Xiaoming Yin

Magnetite/graphene composites: microwave irradiation synthesis and enhanced cycling and rate performances for lithium ion batteries

By employing microwave irradiation as a heat source, magnetite/graphene composites were synthesized by depositing Fe3+ in the interspaces of graphene sheets. The Fe3O4 nanoparticles were dispersed on graphene sheets. As anode materials for lithium ion batteries, they showed high reversible capacities, as well as significantly enhanced cycling performances (about 650 mA h g−1 after 50 cycles) and high rate capabilities (350 mA h g−1 at 5 C). The enhancement could be attributed to graphene sheets, which served as electron conductors and buffers. Our results opened a new doorway for the application of graphene sheets to prepare anode materials of lithium ion batteries with superior performances.

Fast synthesis of SnO2/graphene composites by reducing graphene oxide with stannous ions

This article propounds a new strategy of preparing graphene by reducing GO with stannous ions for the synthesis of SnO2/graphene composites. As anode materials for lithium ion batteries, the composites showed good performance. This opens a new approach for the synthesis of graphene/metal-oxide composites with excellent properties.

A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose

NiO hollow nanospheres were synthesized by controlled precipitation of metal ions with urea using carbon microspheres as templates, which were for the first time adopted to construct a novel amperometric glucose biosensor. Glucose oxidase was immobilized on the surface of hollow nanospheres through chitosan-assisted cross-linking technique. Due to the high specific active sites and high electrocatalytic activity of NiO hollow nanospheres, the constructed glucose biosensors exhibited a high sensitivity of 3.43 microA/mM. The low detection limit was estimated to be 47 microM (S/N=3), and the Michaelis-Menten constant was found to be 7.76 mM, indicating the high affinity of enzyme on NiO hollow nanospheres to glucose. These results show that the NiO hollow nanospheres are a promising material to construct enzyme biosensors.

Synthesis of cobalt ion-based coordination polymer nanowires and their conversion into porous Co3O4 nanowires with good lithium storage properties.

Cobalt ion-based coordination polymer nanowires were synthesized by using nitrilotriacetic acid (NA) as a chelating agent by a one-step hydrothermal approach. In the synthesis, cobalt ions were bonded with amino or carboxyl groups of NA to form one-dimension polymer nanowires, which can be confirmed by FTIR and TGA results. Our experimental results show that the morphologies of polymer nanowires greatly depend on the precursor salts, ratios between deionized water and isopropyl alcohol. The probable molecular formula and growth mechanism have been proposed. After heat treatment, the cobalt ion-based coordination polymer nanowires can be converted into porous Co(3)O(4) nanowires, which completely preserved the nanowire-like morphology. When used as anodes in lithium-ion batteries, the obtained porous Co(3)O(4) nanowires exhibited a high reversible capacity of 810 mA h g(-1) and stable cyclic retention at 30th cycle. The good electrochemical performance could be attributed to the porous nanostructure of Co(3)O(4), which provides pathways for easy accessibility of electrolytes and fast transportation of lithium ions.

Flexible morphology-controlled synthesis of mesoporous hierarchical α-Fe2O3 architectures and their gas-sensing properties

Mesoporous flower-like and urchin-like α-Fe2O3 nanostructures have been successfully synthesized by a simple solution-based reaction and sequential calcination. Detailed experiments demonstrated that the morphology of the hierarchical α-FeOOH precursors could be easily controlled by adjusting the experimental conditions including reactant concentration, solvent composition, reaction time, and reaction temperature. On the basis of time-dependent experiments, a multistage growth mechanism for the formation of the α-FeOOH super-architectures was proposed. In addition, by virtue of the unique hierarchical mesoporous structure and comparative high specific surface area, these obtained α-Fe2O3 nanostructures exhibited enhanced sensing performances to ethanol. This method is expected to be a useful technique for controlling the diverse morphologies of iron oxide superstructures that could meet the demands of a variety of applications, such as gas sensors, lithium-ion batteries, catalysis, waste-water treatment, and pigments.

Mesoporous SnO2@carbon core?shell nanostructures with superior electrochemical performance for lithium ion batteries

SnO2@carbon nanostructure composites are prepared by a simple hydrothermal method. The composite exhibits unique structure, which consists of a mesoporous SnO2 core assembled of very small nanoparticles and a carbon shell with 10 nm thickness. The mesoporous SnO2@carbon core-shell nanostructures manifest superior electrochemical performance as an anode material for lithium ion batteries. The reversible specific capacity of the composite is about 908 mAh g(-1) for the first cycle and it can retain about 680 mAh g(-1) after 40 charge/discharge cycles at a current density of 0.3 C. Moreover, it shows excellent rate capability even at the high rate of 4.5 C. The enhanced performance was attributed to the mesoporous structure and a suitable carbon coating.

A novel non-enzymatic hydrogen peroxide sensor based on Mn-nitrilotriacetate acid (Mn-NTA) nanowires

A novel non-enzymatic hydrogen peroxide sensor was realized from Mn-nitrilotriacetate acid (Mn-NTA) nanowires, which were successfully fabricated via a facile hydrothermal route. Cyclic voltammetry (CV) revealed that the Mn-NTA nanowires exhibited direct electrocatalytic activity for the oxidation of H(2)O(2) in phosphate buffer solution. The sensor showed linear response to H(2)O(2) at the concentrations range from 5 x 10(-6)M to 2.5 x 10(-3)M with a detection limit of 2 x 10(-7)M. The sensitivity was up to 78.9 microA mM(-1)cm(-2). These results indicated that the Mn-NTA nanowires were promising in realizing non-enzymatic H(2)O(2) detection.

Fast Synthesis of Graphene Sheets with Good Thermal Stability by Microwave Irradiation

In recent years, considerable attention has been focused on graphene, because it has shown to possess a wealth of exceptional properties and various promising applications. To realize this promise, reliable methods for the large-scale production of high-quality graphene are required. Epitaxial growth on polycrystalline nickel is being actively pursued, but achieving large graphene domains with uniform properties remains a challenge. The mechanical cleavage of graphite originally led to the discovery of graphene sheets and this method is the process currently used in most fundamental research on graphene. However, the low productivity of this method makes it unsuitable for synthesizing graphene on a large-scale. Instead, the chemical conversion from graphite appears to be a muchmore-efficient approach to bulk production of graphene sheets (GSs). Most chemical syntheses of GSs from graphite begin with graphite oxide (GO) and usually need a reductant. GO can be reduced by H2. [16] However, it is highly explosive and flammable. Hydrazine can also be used to reduce GO. In view of its toxicity and combustibility, precautions must be taken when large quantities of hydrazine are used to prepare GSs on a large-scale. NaBH4 is known to reduce GO in aqueous solution. Owing to its hygroscopic and flammable properties, the secure preservation of sodium borohydride is a difficult task. Furthermore, reducing GO by traditional heating systems (such as an oil bath) is time-consuming. Therefore, those methods are inefficient and not fit for preparing GSs on a large-scale. On the other hand, the thermal stability of carbon materials is an important aspect of their properties. The synthesis of graphene with good thermal stability would provide greater potential for commercial applications. A study reported by Wu et al. found that GSs synthesized by hydrogen-arc discharge exfoliation were of good thermal stability. Unfortunately, to the best of our knowledge, there are only a few papers that have investigated the thermal stability of graphene. As such, the development of a method for synthesizing GSs with good thermal stability from widely available graphite on a large-scale is of great significance. Although various methods for the synthesis of graphene under microwave irradiation have been reported, they all employed either organic solution or poisonous reagents. In this study, GSs with upper thermal stability were rapidly synthesized in aqueous media by a method based on microwave-assisted and ascorbic acid (AA) as a reductant. Microwave adsorption of GO increased its local temperature and pressure, resulting in the elevation of the thermal stability of GSs. It should be noted that the reducing time of GO by using microwave irradiation was shortened to 30 minutes and the reductant of GO was nontoxic and tractable. AA is naturally employed as a reductant in living things, and has also been used to synthesize nanomaterials. Herein, we report the use of this nontoxic and tractable reductant for the preparation of GSs. The synthesis of GSs is shown in Scheme 1. Firstly, GO was dispersed in deionized water with the help of sonication. Secondly, the temperature of the solution around the GO rose drastically under microwave irradiation, becoming evidently higher than other regions, because GO could strongly absorb the energy of microwave irradiation. With the help of a local elevated temperature, GO was reduced by AA within 0.5 hours. In addition, the local high pressure of GO resulting from microwave irradiation may contribute to the good thermal stability of the GSs. For comparison, we also prepared GSs with an oil bath (marked as GSOB). Figure 1 a shows typical FTIR spectra obtained for GO and GSs. The FTIR spectra of GO confirmed the presence of oxygen-containing groups, including C OH (nC OH = 3390 cm ), C O C (nC O C =1230 cm ), and C=O in car[a] M. Zhang , S. Liu, X. M. Yin, Z. F. Du, Q. Y. Hao, D. N. Lei, Prof. Q. H. Li, Prof. T. H. Wang Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education and State Key Laboratory for Chemo/Biosensing and Chemometrics, Hunan University Changsha 410082 (China) Fax: (+86) 0731-88823407 E-mail : thwang@hnu.cn liqiuhon2004@hotmail.com Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000776.