Adsorption and diffusion of molecular nitrogen in single wall carbon nanotubes

Using molecular simulation, the adsorption and self-diffusion of diatomic nitrogen molecules inside a single wall carbon nanotube have been studied over a range of nanotube diameters (8.61-15.66 A) and loadings at temperatures of 100 and 298 K. Nitrogen adsorption energy is found to increase as the nanotube diameter is reduced toward the molecular diameter of nitrogen. A discrete organization of the nitrogen into adsorbed layers is observed at high loadings that follows a regular progression determined primarily by geometric considerations. The formation of an adsorbate core at the center of the nanotube is found to increase the self-diffusion of nitrogen. A "wormlike" phase is found for the adsorbed nitrogen in the (15, 0) carbon nanotube at high loadings and at 100 K.     

Phenanthrene adsorption from solution on single wall carbon nanotubes

Phenanthrene was adsorbed from ethanol solution to the surface of single wall carbon nanotubes, which were previously physically and chemically characterized. Different anionic surfactants were added in the solutions to enhance the phenanthrene solubility and apparently have also improved the dispersion of two respective nanotube samples used. Adsorbed amount was determined through the concentration difference measured by UV-visible spectrophotometry. Results suggest that adsorption of phenanthrene is extremely improved in the case of nanotube purified with higher quality. These findings were confirmed by X-ray photoelectron spectroscopy. The influence of the surfactant on the adsorption kinetics of phenanthrene is suggested to be significant as well.     

Adsorption of xenon on purified HiPco single walled carbon nanotubes

We have measured adsorption of xenon on purified HiPco single-walled carbon nanotubes (SWNTs) for coverages in the first layer. We compare the results on this substrate to those our group obtained in earlier measurements on lower purity arc-discharge produced nanotubes. To obtain an estimate for the binding energy of Xe, we measured five low-coverage isotherms for temperatures between 220 and 260 K. We determined a value of 256 meV for the binding energy; this value is 9% lower than the value we found for arc discharge nanotubes and is 1.59 times the value found for this quantity on planar graphite. We have measured five full monolayer isotherms between 150 and 175 K. We have used these data to obtain the coverage dependence of the isosteric heat. The experimental values obtained are compared with previously published computer simulation results for this quantity.     

Theoretical characterization of thioepoxidated single wall carbon nanotubes

We have studied the external addition of sulfur to the walls of the (5,5) and (10,0) SWCNTs forming a cyclic thioepoxide. The binding energies are close to 32 kcal/mol, but they can be increased to 41 kcal/mol if the sulfur atoms are added forming a line along the axis of the (10,0) SWCNT. The addition of sulfur atoms to the (5,5) SWCNT alters the DOS but the tubes remains metallic. However, for the (10,0) SWCNT the exothermic addition of sulfur atoms can induce strong changes in the DOS, depending on the amount of sulfur atoms added. When we included one sulfur per 120 carbons, the (10,0) SWCNT showed metallic properties.     

Covalent sidewall functionalization of single wall carbon nanotubes

Alkyllithium reagents may be used to attach alkyl groups to the sidewalls of fluoro nanotubes. Thermal gravimetric analysis combined with UV-vis-Nir spectroscopy has been used to provide a quantitative measure of the degree of functionalization. SWNTs prepared using the HiPco process exhibit a higher degree of alkylation than SWNTs from the laser-oven method, indicating that the smaller diameter fluoro tubes are alkylated more readily. The spectral signature of the pristine SWNTs can be regenerated when the alkylated SWNTs are heated in Ar at 500 degrees C, demonstrating that dealkylation occurs at this temperature. TGA-MS analysis using a sample of n-butylated h-SWNTs showed that 1-butene and n-butane are formed during thermolysis.     

Thermochemistry of fluorinated single wall carbon nanotubes.

The gradient corrected Perdew-Burke-Ernzerhof density functional in conjunction with a 3-21G basis set and periodic boundary conditions was employed to investigate the geometries and energies of C(2)F fluorinated armchair single wall carbon nanotubes (F-SWNT's) with diameters ranging from 16.4 to 4.2 A [(12,12) to (3,3)] as well as a C(2)F graphene sheet fluorinated on one side only. Using an isodesmic equation, we find that the thermodynamic stability of F-SWNT's increases with decreasing tube diameter. On the other hand, the mean bond dissociation energies of the C-F bonds increase as the tubes become thinner. The C-F bonds in the (5,5) F-SWNT's are about as strong as those in graphite fluoride (CF)(n)() and are also covalent albeit slightly (<0.04 A) stretched. Whereas a fluorine atom is found not to bind covalently to the concave surface of [60]fullerene, endohedral covalent binding is possible inside a (5,5) SWNT despite a diameter similar to that of the C(60) cage.     

Interaction between alkyl radicals and single wall carbon nanotubes

The addition of primary, secondary, and tertiary alkyl radicals to single wall carbon nanotubes (SWCNTs) was studied by means of dispersion corrected density functional theory. The PBE, B97‐D, M06‐L, and M06‐2X functionals were used. Consideration of Van der Waals interactions is essential to obtain accurate addition energies. In effect, the enthalpy changes at 298 K, for the addition of methyl, ethyl, isopropyl, and tert‐butyl radicals onto a (5,5) SWCNT are: ?25.7, ?25.1, ?22.4, and ?16.6 kcal/mol, at the M06‐2X level, respectively, whereas at PBE/6‐31G* level they are significantly lower: ?25.0, ?19.0, ?16.7, and ?5.0 kcal/mol respectively. Although the binding energies are small, the attached alkyl radicals are expected to be stable because of the large desorption barriers. The importance of nonbonded interactions was more noticeable as we moved from primary to tertiary alkyl radicals. Indeed, for the tert‐butyl radical, physisorption onto the (11,0) SWCNT is preferred rather than chemisorption. The bond dissociation energies determined for alkyl radicals and SWCNT follow the trend suggested by the consideration of radical stabilization energies. However, they are in disagreement with some degrees of functionalization observed in recent experiments. This discrepancy would stem from the fact that for some HiPco nanotubes, nonbonded interactions with alkyl radicals are stronger than covalent bonds. © 2012 Wiley Periodicals, Inc.     

Anion recognition by functionalized single wall carbon nanotubes

Amidoferrocenyl-functionalised single wall carbon nanotubes (Fc-SWNT) are efficient exoreceptors for the redox recognition of H2PO4-.     

单壁碳纳米管中甲烷吸附的分子模拟

采用巨正则系统MonteCarlo方法研究了甲烷在单壁碳纳米管(Singlewallcarbonnanotube,SWNT)中于低温74.05K下的吸附等温线及吸附机理,发现在两个较小的孔径(1.225nm和1.632nm)下单壁碳纳米管中甲烷的吸附有着明显的微孔所独有的“填充效应”,而在2.04nm以上的孔的吸附中会出现毛细凝聚现象。通过模拟知道发生毛细凝聚的必要条件是孔内能至少容纳下两层粒子,此外还导出在恒定温度下毛细凝聚吸附量与SWNT孔径关系。本文还模拟了常温300K下甲烷在SWNT内的吸附,对比了2.04nm和4.077nm两种孔径的SWNT吸附甲烷的等温线,推荐在4.077nm孔中的适宜吸附存储压力为5.0～6.0MPa,吸附质量分数可达16%～19%.     

Combining single wall carbon nanotubes and photoactive polymers for photoconversion

A combination of van der Waals and electrostatic interactions was used to integrate SWNT and a suitably functionalized polythiophene into nanostructured ITO electrodes. In the resulting electron donor/acceptor nanocomposites, polythiophene represents the light-harvesting chromophore that readily donates an excited-state electron to the ground-state electron-accepting SWNT. Upon illumination, monochromatic incident photoconversion efficiencies between 1.2 and 9.3% were determined for single and eight-sandwiched layers, respectively.     

Self-assembled lamellar structures with functionalized single wall carbon nanotubes

Highly ordered self-assembled multi-layer structures with denatured collagen wrapped single wall carbon nanotubes and surfactant systems were obtained through bioinspired methodology.     

Interfacing strong electron acceptors with single wall carbon nanotubes

The complementary use of steady-state and time-resolved spectroscopy in combination with electrochemistry and microscopy are indicative of mutual interactions between semiconducting SWNTs and a water-soluble strong electron acceptor, i.e., perylenediimide. Significant is the stability and the strong electronic coupling of the perylenediimide/SWNT electron donor-acceptor hybrids. Several spectroscopic and spectroelectrochemical techniques, i.e., Raman, absorption, and fluorescence, confirmed that distinct ground- and excited-state interactions occur and that kinetically and spectroscopically well characterized radical ion pair states form within a few picoseconds.     

Length separation of Zwitterion-functionalized single wall carbon nanotubes by GPC

The length-fractionation of shortened (250 to 25 nm), zwitterion-functionalized, single wall carbon nanotubes (SWNTs) has been demonstrated via gel permeation chromatography (GPC). The UV-Vis spectrum of each fraction indicates an apparent "solubilization", as evident by the direct observation of all predicted optically allowed interband transitions between the mirror image spikes in the density of states of both metallic and semiconducting SWNTs with various tube diameters. As evident by the presence or absence of the 270 nm, pi-plasmon absorption, this "solubilization" is a dynamic process and leads to re-aggregation if left undisturbed for a couple of weeks or upon dissociation of the pendant octadecylamine groups. This non-destructive and highly versatile separation methodology opens up an array of possible applications for shortened SWNTs in nanostructured devices.     

The effect of hydroxyl group on the electronic structure of carbon nanotubes with different diameters

A single hydroxyl group is functionalized on both sides of one ring of several carbon nanotubes (CNT) as CNT–OH. The electronic structure and chemical bonding parameters are studied with the help of quantum theory of atoms in molecules (QTAIM). Anionic states of the CNT–O as deprotonated hydroxyl are studied in order to get insight into the nature of CNT–OH species, considering frozen and relaxed geometries of CNT–O compounds. The results show a significant difference between inside or outside substituted hydroxyl groups; and also complicated behavior of the CNT’s diameter, and it can be concluded that hydroxyl group can be used to tune the CNT’s properties, effectively, in interesting application of these nanostructures.     

Molecular dynamics simulation of single wall carbon nanotubes polymerization under compression

Single wall carbon nanotubes (SWCNTs) often aggregate into bundles of hundreds of weakly interacting tubes. Their cross-polymerization opens new possibilities for the creation of new super-hard materials. New mechanical and electronic properties are expected from these condensed structures, as well as novel potential applications. Previous theoretical results presented geometric modifications involving changes in the radial section of the compressed tubes as the explanation to the experimental measurements of structural changes during tube compression. We report here results from molecular dynamics simulations of the SWCNTs polymerization for small diameter arm chair tubes under compression. Hydrostatic and piston-type compression of SWCNTs have been simulated for different temperatures and rates of compression. Our results indicate that large diameter tubes (10,10) are unlike to polymerize while small diameter ones (around 5 A) polymerize even at room temperature. Other interesting results are the observation of the appearance of spontaneous scroll-like structures and also the so-called tubulane motifs, which were predicted in the literature more than a decade ago.     

Selective photochemical functionalization of surfactant-dispersed single wall carbon nanotubes in water

Ultraviolet (UV) irradiation of single wall carbon nanotubes (SWCNTs) individually dispersed in surfactants leads to diameter and type-selective photohydroxylation of the nanotubes. Photohydroxylation of first semiconductor and then small diameter metallic SWCNTs was confirmed after 254 nm UV irradiation in acidic, neutral, and basic aqueous solutions at ambient and elevated temperatures. The increased oxygen content of the SWCNTs after UV irradiation, as detected by X-ray photoelectron spectroscopy, suggests that SWCNTs were hydroxylated by reaction with water. Attenuated total reflectance Fourier transform infrared analysis provides evidence of hydroxyl functional groups on their surface. This photochemical reaction is impeded by molecular oxygen and appears to involve a reactive intermediate generated in the vicinity of semiconducting SWCNTs. This represents a noncontaminating selective reaction in the liquid phase that uses an intrinsic property of the tubes.     

Adsorption and desorption of atrazine on carbon nanotubes

The potential impact of carbon nanotubes (CNTs) on human health and the environment is receiving more and more attention. The high surface area of CNTs tends to adsorb a large variety of toxic chemicals, which may enhance the toxicity of CNTs and/or toxic chemicals. In this study, adsorption and desorption of atrazine on carbon nanotubes from aqueous solution were studied through batch reactors. The adsorption equilibrium isotherms were nonlinear and were fitted by Freundlich, Langmuir, and Polanyi-Manes models. It was found that the Polanyi-Manes model described the adsorption process better than other two isotherm models. Together with the "characteristic curve," the Polanyi adsorption potential theory is applicable to describe the adsorption process of atrazine on CNTs. Thermodynamic calculations indicated that the adsorption reaction of atrazine on CNTs is spontaneous and exothermic. The desorption data showed that no significant desorption hysteresis occurred. High adsorption capacity and adsorption reversibility of atrazine on CNTs suggest that CNTs have high health and environmental risks, whereas they have potential applications for atrazine removal from water.     

Air separation by single wall carbon nanotubes: thermodynamics and adsorptive selectivity

Separation of a nitrogen-oxygen mixture (air) by single wall carbon nanotubes has been studied using grand canonical Monte Carlo simulations at a range of nanotube diameters, temperatures, and pressures. It is demonstrated that depending on these operating parameters, the extent of adsorptive selectivity can vary significantly. Detailed calculations are also presented for the adsorption isotherms, energies, and isosteric heats of pure nitrogen, oxygen, and their mixture at 100 K in a carbon nanotube of 12.53-A diameter. In single-component simulations, it is found that near saturation loading nitrogen forms only an annular layer close to the nanotube wall, while smaller-sized oxygen also occupies the region near the center of the nanotube. In mixture adsorption, the energetically favored nitrogen is preferentially adsorbed at low loadings. However, at high loadings oxygen replaces nitrogen due to the dominant entropic effects, and therefore a high selectivity towards oxygen is observed close to the saturation loading. The effect of the entropic change on mixture adsorption is evident from the calculated isosteric heats of adsorption. The mixture isotherms obtained from simulations are found to be in good agreement with the predictions based only on the pure component simulation results.     

Interactions in single wall carbon nanotubes/pyrene/porphyrin nanohybrids

This work provides an in-depth look at a range of physicochemical aspects of (i) single wall carbon nanotubes (SWNT), (ii) pyrene derivatives (pyrene(+)), (iii) porphyrin derivatives (ZnP(8)()(-)() and H(2)()P(8)()(-)()), (iv) poly(sodium 4-styrenesulfonate), and (v) their combinations. Implicit in their supramolecular combinations is the hierarchical integration of SWNT (as electron acceptors), together with ZnP(8)()(-)() or H(2)()P(8)()(-)() (as electron donors), in an aqueous environment mediated through pyrene(+). This supramolecular approach yields novel electron donor-acceptor nanohybrids (SWNT/pyrene(+)/ZnP(8)()(-)() or SWNT/pyrene(+)/H(2)()P(8)()(-)()). In particular, we report on electrochemical and photophysical investigations that as a whole suggest sizeable and appreciable interactions between the individual components. The key step to form SWNT/pyrene(+)()/ZnP(8)()(-)() or SWNT/pyrene(+)()/H(2)()P(8)()(-)() hybrids is pi-pi interactions between SWNT and pyrene(+), for which we have developed for the first time a sensitive marker. The marker is the monomeric pyrene fluorescence, which although quenched is (i) only present in SWNT/pyrene(+) and (ii) completely lacking in just pyrene(+). Electrostatic interactions help to immobilize ZnP(8)()(-)() or H(2)()P(8)()(-)() onto SWNT/pyrene(+) to yield the final electron donor-acceptor nanohybrids. A series of photochemical experiments confirm that long-lived radical ion pairs are formed as a product of a rapid excited-state deactivation of ZnP(8)()(-)() or H(2)()P(8)()(-)(). This formation is fully rationalized on the basis of the properties of the individual moieties. Additional modeling shows that the data are likely to be relevant to the SWNTs present in the sample, which possess wider diameters.     

Enhanced preconcentration of selected chlorofluorocarbons on multiwalled carbon nanotubes with polar functionalities

Chromatographic monitoring of chlorofluorocarbons in air requires the preconcentration of these highly volatile species. In this paper, we present functionalized multiwalled carbon nanotubes as effective sorbents for a microtrap designed for chlorofluorocarbons preconcentration. Among the commercial carbons and carbon nanotubes studied, functionalization via carboxylation and propyl amine was most effective for dichlorofluoromethane and trichlorofluoromethane (Freon 11), which were selected as representative chlorofluorocarbons. The results show that carbon nanotubes functionalized with a polar groups led to as much as a 300% increase in breakthrough volume and the desorption bandwidth was reduced by 2.5 times.