The synthesis of graphene-semiconductor nanocomposites has attracted increasing attention due to their interesting optoelectronic properties.However the synthesis of such nanocomposites,with decorated particles well dispersed on graphene,is still a great challenge.This work reports a facile,one-step,solvothermal method for the synthesis of graphene-CdS and graphene-ZnS quantum dot nanocomposites directly from graphene oxide,with CdS and ZnS very well dispersed on the graphene nanosheets.Photoluminescence measurements showed that the integration of CdS and ZnS with graphene significantly decreases their photoluminescence.Transient photovoltage studies revealed that the graphene-CdS nanocomposite exhibits a very unexpected strong positive photovoltaic response,while separate samples of graphene and CdS quantum dots(QDs)of a similar size do not show any photovoltaic response.
Based on the inhibition effect on the respiratory chain activity of microorganisms by toxicants, an electrochemical method has been developed to measure the current variation of a mediator in the presence of microorganisms contacted with a toxicant. Microelectrode arrays were adopted in this study, which can accelerate the mass transfer rate of an anaiyte to the electrode and also increase the total current signal, resulting in an improvement in detection sensitivity. We selected Escherichia coli as the testee and the standard glucose- glutamic acid as an exogenous material. Under oxygen restriction, the experiments in the presence of toxicant were performed at optimum conditions （solution pH 7.0, 37℃ and reaction for 3 hr）. The resulting solution was then separated from the suspended microorganisms and was measured by an electrochemical method, using ferricyanide as a mediator. The current signal obtained represents the reoxidation of ferrocyanide, which was transformed to inhibiting efficiency, IC50, as a quantitative measure of toxicity. The IC50 values measured were 410, 570 and 830 mg/L for sodium nitrite, borax and aluminum potassium sulfate, respectively. The results show that the toxicity sequence for these three food additives is consistent with the value reported by other methods. Furthermore, the order of damage degree to the microorganism was also observed to be： sodium nitrite 〉 borax 〉 aluminum potassium sulfate 〉 blank, according to the atomic force microscopy images of E. coli after being incubated for 3 hr with the toxic compound in buffer solutions. The electrochemical method is expected to be a sensitive and simple alternative to toxicity screening for chemical food additives.
We have demonstrated a one-step and effective electrochemical method to synthesize graphene/MnO2 nanowall hybrids （GMHs）. Graphene oxide （GO） was electrochemically reduced to graphene （GN）, accompanied by the simultaneous formation of MnO2 with a nanowall morphology via cathodic electrochemical deposition. The morphology and structure of the GMHs were systematically characterized by scanning electron microscope （SEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and Raman spectroscopy. The resulting GMHs combine the advantages of GN and the nanowall array morphology of MnO2 in providing a conductive network of amorphous nanocomposite, which shows good electrochemical capacitive behavior. This simple approach should find practical applications in the large-scale production of GMHs.
Chengzhou Zhu Shaojun Guo Youxing Fang Lei Han Erkang Wang Shaojun Dong
