Quanyi Hao

A novel nonenzymatic hydrogen peroxide sensor based on MnO2/graphene oxide nanocomposite

A new electrocatalyst, MnO(2)/graphene oxide hybrid nanostructure was successfully synthesized for the nonenzymatic detection of H(2)O(2). The morphological characterization was examined by scanning electron microscopy and transmission electron microscopy. The MnO(2)/graphene oxide based electrodes showed high electrochemical activity for the detection of H(2)O(2) in alkaline medium. The nonenzymatic biosensors displayed good performance along with low working potential, high sensitivity, low detection limit, and long-term stability, which could be attributed to the high surface area of graphene oxide providing for the deposition of MnO(2) nanoparticles. These results demonstrate that this new nanocomposite with the high surface area and electrocatalytic activity offers great promise for new class of nanostructured electrode for nonenzymatic biosensor and energy conversion applications.

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.

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.