Huijuan Yue

Synthesis of graphene-wrapped ZnMn2O4 hollow microspheres as high performance anode materials for lithium ion batteries

Hollow microspheres of ZnMn2O4 wrapped by graphene have been successfully synthesized via a facile APS aided method. Characterization results certify that the reduced graphene sheets have been wrapped around the hollow ZnMn2O4 microspheres. Charge–discharge testing reveals that ZnMn2O4/RGO delivers superior electrochemical properties in terms of specific capacity, cycle stability (1082 mA h g−1 at 100 mA g−1 after 90 cycles) and high rate capability (580 mA h g−1 at 1 A g−1 after 150 cycles). The improved rate capability and cycling performance of the modified ZnMn2O4 microspheres are attributed to the incorporated RGO sheets’ perfect synergy collaborating with the hollow structures, which can provide higher electronic conductivity, a shorter Li+ diffusion path and also buffer the volume change during Li+ insertion and extraction.

Reduced graphene oxide modified mesoporous FeNi alloy/carbon microspheres for enhanced broadband electromagnetic wave absorbers

Absorbers have been investigated widely so as to eliminate or at least significantly attenuate the hazards of electromagnetic radiation. A porous structure is believed to be beneficial for the high-performance of microwave absorption. Here, an embedded magnetic mesoporous composite (FeNi alloyed porous carbon microspheres, FeNi/CS) is for the first time evaluated as a microwave absorbing material. Upon combining reduced graphene oxide (rGO) with the FeNi/CS composite, a multiple-component absorber of FeNi/CS/rGO is synthesized via hydrothermal and freeze-drying processes. Compared to unmodified FeNi/CS, the FeNi/CS/rGO composite provides an effective component and a more specific structure, which is favorable for translating microwave into thermal energy or other forms of energy. The minimum reflection loss (RL) value of the FeNi/CS/rGO composite reaches −45.2 dB at a thickness of 1.5 mm, and the maximum effective microwave absorption bandwidth (RL < −10 dB) is up to 5.0 GHz at d = 1.5 mm. In virtue of the dielectric loss, magnetic loss, unique heterostructure of the absorber, and impedance matching, the FeNi/CS/rGO composite exhibits overwhelming advantages of low density, small thickness, broad bandwidth, strong absorption and high anti-oxidation capability.

A composite electrodeposited PbO2/SnO2 positive electrode material for hybrid supercapacitors

PbO2/SnO2 composites have been prepared by a composite electrodeposition method from Pb2+ solution containing different amounts of suspended nano-SnO2 particles. The chemical composition, crystal structure and surface morphology of the composites were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the composite composed of rutile phase SnO2 and β-PbO2 is rough and porous. The RF of the PbO2/SnO2 composite is approximately 10 times higher than that of the pure PbO2 electrode. The electrochemical behavior and the capacitance performance of the composite are determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge–discharge tests. The composite shows a high specific capacitance up to 208 F g−1, which is four times the specific capacitance of pure PbO2 and two times that of pure SnO2.

Facile synthesis of mesoporous FeNi-alloyed carbonaceous microspheres as recyclable magnetic adsorbents for trichloroethylene removal

Magnetic mesoporous FeNi/CS composites (FeNi alloy embedded in a porous carbon sphere) have been synthesized via a facile one-pot hydrothermal carbonization method, using metal nitrates and glucose as magnetic particle precursors and the carbon source, respectively. The properties of FeNi/CS were characterized with X-ray diffraction (XRD), Raman spectroscopy, a scanning electron microscopy (SEM) system, transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA), nitrogen adsorption/desorption isotherms and a magnetic property measurement system (SQUID-VSM). FeNi/CS derived at different pyrolysis temperatures of 500, 700, 900 °C (FeNi/CS-500, FeNi/CS-700, FeNi/CS-900, respectively) could serve as novel magnetic carbonaceous adsorbents for removing trichloroethylene from aqueous media. FeNi/CS produced at 700 °C has the best removal capacity among all, mainly due to its large surface area, a wider range of pore size distribution, and suitable carbonized extent. The pseudo-second order model is well fitted to the kinetic data, indicating that chemisorption is the primary mechanism of TCE adsorption onto FeNi/CS. Moreover, the obtained magnetic porous composites could be easily separated from solution by using a permanent magnet after adsorbing TCE and used as efficient and recyclable adsorbents in the successive removal of TCE from wastewater.

Economical synthesis of composites of FeNi alloy nanoparticles evenly dispersed in two-dimensional reduced graphene oxide as thin and effective electromagnetic wave absorbers

Developing electromagnetic wave absorbing materials prepared by a facile and economical way is a great challenge. Herein, we report a feasible route to synthesize a series of two-dimensional FeNi/rGO composites by a hydrothermal method followed by a carbonization process. The characterization confirms that nano-sized FeNi alloy nanoparticles are evenly supported onto graphene sheets without aggregation. The homogeneous dispersion of the nanoparticles may result from the introduction of glucose and the oxygen-containing groups on the surface of the graphene oxide. Measurements show that the microwave attenuation capability of the composites can be improved dramatically by adjusting the proportion of dielectric and magnetic components. Consequently, the two-dimensional magnetic material (FeNi/rGO-100) exhibits an excellent microwave absorption performance. In detail, the minimum reflection loss of −42.6 dB and effective bandwidth of 4.0 GHz can be reached with a thinner thickness of 1.5 mm. This study demonstrates that synergistic effects among the magnetic particles, reduced graphene oxide and amorphous carbon layers give rise to the highlighted microwave attenuation ability. Overall, the FeNi/rGO composite is a promising candidate to be used as a microwave absorber, and the feasible and economical method has shown potential application to construct multitudinous two-dimensional materials.

Fabrication of double core–shell Si-based anode materials with nanostructure for lithium-ion battery

Yolk–shell structure is considered to be a well-designed structure of silicon-based anode. However, there is only one point (point-to-point contact) in the contact region between the silicon core and the shell in this structure, which severely limits the ion transport ability of the electrode. In order to solve this problem, it is important that the core and shell of the core–shell structure are closely linked (face-to-face contact), which ensures good ion diffusion ability. Herein, a double core–shell nanostructure (Si@C@SiO2) was designed for the first time to improve the cycling performance of the electrode by utilising the unique advantages of the SiO2 layer and the closely contacted carbon layer. The improved cycling performance was evidenced by comparing the cycling properties of similar yolk–shell structures (Si@void@SiO2) with equal size of the intermediate shell. Based on the comparison and analysis of the experimental data, Si@C@SiO2 had more stable cycling performance and exceeded that of Si@void@SiO2 after the 276th cycle. More interestingly, the electron/ion transport ability of electrode was further improved by combination of Si@C@SiO2 with reduced graphene oxide (RGO). Clearly, at a current density of 500 mA g−1, the reversible capacity was 753.8 mA h g−1 after 500 cycles, which was 91% of the specific capacity of the first cycle at this current density.

One-step synthesis of 5-ethyl-2-methylpyridine from NH4HCO3 and C2H5OH under hydrothermal condition

A simple one-pot approach to synthesizing 5-ethyl-2-methylpyridine(EMP) was established using NH4HCO3 and C2H5OH as starting materials and commercial Cu2O as catalyst and oxidant under hydrothermal condition. Different reaction conditions were researched and the optimal ones were achieved by studying the parameters, that could affect the yield of product and by considering the energy and resource saving. The present study provided an eco-friendly way to obtaining EMP with lower volatility using fewer toxic starting materials.