Enhanced electrochemical properties of LiFePO4 by Mo-substitution and graphitic carbon-coating via a facile and fast microwave-assisted solid-state reaction

A composite cathode material for lithium ion battery applications, Mo-doped LiFePO4/C, is obtained through a facile and fast microwave-assisted synthesis method. Rietveld analysis of LiFePO4-based structural models using synchrotron X-ray diffraction data shows that Mo-ions substitute onto the Fe sites and displace Fe-ions to the Li sites. Supervalent Mo6+ doping can act to introduce Li ion vacancies due to the charge compensation effect and therefore facilitate lithium ion diffusion during charging/discharging. Transmission electron microscope images demonstrate that the pure and doped LiFePO4 nanoparticles were uniformly covered by an approximately 5 nm thin layer of graphitic carbon. Amorphous carbon on the graphitic carbon-coated pure and doped LiFePO4 particles forms a three-dimensional (3D) conductive carbon network, effectively improving the conductivity of these materials. The combined effects of Mo-doping and the 3D carbon network dramatically enhance the electrochemical performance of these LiFePO4 cathodes. In particular, Mo-doped LiFePO4/C delivers a reversible capacity of 162 mA h g(-1) at a current of 0.5 C and shows enhanced capacity retention compared to that of undoped LiFePO4/C. Moreover, the electrode exhibits excellent rate capability, with an associated high discharge capacity and good electrochemical reversibility

CdSe Ring- and Tribulus-Shaped Nanocrystals: Controlled Synthesis, Growth Mechanism, and Photoluminescence Properties

With air-stable and generic reagents, CdSe nanocrystals with tunable morphologies were prepared by controlling the temperature in the solution reaction route. Thereinto, the lower reaction temperature facilitates the anisotropic growth of crystals to obtain high-yield CdSe ring- and tribulus-shaped nanocrystals with many branches on their surfaces. The photoluminescence properties are sensitive to the nature of particle and its surface. The products synthesized at room temperature, whose surfaces have many branches, show higher blue shift and narrower emission linewidths (FWHM) of photoluminescence than that of samples prepared at higher temperature, whose surfaces have no branches. Microstructural studies revealed that the products formed through self-assembly of primary crystallites. Nanorings formed through the nonlinear attachment of primary crystallites, and the branches on the surfaces grew by linear attachment at room temperature. And the structure of tribulus-shaped nanoparticle was realized via two steps of aggregation, i.e., random and linear oriented aggregation. Along with the elevation of temperature, the branches on nanocrystal surfaces shortened gradually because of the weakened linear attachment

Enhanced electrochemical properties of LiFePO4 by Mo-substitution and graphitic carbon-coating via a facile and fast microwave-assisted solid-state reaction

A composite cathode material for lithium ion battery applications, Mo-doped LiFePO4/C, is obtained through a facile and fast microwave-assisted synthesis method. Rietveld analysis of LiFePO4-based structural models using synchrotron X-ray diffraction data shows that Mo-ions substitute onto the Fe sites and displace Fe-ions to the Li sites. Supervalent Mo6+ doping can act to introduce Li ion vacancies due to the charge compensation effect and therefore facilitate lithium ion diffusion during charging/discharging. Transmission electron microscope images demonstrate that the pure and doped LiFePO4 nanoparticles were uniformly covered by an approximately 5 nm thin layer of graphitic carbon. Amorphous carbon on the graphitic carbon-coated pure and doped LiFePO4 particles forms a three-dimensional (3D) conductive carbon network, effectively improving the conductivity of these materials. The combined effects of Mo-doping and the 3D carbon network dramatically enhance the electrochemical performance of these LiFePO4 cathodes. In particular, Mo-doped LiFePO4/C delivers a reversible capacity of 162 mA h g(-1) at a current of 0.5 C and shows enhanced capacity retention compared to that of undoped LiFePO4/C. Moreover, the electrode exhibits excellent rate capability, with an associated high discharge capacity and good electrochemical reversibility

Ni-Doped ZnS Nanospheres Decorated with Au Nanoparticles for Highly Improved Gas Sensor Performance

Novel Ni-doped wurtzite ZnS nanospheres decorated with Au nanoparticles (Au NPs–ZnS NSs) have been successfully fabricated using a simple method involving vacuum evaporation followed by an annealing process. This transition metal-doped gas sensor had high responsivity, extremely fast response and recovery time, and excellent selectivity to formaldehyde at room temperature. The response and recovery time are only 29 s and 2 s, respectively. Since ZnS is transformed into ZnO at a high temperature, superior room temperature-sensing performance can improve the stability and service life of the sensor. The improvement in sensing performance could be attributed to the reduced charge-transfer distance resulting from the creation of a local charge reservoir layer, and the catalytic and spillover effect of Au nanoparticles. The rough and porous spherical structure can also facilitate the detection and diffusion of gases. The as-prepared Au NPs–ZnS NSs are considered to be an extremely promising candidate material for gas sensors, and are expected to have other potential applications in the future

Enhanced rate performance of cobalt oxide/nitrogen doped graphene composite for lithium ion batteries

Ultrafine Co3O4 nanocrystals homogeneously attached to nitrogen doped reduced graphene oxide (rGO) by the hydrothermal reaction method are demonstrated as anode materials for lithium ion batteries. Transmission electron microscope images revealed that the crystal size of Co3O4 in Co3O4/N-rGO and Co3O4/rGO is 5-10 nm, much smaller than that of bare Co3O4, indicating that the reduced graphene oxide sheets with Co3O4 nanocrystals attached could hinder the growth and aggregation of Co3O4 crystals during synthesis. The graphene sheets can also effectively buffer the volume change of Co3O4 upon lithium insertion/extraction, thus improving the cycling performance of the composite electrodes. The doped nitrogen on the reduced graphene oxide can not only improve the conductivity of the graphene sheets, but also introduce defects to store lithium and enhance the connection of the Co3O4 nanocrystals to the graphene sheet, leading to better distribution of Co3O4 on the graphene sheets, and enhanced rate performance. The nitrogen doping combined with the unique structural features is a promising strategy for the development of electrode materials for lithium ion batteries with high electrochemical performance

Detection of Triacetone Triperoxide (TATP) Precursors with an Array of Sensors Based on MoS2/RGO Composites

Triacetone triperoxide (TATP) is a self-made explosive synthesized from the commonly used chemical acetone (C3H6O) and hydrogen peroxide (H2O2). As C3H6O and H2O2 are the precursors of TATP, their detection is very important due to the high risk of the presence of TATP. In order to detect the precursors of TATP effectively, hierarchical molybdenum disulfide/reduced graphene oxide (MoS2/RGO) composites were synthesized by a hydrothermal method, using two-dimensional reduced graphene oxide (RGO) as template. The effects of the ratio of RGO to raw materials for the synthesis of MoS2 on the morphology, structure, and gas sensing properties of the MoS2/RGO composites were studied. It was found that after optimization, the response to 50 ppm of H2O2 vapor was increased from 29.0% to 373.1%, achieving an increase of about 12 times. Meanwhile, all three sensors based on MoS2/RGO composites exhibited excellent anti-interference performance to ozone with strong oxidation. Furthermore, three sensors based on MoS2/RGO composites were fabricated into a simple sensor array, realizing discriminative detection of three target analytes in 14.5 s at room temperature. This work shows that the synergistic effect between two-dimensional RGO and MoS2 provides new possibilities for the development of high performance sensors

Porous Silicon Photonic Crystals Coated with Ag Nanoparticles as Efficient Substrates for Detecting Trace Explosives Using SERS

Picric acid (PA) is an organic substance widely used in industry and military, which poses a great threat to the environment and security due to its unstable, toxic, and explosive properties. Trace detection of PA is also a challenging task because of its highly acidic and anionic character. In this work, silver nanoparticles (AgNPs)-decorated porous silicon photonic crystals (PS PCs) were controllably prepared as surface-enhanced Raman scattering (SERS) substrates using the immersion plating solution. PA and Rhodamine 6G dye (R6G) were used as the analyte to explore the detection performance. As compared with single layer porous silicon, the enhancement factor of PS PCs substrates is increased to 3.58 times at the concentration of 10−6 mol/L (R6G). This additional enhancement was greatly beneficial to the trace-amount-detection of target molecules. Under the optimized assay condition, the platform shows a distinguished sensitivity with the limit of detection of PA as low as 10−8 mol/L, the linear range from 10−4 to 10−7 mol/L, and a decent reproducibility with a relative standard deviation (RSD) of ca. 8%. These results show that the AgNPs-modified PS PCs substrates could also find further applications in biomedical and environmental sensing

Preparation, microstructure and electrochemical performance of nanoparticles LiMn2O3.9Br0.1

LiMn2O3.9Br0.1 nanoparticles were prepared by a room-temperature solid-state coordination method. The structure and morphology of the as-prepared materials were analyzed by X-ray diffractometry and transmission electron microscopy. The results show that the LiMn2O3.9Br0.1 is well-crystallized and consists of monodispersed nanoparticles 80–100 nm in size. Results of electrochemical testing show that the samples prepared at different temperatures have similar electrochemical performance. The initial discharge capacities of LiMn2O3.9Br0.1 prepared at 800 °C and 700 °C are 121 mAh g− 1 and 118.9 mAh g− 1, respectively, higher than for LiMn2O4 prepared using the same method