Nanocarbons by High-Temperature Decomposition of Graphite Oxide at Various Pressures (original) (raw)
Related papers
2013
We have investigated the effect of ambient gas pressure (Argon) used during thermal exfoliation of graphite oxide on the number of graphene sheets in the resulting graphene. The ambience gas Ar pressures used are 80, 25, 1 atmosphere and 10-3 as well as 10-5 torr. We have found curious result that the number of graphene sheets in exfoliated graphene stack is dependent on the applied pressure for exfoliation of graphite oxide (GO). By lowering the exfoliation pressure, the numbers of sheets get reduced. The numbers of sheets in exfoliated graphene stack have been determined by Lorentzian fit of their respective 002 peak of XRD profile. The numbers of sheets have also been confirmed with high resolution transmission electron microscopy (HRTEM). The numbers of sheets in exfoliated graphene stack samples have been found to be 28, 12, 8, 5 and 3 at 80 atm, 25 atm, 1 atm, 10-3 torr and 10-5 torr pressures respectively. The results of present investigation suggest a simple but effective method for synthesizing graphene with a specific number of sheets.
Carbon, 2013
We prepared a series of graphene-like materials by thermal exfoliation/reduction of a graphite oxide (GO) at temperatures between 127°C and 2400°C. The extent of the exfoliation and reduction of the GO at different temperatures, as well as the impact on the resultant graphene-like materials (TRGs), were studied through their chemical/structural characterization. The main oxygen loss was observed at 127°C during the blasting of the GO, which produced its exfoliation into monolayer functionalized TRG with hydroxyl groups and minor amounts of epoxy and carboxyl groups. Above 600°C, the reduction continued smoothly, with oxygen and hydrogen loss and the conversion of hybridised carbon atoms from sp 3 into sp 2 . 1000°C appears to be a critical temperature for the efficiency of the reduction process, as the resulting TRG contained <2% oxygen and 81.5% sp 2 -carbon atoms.
Carbon has been of great scientific and technological interest over all civilizations, mainly because of its application of its own but also in development of products through combinations with other elements. This interest is mainly due to the numerous structures it can be formed of. The latest interests are nanocarbons, mainly carbon nanotubes and graphene. Studies have been performed on wet oxidation of graphite, followed by exfoliation and reduction in order to synthesise graphene. Acid route has been followed for oxidation whereas reduction has been carried out in aqueous medium as well as in DMF. The reactions have been followed using FTIR, TGA and Raman spectroscopy. Reduction of exfoliated graphene oxide sheets in water with hydrazine results in a material with characteristics that are comparable to those of pristine graphite.
Materials Research Bulletin, 2015
Highlights Effect of raw graphite particle size on properties of GO and graphene is reported Size of raw graphite affects oxidation degree and chemical structure of GO Highly oxidized GO results in small-sized but well-exfoliated graphene GO properties affect reduction degree, structure, and conductivity of graphene Abstract We report the effect of raw graphite size on the properties of graphite oxide and graphene prepared by thermal reduction-exfoliation of graphite oxide. Transmission electron microscope analysis shows that the lateral size of graphene becomes smaller when smaller size graphite is used. X-ray diffraction analysis confirms that graphite with smaller size is more effectively 2 oxidized, resulting in a more effective subsequent exfoliation of the obtained graphite oxide toward graphene. X-ray photoelectron spectroscopy demonstrates that reduction of the graphite oxide derived from smaller size graphite into graphene is more efficient. However, Raman analysis suggests that the average size of the in-plane sp 2-carbon domains on graphene is smaller when smaller size graphite is used. The enhanced reduction degree and the reduced size of sp 2carbon domains contribute contradictively to the electrical conductivity of graphene when the particle size of raw graphite reduces.
Journal of Alloys and Compounds, 2012
Chemical reduction of exfoliated graphite oxide (graphene oxide) has become one of the most promising routes for the mass production of graphene sheets. Nonetheless, the material obtained by this method exhibits considerable structural disorder and residual oxygen groups, and reports on their microscopic structure are quite scarce. We have investigated the structure and chemistry of graphene oxide samples reduced to different degrees using atomic force and scanning tunneling microscopy (AFM/STM) as well as X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), respectively. TPD and XPS results indicate that reduction proceeds mainly by eliminating the most labile oxygen groups, which are ascribed to epoxides and hydroxyls on basal positions of the graphene plane. AFM/STM shows that the sheets are composed of buckled oxidized regions intermingled with flatter, non-oxidized ones, with the relative area of the latter increasing with the reduction degree.
Journal of Nano- and Electronic Physics, 2021
Graphene derivatives show extraordinary mechanical, optical, and electronic properties, which gave rise to high scientific interest and huge potential for a variety of applications. Raman spectroscopy is a versatile tool to characterize and identify the chemical and physical properties of graphene derivatives. We describe essential Raman scattering processes of the first-(G) and second-order (D, G*, 2D, G + D, 2G) modes in GO and r-GO prepared by a high-pressure growth approach. In r-GO, the linewidth is broadened and slightly red-shifted in all the bands, in comparison with GO because of strain development during the high-pressure growth approach (hydrothermal process) as a result of removal of oxygen functionalities. A normalized intensity ratio (ID/IG) for GO and r-GO is discussed. In both the samples, ID/IG is high which indicates the small size of GO and r-GO and the presence of turbostratic carbon and disordered structures. The peak fitting of the 2D band exhibits four Lorentzian peaks, and the intensity of the 2D band with respect to the G band is strongly reduced, which confirms that we have successfully synthesized bilayer/ trilayer GO and r-GO. For GO and r-GO, the crystallite size (La) is calculated. The existence of the 2D band confirms that we have successfully synthesized high-quality GO and r-GO.
High-pressure phase of cold-compressed bulk graphite and graphene nanoplatelets
Physical Review B
We have studied the high-pressure vibrational and structural behavior of bulk graphite and graphene nanoplatelets at room temperature by means of high-pressure Raman spectroscopic and x-ray diffraction probes. We have detected a clear pressure-induced structural transition in both materials, evidenced by the appearance of new Bragg peaks and Raman features, deviating from the starting hexagonal graphitic structure. The high-pressure phase is identified as a partially disordered orthorhombic structure, consisting of mixed sp 2and sp 3-type bonding. Our experimental findings serve as direct evidence for the existence of a metastable transient modification in cold compressed carbon, lying between the sp 2-type graphite and sp 3-type diamond allotropes.
Carbon
Chemical exfoliation of graphite under strong oxidizing conditions yields graphene oxide nanosheets with oxy functional groups on the carbon basal plane. The importance of ozone in the chemical oxidation mechanism of graphite by the widely-used Hummers' method has been largely overlooked. Herein we demonstrate that the ozonolysis of graphite leads to the formation of secondary epoxy and peroxymonosulfate ester functional groups arising from a rotationally hindered Criegee intermediate and sulfuric acid, in a strongly favored thermodynamic process. This mechanistic step is followed by formation of adjacent epoxy and hydroxy groups as major functionalities on graphene oxides via a radical process, and leaves a significant amount of unreacted peroxides well above levels previously recognized. The thermal decomposition of graphene releases sulfur oxygen species (SO 2 and SO), but does not appear to release ozone even if this reaction pathway is moderately favored thermodynamically. We propose a new structural model for graphene oxide based on detailed chemical and spectroscopic data that provides insight into observed chemical reactivity and physical properties, including the antimicrobial activity and protein deactivation.
OXIDATION-REDUCTION OF NATURAL GRAPHITE- A STEP TOWARDS SYNTHESIS OF GRAPHENE
Carbon has been of great scientific and technological interest over all civilizations, mainly because of its application of its own but also in development of products through combinations with other elements. This interest is mainly due to the numerous structures it can be formed of. The latest interests are nanocarbons, mainly carbon nanotubes and graphene. Studies have been performed on wet oxidation of graphite, followed by exfoliation and reduction in order to synthesise graphene. Acid route has been followed for oxidation whereas reduction has been carried out in aqueous medium as well as in DMF. The reactions have been followed using FTIR, TGA and Raman spectroscopy. Reduction of exfoliated graphene oxide sheets in water with hydrazine results in a material with characteristics that are comparable to those of pristine graphite.