Synthesis of carbon nanostructures from residual solids waste tires

This article presents the results of the synthesis and morphological characterization of carbon nanostructures obtained from the decomposition of residual solid from waste tires (RSWT) in quartz tubes under reduced pressure (1.33 Pa) at 900°C for 15 min. The synthesis led to the formation of two phases, a fragmented solid black powder composed of multi‐walled carbon nanotubes (MWCNTs), onion‐type fullerenes, and spheres, and a very bright metallic dark film. Analysis by microscopy (SEM and TEM) showed that the MWCNTs had an average diameter of approximately 25 nm and a length greater than 100 nm while the diameter of the onion‐type fullerenes was found to be 8 nm. The nanospheres showed different diameters ranging from 500 nm to 1.5 μm, and some had a metallic core surrounded by layers of carbon. The infrared spectra of the nanotubes exhibited absorption bands at 1558 and 1458 cm^?1, corresponding to C?C and C? C bonds, and signals at 3438 and 1080 cm^?1 related to the OH and C? O groups from oxidized graphite as it was identified in the dark film. The Raman spectra of the carbon nanostructures present D and G‐bands at 1331 and 1597 cm^?1, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Bomb calorimetry as a bulk characterization tool for carbon nanostructures

Multiwalled carbon nanotubes (MWCNTs) consisting of coaxial graphene cylinders (cylindrical MWCNTs), cones (herringbone MWCNTs) or carbon fibers were combusted in an isothermal bomb calorimeter. Their standard enthalpies of formation were determined to be 16.56 ± 2.76 kJ mol⁻¹(C – per carbon mol) for carbon fibers, 21.70 ± 1.32 kJ mol⁻¹(C) for herringbone MWCNTs and 8.60 ± 0.52 kJ mol⁻¹(C) for cylindrical ones. All materials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetry, and elemental analysis. A linear correlation between the standard enthalpies of formation and D/G and G′/G Raman bands ratio (D – band is centered at 1350 cm⁻¹, G – 1585 cm⁻¹, G′ – 2700 cm⁻¹) demonstrates the applicability of bomb calorimetry for characterization of the “defectiveness” of the bulk carbon material in the sense Raman spectroscopy is widely used nowadays. Also, we show that the calorimetry may be used to estimate the oxygen content in the bulk carbon nanomaterials, as there is a linear correlation between the oxygen content (both total content and in carboxyl groups separately) and the standard enthalpies of formation for herringbone nanotubes oxidized by nitric acid.     

Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Electrochemical polymerization of 2,2′-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430-1450 cm⁻¹ indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600-800 cm⁻¹ resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH₄OH solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm⁻¹.     

Pressure dependence of Raman modes in double wall carbon nanotubes filled with 1D Tellurium

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in nanoscience. In this work, capillary effect was used to fill double wall carbon nanotubes (DWCNTs) with trigonal Tellurium. The samples are characterized by high resolution transmission electronic microscopy and Raman spectroscopy. In order to investigate their structural stability and unravel the differences induced by intershell interactions, unpolarized Raman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room temperature and high pressure. Up to 11 GPa we found a pressure coefficient of 3.7 cm⁻¹ GPa⁻¹ for the internal tube and 7 cm⁻¹ GPa⁻¹ for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition was observed in the studied range.     

Linear carbon chains encapsulated in multiwall carbon nanotubes: Resonance Raman spectroscopy and transmission electron microscopy studies

In this paper we report the characterization of linear carbon chains encapsulated in multiwalled carbon nanotubes by using Raman spectroscopy and transmission electron microscopy. The chains are characterized by strong vibrational peaks around 1850 cm⁻¹ and both the frequency and intensity of these peaks were found to be dependent on laser excitation energy. Furthermore, resonance Raman spectroscopy was used for constructing the resonance window of the linear carbon chains. The Raman spectroscopy data showed that long chains have lower highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and weaker carbon–carbon bonds. Besides the spectroscopy evidence for the linear carbon chain, we used scanning transmission electron microscopy/electron energy loss spectroscopy analysis of the nanotube cross section to unambiguously show the existence of a 1D structure present within the innermost carbon nanotube with an unprecedented clarity compared to previous reports on this kind of system.     

Effective synthesis of well graphitized high yield bamboo-like multi-walled carbon nanotubes on copper loaded α-alumina nanoparticles

A high-yield bamboo like multiwalled carbon nanotubes (CNTs) were successfully synthesized on copper substituted alumina nanoparticles by thermal chemical vapor deposition (CVD) technique under atmospheric pressure. The obtained products were characterized by various techniques like FESEM with EDX, HRTEM and Raman spectroscopy, which reveals the formation of CNTs and are of bamboo shaped (stacking arrangement) multiwalled type with graphene layers having a diameter between 4 and 9 nm. The appearance of two peaks at 1597 cm^− 1 and 1302 cm^− 1 in Raman spectra are noticed as G-band and D-band for graphitic nature and defects due to bending & curvature of bamboo like carbon nanotubes (b-CNTs), respectively. The influence of reaction parameters such as time, temperature and flow rate was also studied to increase the carbon yield.     

Enhanced conductivity and fluorescence of polyaniline doped with Eu3+, Tb3+, and Y3+ ions

The doped polyaniline (PANI) with rare earth ions, which exhibits an increasing conductivity and strongly enhanced fluorescence emission, was prepared by dispersing PANI powder suspension in acetonitrile solution containing rare earth ions according to different mass ratios of rare earth ions to PANI at room temperature. The structure of the doped PANI was characterized by the spectra of FTIR, Raman, UV-vis, and XRD. Red-shifted change for the quinoid and benzenoid stretching vibration is observed in IR and Raman spectra after doping rare earth cations, and UV-vis absorption peak also presents a red-shift, indicating that the doped PANI possesses a better delocalization of electrons along the mainchain backbone. The experimental data show that the electrical and optical behaviors of PANI strongly depend on the species of rare earth cations and their concentration. It is found that enhancing fluorescence for the doped PANI is observed by comparing with emeraldine base (EB). Moreover, the conductivity of the protonated PANI samples doped with Eu³⁺, Tb³⁺, and Y³⁺ ions, increases from 2.1 × 10⁻⁴ to 3.33 S cm⁻¹, 1.50 × 10⁻¹ S cm⁻¹ and 2.26 × 10⁻¹ S cm⁻¹. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Spectroscopic study on the centrifugal fractionation of soluble single-walled carbon nanotubes

Optical absorption and resonant Raman spectra are proven to be convenient and effective to monitor the centrifugal fractionation and to evaluate the quality of soluble single-walled carbon nanotubes (SWNTs) achieved by inorganic oxidation and organic functionalization. Through a systemic study of a series of centrifuged solutions, we confirmed that heavily functionalized amorphous carbon was fractionated into the early centrifuged solutions, whereas lightly functionalized graphite fragments as well as polyhedral carbon and metal catalysts particles were fractionated into the late centrifuged solutions and centrifuged residue, and then highly pure and well dispersed SWNTs were collected from the middle centrifuged solutions. It is proposed that the purity, dispersibility, and aggregation state of SWNTs can be qualitatively estimated by the relative intensity of their absorption features, the fine structure and slope of their absorption curves. The Raman features of centrifuged SWNTs are found systematically up-shifted except the disorder-induced D band in comparison with those of as-prepared material, indicating that the SWNTs in centrifuged solutions are individual or in thin bundles. Two new features were identified at 1428 and 941 cm⁻¹ in the Raman spectrum of thermally annealed centrifuged SWNTs, which were assigned to achiral nanotubes and combined mode, respectively.     

Studying the local character of Raman features of single-walled carbon nanotubes along a bundle using TERS

Here, we show that the Raman intensity of the G-mode in tip-enhanced Raman spectroscopy (TERS) is strongly dependent on the height of the bundle. Moreover, using TERS we are able to position different single-walled carbon nanotubes along a bundle, by correlating the observed radial breathing mode (RBM) with the AFM topography at the measuring point. The frequency of the G^- mode behaves differently in TERS as compared to far-field Raman. Using the RBM frequency, the diameters of the tubes were calculated and a very good agreement with the G^- -mode frequency was observed.     

Influence of CVD parameters on Co-TiO2/CNT properties: A route to enhance energy harvesting from sunlight

Carbon nanotubes (CNTs) have been employed to enhance the photoactivity of titanium dioxide (TiO₂). In this work, CNTs were deposited by chemical vapor deposition (CVD) onto the surface of anodized Co-TiO₂ nanotubes. The influence of CVD parameters (time and temperature) on the Co-TiO₂/CNT structure and properties was investigated. We studied three synthesis times (10, 20, and 30 min) and two synthesis temperatures (700 and 800°C). The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD). The photocurrent performance of the electrodes was determined by linear voltammetry. The results showed the successful formation of Co-TiO₂/CNT hybrid structures. The shortest synthesis time produced higher quality CNTs. The samples synthesized at 700 and 800°C for 10 min exhibited a current density of 1.13 mA.cm⁻² and 7.84 mA.cm⁻², respectively, which is 9 and 65 times greater than the Co-TiO₂ sample. The synergistic effect of the CNT deposition and the crystalline phase composition significantly improved the photoresponse of TiO₂. The proper choice of synthesis parameters allowed the control of the sample structure, leading to the production of electrodes with better light-harvesting performance.     

Thermal performance of vertically-aligned multi-walled carbon nanotube array grown on platinum film

Vertically-aligned carbon nanotube array is expected to inherit high thermal conductivity and mechanical compliance of individual carbon nanotube and serve as thermal interface material. In this paper, vertically-aligned multi-walled carbon nanotube arrays have been directly grown on Pt film and the thermal performance has been studied by using laser flash technique. The determined thermal diffusivity decreases from 0.187 to 0.135 cm² s⁻¹ and the thermal conductivity increases from 1.8 to 3.1 W m⁻¹ K⁻¹ as temperature increases from 243.2 to 453.2 K. The fracture surface of the array peeled off the Pt film was characterized by scanning electron microscopy. It has been illustrated that the tearing surface is not smooth but fluffy with torn carbon nanotubes, indicating strong interfacial bonding and consequent small interface resistance between carbon nanotube array and Pt film. According to Raman spectra and transmission electron microscopy image, the possible mechanisms responsible for the thermal transport degradation are low packing density, twist, and the presence of impurities, amorphous carbon, defects and flaws. The influence of intertube van der Waals interactions has been studied by comparing the phonon dispersion relations and is expected to be not significant.     

Surface-Enhanced Vibrational Spectroscopy: SERS and SEIRA

With respect to the origin of single-molecule sensitivity in surface-enhanced Raman scattering, elastic scattering and emission spectra were investigated for Ag particles adsorbed with dye. The scattering peak observed at 600–650 nm was extinguished during the inactivation process of an enormous SERS signal, whereas localized surface plasmon (LSP) peaks located at 520 nm and 730 nm did not change significantly. The scattering peak at 600–650 nm arises from increased electromagnetic coupling between the LSP of adjacent Ag particles through dye molecules. In addition, distinct emission peaks were observed at 550–600 nm and 600–750 nm for hot Ag particles with adsorbates. These bands were attributed to emissive relaxation of metal electrons and fluorescence of molecules, respectively. Furthermore, the shorter wavelength peak showed invariant Stokes shift irrespective of excitation wavelengths, most probably arising from inelastic scattering of excited electrons by adsorbed molecules. The adsorbed state of CO and related species on the Pt film electrode was investigated using attenuated total reflection—surface-enhanced infrared absorption spectroscopy. Intermediate species were found on the bare Pt surface in 1 mM CH₃OH + HClO₄ solutions at +0.2 V ≤ E ≤ +0.6 V that give absorption peaks at 1405 cm⁻¹ and 1300 cm⁻¹. These bands can be attributed to carbonate species or -COH. Water molecules located at the hydrophobic interfaces between CO and electrolyte solutions were evidenced by a quite high OH stretch absorption at 3664–3646 cm⁻¹, as well as a lower broad peak at ca. 3480 cm⁻¹.     

Design and evaluation of the interface between carbon nanotubes and natural rubber

To design the interface between carbon nanotubes and natural rubber (NR), a silane coupling agent, bis(3‐triethoxysilylpropyl) tetrasulfide (TESPT), was used to modify the surface of multiwalled carbon nanotubes (MWCNTs) in a two‐step method, and the silane‐modified multiwalled carbon nanotubes (s‐MWCNTs) were combined with NR by solvent casting. The s‐MWCNTs with an amorphous layer were visualized by transmission electron microscopy, the functional groups of which were confirmed by Raman and Fourier transform infrared analyses, and the functionalization degree was characterized by thermogravimetric analysis. The interface between s‐MWCNTs and NR was investigated by Raman analysis and field emission scanning electron microscopy (FESEM). Raman analysis showed a shift from 1,340 to 1,353 cm⁻¹ of D band of s‐MWCNTs in the NR/s‐MWCNT composite, and FESEM observation indicated that s‐MWCNTs were embedded deeply in NR. All of these results proved that s‐MWCNTs were grafted with TESPT and they reacted with the active double bonds of NR to form a strong interface. The improved interface resulted in an extreme nonlinear viscoelastic behavior and enhanced dynamic mechanical property of NR/s‐MWCNT composite as compared to NR/MWCNT composite. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Determination of density and birefringence of poly(ethylene terephthalate) fibers using Raman microscopy

Multiple regression analysis has been used to calibrate polarized Raman spectra of poly(ethylene terephthalate) fibers in terms of density and birefringence. The calibration spans PET fibers having a wide range of density and birefringence values. The calibration required the Raman spectrum in only one polarization direction, that is, with the polarization directions of the incident and scattered light parallel to each other and to the fiber axis. The peak at 631 cm⁻¹, which has been used previously as an internal standard band, could be used for the prediction of density, but not for the prediction of birefringence. The peak at 702 cm⁻¹ was found to be a good internal standard band for both density and birefringence. Density could be predicted with a standard error of prediction of 0.003 g/cc using only the ratio of the intensity of the band at 996 cm⁻¹ to that of 702 cm⁻¹ and the full width at half maximum of the 1725-cm⁻¹ band. Birefringence was predicted with a standard error of 0.01 using the ratios of the intensities of the bands at 996 and 1616 cm⁻¹ to that of the 702-cm⁻¹ band. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 943–952, 1999     

Infrared Properties of Magnesium Oxide

The absorption spectrum of polycrystalline and single-crystal magnesium oxide was determined in the 4000 to 166 cm⁻¹ spectral region. In the range 4000 to about 1100 cm⁻¹, the absorption coefficient of the polycrystalline MgO was higher than that of the single-crystal MgO owing to scattering by the grain boundaries. This scattering decreased with increase of the grain diameter. No difference in reflectivity could be detected between the polycrystalline and single-crystal material in the 4000 to 300 cm^−lwave number region. The optical constants, n and k, were determined by the classical dispersion theory, assuming a single oscillator. From the maximum reflectivity, the resonance frequency was at 428 cm⁻¹; the value obtained from the acoustical vibration was at 475 cm⁻¹. The corresponding s factors were 0.64 and 0.72, respectively.     

Rapid oxidative activation of carbon nanotube yarn and sheet by a radio frequency,atmospheric pressure,helium and oxygen plasma

Carbon nanotube yarn and sheet were activated using radio frequency, atmospheric pressure, helium and oxygen plasmas. The nanotubes were exposed to the plasma afterglow, which contained 8.0 × 10¹⁶ cm⁻³ ground state O atoms, 8.0 × 10¹⁶ cm⁻³ metastable O₂ (¹Δ_g), and 1.0 × 10¹⁶ cm⁻³ ozone. X-ray photoelectron spectroscopy and infrared spectroscopy revealed that 30 s of plasma treatment converted 25.2% of the carbon atoms on the CNT surface to oxidized species, producing 17.0% alcohols, 5.9% carbonyls, and 2.3% carboxylic acids. The electrical resistivity increased linearly with the extent of oxidation of the CNT from 4 to 9 × 10⁻⁶ Ω m. On the other hand, the tensile strength of the yarn was decreased by only 27% following plasma oxidation.     

Irradiation damage in xenon-irradiated α-Al2O3 before and after annealing

The irradiation damage build-up of α-Al₂O₃ under Xe²⁰⁺ ion irradiation has been investigated by a combination of Raman spectroscopy and transmission electron microscopy. α-Al₂O₃ crystalline was irradiated with 5 MeV Xe²⁰⁺ ions to fluences of 1 × 10¹⁴ cm⁻², 5 × 10¹⁴ cm⁻², 1 × 10¹⁵ cm⁻² and 5 × 10¹⁵ cm⁻² at room temperature. No amorphous phase was formed under the experimental condition. The Raman intensities of feature peaks of Al₂O₃ decrease after Xe ion irradiation. The interstitial-type dislocation loops with Burgers vectors of b = 1/3 < 10-11> on the {10-10} and (0001) habit planes were found. The formation of basal and prism dislocation loops is related to the lattice damage and position. After annealing, the Raman intensities of feature peaks of Al₂O₃ increases with annealing temperature. With annealing at 1500℃ for 30 min, lattice defects were completely annealed out in the near surface region. Meanwhile, long dislocations and facet cavities on long dislocations were found in the Xe deposition region. Some lattice defects beyond the projected region were found due to the diffusion toward deep region during thermal annealing.     

Spectral properties of single-walled carbon nanotubes encapsulating fullerenes

Single-walled carbon nanotubes (SWCNTs) with diameter ranged from 1.22 to 1.6 nm filled with C₆₀, C₇₀ and C₆₀H₂₈ molecules (peapods), as well as double-walled carbon nanotubes (DWCNTs) derived from peapods, were studied by HRTEM, UV-vis-NIR and Raman spectroscopy. Suspensions with accurate concentration were used for spectroscopic studies to enable quantitative comparison of different substances. Filling of the SWCNTs with C₇₀ molecules resulted in a reduced van der Waals interaction between the tubes in a bundle. The DWCNTs have lower intensity of the van Hove bands and weaker photoluminescence. Raman spectra at 633 and 1064 nm excitation wavelengths reveal that RBM frequencies of C₆₀ and C₇₀ peapods are equally downshifted compared to empty tubes. It was found that filling of the nanotubes with C₆₀ and C₇₀ caused spectral shifts of absorption bands: thin tubes display red shifts, while thick ones show blue shifts. DWCNTs and C₆₀H₂₈@SWCNTs do not show any shifts. All the results suggest that the filling of nanotubes with fullerenes alters the average diameter of the electron cloud around SWCNT framework; namely, it increases for thin SWCNTs, and decreases for thick ones. Our attempts to structurally assign thick nanotubes using reported extrapolations from data for thin tubes were unsuccessful.     

Synthesis and properties of polydiacetylene-containing polyesters

A series of diacetylene-containing polyesters with number-average molar masses (GPC) in the range 900–4200 g mol⁻¹ were prepared from terephthaloyl chloride and hexa-2,4-diyne-1,6-diol using benzoyl chloride as a monofunctional reactant for control of molar mass. Degrees of crystallinity were estimated from WAXD to be up to 29%. Correlations between molar mass, melting behaviour, degree of crystallinity and thermal cross-polymerisation of diacetylene-containing polyesters have been established using hot-stage microscopy, DSC and resonance Raman spectroscopy. The polyester with M̄_n of 1264 g mol⁻¹ gave the best balance between processability and the ability to cross-polymerise efficiently. Its degree of crystallinity before cross-polymerisation was estimated from WAXD measurments to be 24%, a value coincident with the percentage conversion of diacetylene units to polydiacetylene chains measured by ¹³C solid-state NMR. The optimum conditions for compression moulding the polyester to produce a material with a strong Raman spectrum involved heating under vacuum at 120°C for 6h after an initial 3 h heat-up period. The material thus produced gave an intense Raman CC stretching band, which upon tensile deformation shifted linearly with strain to lower wavenumber by 12.0 cm⁻¹ %⁻¹. The potential use of the diacetylene-containing polyesters in the preparation of model blends for use in quantitative micromechanics studies of stress transfer between phases is briefly discussed.     

Synthesis of carbon nanotubes grown by hot filament plasma-enhanced chemical vapor deposition method

We prepared two kinds of catalytic layers onto n-typed silicon substrate—nickel by r.f.-magnetron sputtering and iron (III) nitrate metal oxide by spin coating. For iron (III) nitrate metal oxide 0.5 mol of ferric nitrate nonahydrate [Fe₂(NO₃)₃·9H₂O] ethanol solution was coated onto silicon by spin coater at different rotation speeds (rev./min). Carbon nanotubes were synthesized on both Ni and iron (III) nitrate metal oxide layers by the HFPECVD (hot filament plasma-enhanced chemical vapor deposition) method. We used ammonia (NH₃) and acetylene (C₂H₂) for the dilution gas and a carbon precursor for the growth of the carbon nanotubes, respectively. We could observe the relationship between the catalytic cluster density and the nanotube density with scanning electron microscopy (SEM) images. The density of carbon nanotubes on iron (III) nitrate metal oxide was controlled by the rev./min of the spin coater. Transmission electron microscopy (TEM) image shows multi-walled carbon nanotube where the catalyst was found in the tip of the carbon nanotube. Electron dispersive X-ray spectrometry (EDS) peaks for CNT's tip show that it was constituted with nickel and iron, respectively. Raman spectroscopy of nanotubes shows D-band and G-band peaks approximately 1370 and 1590 cm⁻¹.