Graphene In Suspensions Research Articles

Experimental Study on Green Concrete using Graphene

The paper considers methods for concrete modification using low-layer graphene and grapheme oxide. It was found that graphene oxide and low-layer graphene obtained by liquid-phase shear exfoliation significantly increase the strength of concrete. In our opinion, low-layer graphene has better prospects since it is cheaper and its production technology is environmentally friendly. The viability and future of graphene largely depends on the availability of such a method that allows mass production of high-quality graphene at an affordable price. In this regard, liquid- phase separation of graphite with the formation of low-layer graphene, which can be used to modify concrete, turned out to be a competitive solution. The following main tasks were formulated in order to solve the organizational problems of low- layer grapheme industrial production: reducing the concentration of low-layer grapheme in concrete; increasing the concentration of low-layer graphene in suspension; developing an industrial technology for the production of concentrate with a high content of low- layer graphene; conducting full-scale experimental studies to determine the optimal concentration of low-layer graphene in concrete.

In English

To study the influence of graphene (GN) and the low-intensity electromagnetic radiation (LEMP) in the range of 39.5–48.0 GHz on the vital activity of the Saccharomyces cerevisiae yeast, an investigation of the rate of gassing power of yeast suspensions in the concentration of 0.03–0.12 wt. % by means of a volumetric method is reported. Three independent series of experiments were performed: the first one included the dependence of gassing power rates of yeast suspensions on the GN concentrations; the second and third ones were done to research the rates of gassing power in the presence GN and at various LEMR frequencies, where the irradiation procedure was different. It has to be noted that the yeast aqueous suspensions (alone and in the combination with GN) were irradiated in the second series while the yeast in anabiotic state were irradiated afterward the substrate with GN was added in the third series. The respiration intensity of the yeast suspensions was assessed comparing with the blank during each experiment. The vital processes of yeast suspensions are increased by 20-25% compared to the blank in the presence of GN in the suspension, but no change of the gassing power rate behavior (as namely an acceleration or deceleration of lag phase, the change of the curve shape, etc.) in the presence of GN was observed in some cases. The presence of GN in suspensions containing dry yeast is a motivating factor. The initial stage is more sensitive to the presence of GN in the suspension. The activity of the yeast at the final stage is more stable, almost linear and independent on the GN content in the GN concentration range. The value of the relative gassing power rate of the yeast suspensions containing GN is higher than that of blank experiment (about 30%).The mechanism of LEMR influence on microorganisms is under discussion for a long time, there is no common hypothesis concerning the reasons of this phenomenon, as the radiation wavelength significantly exceeds not only the size of the cell organelles, but also the size of the cell. Periodicity of the peaks in the case of yeast may indicate that the resonance phenomenon takes place not due to the actions of the first harmonics but as a result of its higher one. Namely, if the living organisms were exposure to the irradiation with monochromatic LEMR sources in the millimeter range, the resonance effect would not occur. It must be noted that the effect of resonance action can occur in the radio transparent atmosphere ( l = 8–14, 50–100 microns) as radiation passes the waveguides filled with air and the filtration of the signal by the atmosphere components may occur.

Noncovalent Functionalization of Graphene in Suspension

Suspensions of graphene, prepared from graphite foil by sonochemical exfoliation, have been treated with new nonpolar pyrenebutyric amides. The assemblies, in suspension and after deposition on solid supports, were characterized by NMR, absorption, and fluorescence spectroscopy and by transmission electron microscopy, where the well-defined shape and size of an appended [60]fulleropyrrolidine unit facilitates TEM detection of the nonstationary molecules. The accumulated evidence, also including direct comparisons of carbon nanotubes treated with pyrene amides under the same conditions, proves the successful noncovalent functionalization of graphene suspended in non-polar solvent with non-polar pyrene derivatives.

Preparation and Dispersion of Polyacrylamide-Grafting Graphene

Graphene has weak interface compatibility to its solvent, and it is easy to get agglomeration in the solvent. In this paper, graphehe is modified by grafting method to improve the aqueous dispersion. Oxidized graphene is firstly prepared by modified Hummer’s method and supersonic exfoliation. Then oxidized graphene is grafted by hydrophilic polymer polyacrylamide (PAM) and deoxidized into modified graphene. The product is characterized by TEM, FTIR, Raman spectroscopy and sedimentation test. And the result demonstrates a modified graphene is successfully synthesized and its compatibility to the media is enhanced as assumption. When the ratio between PAM and graphene is 1:10, the suspension absorbance is improved as twice as common graphene’s. Meanwhile the concentration of graphene in suspension can reach 0.05mg/ml without any agglomeration.

FEMTOSECOND PHOTOEXCITED CARRIER DYNAMICS IN REDUCED GRAPHENE OXIDE SUSPENSIONS AND FILMS

We report ultrafast response of femtosecond photoexcited carriers in single layer reduced graphene oxide flakes suspended in water as well as few layer thick film deposited on indium tin oxide coated glass plate using pump–probe differential transmission spectroscopy at 790 nm. The carrier relaxation dynamics has three components: ~200 fs, 1 to 2 ps, and ~25 ps, all of them independent of pump fluence. It is seen that the second component (1 to 2 ps) assigned to the lifetime of hot optical phonons is larger for graphene in suspensions whereas other two time constants are the same for both the suspension and the film. The value of third order nonlinear susceptibility estimated from the pump–probe experiments is compared with that obtained from the open aperture23 Z-scan results for the suspension.

Stirring-induced aggregation of graphene in suspension

Graphene in suspension undergoes stirring-induced aggregation that leads to reversible agglomeration and folding/scrolling, all of which affects the Raman spectra; the findings are of importance in all solution-based protocols for graphene preparation and processing.