspheres were characterized by various analytical techniques. Photocatalytic performances were evaluated by the photocatalytic elimination of rhodamine B (RhB) under visible light irradiation. Compared with the Fe3O4@SiO2@ZnO microspheres, the Fe3O4@SiO2@ZnO/CdS microspheres show remarkably enhanced visible light photocatalytic activity, benefiting from the sensitization of CdS, which can extend the visible light absorption and facilitate the separation of photoinduced carriers. The amount of CdS in the core–shell microspheres can be controlled by adjusting the SILAR cycles. The effect of the CdS loading amount on the photocatalytic activity was also investigated and the results indicate that Fe3O4@SiO2@ZnO/CdS with 10.1 wt% CdS exhibits the best photocatalytic ability. Furthermore, it is worth noting that these multifunctional microspheres exhibit excellent magnetic response and high stability. The core–shell photocatalysts can also maintain high photocatalytic activity even after running for five cycles.

Investigation of composition dependent structural and optical properties of the Zn(1-x)Cd(x)S, coaxial Zn(0.99-x)Cd(x)Cu(0.01)S/ZnS, Zn(0.99-x)Cd(x)Mn(0.01)S nanorods generated by a one-step hydrothermal process.

High-quality Zn(1-x)Cd(x)S, coaxial Zn(0.99-x)Cd(x)Cu(0.01)S/ZnS and Zn(0.99-x)Cd(x)Mn(0.01)S nanorods (NRs) were synthesized through a one-step hydrothermal method. The composition of the alloyed NRs was adjusted by controlling the Zn/Cd molar ratios. The results showed that all of the samples had a good crystallinity with the typical hexagonal wurtzite structure. The Zn/Cd molar ratios and Cu and Mn doping played an important role in affecting the final structure, morphology and optical properties of the alloyed NRs. The successive shift of the XRD and PL patterns indicated that the NRs obtained were not a mixture of ZnS and CdS, but the Zn(1-x)Cd(x)S solid solution. After doping Cu(2+) (1%) ions into the Zn(1-x)Cd(x)S NRs, the samples exhibited highly crystalline coaxial Zn(0.99-x)Cd(x)Cu(0.01)S/ZnS core-shell NRs and showed a strong green emission peak centered at 509.6 nm. After doping Mn(2+) (1%) ions into the Zn(1-x)Cd(x)S NRs, the samples exhibited a better crystal quality and showed a strong yellow-orange emission peak centered at 583 nm.

Controllable morphology and tunable colors of Mg and Eu ion co-doped ZnO by thermal annealing

Mg2+ and Eu3+ co-doped ZnO nanostructures were prepared by an environmentally friendly method. With an increase in the annealing temperature, the Mg2+ and Eu3+ co-doped ZnO nanosheets, composed of aggregated crystallites, experienced structural evolution from individual nanochains to partially sintered short rods and finally smooth nanorods. Consequently, the optical properties of Mg2+ and Eu3+ co-doped ZnO changed accordingly, shown here for white, green and yellow emitting segments. This study on the correlation between the sintered structure and optical properties shows that controlled thermal annealing affects the stress through structural evolution of the Mg2+ and Eu3+ co-doped ZnO nanocrystallites.

The electrical transportation and carrier behavior of ZnSe under high pressure

With in situ electrical resistivity and Hall effect measurement, electrical transportation property and charge carrier behavior of ZnSe were investigated under high pressure using a diamond anvil cell (DAC). The electrical resistivity changed discontinuously at 7.7 and 11.9 GPa, corresponding to the phase transitions of ZnSe. In the pressure interval of 7.7–11.9 GPa, the electrical resistivity changed continuously, indicating the existence of the intermediate phase between the zinc blende and rock salt phases. The difference of carrier characteristic between the intermediate and rock salt phases can also suggest the existence of the intermediate phase. For the intermediate phase, the increase in electrical resistivity is from the decrease in mobility. While for the rock salt phase, the increase in charge carrier concentration leads to the decrease in electrical resistivity.

Mixed conduction in BaF2 nanocrystals under high pressure

The charge transport behavior of barium fluoride nanocrystals has been investigated by in situ impedance measurement up to 23 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in BaF2 nanocrystals include both F− ions and electrons. Pressure makes both the F− ions diffusion and electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the Fm3m and Pnma phases more difficult. The electron conduction plays a dominant role in the transport process. In the Fm3m and Pnma phases, the electron transference number increases with increasing pressure.

High pressure impedance spectroscopy of SrF2 nanocrystals

ABSTRACT The charge transport behavior of strontium fluoride nanocrystals has been investigated by in situ impedance measurement up to 41 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in SrF2 nanocrystals include both F− ions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the Fm3m and Pnma phases more difficult.

Blocking the Formation of Zn2+/Dye Complexes in Dye-Sensitized Solar Cells by Inserting CdS Quantum Dots into Sandwich Layer

ZnO NRAs are grown on ITO substrates by a simple chemical method. CdS QDs were deposited on ZnO NRAs by SILAR. N719 was synthesized by dipping method. J–V analysis indicates that by inserting a layer of CdS QDs, the conversion efficiency of DSSCs was improved obviously. The device with CdS QDs shows the higher conversion efficiency due to the three reasons: (1) CdS QDs enhanced adsorption spectra of DSSCs in the visible region; (2) CdS QDs block the formation of Zn2+/dye complex, it is beneficial for electros transport from dye to ZnO photoanode. It is the key to obtain higher conversion efficiency; (3) FRET dynamics exists by the introduction of CdS QDs.

Carrier Density-Dependent Localized Surface Plasmon Resonance and Charge Transfer Observed by Controllable Semiconductor Content

We discuss how the controllable carrier influences the localized surface plasmon resonance (LSPR) and charge transfer (CT) in the same system based on ultraviolet-visible and surface-enhanced Raman scattering (SERS) measurements. The LSPR can be easily tuned from 580 to 743 nm by changing the sputtering power of Cu2S in the Ag and Cu2S composite substrate. During this process, surprisingly, we find that the LSPR is proportional to the sputtering power of Cu2S. This observation indicates that LSPR can be accurately adjusted by changing the content of the semiconductor, or even the carrier density. Moreover, we characterize the carrier density through the detection of the Hall effect to analyze the Raman shift caused by CT and obtain the relationships between them. These fundamental discussions provide a guideline for tunable LSPR and the investigation of CT.

Defects driven photoluminescence property of Sm-doped ZnO porous nanosheets via a hydrothermal approach

Samarium doped ZnO porous nanosheets were prepared via a hydrothermal approach and well characterized by X-ray diffraction (XRD), Raman spectroscopy, transition electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and UV–vis absorption spectroscopy. With increasing the Sm3+ doping concentrations, the crystallization of the thin nanosheets with irregular porosities became worse and the size of the porosities in the nanosheets gradually diminished due to the obstructions of Zn–O–Sm and the generated volatile gas. It was also found that the Sm3+ ions not only acted as the donors sinks to modulate the defects in host, but also expanded the visible light response of the ZnO. The slight redshift of UV NBE (near-band edge) emission as compared to undoped one indicated the band gap of the doped nanosheets became narrower due to the combination of the formed impurity band and the strong exchange interactions between electrons. The kinds of the defects as the deep-level-defect luminescent centers in DLE (deep-level emission) varied with the Sm3+ doping concentrations, and the detail change of the defects was also discussed in detail. These findings would be useful for the material design and defect modification for optical applications.