Dispersion of single-walled carbon nanotubes in dimethylacetamide and a dimethylacetamide–cholic acid mixture

A way of dispersing single-walled carbon nanotubes in preparing stable suspensions with high concentrations of individual nanotubes in amide solvents is described. The obtained suspensions are studied via Raman spectroscopy. The dependence of the degree of single-walled carbon nanotube (SWNT) dispersion in individual and mixed amide solvents on the type of solvent, the mass of nanotubes, and the concentration of cholic acid is established. A technique for processing spectral data to estimate the diameters and chiralities of individual nanotubes in suspension is described in detail.     

Experimental study on rheological behavior of water–ethylene glycol mixture in the presence of functionalized multi-walled carbon nanotubes

Journal of Thermal Analysis and Calorimetry - This paper examines the rheological behavior of water (60%vol.)–ethylene glycol (40%vol.) mixture in the presence of functionalized multi-walled...     

Radiation-induced grafting of multi-walled carbon nanotubes in glycidyl methacrylate–maleic acid binary aqueous solution

With the aim to improve the compatibility between multi-walled carbon nanotubes (MWCNTs) and nylon-6, purified MWCNTs (p-MWCNTs) were grafted successfully with glycidyl methacrylate–maleic acid in aqueous solution using a single-step radiation method. The chemical structure and morphology of grafted p-MWCNTs (g-MWCNTs) was investigated by micro-FTIR, Raman spectroscopy and transmission electron microscopy. The prepared nylon-6/g-MWCNTs composite has higher mechanical strength and heat distortion temperature due to improved dispersion and compatibility than those of nylon-6/p-MWCNTs.     

Multi-walled carbon nanotubes–dispersive solid-phase extraction combined with nano-liquid chromatography for the analysis of pesticides in water samples

In this work, the simultaneous separation of a group of 12 pesticides (carbaryl, fensulfothion, mecoprop, fenamiphos, haloxyfop, diclofop, fipronil, profenofos, fonofos, disulfoton, nitrofen, and terbufos) by nano-liquid chromatography with UV detection is described. For the analyses, a 100 μm internal diameter capillary column packed with silica modified with phenyl groups was used. Experimental parameters, including the use of a trapping column for increasing the sensitivity, were optimized and validated. A preliminary study of the applicability of a rapid and practical dispersive solid-phase extraction (DSPE) procedure was developed for the extraction of some of these pesticides (carbaryl, fensulfothion, fenamiphos, fipronil, profenofos, fonofos, disulfoton, nitrofen, and terbufos) from Milli-Q water samples using multi-walled carbon nanotubes (MWCNTs). The method was validated through a recovery study at three different levels of concentration, obtaining limits of detection in the range 0.016–0.067 μg/L (below European Union maximum residue limits) for the majority of the pesticides. In this work, MWCNTs were reused up to five times, representing an important reduction of the waste of stationary phase. Furthermore, DSPE permitted a clear diminution of the total sample treatment time with respect to conventional SPE.     

Hydrogen adsorption in the series of carbon nanostructures: Graphenes–graphene nanotubes–nanocrystallites

A comparative analysis of hydrogen absorption capability is performed for the first time for three types of carbon nanostructures: graphenes, oriented carbon nanotubes with graphene walls (OCNTGs), and pyrocarbon nanocrystallites (PCNs) synthesized in the pores of TRUMEM ultrafiltration membranes with mean diameters (D_m) of 50 and 90 nm, using methane as the pyrolized gas. The morphology of the carbon nanostructures is studied by means of powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). Hydrogen adsorption is investigated via thermogravimetric analysis (TGA) in combination with mass-spectrometry. It is shown that only OCNTGs can adsorb and store hydrogen, the desorption of which under atmospheric pressure occurs at a temperature of around 175°C. Hydrogen adsorption by OCNTGs is quantitatively determined and found to be about 1.5% of their mass. Applying certain assumptions, the relationship between the mass of carbon required for the formation of single-wall OCNTGs in membrane pores and the surface area of pores is established. Numerical factor Ψ = m_dep/m_calc, where m_dep is the actual mass of carbon deposited upon the formation of OCNTGs and mcalc is the calculated mass of carbon necessary for the formation of OCNTGs is introduced. It is found that the dependence of specific hydrogen adsorption on the magnitude of the factor has a maximum at Ψ = 1.2, and OCNTGs can adsorb and store hydrogen in the interval 0.4 to 0.6 < Ψ < 1.5 to 1.7. Possible mechanisms of hydrogen adsorption and its relationship to the structure of carbon nanoformations are examined.     

Flow structure of water in carbon nanotubes: poiseuille type or plug-like?

We have conducted molecular dynamics simulations of water flow in carbon nanotubes (CNTs) for (6,6) to (20,20) CNTs at a streaming velocity of 100 ms. The fluidized piston model (FPM) and the ice piston model (IPM) are employed to drive flow through the CNTs. The results show that the single-file water flow inside (6,6) CNT has a convex upward streaming velocity profile, whereas the velocity profiles in (10,10) to (20,20) CNTs are flat except near the tube wall. The flow structure of cylindrical water in the (8,8) CNT is intermediate between that for the (6,6) CNT and the larger CNTs. The flow parameters are found not to exhibit any dependence on streaming velocity at up to 300 ms in the (12,12) CNT. The hydrogen bond lifetimes of water flowing in CNTs tend to be longer than for the corresponding equilibrium states, and nonzero flow does not reduce the microscopic structure or structural robustness (hydrogen bond lifetime). Although the atomic density profile varies with tube diameter, reflecting the change in static microscopic structure of flow from single file to cylindrical, tube diameter does not induce a clear transition in streaming velocity, temperature, or hydrogen bond lifetime over this diameter range. The results suggest that water flow in CNTs of this size is more pluglike than Poiseuille type, although the flow structure does not strictly accord with either definition.     

Adsorptive characteristics of isoniazid on powdered activated carbon: π–π Dispersion interactions at the solid–solution interface

The presence of antibiotic residues in the aquatic environment poses a potential risk to living organisms due to the development of antibiotic resistance in bacteria. In the present study, the removal of isoniazid by commercial powdered activated carbon was studied in aqueous solutions. The adsorption experiments were done as a function of time, concentration, temperature, and pH in order to understand the adsorption mechanism. The Langmuir and the Freundlich isotherms were used to model the equilibrium data. The results showed that isoniazid was physisorbed on the surface of the activated carbon by π–π dispersion interactions.     

Flow injection solid-phase extraction using multi-walled carbon nanotubes packed micro-column for the determination of polycyclic aromatic hydrocarbons in water by gas chromatography–mass spectrometry

A flow injection solid-phase extraction preconcentration system using a multi-walled carbon nanotubes (MWCNTs) packed micro-column was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in water by gas chromatography–mass spectrometry (GC–MS). The preconcentration of PAHs on the MWCNTs was carried out based on the adsorption retention of analytes by on-line introducing the sample into the micro-column system. Methanol was introduced to elute the retained analytes for GC–MS analysis using selected ion monitoring (SIM) mode. Important influence factors were studied in detail, such as sample acidity, sample flow rate, eluent flow rate and volume, dimensions of MWCNTs and amounts of packing material. Limits of detection of 16 PAHs for an extraction of 50 mL water sample were in the range of 0.001–0.15 μg L⁻¹, and the precisions (RSD) were in the range of 4–14%. The optimized method was successfully applied to the determination of 16 PAHs in surface waters, with recoveries in the range of 72–93% for real spiked sample.     

Combination self-assembly of β-sheet peptides and carbon nanotubes: functionalizing carbon nanotubes with bioactive β-sheet block copolypeptides

Understanding the self-assembly behavior of β-sheet peptides is important, not only in constructing bioactive peptide nanostructures, but also in inhibiting uncontrollable protein aggregation in protein-misfolding diseases. Here, the first systematic investigation of combination self-assembly between β-sheet block copolypeptides and CNTs is presented, demonstrating the presence of several different association modes during the combination self-assembly process. Bioactive β-sheet block copolypeptides can self-assemble by themselves, or can be used to functionalize CNT hybrids depending on the situation. This behavior may be important both for fabricating bioactive peptide/CNT hybrids and for controlling/inhibiting protein-misfolding diseases.     

Towards surface acid–base property of the carboxylic multi-walled carbon nanotubes by zero current potentiometry

The surface acid–base property of carboxylic multi-walled carbon nanotubes (MWNTs) is investigated by zero current potentiometry with a new electrochemical measurement system. The pH dependent interface potential variation at the interface of carboxylic MWNTs/solution is investigated by measuring zero current potential E_zcp. In the pH range of 1–11, the pH response of carboxylic MWNTs exhibits two linear relationships according to the following equations: E_zcp = 0.791–0.0535 pH (pH 1–5.1) and E_zcp = 0.643–0.0241 pH (pH 5.1–11), respectively. The intersection at pH 5.1 of two regions indicates the surface pK_a value of carboxylic group terminated MWNTs.     

One-step synthesis of water–dispersible carbon nanocapsules by pulsed arc discharge over aqueous solution under pressurized argon

Research on Chemical Intermediates - Water–dispersible carbon nanocapsules were synthesized in a one-step process by a pulsed arc discharge over glycine solution under pressurized argon....     

Test of the water adsorption model of organic electrocatalysis in the carbon monoxide–silver system in alkaline medium

A test has been carried out of the model of T. Iwasita, X.H. Xia, H.-D. Liess, W. Vielstich [J. Phys. Chem. B. 101 (1997) 7542], according to which the maximum at about the same potential in both the positive and negative sweeps in cyclic voltammograms (CVs) of small organic molecules on Pt is due to the concurrence of two processes with opposite potential dependences, adsorption of the organic compound and electrooxidation of its intermediates, which decrease and increase, respectively, with increasing potential. In turn, the decrease with increasing potential of the adsorption of the undissociated organic is due to its increasing displacement by molecular water, this competition occurring because the two molecular compounds have similar, low values of the adsorption energy. According to the model of T. Iwasita, X.H. Xia, H.-D. Liess, W. Vielstich [J. Phys. Chem. B. 101 (1997) 7542], with CO on Pt no anodic currents are observed in the negative sweep because of the high adsorption energy of CO on Pt, which precludes its displacement by water. Therefore, the model has been tested with the CO–Ag system, for which anodic currents should be observed in the negative sweep, since the adsorption energy of CO on Ag is very low. Effectively, this has been found to be the case, which indicates that the model is indeed applicable to the CO–Ag system over the tested pH range, 10–14. At pH⩽11 adsorbed CO was displaced from the surface of Ag by N₂ bubbling, while it was not at pH⩾12. However, even at pH⩾12 the adsorption energy of CO on Ag should be rather weak, since anodic currents appeared in the negative sweep in CO-saturated solution over the whole pH range tested, 10–14.     

Micellisation thermodynamics of sodium lauroylsarcosinate in water–alcohol binary mixtures

Aggregation of sodium lauroylsarcosinate (SLS) in aqueous solutions of methanol, ethanol, propanol and ethylene glycol at 288–313 K has been determined from conductivity measurement in the range 0–20% v/v of additives. The precise values of the critical micelle concentration (CMC) and the degree of counter-ion dissociation of micelles were obtained at each temperature by fitting the specific conductivity-surfactant concentration curve to the integrated form of the Boltzmann-sigmoid equation. The CMC was found to increase with increase in additive concentrations in the case of methanol and ethylene glycol, while it decreases with increase in ethanol and propanol concentration. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellisation. The Gibbs free energies were observed to vary only slightly with temperature and additive concentrations. Enthalpy–entropy compensation was observed for all the systems with a constant compensation temperature of ≈300 K and negative compensation enthalpy.