Xiaoyan Jing

Trisodium citrate assisted synthesis of ZnO hollow spheres via a facile precipitation route and their application as gas sensor

To enrich the variety of zinc oxide, a facile trisodium citrate assisted alkaline precipitation route was developed to prepare ZnO hollow spheres with partial open gaps comprised of a mass of nanoparticles. The composition, morphology and structure of the product were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the final products were pure hexagonal phase (zincite), and the ZnO shell was composed of a polycrystalline aggregation of nanoparticles. Trisodium citrate played a crucial role as a capping agent in the formation of the ZnO hollow spheres. The ZnO with hollow morphology exhibited excellent gas response. This result indicated that the annealed ZnO with hollow sphere architecture is a promising candidate for gas sensing applications.

Self-assembly of ZnO nanoparticles into hollow microspheres via a facile solvothermal route and their application as gas sensor

In order to enrich the variety of zinc oxide (ZnO), well-defined ZnO hollow microspheres self-assembled by a mass of nanoparticles were successfully synthesized through a facile solvothermal process employing polyethylene glycol 400 (PEG 400) as the solvent. PEG 400 played a crucial role as a nonionic surfactant in the formation of the ZnO hollow spheres. The plausible formation mechanism was described as self-assembly of nanoparticles, Ostwald ripening, and crystal growth process. The gas sensing performances of the ZnO hollow spheres have been investigated carefully. The results indicate that the prepared ZnO hollow sphere architecture is a promising material for gas sensing applications. In addition, hollow structures have attracted considerable attention because of their unique properties and wide potential applications. The present chemical technique is expected to be useful to prepare other metal oxides or hollow architectures.

The synthesis of a manganese dioxide–iron oxide–graphene magnetic nanocomposite for enhanced uranium(VI) removal

In this study, we have developed a facile route for the fabrication of a manganese dioxide–iron oxide–reduced graphite oxide magnetic nanocomposite (MnO2–Fe3O4–rGO). The as-obtained nanomaterial (MnO2–Fe3O4–rGO) was characterized using transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface area measurements. The MnO2–Fe3O4–rGO composite shows extraordinary adsorption capacity and fast adsorption rates for the removal of uranium(VI) in aqueous solution. The influence of factors including the dosage of the MnO2–Fe3O4–rGO composite used, pH of aqueous solution, and temperature were investigated. The thermodynamic parameters, including Gibbs free energy (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°) for the process, were calculated using the Langmuir constants. The results show that a pseudo-second-order kinetics model can be used to describe the uptake process using a kinetics test. Our present study suggests that the MnO2–Fe3O4–rGO composite can be used as a potential adsorbent for sorption of uranium(VI) as well as for providing a simple, fast separation method for the removal of uranium(VI) ions from aqueous solution.

Facile growth of hollow porous NiO microspheres assembled from nanosheet building blocks and their high performance as a supercapacitor electrode

Self-assembled hollow flowerlike NiO as a promising supercapacitor material has been fabricated by a facile hydrothermal process and the formation mechanism of the flowerlike morphology is investigated. The structure and morphology of the NiO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) etc. and the surface area of the NiO sample was analyzed by measuring its N2 adsorption–desorption isotherms. The results indicated that the addition of P123 inhibited the grain growth of NiO, and with the assistance of P123, the nanoparticles assembled into flowers. The electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results suggest that the flowerlike NiO has good electrochemical reversibility and displays superior capacitive performance with large capacitance (619 F g−1), as well as excellent cycling stability after 1000 cycles.

Manganese dioxide core–shell nanowires in situ grown on carbon spheres for supercapacitor application

A manganese dioxide (MnO2) core–shell nanostructure has been in situ grown on carbon spheres to form a core–shell MnO2–MnO2/C composite electrode material as a supercapacitor via an effective two-step hydrothermal method. Such a nanostructure enhances the specific surface area of MnO2, and effectively decreases the ion diffusion and charge transport resistance in the electrode reaction. The morphology and structure of the as-prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform IR (FT-IR) spectra. The electrochemical behavior of the as-prepared electrode was evaluated by cyclic voltammetry (CV), electrochemical impedance spectrometry (EIS) and chronopotentiometry tests in a 1 M Na2SO4 aqueous electrolyte. Results reveal that the prepared electrode exhibits good electrochemical reversibility, a high specific capacitance (225 F g−1 at 2 mA cm−2) and excellent cycling stability with a retention ratio of 90% after 5000 cycles.

Porous tungsten trioxide nanolamellae with uniform structures for high-performance ethanol sensing

Tungsten trioxide nanostructures have received considerable attention due to their enhanced gas sensing properties and promising applications in the sensing field. Herein, tungsten oxide (WO3) with a lamellar structure was prepared by a facile but feasible hydrothermal process and applied for gas detection. The structures, morphologies and surface characteristics of the as-obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller analysis. The uniform nanolamellae were constructed from many substructures, primarily nanoparticles, resulting in desirable porous structures. To highlight the potential applications, gas sensors based on the as-synthesized products were fabricated to test their sensing performance. The test data indicated that the porous WO3 nanolamellae had superb kinetic response and remarkable selectivity towards some volatile organic compounds (VOCs), particularly ethanol, at an operating temperature of 200 °C. As such, we believe that these porous WO3 nanolamellae are promising as a potential high-performance sensing material for ethanol detection.

Preparation and Characteraction of New Magnetic Co–Al HTLc/Fe3O4Solid Base

Novel magnetic hydrotalcite-like compounds (HTLcs) were synthesized through introducing magnetic substrates (Fe3O4) into the Co–Al HTLcs materials by hydrothermal method. The magnetic Co–Al HTLcs with different Fe3O4contents were characterized in detail by XRD, FT-IR, SEM, TEM, DSC, and VSM techniques. It has been found that the magnetic substrates were incorporated with HTLcs successfully, although the addition of Fe3O4might hinder the growth rate of the crystal nucleus. The morphology of the samples showed the relatively uniform hexagonal platelet-like sheets. The grain boundaries were well defined with narrow size distribution. Moreover, the Co–Al HTLcs doped with magnetic substrates presented the paramagnetic property.

Preparation of magnetic calcium silicate hydrate for the efficient removal of uranium from aqueous systems

To obtain an adsorbent for uranium with superb adsorption capacity, a rapid adsorption rate and quick magnetic separation, magnetic calcium silicate hydrate (MCSH) is fabricated through in situ growth of calcium silicate hydrate (CSH) onto the surface of the magnetic silica microspheres via a sonochemical method. The chemical components, and structural and morphological properties of MCSH are characterized by FTIR, XRD, TG, VSM, SEM, TEM and N2 adsorption–desorption methods. The results show that MCSH with a mesoporous structure is constructed by an agglomeration of CSH nanosheets. The BET specific surface area and saturation magnetization of MCSH are determined to be 196 m2 g−1 and 15.4 emu g−1, respectively. Based on the synthetic MSCH, adsorption isotherms, thermodynamics and kinetics are investigated. The adsorption mechanism fits the Langmuir isotherm model with a maximum adsorption capacity of 2500 mg g−1 at 298 K. The calculated thermodynamic parameters demonstrate that the adsorption process, which is in accordance with a pseudo-second-order model, is spontaneous and endothermic. MCSH exhibits a quick and highly efficient adsorption behavior, and more than 80% of uranium (1000 mg L−1) is adsorbed in the first 10 min. The superb adsorption capacity and rapid adsorption rate are likely attributed to the ultrahigh specific surface area and facile exchanges of uranium ions and calcium ions of CSH ultrathin nanosheets. These results demonstrate that MSCH is an excellent adsorbent for uranium removal from aqueous systems.

Uranium extraction using a magnetic CoFe2O4–graphene nanocomposite: kinetics and thermodynamics studies

A novel magnetic nanocomposite (CoFe2O4–rGO), consisting of reduced graphene oxide (rGO) and CoFe2O4 nanoparticles, was fabricated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and a vibrating sample magnetometer (VSM) were used to characterize the CoFe2O4–rGO. The results indicate that CoFe2O4 nanoparticles have been successfully installed on the surface of rGO. Uranium adsorption (from synthetic solutions) has been investigated in batch systems. Moreover, the effects of different experimental parameters, such as initial solution pH (controlled with nitric acid), equilibration time, initial uranium concentration and temperature, on sorption performance have been investigated. The results show that the kinetic data can be efficiently modelled using the pseudo-second-order equation. Furthermore, the Langmuir equation fits the sorption isotherms well. In addition, the values of thermodynamic parameters (ΔG° and ΔH°) show that the process is spontaneous and exothermic. These experimental results demonstrate the potential application of CoFe2O4–rGO in radionuclide cleanup.

Controllable synthesis and enhanced gas sensing properties of a single-crystalline WO3–rGO porous nanocomposite

In this paper, we report on a facile hydrothermal approach combined with a subsequent annealing process for the controllable synthesis of a single-crystalline WO3–rGO porous nanocomposite. The crystal structure, morphology and chemical composition of the as-obtained product were well-characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Brunauer–Emmett–Teller analysis. The results indicate that this hybrid structure is composed of single-crystal WO3 porous nanoflakes with a size of 500 × 500 nm2 growing through or anchoring into a sheet-like rGO matrix. We explore the sensing performance of the gas sensor based on the as-synthesized product. Impressively, gas testing shows that the WO3–rGO nanocomposite exhibits an excellent kinetic response speed and good sensitivity toward NO2 and some volatile organic compound pollutants at a low temperature (90 °C). The pseudo 3-D structure provides many channels for gas diffusion and clearly enhances sensing properties. As such, this graphene-based composite shows promising potential as a high-performance gas sensing material for real-time gas detection.