skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers

Abstract

The graphene interlayer spacing in pure graphite is known to have a minimum value of dmin = 0.3354 nm, while defective graphites typically have larger interlayer spacings. Using transmission electron microscopy and X-ray diffraction, we find that the graphene interlayer spacing in multi-walled carbon nanofibers heat treated above ≈ 2800 K is distinctly smaller than dmin. To explain this unusual observation, we investigate the structural properties of carbon nanotubes using a multiscale approach rooted in extensive first-principles calculations, specifically allowing the nanotube cross-sections to polygonize. We show that, whereas normal nanotubes are favored energetically at low temperatures, the configuration entropy associated with Stone-Wales defect creation at high temperatures makes the polygonal shape of large nanotubes or nanofibers thermodynamically stable, accompanied by a reduction in the graphene interlayer spacing. These unique predictions are confirmed in further experimental tests.

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931489
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 75
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; CARBON FIBERS; NANOTUBES; LAYERS; ENTROPY; GRAPHITE; SHAPE

Citation Formats

Yoon, Mina, Howe, Jane Y, Eres, Gyula, and Zhang, Zhenyu. Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.75.165402.
Yoon, Mina, Howe, Jane Y, Eres, Gyula, & Zhang, Zhenyu. Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers. United States. doi:10.1103/PhysRevB.75.165402.
Yoon, Mina, Howe, Jane Y, Eres, Gyula, and Zhang, Zhenyu. Mon . "Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers". United States. doi:10.1103/PhysRevB.75.165402.
@article{osti_931489,
title = {Polygonization and Anomalous Graphene Interlayer Spacing of Multi-Walled Carbon Nanofibers},
author = {Yoon, Mina and Howe, Jane Y and Eres, Gyula and Zhang, Zhenyu},
abstractNote = {The graphene interlayer spacing in pure graphite is known to have a minimum value of dmin = 0.3354 nm, while defective graphites typically have larger interlayer spacings. Using transmission electron microscopy and X-ray diffraction, we find that the graphene interlayer spacing in multi-walled carbon nanofibers heat treated above ≈ 2800 K is distinctly smaller than dmin. To explain this unusual observation, we investigate the structural properties of carbon nanotubes using a multiscale approach rooted in extensive first-principles calculations, specifically allowing the nanotube cross-sections to polygonize. We show that, whereas normal nanotubes are favored energetically at low temperatures, the configuration entropy associated with Stone-Wales defect creation at high temperatures makes the polygonal shape of large nanotubes or nanofibers thermodynamically stable, accompanied by a reduction in the graphene interlayer spacing. These unique predictions are confirmed in further experimental tests.},
doi = {10.1103/PhysRevB.75.165402},
journal = {Physical Review B},
number = ,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The surface functionality and interlayer spacing changes induced by {gamma}-ray irradiation were investigated in multi-walled carbon nanotubes (MWCNTs). The modification effect of MWCNTs irradiated in air and epoxy chloropropane (ECP) was characterized by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. The results indicated that {gamma}-ray irradiation in two different media improved the amount of oxygen-containing functional groups on nanotube surface, and the irradiation in ECP was more efficient. Compared with the pristine MWCNTs, the MWCNTs irradiated in air exhibited a decrease in width of G band and intensity ratio of D to G band in the Raman spectra andmore » an increase in intensity and diffraction angle of (002) characteristic x-ray peak. However, the MWCNTs tended to show the opposite behaviors in Raman spectra and x-ray diffraction patterns after they were irradiated in ECP. This preliminary study suggests that {gamma}-ray irradiation in air can meaningfully decrease the interlayer distance of MWCNTs and improve the graphitization of MWCNTs, while irradiation in ECP disorders and breaks the structure of MWCNTs. It is worth expecting that MWCNTs can be functionalized by {gamma}-rays in reactive liquid and also be employed for preventing {gamma}-ray radiation from reaching sensitive materials at least for short term experiments in air.« less
  • Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leadsmore » to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.« less
  • La{sub 2}CuO{sub 4} nanofibers (ca. 30 nm in diameter and 3 {mu}m in length) have been grown in situ by using single walled carbon nanotubes (SWNTs; ca. 2 nm in inner diameter; made via cracking CH{sub 4} over the catalyst of Mg{sub 0.8}Mo{sub 0.05}Ni{sub 0.10}Co{sub 0.05}O {sub x} at 800 deg. C) as templates under mild hydrothermal conditions and a temperature around 60 deg. C. During synthesis, the surfactant poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and H{sub 2}O{sub 2} were added to disperse SWNTs and oxidize the reactants, respectively. The structure of La{sub 2}CuO{sub 4} nanofibers was confirmed by powder X-ray diffractionmore » (XRD) and their morphologies were observed with field emission scanning electron microscope (FESEM) at the hydrothermal synthesis lasting for 5, 20 and 40 h, respectively. The La{sub 2}CuO{sub 4} crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. Twenty hours is an optimum reaction time to obtain regular crystal fibers. The La{sub 2}CuO{sub 4} nanofibers are probably cubic rather than round and may capsulate SWNTs. - Graphical abstract: La{sub 2}CuO{sub 4} nanofibers have been grown in situ by using single walled carbon nanotubes as templates under mild hydrothermal conditions and a temperature around 60 deg. C. The La{sub 2}CuO{sub 4} crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. The La{sub 2}CuO{sub 4} nanofibers are probably cubic rather than round and may capsulate SWNTs.« less
  • The aim of this research was to determine the best nano hybrid that can be used as a Pickering emulsion Chemical Enhanced Oil Recovery (C-EOR). Therefore, we have prepared different carbon structures nano hybrids with SiO{sub 2} nano particles with different weight percent using sol-gel method. The as-prepared nano materials were characterized with X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and Thermal Gravimetric Analysis (TGA). Pickering emulsions of these nanohybrids were prepared at pH=7 in ambient temperature and with distilled water. Stability of the mentioned Pickering emulsions was controlled for one month. Emulsion phase morphology was investigated usingmore » optical microscopic imaging. Evaluation results demonstrated that the best sample is the 70% MWCNT/SiO{sub 2} nanohybrid. Stability of the selected nanohybrid (70% MWCNT/SiO{sub 2} nanohybrid) was investigated by alteration of salinity, pH and temperature. Results showed that the mentioned Pickering emulsion has very good stability at 0.1%, 1% salinity, moderate and high temperature (25 °C and 90 °C) and neutral and alkaline pH (7, 10) that is suitable for the oil reservoirs conditions. The effect of the related nano fluid on the wettability of carbonate rock was investigated by measuring the contact angle and interfacial tension. Results show that the nanofluid could significantly change the wettability of the carbonate rock from oil wet to water wet and can decrease the interfacial tension. Therefore, the 70% MWCNT/SiO{sub 2} nanohybrid Pickering emulsion can be used for Chemical Enhanced Oil Recovery (C-EOR).« less
  • The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carbon nanotubes have been investigated using neutron diffraction (ND). Hydrogen-deuterium substitution in THF, as well as the study of different alkali-based compounds, allow a layered structure around the nanotubes to be determined. ND results indicate that the alkali cations form a monolayer surrounding each tube of the bundle, while THF molecules intercalate between the decorated tubes and at the surface of the bundles. In spite of this insertion, the triangular bundle structure is preserved, albeit with a much larger lattice parameter, which depends on the size of the insertedmore » cation.« less