Dawei Meng

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).

Effects of citric acid and urea on the structural and morphological characteristics of BiVO4 synthesized by the sol–gel combustion method

Micro-sized spherical BiVO4 photocatalysts composed of nanoparticles were synthesized by the sol–gel combustion method. The effects of citric acid and urea on the structural and morphological characteristics of samples were studied by X-ray diffraction, field emission scanning electron microscopy, N2 adsorption and desorption and UV–Vis spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of rhodamine B under visible light. The results showed the sphere-shaped BiVO4 sample to have excellent photocatalytic performance compared with the bulk sample prepared by solid-state reaction. This enhancement could be attributed to the special spherical morphology, which enhanced the absorption ability, increased the separation efficiency of photon-generated carriers and improved surface reaction sites for consumption of photon-generated carriers.Graphical AbstractUniform micro-sized spherical BiVO4 samples composed of nanoparticles were successfully synthesized by the sol–gel combustion method. The relationships between the morphologies and citric acid with urea contents were studied by using the field emission scanning electron microscopy (FE-SEM) technology.FE-SEM images of the samples (A) the samples synthesized with different citric acid contents and (B) the samples synthesized with different urea contents

Enhanced visible light photocatalytic performances of self-assembled hierarchically structured BiVO4/Bi2WO6 heterojunction composites with different morphologies

Novel self-assembled hierarchical BiVO4/Bi2WO6 heterostructured composites with different morphologies were controllably synthesized via a facile and template-free solvothermal method. The effects of the molar ratio of V to W on the structure, morphology, photocatalytic activity and photoelectrochemical properties of the BiVO4/Bi2WO6 composite photocatalysts were investigated in detail. The results showed that all the BiVO4/Bi2WO6 composites exhibited much better photocatalytic activities for methylene blue (MB) degradation and photoelectrochemical performances than pure BiVO4 and Bi2WO6. Among the composites, the BiVO4/Bi2WO6 microsphere with the molar ratio of V to W of 2 : 1 exhibited the best photocatalytic performance. The mechanism of enhanced activity was systematically investigated by UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and photo-electrochemical methods including transient photocurrent responses, electrochemical impedance spectroscopy (EIS) and Mott–Schottky plots. The enhanced photocatalytic activity could be ascribed to the tetragonal–monoclinic heterophase structure, high surface oxygen vacancy concentration, narrow band gap energy and mainly the formed heterojunction structure which could effectively promote the separation of photogenerated electron–hole pairs. In addition, a possible photocatalytic mechanism for the enhanced photocatalytic activity was proposed on the basis of the calculated energy band positions of BiVO4 and Bi2WO6.

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 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.

Solution Growth of Two-Dimensional Bi2Se3 Nanosheets for Two-Color All-Optical Switching

Two-dimensional Bi2Se3 nanosheets with hexagonal shape are synthesized by a solution synthetic route. The Bi2Se3 nanosheets are 120 nm in edge width and 7 nm in thickness. The size of the Bi2Se3 nanosheets can be controlled by choosing different kinds of reducing agents including hydroxylamine and ethylenediamine. Subsequently, we demonstrate a configuration of two-color all-optical switching based on plasma channels effect using the as-synthesized Bi2Se3 nanosheets as an optical media. The signal light can be modulated as two states including dot and ring shape by changing the intensity of control light. The modulated signal light exhibits excellent spatial propagation properties. As a type of interesting optical material, ultrathin two-dimensional Bi2Se3 nanosheets might provide an effective option for photoelectric applications.

Photoluminescence and Photocatalytic Activity of ZnO/Mn Hierarchical Structures

ZnO/Mn hierarchical structures have been synthesized by a facile one-step solution route at room temperature and their structure, morphology, photoluminescence, and photocatalytic activity fully investigated. Reduced crystallite size and increased microstrain of ZnO were found on incorporation of Mn ions. Room-temperature photoluminescence spectra of the as-synthesized ZnO/Mn hierarchical structures presented violet and blue emission. Meanwhile, ZnO/Mn hierarchical structures exhibited enhanced photocatalytic activity compared with pristine ZnO. Optimal content (5%) of Mn ions in the ZnO matrix will lead to the highest photodegradation efficiency.