Xuehua Yan

Controllable synthesis, characterization and growth mechanism of three-dimensional hierarchical PbWO4 microstructures

We report on the synthesis of three-dimensional (3D) hierarchical PbWO4 microstructures by an oil-in-water microemulsion-mediated route. As-prepared PbWO4 samples are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A possible three-step growth mechanism of PbWO4, in which initial nucleation, self-assembly (oriented aggregation), and subsequent crystal growth (Ostwald ripening) are involved, is proposed to explain the formation of PbWO4 microstructures based on observations of a time-dependent morphology evolution process. The approach is facile, environmentally friendly, and provides a new strategy in the use of microemulsion systems for material design and processing. The oil-in-water microemulsion technique presented here offers promising microstructured media for the synthesis of other inorganic materials with complex 3D architectures and unique morphologies and properties.

Facile self-assembly of Fe3O4 nanoparticles@WS2 nanosheets: A promising candidate for supercapacitor electrode

Graphene-like dichalcogenides with huge surface area and nanostructured transition metal oxides with extraordinarily high theoretical capacities could be composited as promising electrode candidates for supercapacitors. In this work, monolayer and few-layers WS2 nanosheets were exfoliated by combination of ball-milling and sonication. A facile strategy for the hierarchical self-assembly of Fe3O4 nanoparticles (Fe3O4NPs) on WS2 nanosheets was developed to synthesize Fe3O4NPs@WS2 nanocomposites via hydrothermal method. Fe3O4NPs are uniformly dispersed on the WS2 nanosheets without aggregation. The particle size of Fe3O4NPs is about 3 nm. The nanocomposite shows strong enhancements of electrochemical behaviors. This self-assembly synthesis strategy may have great prospects for other 0D/2D nanocomposites in supercapacitors and other energy devices.

Enhanced visible-light-driven photocatalytic activity of CeVO4/graphitic C3N4 photocatalysts for organic dye degradation

Abstract A novel CeVO4/graphitic carbon nitride (CeVO4/g-C3N4) photocatalyst was prepared via a facile mixing and calcination method. The photocatalytic performance of the CeVO4/g-C3N4 samples was evaluated by degrading methylene blue (MB) under visible light irradiation. The results show that all photocatalysts compared to pure CeVO4 and g-C3N4 exhibit enhanced photocatalytic activity. The sample prepared using 0·1 g CeVO4 and 2 g dicyandiamide shows the optimal removal rate constant of 0·022 min−1, which is two times and 18 times larger than that of g-C3N4 and CeVO4, respectively. The enhancement of photocatalytic activity could be attributed to the strong absorption in the visible region along with the formation of a heterojunction between CeVO4 and g-C3N4, which could efficiently suppress the recombination of the photogenerated electron-hole pairs. A possible enhanced photocatalytic mechanism of CeVO4/g-C3N4 is proposed. Finally, the photocatalyst shows good stability and reusability after four consecutive catalytic runs.

A novel and efficient synthesis of reduced TiO2/C nanocomposites with mesopores for improved visible light photocatalytic performance

Abstract There are some problems in TiO2, such as poor visible light response, low surface area and high electro-hole combination efficiency, which limit its applications. A novel and efficient solvothermal method was developed using TiCl3 and glucose to prepare reduced TiO2/C (r-TiO2/C) nanocomposites. The results show that TiO2 in composite is anatase and reduced. Transmission electron microscope analysis indicates that the composites are composed of r-TiO2 and amorphous carbon in size of 8–14 nm. All samples have a good response in visible light and near infrared region. When 1.5 mmol glucose was used, the sample has the lowest band gap 1.30 eV according to Ultraviolet–visible spectroscopy, the degradation ratio of which for Rhodamine B reaches 92% after 70 min under visible light irradiation.

One-step and large-scale preparation of TiO2/amorphous carbon composites with excellent visible light photocatalytic properties

Poor visible light response and high electron–hole recombination efficiency of TiO2 are main problems which limit its applications. A facile method was developed to prepare reduced TiO2/amorphous carbon composites with particle sizes of about 10–20 nm, which have good visible light absorption and low band gap energy (1.37 eV). The results show that the composite prepared using 1.5 mmol ascorbic acid at 180 °C has good crystallinity, strong visible light absorption and enhanced catalytic activity. The degradation efficiency of the samples for rhodamine B reaches 90% after 100 min under visible light irradiation.

Ultra-Small Fe3O4 Nanoparticles Decorated WS2 Nanosheets with Superior Electrochemical Properties for Supercapacitors

Fe₃O₄ nanoparticles/WS₂ nanosheets nanocomposite was successfully synthesized in this study by a one-step hydrothermal method. Three different contents of Fe₃O₄ in the nanocomposite were prepared by changing the quantity of FeCl₃·6H₂O, ascorbic acid and NaHCO₃. Fe₃O₄ nanoparticles are about 3 nm in diameter and combined with WS₂ to form stable heterojunctions, which are good for releasing the volume change of electrode materials in charge/discharge procedure. Because of the large theory capacitance of Fe₃O₄ nanoparticle, the specific capacitance of the Fe₃O₄ nanoparticles/WS₂ nanosheets nanocomposites increase with increasing content of Fe₃O₄ nanoparticles. When the weight ratio for Fe₃O₄ nanoparticles to WS₂ nanosheets is up to 8:10, the specific capacitances of the nanocomposite are 83.85 F g-1 and 149.25 F g-1 as the scanning rate at 20 mV s-1 and the current density at 0.5 A g-1, respectively. Both of them of Fe₃O₄ nanoparticles/WS₂ nanosheets are as almost 7 times high as that of WS₂ nanosheets under the same measurement condition. This work shows that the Fe₃O₄ nanoparticles/WS₂ nanosheets nanocomposite will be a kind of potential electrode materials for supercapacitors.

Thermal expansion, electrical conductivity and hardness of Mn3Zn0.5Sn0.5N/Al composites

Abstract Mn3Zn0.5Sn0.5N/Al composites were successfully prepared by sintering at 623 K and 723 K. It is found that the thermal expansion of Al is effectively decreased with the addition of negative thermal expansion material Mn3Zn0.5Sn0.5N, which plays the role of the thermal expansion compensator in the composite system. The thermal expansion of composites can be tailored by adjusting the volume fraction of Mn3Zn0.5Sn0.5N. In particular, 40 vol.%-Mn3Zn0.5Sn0.5N/Al composite sintered at 723 K has a low thermal expansion coefficient of 2.38×10−6 K−1. The thermal expansion of Mn3Zn0.5Sn0.5N/Al composites matches well with those calculated from the rule of mixture (ROM) estimation. The ROM model can be used to predict the thermal expansion of Mn3Zn0.5Sn0.5N/Al composite and design Mn3Zn0.5Sn0.5N/Al composite with a particular thermal expansion. Mn3Zn0.5Sn0.5N/Al composites exhibit excellent electrical conductivities at the level of 104 S/cm. The hardness of the as-prepared composites increases by adding Mn3Zn0.5Sn0.5N in Al.

Sb2WO6 nanoparticles coated TiO2 nanobelts exhibiting remarkable photo-catalyst response

Abstract Sb2WO6/TiO2 composites with different contents of Sb2WO6 were successfully synthesized through a facile hydrothermal method. The Sb2WO6/TiO2 composites were characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectra (UV–vis DRS), photoluminescence spectra (PL), scanning electron microscope (SEM) and transmission electron microscope (TEM). Sb2WO6 nanoparticles are distributed uniformly on the surface of TiO2 nanobelts in the prepared Sb2WO6/TiO2 composites. The effect of Sb2WO6 content on the photocatalytic activity of composites is studied by UV–vis DRS and PL. All Sb2WO6/TiO2 photocatalysts show enhanced photocatalytic activity and excellent recycling property for degrading rhodamine B (RhB) under visible light irradiation. The 30% Sb2WO6/TiO2 sample shows the best photocatalytic activity. Its kinetic constant (0·476/h) is 21·6 times higher than that of TiO2. The possible photocatalytic mechanism is discussed according to the trapping experiments of active species. The improved photocatalytic activity for the Sb2WO6/TiO2 catalyst may be attributed to the synergetic effect between Sb2WO6 nanoparticles and TiO2 nanobelts. The enhanced photocatalytic activity and excellent stability make this material a promising candidate for degrading environmental pollutants in the future.

Novel CsxWO3/TiO2 Microspheres as Enhanced Visible Light Photocatalysts for Dye Pollutant Treatments

CsxWO3/TiO2 composites with different contents of CsxWO3 were successfully synthesized in this study by a facile hydrothermal process. CsxWO3/TiO2 composites were characterized by XRD, Raman, UV-visible diffuse reflectance spectra (DRS), photoluminescence spectra (PL) and SEM. TiO2 nanoparticles were distributed uniformly on the surface of the CsxWO3 microsphere in the prepared CsxWO3/TiO2 composites, and they formed heterojunctions with CsxWO3. The effect of CsxWO3 on the photoactivities of composites was investigated via DRS and PL. All CsxWO3/TiO2 catalysts showed enhanced photocatalytic activity for degrading rhodamine B under visible light irradiation. The 50% CsxWO3/TiO2 sample showed the best photocatalytic activity and its kinetic constant was 20 times larger than that of TiO2. The possible photocatalytic mechanism is also discussed from the trapping experiments of active species. The improved photocatalytic activity for the CsxWO3/TiO2 catalyst may be attributed to the synergetic effect between CsxWO3 microspheres and TiO2 nanoparticles. This novel photocatalyst can be used to degrade environmental pollutants in the future.

Liquid Exfoliation and Electrochemical Properties of WS2 Nanosheets

Commercial WS2 powders were exfoliated in sodium dodecyl sulfate solution with a combination of ball-milling and sonication. WS2 nanosheets can be uniformly dispersed in the solution. The layers and thicknesses of WS2 nanosheets could be tailored via changing the ball-milling speed. The effects of the ball-milling speed on crystallinity and morphology of the samples were analyzed. The results show that the layer structure of WS2 nanosheets is destroyed and the crystallinity is decreased with increase of the ball-milling rate. The monolayer WS2 nanosheets at 200 rpm are obtained, which are mesoporous with the specific surface area as 5.419 m2 g-1. The specific capacitance and charge/discharge efficiency of WS2 nanosheets at 200 rpm are better than those of other samples. Its specific capacitance under the scanning rate of 20 mV s-1 and the current density of 0.5 A g-1 are 13.46 F g-1 and 22.50 F g-1, respectively. The charge/discharge curve of WS2 nanosheets at 200 rpm is a symmetrical triangle, which shows rapid charge and slow discharge. It means that WS2 nanosheets at 200 rpm has good electrochemical reversibility. The load transfer resistance and the internal series resistance of this sample are 84.60 Ω and 4.18 Ω, respectively.