A photoelectron spectroscopy study of ion-irradiation induced defects in single-wall carbon nanotubes

Valence band and core level photoemission spectroscopies were used to study the changes brought about by irradiation of a single-wall carbon nanotube (SWCNT) film by 3 keV Ar⁺ ions at room temperature. At low ion doses (low defect density) an increase in spectral intensity near the Fermi level (E_F) is observed, associated with formation of localized defect-related states. These states are acceptor-like as evidenced by a shift to lower binding energy for both valence band features and the C1s core level. For large ion doses (high defect density) the spectral intensity near E_F decreases, valence band features associated with delocalized π bonding disappear, and a core level component associated with sp³ bound carbon appears. This behaviour is attributed to amorphisation of the SWCNT films and occurs at ion doses consistent with those theoretically predicted.     

Atomic oxygen functionalization of double walled C nanotubes

The interaction of atomic oxygen with double walled C nanotubes at room temperature was studied by high resolution photoemission spectroscopy with synchrotron radiation. The nature of the chemical species formed on the nanotube sidewalls was followed from the initial adsorption up to advanced oxidation stages, whereas the thermal evolution of the O-related chemical species was monitored by fast photoemission. At the beginning of oxidation O atoms preferentially chemisorb forming C-O-C bonds, in ether and epoxy structures, which originate different components in the O1s spectra and exhibit different thermal stability. The onset of sp² lattice distortion is attested by the appearance of C-C bonds intermediate between sp² and sp³ configurations. The formation of double and triple C-O bonds is favored at later oxidation stages, and is accompanied by increasing lattice amorphization and decreasing emission in the Fermi level region. After annealing at 950 °C the O1s signal disappears and the presence of lattice defects emerges from the C1s line shape. This result, together with the chemical inertness of the deoxygenated nanotubes towards CO and O₂ adsorption suggests that the dangling bonds are promptly healed by thermal annealing and only stable topological defects are retained in the nanotube lattice.     

Infra-red bandshapes of methylene-d2 bending vibrations in n-hexatriacontane-n-hexatriacontane-d74

Infra-red spectra in the CD₂ bending vibration region (1080–1100 cm^?1) have been analysed for mixtures of deuterated and hydrogenated hexatriacontane. The i.r. data analyses are based on lattice dynamical calculations of guest deuterated molecules in the host n-C₃₆H₇₄ and infrared intensities calculated using the electro-optical parameter method. The calculated band profiles as a function of the deuterated molecule concentration compare favourably to experimental spectra taken at 80K. The high resolution, low temperature spectra reveal features heretofore only observed at much higher concentrations of deuterated species. Self deconvolution procedures were used to further resolve the spectra. Excellent agreement was found between calculated and experimental ratios of the i.r. intensity of certain dimer arrangements to that of singlet molecules. This intensity ratio was found to be a better measure of deuterated species concentration than the halfwidth of the CD₂ bending vibration band that had been previously used.     

Thermal,mechanical, and rheological properties of biodegradable polybutylene succinate/carbon nanotubes nanocomposites

Biodegradable poly(butylene succinate)/carbon nanotubes nanocomposites were prepared by melt mixing process, and the influence of carbon nanotubes on the properties of the nanocomposites was investigated. Differential scanning calorimetry showed that crystallization temperature (T_c) increase with increasing carbon nanotube content. Improvement of tensile modulus was observed by the addition of carbon nanotubes compared with pure poly(butylene succinate). Electrical conductivity showed that conductivity of polybutylene succinate/carbon nanotube composites increased with addition of carbon nanotube content. The storage moduli of polybutylene succinate/carbon nanotube composites are higher than the neat polybutylene succinate. The processability of polybutylene succinate/carbon nanotubes composites was improved and more pronounced in higher content of carbon nanotubes. POLYM. COMPOS., 31:1309–1314, 2010. © 2009 Society of Plastics Engineers     

Interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) and poly(p-phenylene α-phenyl vinylene)

We have investigated the interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) (PPV-DP) and poly(p-phenylene α-phenyl vinylene) (PPV-P) using X-ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of Ca? O, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about ?1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form Ca? C species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the Ca? O and Ca? C species and the overlayer is pure beyond 15 Å of Ca coverage.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

Iron oxide supported sulfated TiO2 nanotube catalysts for NO reduction with propane

Sulfated TiO₂ nanotubes and a series of iron oxide loaded sulfated TiO₂ nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N₂-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H₂-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO₂ nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO₂ catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction.     

Fabrication and Characterization of High-Performance Diglycidyl Ether of Bisphenol-A/Tetrabromobisphenol-A Blend Reinforced with Multiwalled Carbon Nanotube Composite

The nanocomposite of diglycidyl ether of bisphenol-A and diglycidyl ether of bisphenol-A/tetrabromobisphenol-A blend with purified multiwalled carbon nanotube and acid-functional multiwalled carbon nanotube were processed by solution route. According to field emission scanning electron microscope, diglycidyl ether of bisphenol-A/purified multiwalled carbon nanotube depicted poor dispersion and aggregated morphology, however, diglycidyl ether of bisphenol-A/acid-functionalized multiwalled carbon nanotube revealed better dispersion in matrix. The diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/purified multiwalled carbon nanotube had higher thermal stability as T₀ of 369°C and T_max of 569°C were observed. Nonflammability of diglycidyl ether of bisphenol-A/tetrabromobisphenol-A blend-based material was 44%, i.e., higher than diglycidyl ether of bisphenol-A/purified multiwalled carbon nanotube series. Diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/purified multiwalled carbon nanotube 0.1 had crystalline morphology with diffractions at 12.77° and 26.8°. The diglycidyl ether of bisphenol-A/tetrabromobisphenol-A/multiwalled carbon nanotube nanocomposite revealed electromagnetic interference shielding effectiveness of ～12.1?dB, i.e., desired for aerospace applications.     

Synthesis and Raman characterization of boron-doped single-walled carbon nanotubes

A systematic study was carried out to dope single-walled carbon nanotube (SWNT) bundles with varying amounts of boron using the pulsed laser vaporization technique. Targets containing boron concentrations ranging from 0.5 to 10 at.% boron were prepared by mixing elemental boron with carbon paste and the Co/Ni catalysts. The laser-generated products that were obtained from these targets were characterized by high resolution transmission electron microscopy, electron energy loss spectroscopy (EELS), thermoelectric power (TEP) measurements, and Raman scattering experiments. Electron microscopy and Raman studies revealed that the presence of various levels of boron concentration in the target strongly affected the products that were prepared. SWNTs were found in the products prepared from targets containing up through 3 at.% boron, and high resolution EELS estimated that less than 0.05-0.1 at.% boron is present in the SWNT lattice. The absence of SWNT bundles in the products derived from targets containing more than 3 at.% boron implies that the presence of excess boron in the carbon plume severely inhibits the carbon nanotube growth. The overall effect of the boron incorporation primarily leads to: (i) a systematic increase in intensity of the disorder-induced band (D-band) upon boron doping, with increasing D-band intensity observed for higher doping levels, (ii) a systematic downshift in the G′-band frequency due the relatively weaker C-B bond, and (iii) a non-linear variation in the RBM and G′-band intensities which is attributed to shifts in resonance conditions in the doped tubes. Resonant Raman spectroscopy thus provides large changes in the intensity of prominent features even when the dopant concentration is below the detectable limit of EELS (0.05-0.1 at.%). Thermoelectric power data also provide complementary evidence for the presence of a small boron concentration in the SWNT lattice which transforms the SWNTs into a permanently p-type material.     

Thermosetting polyurethane multiwalled carbon nanotube composites

Thermosetting polyurethane (PU) multi‐walled carbon nanotube (MWCNT) nanocomposites at loadings up to 1 wt % were prepared via an addition polymerization reaction. The morphology of the nanocomposites and degree of dispersion of the MWCNTs was studied using a combination of scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and wide angle X‐ray diffraction (WAXD), and revealed the nanotubes to be highly dispersed in the PU matrix. Addition of just 0.1 wt % MWCNTs resulted in significant enhancements in stiffness, strength and toughness. Increases in Young's modulus, % elongation at break and ultimate tensile strength of 561, 302 and 397% were measured for the nanocomposites compared to the unfilled PU. The effect of the MWCNTs on the modulus of the PU was evaluated using the Rule of Mixtures, Krenchel and Halpin‐Tsai models. Only the Halpin‐Tsai model applied to high aspect ratio nanotubes was in good agreement with the modulus values determined experimentally. Strong interfacial shear stress was found between PU chains and nanotubes, up to 439 MPa, calculated using a modified Kelly‐Tyson model. Evidence for strong interfacial interactions was obtained from the Raman spectra of both the precursor materials and nanocomposites. When the MWCNTs were added to the isophorone diisocyanate an up‐shift of 14 cm^?1 and on average 40 cm^?1 was obtained for the position of the carbon‐hydrogen (C? H) out‐of plane bending (766 cm^?1) and isocyanate symmetric stretch (1420 cm^?1) modes respectively. Moreover, an up‐shift of 24 cm^?1 was recorded for the nanotube tangential mode (G‐band) for the 1.0 wt % nanocomposite because of the compressive forces of the PU matrix acting on the MWCNTs. The dynamic mechanical (DMA) properties of the PU thermoset and the nanocomposites were measured as a function of temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influences of different gravity environments on the curing process and cured products of carbon‐nanotube‐reinforced epoxy composites

The influences of different gravity environments on the curing process and the cured products of carbon‐nanotube‐reinforced epoxy composites were investigated in this study. Different gravity environments were simulated with a superconducting magnet on the basis of which resin matrix composites with different amino‐functionalized multiwalled carbon nanotube (NH₂‐MWCNT) concentrations of 0.1, 0.3, 0.5, and 1 wt % were tested. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis (TMA), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and three‐point bending tests were used to analyze the characteristics of different curing processes and cured products. From the results, we observed that the curing rate of the epoxy composites was influenced by different gravity values, and there was anisotropy in the NH₂‐MWCNT‐reinforced epoxy composites cured in the simulated microgravity environment. More effects of gravity on the curing process and cured products could be obtained through detailed experiments and discussion; this is important and fundamental for improving and enhancing the properties of composite materials used in different gravity environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41413.     

XPS study of carbon in electrochemical reduction products of poly(tetrafluoroethylene)

XPS spectra of reaction products of poly(tetrafluoroethylene) with lithium amalgam were studied. The primary reaction product is a mixture of LiF and elementary carbon in the sp- state in a molar ratio of 2:1. This carbon is very reactive, among others also with respect to air oxidation at room temperature leading to the formation of surface oxides with a well-defined chemical shift of the C 1s photoemission band, which can be attributed to COOH groups. The binding energy of 1s electrons in C atoms of the basic skeleton hidden in LiF is markedly higher than with other known modifications of carbon. The carbonaceous materials formed by the leaching out of LiF with water, or by the removal of LiF by melting, contain, after air oxidation, various types of surface oxides. The binding energy of C 1s photoelectrons in the resulting skeletons is comparable with that of other carbonaceous materials.     

Evidence of band bending and surface Fermi level pinning in graphite oxide

We present the electronic structure of graphite oxide in the vicinity of the Fermi level measured using ultraviolet photoemission and inverse photoemission spectroscopies and compare it with X-ray absorption spectra. The expected p-type behavior of graphite oxide is not observed at the surface and the presence of band bending is invoked. The observed electronic structure of graphite oxide exhibited an n-type semiconducting band structure with a band gap of 2.3 ± 0.4 eV. An oxygen related state, at 0.8 eV above Fermi level, and the suppression of the unoccupied carbon weighted states at the conduction band minimum suggests that the oxygen vacancies at the surface of graphite oxide contribute to the n-type semiconducting electronic structure of the surface.     

Chemically resolved dynamical imaging of catalytic reactions on composite surfaces

The catalytic reduction of NO by hydrogen is investigated at (T = 650 K and (p≈10^-6 mbar on a microstructured Rh/Pt(100) surface consisting of Pt(100) domains surrounded by a 600 Åthick Rh film. Synchrotron radiation scanning photoemission microscopy (SPEM), using photons focused into a spot of less than 0.2 μm diameter, is employed as a spatially and chemically resolving in situ technique. The chemical waves which arise in the bistable system NO+H₂/Rh are imaged with SPEM monitoring the N 1s and O 1s photoelectrons. The reaction fronts initiate transitions from an inactive oxygen-covered surface (Θ_O≈0.25 ML) to a reactive nitrogen-covered surface (Θ_N≈0.06 ML). At the Pt/Rh interface, synergetic effects can be observed: the chemical waves on the Rh film nucleate preferentially at the Pt/Rh interface. This nucleation is poisoned by carbon contamination on the Pt area but is prevented in the vicinity of the Pt/Rh interface by the adjacent clean Rh film. No segregation of Pt to the surface was observed for the 600 Å thick Rh film.     

High impact strength epoxy nanocomposites with natural nanotubes

Epoxy-based nanocomposites were prepared with natural nanotubes from halloysite, a clay mineral with the empirical formula Al₂Si₂O₅(OH)₄. The morphology of the nanotubes was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and was found geometrically similar to multi-walled carbon nanotubes. The thermal and mechanical properties of the nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical analysis, Charpy impact and three-point bending tests. The results demonstrated that blending epoxy with 2.3 wt% halloysite nanotubes increased the impact strength by 4 times without scarifying flexural modulus, strength and thermal stability. Unique toughening mechanisms for this improvement were investigated and discussed. It was proposed that impact energy was dissipated via the formation of damage zones with a large number of micro-cracks in front of the main crack. The micro-cracks were stabilized by nanotube bridging. Nanotube bridging, pull-out and breaking were also observed and proposed as the major energy dissipating events. The findings of this work suggest that halloysite nanotube may be an effective impact modifier for epoxy and other brittle polymers.     

Raman spectroscopy of HiPCO single-walled carbon nanotubes at 300 and 5 K

Single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO method) and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K. Raman spectra have been observed at λ_exc=632.8 and 441.6 nm laser excitation in the range of 160-1800 cm⁻¹. In the low-frequency part of the spectra (the radial breathing mode range) eleven narrow lines can be detected at low temperatures, enabling an estimation of nanotube diameters (0.8-1.3 nm) and chirality. The width at half-maximum intensity of these spectral lines is about 3-4 cm⁻¹ at 5 K. The Stokes and anti-Stokes spectra are measured at λ_exc=632.8 nm at room temperature. The most intense lines in these spectra are caused with the resonant Raman-scattering process. With increasing temperature from 5 to 300 K the shift (3-4 cm⁻¹) of the most intense high-frequency component of the tangential mode (G mode) to lower frequency is observed. Based on the analysis of the Stokes/anti-Stokes spectra and the G band shape, the corresponding lines were identified with metallic or semiconducting type of nanotubes.     

Preparation and properties of multi-walled carbon nanotube/carbon/polystyrene composites

Multi-walled carbon nanotube (MWCNT)/C/polystyrene (PS) composite materials were prepared by in situ polymerization of monomer in preformed MWCNT/C foams. MWCNT/C foams were preformed using polyurethane foam as template. The preformed MWCNT/C foams had a more continuous conductive structure than the carbon nanotube networks formed by free assembly in composites. The structure of the MWCNT/C foam network was characterized with scanning electron microscopy. The MWCNT/C/PS composites have an electric conductivity higher than 0.01 S/cm for a filler loading of 1 wt.%. Enhancement of thermal conductivity and mechanical properties by the preformed MWCNT/C foam were also observed.     

Electrochemical characterization of carbon nanotubes as electrode in electrochemical double-layer capacitors

Carbon nanotubes uniformly 50 nm in diameter were directly grown on graphite foil. Cyclic voltammetry (CV) shows that the carbon nanotube/graphite foil electrode has a high specific capacitance (115.7 F/g at a scan rate of 100 mV/s) and exhibits typical double-layer behavior. A rectangular-shaped CV curve persists even at a scan rate of 100 mV/s in 1.0 M H₂SO₄ aqueous solution, which suggests that the carbon nanotube electrode could be an excellent candidate as the electrode in electrochemical double-layer capacitors. In addition, the influence of the potential scan rate, aging, and the electrolyte solution on the specific capacitance of nanotube electrodes was also studied.     

Enhanced inactivation of E. coli bacteria using immobilized porous TiO2 photoelectrocatalysis

Immobilized TiO₂ nanotube electrodes with high surface areas were grown via electrochemical anodization in aqueous solution containing fluoride ions for photocatalysis applications. The photoelectrochemical properties of the grown immobilized TiO₂ film were studied by potentiodynamic measurements (linear sweep voltammetry), in addition to the calculation of the photocurrent response. The nanotube electrode properties were compared to mesoporous TiO₂ electrodes grown by anodization in sulfuric acid at high potentials (above the microsparking potential) and to 1 g/l P-25 TiO₂ powder. Photocatalyst films were evaluated by high resolution SEM and XRD for surface and crystallographic characterization. Finally, photoelectrocatalytic application of TiO₂ was studied via inactivation of E. coli. The use of the high surface area TiO₂ nanotubes resulted in a high photocurrent and an extremely rapid E. coli inactivation rate of ∼10⁶ CFU/ml bacteria within 10 min. The immobilized nanotube system is proven to be the most potent electrode for water purification.