X-ray absorption near-edge structure and photoelectron spectroscopy of single-walled carbon nanotubes modified by a HBr solution

X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron spectroscopy (PES) have been used to investigate single-walled carbon nanotubes (SWNTs) modified by immersion in a HBr solution at room temperature. After treatment XANES spectra of SWNTs show a new pronounced feature, which has been assigned to new bonds between the sidewall of the SWNTs and Br atoms. This investigation demonstrates the unique capabilities of the XANES spectroscopy as a tool to achieve structural and bonding information of carbon nanotubes induced by chemical processes.     

Immobilization of amines at carbon fiber surfaces

The reaction between amines acting as nucleophiles and the C=C bonds on the carbon fiber surface acting as electrophilic vinyl groups has not yet been explored. In this contribution it is demonstrated that both thermal reactions and electrochemical oxidation of amines at carbon fibers allow the covalent bonding of these molecules directly to the carbon fiber surface, presumably via nucleophilic attack of the amine at electrophilic C=C sites at the surface and subsequent formation of C–N bonds between the surface and the amine. A novel strategy for a quantitative assay of the number of amines attached to the surface is developed in which Fe(CN)₆³⁻ is electrostatically bound to the protonated, cationic amine sites, followed by electrochemical determination of the amount of bound Fe(CN)₆³⁻ as a function of its concentration in solution. Analysis of the isotherm for this electrostatic binding process then provides a measure of the number of interfacially immobilized amines. The composition of the amine layer is also probed using X-ray photoelectron spectroscopy (XPS). Mechanisms are discussed by which attachment of amines at the electrophilic vinyl groups of the carbon fibers can occur. The likely influence that this type of reaction has on the interfacial shear strength in carbon fiber/epoxy composite materials is also discussed.     

Estimation of kinetic parameters of the passive state of carbon steel in mildly alkaline solutions from electrochemical impedance spectroscopic and X-ray photoelectron spectroscopic data

The unambiguous interpretation of electrochemical impedance spectra of complex systems such as passive metals and alloys in terms of an unique kinetic model is often hampered by the large number of adjustable modeling parameters. In this paper, a combination of in situ electrochemical data and ex situ surface analytical information is employed to validate the estimates of kinetic and transport parameters of the passive state of carbon steel. For the purpose, electrochemical impedance spectroscopic and X-ray photoelectron spectroscopic data for the oxidation of carbon steel in mildly alkaline solutions are quantitatively compared with the predictions of the Mixed-Conduction Model for oxide films that represent the passive oxide as an intermediate phase between magnetite and maghemite. Estimates of the kinetic rate constants at the film interfaces, as well as the diffusion coefficients and field strength in the film are obtained and their relevance for the corrosion mechanism of carbon steel is discussed.     

Detection of low concentration oxygen containing functional groups on activated carbon fiber surfaces through fluorescent labeling

Covalent fluorescent labeling of surface species (FLOSS) was used to detect relatively low concentrations of surface functional groups (OH, COOH and CHO) on activated carbon fiber surfaces. The chromophores were attached to the surface through a reaction specific to each type of surface functional group. FLOSS indicated the presence of 8.7 × 10¹¹ COOH groups/cm² and 1.3 × 10¹² CHO groups/cm² on the ACF 25 fiber surface. Neither the infrared spectrum nor the X-ray photoelectron spectrum showed evidence of the existence of those low concentration groups. The concentration of OH groups on the fiber surface was lower than the detection limit (∼10¹⁰/cm²) of FLOSS under the present conditions. The FLOSS results for CHO and COOH groups were compared with the concentrations determined by Boehm titration (3.11 × 10¹³/cm² for CHO and 1.05 × 10¹³/cm² for COOH). The limited accessibility of the ACF surface to relatively large chromophores is one of the main reasons for the discrepancy between these two methods. FLOSS detects only exposed functional groups as opposed to functional groups hidden in small pores. This apparent limitation, however, highlights the surface sensitivity and specificity of FLOSS technique.     

X-ray absorption near edge structure and X-ray photoelectron spectroscopy studies of chloride in passive oxide films

X-ray absorption near edge structure (XANES), utilizing both electron yield and X-ray fluorescence detectors, and X-ray photoelectron spectroscopy (XPS) were used to follow chloride uptake by oxide-covered aluminum in 0.1 M NaCl solutions. The aluminum samples were polarized at selected potentials below (less positive than) the pitting potential. The electron yield XANES and XPS showed multiple peaks. The XPS chloride spectra showed two distinct sets of doublets. One doublet is related to chloride on the surface and the second is related to chloride incorporated in the oxide film. The XANES results also showed two peaks which are attributed to chloride on the surface and in the bulk of the oxide.     

X-ray photoelectron spectroscopic study of the ability to monofunctionalize polymer surfaces by low energy atomic bombardment

Low energy atomic bombardment is designed to limit the potentially reactive species to the atoms which are present in a radiofrequency (r.f.) plasma discharge. This might give the ability to monofunctionalize surfaces for specific applications such as biocompatibility. Bombardment of polystyrene and poly(trans)isoprene with nitrogen atoms does not result in the incorporation of any heteroatoms at the polymer surface. Other attempts were made on poly(acrylic acid) and poly(methyl methacrylate) without any results, even though the samples had been activated by argon ion bombardment; the thermalized atoms seem to have insufficient energy to functionalize these polymers. In contrast, ion bombardment performed with low energy nitrogen ions (500–1500eV) is able to incorporate a majority of amine functions. © 1998 Society of Chemical Industry.     

Experimental comparison of N(1s) X-ray photoelectron spectroscopy binding energies of hard and elastic amorphous carbon nitride films with reference organic compounds

In this work, hard and elastic amorphous carbon nitride (a-CN_x) films were deposited by DC magnetron sputtering on heated Si(001) substrates at 400 °C. Nanoindentation results confirmed that the films were highly compliant and had high elastic recovery. X-ray photoelectron spectroscopy (XPS) was used to investigate nitrogen bonding by directly comparing the N(1s) spectra of a-CN_x with the N(1s) peak positions of a variety of organic compounds that were characterized in the same XPS system. The N(1s) XPS spectra of hard and elastic a-CN_x is resolved into two dominant intensity contributions at 398.5 and 400.6 eV. We show that the N(1s) spectra of a-CN_x do not conclusively support a film-structure model with nitrogens bonded to sp³ carbons. We offer an alternate interpretation based on the presented data and previous XPS, nuclear magnetic resonance (NMR), and computational work. Together, the data suggest that hard and elastic a-CN_x consists of an sp² carbon network and that single-atom vacancy defects, as found in a graphite layer, may be present in the material. This implies that the low binding energy N(1s) component at 398.5 eV may be due to pyridine-like nitrogen bonded at the perimeter of a vacancy defect.     

Structural characterization of N-containing activated carbon fibers prepared from a low softening point petroleum pitch and a melamine resin

The incorporation of heteroatoms like N in activated carbons is of interest to modify the surface chemistry of the materials and, then, to improve their behavior as catalyst or catalyst support. In this work, N-containing activated carbon fibers have been prepared using a petroleum pitch with a low softening point and an N-containing resin. The novelty of the preparation method is that it involves the steps used in the synthesis of activated carbon fibers, i.e. spinning, stabilization, carbonization and activation. The materials have been characterized with techniques such as XPS and UPS, which allows us to follow the changes in both the chemical state of N species and the valence band structure of the carbon samples during the preparation steps.     

Bulk and surface chemical functionalities of type III PAN-based carbon fibres

PAN-based carbon fibres carbonised at relatively low temperature, i.e. type III carbon fibres, were submitted to heat treatment at 2300 °C (GR) or oxidation in nitric acid. The samples were characterised by XPS, FTIR, wetting measurements, gas adsorption, elemental analysis and acid/base titration. While oxidation only slightly affects the nitrogen concentration, it produces an appreciable change in the nature of the chemical functions, namely the conversion of pyridine-type nitrogen and quaternary nitrogen into aliphatic functions. Oxidation treatment modifies all the material constituting the fibre, the oxygen concentration being about 1.5 times higher at the fibre external surface compared with the whole material. Three components (531.2, 532.6 and 533.8 eV) are clearly identified in the oxygen XPS peak, allowing a comparison to be made between the whole material and the external surface regarding chemical species. The acidic groups are mainly carboxyl. Fibres submitted to extensive oxidation also show a high basicity, attributed mainly to calcium carboxylate. Although the acidic and basic groups present in the whole material can be titrated with aqueous solutions, the fibres develop only a very small surface area and no microporosity as determined by krypton adsorption. The material may be viewed as a sponge, collapsed when dry but able to swell in water and developing a high cation-exchange capacity.     

Atomic force microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and thermal studies of the new melamine fiber

This paper reports the characterization of unaged and aged melamine fibers using various characterization techniques including atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. Since melamine fiber is a relatively new fiber, very few studies on its characterization have been made. Morphological studies of the fiber surface using SEM display die lines running along the filament surface, which are characteristics of synthetic fibers and generally occur during spinning of the molten prepolymer through the spinnerets. AFM studies show that the surface of a melamine fiber filament contains a large number of hills and valleys, which are triangular in shape. AFM roughness analysis shows that melamine fiber surface is considerably rough which may aid in adhesion of the fiber with polymeric matrices. Ageing causes an increase in the surface roughness with simultaneous increase in the crystallinity of the fiber from 19.4% to 22.6%. In XPS studies, high concentrations of carbonyl and hydroxyl groups on the filament surface have been detected. Ageing causes a reduction in the hydroxyl group concentration and an increase in the carbonyl group concentration due to surface oxidation. The reduction in the surface hydroxyl groups due to ageing has also been detected in the Fourier-Transform infrared (FT-IR) spectra of the aged fibers. Thermogravimetric (TG) studies reveal a high thermal stability of the melamine fiber even in an oxidative environment such as air.     

Electrochemical studies of the interaction between a modified activated carbon surface and heavy metal ions

Cyclic voltammetric studies of the influence of surface chemistry on the electrochemical behaviour of powdered activated carbon electrodes (PACE) in the presence of selected heavy metal ions (Pb²⁺, Hg²⁺, Cd²⁺) in bulk solution and pre-adsorbed on carbon were carried out. The variety of surfaces was achieved via the modification of carbon samples by heat treatment under vacuum and in an oxygen/ammonia atmosphere, as well as oxidation with conc. nitric acid. The chemical structures of the modified carbon surfaces were characterised by XPS and standard pH-titration. The adsorption capacities of the modified carbon samples towards the heavy metal ions in question were estimated. The mechanisms of adsorption processes of metal species on carbon surfaces were analysed and described on the basis of their electrochemical behaviour. The nature of the interactions between the modified carbon surfaces and adsorbed cations is discussed.     

Surface functionalization and characterization of graphitic carbon nanofibers (GCNFs)

The preparation and characterization of herringbone graphitic carbon nanofibers (GCNFs) surface-derivatized with reactive linker molecules derived from four diamines and three triamines is reported. Surface carbon sites of as-prepared GCNFs are oxidized to carboxylic acid groups by nitric acid and covalently bound to seven different linker molecules containing pendant amino groups using carboxylate amidation chemistry. GCNF materials are characterized by TEM, IR, TGA, laser-desorption/ionization (LDI) mass spectrometry, and by elemental analysis. Approximate GCNF/(linker molecule)_x compositions are proposed consistent with acid-uptake and elemental analysis data. Direct evidence for the presence and composition of surface-bound linker molecules is provided by LDI mass spectrometry and by quantitative XPS analysis of trifluoroacetylated derivatives. The reactivity of pendant amino groups present within attached linker molecules is determined quantitatively via Fmoc analysis and synthetically by effecting nucleophilic ring-opening oligomerization of epoxy monomer.     

Sulfurization of a carbon surface for vapor phase mercury removal - II: Sulfur forms and mercury uptake

Sulfur forms deposited on carbonaceous surfaces after exposure to hydrogen sulfide were analyzed using XPS and XANES. Higher temperatures promote the formation of organic sulfur and the presence of H₂S during the cooling process increased elemental sulfur content. Temperatures between 400-600 °C were found to be optimal for producing effective mercury uptake sorbents. The increased amount of sulfur deposited during the cooling process in the presence of H₂S was very effective towards Hg uptake in nitrogen. Correlation of mercury uptake capacity and the content of each sulfur form indicated that elemental sulfur, thiophene, and sulfate are likely responsible for mercury uptake, with elemental sulfur species being the most effective.     

Surface carbonation of synthetic C-S-H samples: A comparison between fresh and aged C-S-H using X-ray photoelectron spectroscopy

This paper presents a continuation of studies into silicate anion structure using X-ray photoelectron spectroscopy (XPS). A series of C-S-H samples have been prepared mechanochemically, and then stored under ambient conditions for six months. Storage led to surface carbonation, the extent of which was dependent upon the calcium/silicon ratio of the fresh sample. Carbonation arose through decalcification of the C-S-H, leading to increased silicate polymerisation. The surfaces of the most calcium-rich phases (C/S = 1.33 and 1.50) underwent complete decalcification to yield silica (possibly containing some silanol groups) and calcium carbonate. Carbonation, and hence changes in silicate anion structure, was minimal for the C-S-H phases with C/S = 0.67 and 0.75.     

Matrix formulation and interfacial enhancement of an aeronautical carbon fabric/epoxy composites fabricated via resin transfer molding (RTM) technique

Flexural strength and interlaminar shear strength of fiber-reinforced composites are among the most concerned properties in the aeronautical sector, which are ameliorated in combination through matrix formulation and interfacial enhancement in this study. A thermosetting matrix resin consisting of diglycidyl ether of bisphenol A and diglycidyl ester of aliphatic cyclo was formulated to cater to the requirements of carbon fabric/epoxy composites fabricated by resin transfer molding (RTM) technique. The toughness and thermal stability of the formulated epoxy resin were studied in consideration of the compromise among processability, thermal and mechanical properties for potential aeronautical applications. The processability of the matrix resin suitable for RTM technique was evaluated with respect to temperature-dependent and time-dependent viscosity. A regime for the curing and post-curing cycles was established according to the differential scanning calorimeter data. Air plasma is introduced herein as a technique to enhance the interfacial adhesion of carbon fabric/epoxy composites. Composites based on the epoxy system and plasma-treated carbon fabric were fabricated using the RTM technique. The reactive groups introduced by plasma treatment are responsible for the significant improvements of mechanical properties of the resulting composites. The microscopy pictures of the fracture surfaces confirm that the failure mode of carbon fabric/epoxy composites has changed initially from primarily adhesive failure to cohesive failure.     

Preparation of emulsion‐type thermotolerant sizing agent for carbon fiber and the interfacial properties of carbon fiber/epoxy resin composite

A modified resin was synthesized through the reaction between dodecylamine and tetraglycidyldiaminodiphenylmethane (TGDDM), which was used as the film former of sizing agent for carbon fiber (CF). The sizing agents were prepared through phase inversion emulsification method. Fourier transform infrared spectroscopy (FTIR) was utilized to analyze the modified resin. Particle sizes of the sizing agents were tested to evaluate their stabilities. Differential scanning calorimetry (DSC) results demonstrated that the glass transition temperature (T_g) of the modified TGDDM is much higher than the T_g of the cured epoxy resin E‐44. The influences of the sizing treatment on CF were investigated by abrasion resistance, fluffs, and stiffness tests. The maximum abrasion resistance increased by 172.8%, compared with the abrasion resistance of the desized CF. Interlaminar shear strength (ILSS) results of the CF/TGDDM composites indicated that the interfacial adhesion between CF and matrix resin was greatly improved after CF was sized. The maximum ILSS value could obtain a 29.16% improvement, compared with the ILSS of the desized CF composite. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41882.     

Covalent binding of amino,carboxy, and nitro-substituted aminopropyltriethoxysilanes to oxidized silicon surfaces and their interaction with octadecanamine and octadecanoic acid studied by X-ray photoelectron spectroscopy and ellipsometry

Three silanized silicon substrates were prepared by treating cleaned oxidized silicon wafers with N-(3-triethoxysilylpropyl)octadecanamide (1), 9-[N-(triethoxysilylpropyl)amino]-9-oxononanoic acid methyl ester (2), and N-(3-triethoxysilylpropyl)-12-nitrododecanamide (4). The carbomethoxyl of 2 immobilized on silicon was hydrolysed to yield the corresponding ω-carboxylic surface (3) and the nitro group of the surface 4 reduced to afford the ω-amino surface (5). All five silanized surfaces were treated with octadecanoic acid and octadecanamine used as models for acidic and basic polymeric adhesives and the interactions were followed by ellipsometry and X-ray photoelectron spectroscopy. While the surfaces 1 and 2 reacted only by physisorption, the carboxylic surface 3 and the amino surface 5 showed a strong reaction with octadecanamine and octadecanoic acid, respectively. The nitro surface 4 exhibited a strong interaction with both probes, but by different pathways.     

Preparation and characterisation of single-walled carbon nanotubes functionalised with amines

The amines octadecylamine, 2-aminoanthracene, 1-H,1-H-pentadecafluorooctylamine, 4-perfluorooctylaniline and 2,4-bis(perfluorooctyl)aniline, have been reacted with chemically modified single-walled carbon nanotubes (SWCNTs). The chemical modification consisted on a thermal treatment in air of arc discharge-grown SWCNTs with an optional purification with HNO₃. The selected amines have been allowed to interact with the obtained materials and with those resulting from an additional treatment with thionyl chloride. The resulting materials were characterised with different spectroscopic techniques such as X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy and fluorescence spectroscopy complemented with the thermogravimetric analysis and transmission electron microscopy. The chemically modified SWCNTs exhibit different solubility properties depending on the amines and the solvents used.     

A SERS spectroelectrochemical investigation of the interaction of 2-mercaptobenzothiazole with copper, silver and gold surfaces

The interaction of the sulfide mineral flotation collector, 2-mercaptobenzothiazole, with silver, copper and gold surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. 2-mercaptobenzothiazole, the copper, silver and gold compounds of this species, and the dithiolate, 2,2-dithiobis(benzothiazole) were characterised by ¹³C NMR and Raman spectroscopy to provide a basis for identifying surface species. SERS investigations showed that, at pH 4.6 where the solution species is in the protonated form, and at 9.2, where it is present as the ion, adsorption on each metal occurs over a wide potential range. Attachment of the organic compound occurs through bonding between the exocyclic sulfur atom and metal atoms in the surface. X-ray photoelectron spectroscopy confirmed that the adsorbed layer was of monolayer thickness. Adsorption of the protonated 2-mercaptobenzothiazole occurs on copper at pH 4.6 at potentials below that at which charge transfer adsorption commences.