Effect of alkyl carbon chain length and ethylene oxide content on the performance of linear alcohol ethoxylates

A grid of 30 surfactants varying from C₈ to C₁₈ in carbon chain length and from 40 to 80% in ethylene oxide (EO) content were examined to determine the effect of molecular structure on the physical properties (density, melting point, solution viscosity) and performance properties (surface activity, detergency, hard-surface cleaning, foaming, wetting) of linear alcohol ethoxylates. Results show that while physical propeties are influenced primarily by EO content, both carbon chain length and EO content are important to performance. Optimum carbon chain length is also shown to depend strongly on surfactant concentration. Presented at the AOCS meeting in New Orleans in May 1987.     

Synthesis and characterization of phosphorus–nitrogen doped multiwalled carbon nanotubes

Phosphorus–nitrogen doped multiwalled carbon nanotubes (CN_xP_y) were prepared using a floating catalyst chemical vapor deposition method. Triphenylphosphine (TPP), as phosphorus (P) precursor, was used to control the structure of the CN_xP_y. Transmission electron microscope (TEM) observation indicated that with the increase of TPP amount, the outer diameter and wall thickness of the CN_xP_y gradually increased, while their inner diameter decreased. TEM and backscattered electron imaging revealed that structural changes of the nanotubes could be attributed to the shape change of the catalyst particles, from conical for nitrogen-doped carbon nanotubes (CN_x) to elongated for CN_xP_y, with the addition of TPP. X-ray photoelectron spectroscopy analysis demonstrated that the P content in CN_xP_y can reach as high as 1.9 at.%. Raman analysis indicated that CN_xP_y had a lower crystallinity than CN_x.     

Effect of alkyl carbon chain length and ethylene oxide content on the performance of linear alcohol ether sulfates

A series of linear alcohol ether sulfates varying in alkyl carbon chain length and ethylene oxide content was evaluated with respect to surface activity, viscosity, foaming, and detergency. Performance data agree well with surface property data. A low level of EO is best in terms of effectiveness and efficiency in lowering surface tension, which is why a low-mole ether sulfate salt-thickens better, produces foam which is more tolerant of soil, and gives good detergency performance. A lauryl-range alkyl carbon chain length is best for foaming and salt-thickening, but a higher carbon chain length appears to be better for detergency performance.     

A co-pyrolysis route to synthesize nitrogen doped multiwall carbon nanotubes for oxygen reduction reaction

Nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) have been synthesized by a co-pyrolysis route of iron(II) phthalocyanine (FePc) loaded and PEO₂₀–PPO₇₀–PEO₂₀ retained in mesoporous silica. In this process, FePc was used as both Fe-catalyst, carbon and nitrogen sources, and P123-containing mesoporous silica was employed as both the substrate and carbon seeds/source for the growth of N-MWCNTs. The obtained samples have well-defined morphology and graphitic structure, and show high electrochemical catalytic activity and stability for oxygen reduction reaction, attributing to the highly graphitic structure and the pyridinic-type nitrogen in the N-MWCNTs. The power density of a single fuel cell using N-MWCNT as cathodic catalyst was measured to be 67.7% of that of a standard single cell using 40% Pt/C as cathodic catalyst.     

Tailoring the structure and nitrogen content of nitrogen-doped carbon nanotubes by water-assisted growth

Vertically aligned nitrogen-doped carbon nanotubes (NCNTs) were synthesized by the pyrolysis of acetonitrile in the presence of ferrocene catalyst (2 wt.%) with water assistance. Herein, we demonstrated that water could be a special tool to shape the structure of the NCNTs and it can be injected as much as 33.3 wt.% to grow NCNTs. More significantly, the nitrogen content of NCNTs and their tubular microstructures including tube diameter and wall thickness can be finely tailored by water introduction, which may further modulate their film electrical conductivity and electrocatalytic activities for oxygen reduction reactions.     

Synthesis and characterization of multiwalled carbon nanotubes-protoporphyrin IX composites using acid functionalized or nitrogen doped carbon nanotubes

In this research we describe the synthesis and characterization of composite materials based on multiwalled carbon nanotubes and protoporphyrin IX. We compare the results of using three types of carbon nanotubes: pristine (diameter < 10 nm), acid functionalized (diameter < 10 nm), and nitrogen doped carbon nanotubes (diameter ≈ 20 nm). Carbon nanotubes were mixed with protoporphyrin IX via two simple and straightforward methods using sonication, or heating-stirring. The characterization of the composites was done by Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, ultraviolet-visible and fluorescence spectroscopy and infrared spectroscopy. A diversity of coatings of the nanotubes by protoporphyrin were obtained depending on the type of nanotube used or the method of synthesis. Some carbon nanotubes increased their diameter up to 40% after the reaction with protoporphyrin. Percentages by weight up to 20% of protoporphyrin were measured by thermogravimetric analysis. We obtained experimental evidences by different techniques of the electronic interaction and the formation of covalent bonds between both constituents, above all for the composites using nanotubes < 10 nm in diameter. Some of these evidences were ~ 98% of fluorescence quenching, reduction in the intensity of the absorption bands in ultraviolet visible spectroscopy, strong reduction in the intensity of some bands in Raman spectroscopy, red and blue shifts, as well as the presence of new absorption bands in infrared spectroscopy. Nitrogen doped carbon nanotubes showed low chemical reactivity to protoporphyrin IX, perhaps due to their lower acceptor character as they could have charge transfer from nitrogen dopants to the nanotube network, or because of their metallic character.     

Electrocatalytic activity of nitrogen doped carbon nanotubes with different morphologies for oxygen reduction reaction

Nitrogen doped carbon nanotubes (NCNTs) were synthesized by a single step chemical vapor deposition technique using either ferrocene or iron(II) phthalocyanine as catalyst and pyridine as the carbon and nitrogen precursor. Variations in surface morphology and electrocatalytic activity for oxygen reduction reaction (ORR) were observed between the NCNTs synthesized using different catalysts. The structural and chemical characterizations were carried out using transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical activity of NCNTs was evaluated with rotating ring disc electrode (RRDE) voltammetry. Structural characterization suggested more defects formed on the NCNTs synthesized from ferrocene (Fc-NCNTs) which led to a rugged surface morphology compared to the NCNTs synthesized from iron(II) phthalocyanine (FePc-NCNTs). Based on the RRDE voltammetry study, Fc-NCNTs demonstrated much higher activity for ORR than FePc-NCNT. Evidences from the structural and chemical characterizations illustrate the potential impact of catalyst structure in shaping the surface structure of NCNTs and the positive effect of surface defects on ORR activity. These results showed that potential improvements on ORR activity of NCNTs could be achieved by tailoring the surface structure of NCNTs by using catalysts with different structures.     

The use of carbon nanotubes in textile printing

The characteristic properties of carbon nanotubes (CNTs), particularly their heat conduction, electrical conductivity, high modulus of elasticity, high strength, and resistance to chemicals, have resulted in widespread application of CNTs in nanotechnologies. In this study, CNTs were used to impart specific functionality to textiles by printing techniques. To this aim, modified commercial aqueous dispersions of multiwalled CNTs from Nanocyl^® were used for preparing special compositions as paste for printing by conventional techniques (screen printing) and as inks for ink‐jet printing to bestow the fabric antistatic and antibacterial properties. Taking into account the importance of the dispersion level of CNT in the printing composition from the point of view of antistatic properties, the quality of the CNT dispersion was assessed on the basis of particle size distribution by means of a DLS PSS Nicomp device. Printings were done on two types of woven fabrics: 100% cotton and 30/70% cotton/polyester blend. The CNTs used in printing were found to impart antistatic and antibacterial properties to the printed fabrics. These imparted properties were resistant to repeated washing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The use of carbon nanotubes with and without nitrogen doping as support for ruthenium catalysts in the ammonia decomposition reaction

Ru catalysts were supported on two different carbon materials, multiwall carbon nanotubes and bamboo-like carbon nanotubes doped with nitrogen, which were synthesized by catalytic chemical vapour deposition of C₂H₂/H₂/N₂ or C₂H₂/NH₃/H₂/N₂, respectively, over Fe/SiO₂ catalyst. All the carbon supports and/or the prepared Ru catalysts were characterized by several techniques including transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ adsorption isotherms and CO chemisorption. The Ru catalysts were tested in the catalytic ammonia decomposition reaction. High yields towards hydrogen production were achieved. Carbon nanotubes were heated in an inert atmosphere at temperatures up to 1773 K in order to study the effects of such support treatments on the ammonia decomposition reaction. The elimination of acidic groups from the surfaces, prior to catalyst preparation, and/or the surface graphitization of the materials produced a higher catalytic activity during the reaction. The catalytic activity of Ru particles was significantly improved when supported on carbon nanotubes doped with nitrogen.     

Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion

High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29 nm and 57 nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the I_D/I_G (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels.     

The use of water-soluble pyrene derivatives to probe the surface of carbon nanotubes

The influence of carbon nanotube (CNT) curvature and graphitization, pyrene derivative steric hindrance and pyrene diffusion in solution on the adsorption on CNTs of three water soluble pyrene derivatives was investigated. This study demonstrates that the diffusion effect can easily be eliminated by magnetic stirring. It also proves that more the CNT surface is flat (low curvature) and well graphitized, easier the adsorption is. In the second part of the work, the polyaromatic derivatives adsorption on the CNT surface is used to determine the specific surface of the samples with the help of BET and Langmuir equation. It is shown that the specific surface obtained corresponds to what is known for the CNT, taking into account their treatments (freeze-drying, high temperature evacuation, etc.).     

The doping of carbon nanotubes with nitrogen and their potential applications

This contribution provides a comprehensive overview of the experimental and theoretical topics related to the introduction of nitrogen into both single- and multi-walled carbon nanotube structures. It covers the synthesis, characterization and analysis of the potential applications of carbon nanotubes based on intrinsic changes in properties induced upon nitrogen incorporation. The reason why nitrogen-doped carbon nanotubes are the target of several investigations is explained not only from the state-of-the-art research point of view but special attention is given to present the results available in the literature weighed against the ideal materials expected for applications. A comparison with other nitrogen-doped carbon systems is also provided.     

Enhancing the catalytic activity of carbon nanotubes by nitrogen doping in the selective liquid phase oxidation of benzyl alcohol

Nitrogen-doped carbon nanotubes (N-CNTs) were prepared by chemical vapor deposition method and employed as carbon-based catalysts for selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen as the terminal oxidant under the mild reaction conditions. The results showed that the N-CNTs exhibited much higher activity than the undoped CNTs, and the improved catalytic activity was probably attributed to the introduction of electron-rich nitrogen atoms in the graphitic domains enhanced electron transfer. Moreover, N-CNTs displayed excellent stability without an obvious loss in activity and selectivity for benzyl alcohol oxidation after eight cycling reactions. The results presented herein pave the way for the development of novel carbon catalyst for the liquid-phase oxidation of benzyl alcohol.     

Effect of polymer chain length on the solubility of polystyrene grafted single‐walled carbon nanotubes in tetrahydrofuran

BACKGROUND: While carbon nanotubes are highly interesting materials for a variety of applications, their inherent insolubility limits widespread applications and solution‐phase processing. It is known that chemical functionalization can overcome this insolubility problem, and covalent grafting of polymers to the nanotube surface has been shown to be effective. In this study, the effect of polymer molecular weight on the solubility of polymer–nanotube conjugates was investigated. RESULTS: A series of nitroxide‐capped polystyrene polymers ranging in molecular weight from 2900 to 105 000 g mol^?1 were grafted to single‐walled carbon nanotubes (SWNTs). The resulting polystyrene–SWNT conjugates exhibited different degrees of solubility in tetrahydrofuran. Subsequent thermogravimetric and UV‐visible spectroscopy analyses indicated that carbon nanotube solubility reached a maximum when a polymer sample with a weight‐average molecular weight of 10 000 g mol^?1 was used. Higher and lower molecular weights resulted in reduced solubilities. CONCLUSION: Polymer chains of intermediate length maximize SWNT solubility, while lengths that are too low or too high seem to diminish the ability of the polymer–SWNT conjugates to remain in solution. Copyright © 2008 Society of Chemical Industry     

Synthesis,characterization, and electrical properties of nitrogen-doped single-walled carbon nanotubes with different nitrogen content

Nitrogen-doped single walled carbon nanotubes (SWCNTs) have been synthesized via the thermal decomposition of ferrocene using different ratios of acetonitrile/ethanol feedstock mixtures during the chemical vapor deposition process. The experiments were performed at 950 °C and 2 bar. The concentration of acetonitrile in the mixtures was varied from 0% to 100%. High resolution transmission electron microscopy and Raman spectroscopical measurements revealed the formation of SWCNTs for all mixtures. X-ray photoelectron spectroscopical analysis show nitrogen doping levels of up to 2 at.%. The doping levels increase as the acetonitrile concentration increases. The nitrogen incorporation is predominantly in the pyridine form. Electrical conductivity measurements show the dependence of conductivity as a function of nitrogen incorporation in the SWCNTs.     

On the bonding environment of phosphorus in purified doped single-walled carbon nanotubes

In this work, phosphorous-doped single-walled carbon nanotubes have been synthesized by the thermal decomposition of trimethylphosphine using a high-vacuum chemical vapor deposition method. Furthermore, a modified density-gradient-ultracentrifugation process has been applied to carefully purify our doped material. The combined use of Raman and X-ray photoelectron spectroscopy allowed us to provide the first insight into the bonding environment of P incorporated into the carbon lattice, avoiding competing signals arising from synthesis byproducts. This study represents the first step toward the identification of the bonding configuration of P atoms when direct substitution takes place.     

Hierarchical morphology of carbon single-walled nanotubes during sonication in an aliphatic diamine

Dispersion of single-walled carbon nanotubes (SWNTs) by sonication into diamine curing agents is studied as a means to improve the dispersion of SWNTs in cured epoxy. Cured and uncured specimens are analyzed by light microscopy, electron microscopy, light scattering (LS), ultra small-angle X-ray scattering (USAXS), electrical conductivity and Raman spectroscopy. A flexible diamine (D2000) forms a stable SWNT suspension leading to good homogeneity in both the diamine and the cured epoxy. High resolution transmission electron microscopy (TEM) shows that small ropes of SWNTs (mostly under 15 nm) are present despite the sample's visual homogeneity. Further morphological investigation of cured and uncured D2000 resins using light and small-angle X-ray scattering indicates that the SWNTs are networked into fractal clusters that electrically percolate at low SWNTs loadings (0.05 wt%).     

Direct and large scale electric arc discharge synthesis of boron and nitrogen doped single-walled carbon nanotubes and their electronic properties

Boron and nitrogen co-doped single-walled carbon nanotubes (BN-SWCNTs) were directly synthesized at large scale using an electric arc discharge method. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and UV-vis-NIR spectroscopy were performed to investigate structure and properties of BN-SWCNTs. These results show that the band gaps of SWCNTs have been tuned greatly with B and N doping.     

Calculation of the chirality-dependent orbital magnetic anisotropy in doped semiconducting single-walled carbon nanotubes

We calculate the orbital magnetic anisotropy (Δχ) of semiconducting single-walled carbon nanotubes at different carrier densities using a nearest-neighbor tight-binding model. Kataura plots of Δχ exhibit 2n + m family groupings and chiral index dependence at all carrier densities which are consistent with the trigonal warping effect. The diameter dependence of Δχ varies strongly with carrier density. We fit our data with a symmetry-restricted model to obtain approximate analytic expressions for Δχ as a function of nanotube chirality and carrier density. Our results illustrate the important role of doping on the magnetic properties of carbon nanotubes. Experimental studies of Δχ should take these effects into account for accurate interpretation of their results.     

Comparison of structural changes in nitrogen and boron-doped multi-walled carbon nanotubes

We investigated the effect of the reaction parameters on the structure of multi-walled carbon nanotubes containing different concentrations of nitrogen and boron. The nanotubes were produced using a ‘standard’ aerosol chemical vapour deposition technique in conjunction with benzylamine, triethylborane, hexane and toluene mixtures. These precursors were thermally decomposed between 800 and 1100 °C under argon at atmospheric pressure. By varying the precursor concentrations, the nitrogen and boron content of the nanotubes could be altered between 0-2.2 and 0-0.5 at.% respectively. Using a typical laboratory-sized 50 cm long tube furnace, yields between 0.3 and 1.5 g of nanotubes/10 min were relatively easily achieved. Moreover, we show that doping carbon nanotubes with heteroatoms, such as B and N, can be used to control nanotube diameters, change their defect density, and manipulate their oxidation resistance within a range of ca. 170 °C. Hence, we show that it is possible to tune nanotube properties within a certain interval and to produce nanotubes with relatively well defined properties in quantities usable for further characterisation and for studying their viability in applications such as composite materials, gas sensors, capacitors, and electronic components.