Yongqian Wang

Controllable fabrication of nanostructured copper compound on a Cu substrate by a one-step route

We report a one-step corrosion process to synthesize nanostructured CuO thin films at room temperature. The reaction time has great effect on the composition and microstructure of products to control the size and shape of the copper compound. X-ray diffraction studies showed the transformation of nanograins from Cu(OH)2 nanowires to flower-like CuO and to dispersed CuO nanosheets. The optical properties of CuO nanosheets were investigated by using UV-vis spectroscopy with considerable blue-shift in the optical band gap (Eg = 1.8 eV) due to the quantum confinement effect. Additionally, the photocatalytic activities of as-prepared copper compound films were determined by measuring the degradation of methyl blue (MB) to find out their potential application in waste water treatment. The photoluminescence (PL) spectrum showed both UV as well as visible emission peaks, indicating their good optical properties. Moreover, a reasonable growth mechanism for the formation of the CuO nanostructure is proposed by means of a scanning electron microscope (FESEM).

Modification of kaolinite with alkylimidazolium salts

We have demonstrated that the d-spacing and thermal stability of the alkylimidazolium intercalated kaolinite compounds can be controlled by adjusting chain length of the alkyl groups. The composites were synthesized by displacement method using selected imidazolium ionic liquids bearing different short alkyl chains as guest molecules. The effects of the length of alkyl side chain on d-spacing and thermal stability of the ionic liquids–kaolinite intercalations were investigated by XRD and TG-DSC. Results revealed that in these composites, increasing the length of alkyl substituent led to larger d-spacing and decreased thermal stability. Temperature was found to have influence on the intercalation ratio but not on the d-spacing of final product. The present study shows an easy way of tailoring the performance of these intercalations via small variation of guest ionic liquids, providing the possibility of finding “species-specific” modifier for fully exfoliated nanocomposites.

Synthesis, characterization and properties of Ce-modified S2O82−/ZnAl2O4 solid acid catalysts

A new spinel solid acid catalyst of S2O82−/ZnAl2O4-x wt% Ce was simply prepared by modifying S2O82−/ZnAl2O4 with Ce for acid catalysis of acetic acid and n-butanol. The prepared catalysts were characterized by means of XRD, IR, TG, XPS, NH3-TPD, SEM and N2-physisorption. The experimental results showed S2O82−/ZnAl2O4-x wt% Ce solid acid catalysts belonged to the spinel-type ZnAl2O4 structure. The addition of Ce played a key role in stabilizing the surface sulfur species and consequently increasing the acid strength of S2O82−/ZnAl2O4-x wt% Ce. The appropriate modification of Ce was 4 wt% and S2O82−/ZnAl2O4-4 wt% Ce catalyst had 95.9% esterification efficiency under the optimum reaction conditions. Compared with unmodified S2O82−/ZnAl2O4 catalyst, S2O82−/ZnAl2O4-4 wt% Ce solid acid catalyst showed much better reusability, which could remain above 80% esterification even after being used for six times. The loss of sulfur species on the surface of S2O82−/ZnAl2O4-4 wt% Ce solid acid was one of the essential reasons for its deactivation during the acid catalyzed reaction.

Confined assembly of TiO 2 nanostructures in the nanochannels of AAO membrane

Nanochannels were attractive nanostructures due to their special small sizes and biomimetic functions. Here we reported a novel hybrid nanochannel, which combined with TiO2 nanostructures and anodic aluminum oxide (AAO) membrane. We used a facile solution-dipping method to make TiO2 nanostructures assemble in the nanochannnels of AAO membrane. The morphologies of nanochannels were monitored by field emission scanning electron microscopy and the micro-regional compositions were characterized by energy dispersive spectrometer. Optical information of the nanochannels were recorded by ultraviolet–Visible spectrophotometer, and the ionic current through nanochannels was recorded by an electrochemical workstation. From the results, the TiO2 nanostructures were well-anchored on the walls of nanochannels and the size of nanostructures was uniform. The optical properties and ionic current of hybrid nanochannels would change when the conditions of dipping method changed. For this, this nanochannel had huge potential in the field of photovoltaic conversion, ionic rectifier and biosensor.

New thoughts into the fabrication of ZnO nanoparticles: confined growth in the channels of AAO membrane and its formation mechanisms

Nanoparticles possess improved properties which are supported by the specific characteristics such as size, distribution and morphology. The synthesis of zinc oxide nanoparticles (ZnO-NPs) has attracted a great deal of attention for their wide and advanced applications. Confined growth of ZnO-NPs in the channels has been more superior for it offers finer tailoring of size and shape based on the pore size of anodic aluminum oxide (AAO) membrane. In our research, we have conducted a comparative study of the synthesis of ZnO-NPs through three different methods with the template synthesis of AAO membrane. The results indicate that the electrochemical deposition is preferable to the other two for it gives a narrow and dense distribution of ZnO-NPs. The growth processes and mechanisms of these various methods have also been summarized thoroughly. This work may provide us with some new thoughts into the fabrication of NPs and give us a blueprint to “design” materials.

Synthesis of S-doped hierarchical ZnO nanostructures via hydrothermal method and their optical properties

Herein, hierarchical flower-like ZnO nanostructures and S-doped ZnO flower-like hierarchical nanostructures composed of porous nanosheets were synthesized via a one-step hydrothermal method. In this method, Zn(NO3)2·6H2O was used as a precursor and CS(NH2)2 was the dopant. Field emission scanning electron microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV–Vis absorption spectra and photoluminescence spectra (PL) were used to characterize the samples. It demonstrates that small portions of S are successfully incorporated into the lattice of the ZnO nanostructures. The incorporation of S into ZnO is supported by broadening and lower Bragg angle shift in XRD pattern and EDS analysis. Cell Parameters of hierarchical flower-like S-doped ZnO nanostructures are obtained from Rietveld Analysis. The results show that the molar ratio of Zn and S determines the structure, surface morphology and optical properties of the samples significantly. PL spectra show that the effective S doping enhances the green emission and suppresses the near band gap emission.

Synthesis and Photocatalytic Properties of Ce-Doped TiO2 Nanotube Arrays via Anodic Oxidation

Ce-doped TiO2 nanotube arrays (TNAs) were prepared successfully through one-step anodic oxidation methods. The structural and morphological features of the TNAs were monitored by x-ray diffraction and field emission scanning electron microscopy with energy dispersive spectroscopy. Ultraviolet–visible light absorption spectra showed the light absorption performances of TiO2 nanotubes in both ultraviolet (UV) and visible light regions. Also, the photocatalytic activities of these samples were measured by the photodegradation rate of methylene blue (MB). The result indicated that doping a moderate amount of cerium ions into TNAs increased the absorption of both ultraviolet light and visible light obviously. However, the excess amount of doping ions would destroy the tubular structure severely and decrease the specific surface area of TNAs sharply. It could directly lead to the decreasing of photocatalytic activitity of TNAs. Furthermore, the best photodegradation rate of the Ce-doped TNAs on MB reached to 95.6%, which had a huge improvement comparing with pure TNAs.

Controllable synthesis, characterization of ZnS nanostructured spheres

ZnS nanostructured spheres have been synthesized successfully without the assisted of surfactant, templates or capping agent via a facile hydrothermal method. Structural, morphological and optical characterization was fully performed. On the basis of characterization results, it was founded that the concentration of sulfur sources, hydrothermal reaction time and reaction temperature had an important effect on the formation of ZnS nanostructured spheres. The reason that reaction parameters are how to affect the formation of nanostructured spheres was investigated and discussed in detail. The formation mechanism of nanostructured spheres was innovatively proposed based on experimental results. The strong green PL emission of such structures would provide a potential application in novel luminescent devices. In addition, the route for the synthesis of ZnS nanostructures will be a promising way in the industrial application.

Controllable synthesis of self-assembled MoS2 hollow spheres for photocatalytic application

MoS2 hollow spheres were controllably synthesized with the assistance of surfactant [polyvinyl pyrrolidone (PVP)] through a facile hydrothermal method. Our moderate synthetic route also yielded a large quantity MoS2 nanospheres and nanosheets by adjusting the additive concentration of PVP. The MoS2 nanosheets were synthesized without the addition of PVP. With the gradual increase of additive concentration of PVP, the MoS2 nanosheets assembled into MoS2 nanospheres and the MoS2 nanospheres further assembled into the MoS2 hollow spheres. Meanwhile, a reasonable growth mechanism related to the formation of MoS2 structures was proposed preliminarily. Moreover, the light absorption and photocatalytic properties of synthesized MoS2 structures were investigated. The results indicated that MoS2 hollow spheres exhibited excellent photocatalytic properties, which could be attributed to the unique structure feature, distribution characteristic, abundant of photoactive sites. Thus, it indicated for a huge potential for application in photocatalytic materials, which could solve the water pollution all around the world.

Enhanced Photocatalytic Activity of La 3+ -Doped TiO 2 Nanotubes with Full Wave-Band Absorption

TiO2 nanotubes doped with La3+ were synthesized by anodic oxidation method and the photocatalytic activity was detected by photodegrading methylene blue. As-prepared samples improved the absorption of both ultraviolet light and visible light and have a great enhancement on the photocatalytic activity while contrasting with the pristine TiO2 nanotubes. A tentative mechanism for the enhancement of photocatalytic activity with full wave-band absorption is proposed.