Donglai Han

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.

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.

Effects of surface modification and SiO2 thickness on the optical and superparamagnetic properties of the water-soluble ZnS:Mn2+ nanowires/Fe3O4 quantum dots/SiO2 heterostructures

In this paper, one-dimensional ZnS:Mn2+ nanowires (NWs)/Fe3O4 quantum dots (QDs)/SiO2 heterostructures were successfully synthesized by the Stober method to form the water-soluble fluorescent/superparamagnetic nanocomposites. The average diameter of the ZnS:Mn2+ NWs, Fe3O4 QDs and ZnS:Mn2+ NWs/Fe3O4 QDs/SiO2 heterostructures was about 6–8 nm, 4–5 nm and 18 nm, respectively. The Fe3O4 QDs were covalently linked to the ZnS:Mn2+ NWs by the conjugation of the hydroxyl groups on the surface of the QDs and the carboxyl groups modified on the surface of the NWs. It was found that the covalent bonds between the NWs and QDs could effectively suppress the energy transfer from the ZnS:Mn2+ NWs to the Fe3O4 QDs. As the SiO2 shell thickness increased, the fluorescence intensity reached the highest value when the hydrolysis time of tetraethyl orthosilicate was 5 hours, which was comparable to that of the ZnS:Mn2+ NWs. The superparamagnetic properties of the heterostructures were observed at room temperature, which decreased as the SiO2 thickness increased.

One-step hydrothermal synthesis of shape-controlled ZnS–graphene oxide nanocomposites

Abstract Shape-controlled ZnS–graphene oxide (GO) nanocomposites were successfully synthesized via an easy one-step hydrothermal method by changing the solvents. The sample prepared in ethytleneglycol and water (1:1 in volume ratio) yielded ZnS nanoparticles (NPs)–GO nanocomposites. The sample prepared in ethylenediamine and water (1:1 in volume ratio) yielded ZnS nanowires (NWs)–GO nanocomposites. The sample prepared in ethytleneglycol, ethylenediamine and water (1:1:2 in volume ratio) yielded ZnS nanorods (NRs)–GO nanocomposites. The results showed that the GO in the composite were exfoliated and decorated with ZnS NPs, NWs and NRs. The photoluminescence intensity of the ZnS–GO nanocomposites exhibited a clearly quenching in comparison with that of ZnS.

Effects of Nd concentration on structural and magnetic properties of ZnFe2O4 nanoparticles

Zinc ferrite nanomaterials have been received significant attention in recent years on account of their potential applications in the fields of electronics, optoelectronics and magnetics. To enhance the magnetic properties of zinc ferrites, Nd-doped zinc ferrites (ZnFe2−xNdxO4, x = 0, 0.01, 0.02, 0.03) nanoparticles (NPs) have been prepared by the sol–gel method. The effects of Nd doping concentration on the structural and magnetic properties of zinc ferrites were studied. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the Nd ions were incorporated into the crystal lattice of ZnFe2O4 and substituted for the Fe3+ sites. Unlike pure zinc ferrites with paramagnetism, Nd doped ZnFe2O4 NPs were superparamagnetic at room temperature. Vibrating sample magnetometry results showed, with the increase of Nd content, the saturation magnetization of Nd doped ZnFe2O4 NPs increased.

Effects of annealing temperature on the magnetic properties of ZnFe1.97Eu0.03O4 nanoparticles

Abstract The ZnFe1.97Eu0.03O4 nanoparticles were prepared with sol–gel method. The effects of sintering temperature on the structural, morphological and magnetic properties were investigated in detail. The results revealed that the ZnFe1.97Eu0.03O4 NPs exhibited weak ferromagnetic properties due to the formation of defects in ZnFe2O4 caused by Eu3+ doping. Moreover, the increased sintering temperature not only enlarged the grain size but also decreased the magnetization of ZnFe1.97Eu0.03O4 NPs due to the decrease of defects in the crystal lattices.

Secondary Growth of ZnO Nanorods to Enhance the Photovoltaic Performance of CdS Quantum Dots Sensitized Solar Cells

We construct CdS quantum dots (QDs) sensitized solar cells with ZnO nanorods as photoanodes. To enlarge the QDs loading surface of ZnO nanorods, we perform primary and secondary growth to obtain ZnO nanorods with different length. We investigate its influence on the photovoltaic performance of the solar cells. The photovoltaic performance for ZnO nanorods photoanodes with secondary growth exhibits a 41% enhancement in energy conversion efficiency compared to the ZnO nanorods photoanodes with primary growth.