No abstract

Graphene has been enjoyed significant recent attention due to its potential applications in electronic and optoelectronic devices. Graphene is usually prepared via Hummers' method or modified Hummers' methods. These methods are the most suitable for the large-scale production of single graphene at low cost. But their main drawbacks are the use of strong oxidizing agents which make graphene films separating into small sheets and this extremely decrease the electrical conductivity of graphene. Herein, we report an inexpensive, fast and facile method for preparation of a double layer structured transparent, flexible hybrid electrode from silver nanowires (Ag NWs) with chemically converted graphene (CCG) coating on arbitrary substrate. These films dramatically decreases the resistance of graphene films and exhibited high optical transmittance (82.4 %) and low sheet resistance (18 Ω/ sq), which is comparable to ITO transparent electrode. The ratio of direct conductivity to optical conductivity DC/OP = 104 of this electrode is very close to that displayed by commercially available ITO. Especially, the whole fabrication process is carried out at low temperature. The graphene films are spin coated directly on the substrate without transferring therefore eliminating troubles that are brought from the transfer method.

Gas sensing is one of the most promising applications for reduced graphene oxide (rGO). High surface-to-volume ratio in conjunction with remaining reactive oxygen functional groups translates into sensitivity to molecular on the rGO surface. The response of the rGO based devices can be further improved by functionalizing its surface with metal nano-materials. In this paper, we report the ammonia (NH3) sensing behavior of rGO based sensors functionalized with nano-structured metal: silver (Ag) or platinum (Pt) or gold (Au) in air at room temperature and atmospheric pressure. The gas response is detected by the monitoring changes in electrical resistance of the rGO/metal hybrids due to NH3 gas adsorption. Compared to bare rGO, significantly improved NH3 sensitivity is observed with the addition of nano-structured metals. These materials are applied to play the small bridges role connecting many graphene islands together to improve electrical conduction of hybrids while maintaining the inherent advantage of rGO for NH3 gas sensitivity.

Drosera burmanni Vahl, one of three Drosera species in Vietnam, has been successfully cultured in vitro. Our previous researchs have shown that extracts of Drosera burmanni Vahl contain bioactive compounds such as naphthoquinone, anthraquinone. To obtain cell biomass as well as increase secondary metabolites, callus and cell suspension culture of Drosera burmanni Vahl become extremely urgent. Therefore, in this study, we focused on building Drosera burmanni Vahl callus and suspension culture process to obtain quinone. Our results show that the most optimized medium for callus culture is Gamborg’s B5, saccharose 20g/l, casein 100 mg/l, PVP 1g/l. To induce callus culture, the best hormone’s concentration is 2,4-D 0,2 mg/l, NAA 0,2 mg/l. Growing callus and increasing cell biomass in suspension culture are the same culture type. The peak of growing phase is on 12th. HPLC analysis showed present of plumbagin, one of quinone bioactive compounds determined in Drosera species, on cultured cell suspension.

In this report, we present a rapid and efficient polyol method - the solution-phase approach for the large scale synthesis of silver nanowires with diameters in the range of 40 - 50 nm, and lengths up to 20 μm. Although the polyol process is a popular method of preparing metal nanostructures, so far most of the published works mainly focused on the synthesis process regardless of amount of surfactants. In this article, we successfully synthesized large-scale uniform silver nanowires with high aspect ratios by introducing the long-chain PVP (MW = 58 000) and investigated the effect of the amount of PVP on the synthesis of Ag nanowires by studying their morphologies, structures and optical properties. The dependency of nanowire morphology and aspect ratio on synthesis parameters was shown via SEM images. The diameter of nanowires decreased when the molar ratio of PVP to silver nitrate was increased. Further more, the molar ratios decided the morphology (particle, rod or wire) of the Silve solution. Synthesized silver nanowires were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). This aqueous dispersions of silver nanowires were used to prepare thin, flexible, transparent, conducting films on polyethylene terephthalate substrate (PET) by spraying method. The prepared silver nanowire films on PET substrate had a transparency of 82% and sheet resistance of 10 Ω/□.