Adsorption Of Carbon Nanotubes Research Articles

Piezoresistive Silicon Microresonator for Measurements of Hydrogen Adsorption in Carbon Nanotubes

In this paper, the mass detection of hydrogen adsorption using a piezoresistive resonant silicon microresonator is presented. The working principle relies on the resonant frequency shifts of the cantilevered resonator with a sample due to hydrogen adsorption. The mass of adsorbed hydrogen in carbon nanotubes (CNTs) grown on the resonator is measured experimentally after exposing to high pressure hydrogen. The mass of CNTs on the resonator is measured from resonant frequency change after the removal. According to masses of the adsorbed hydrogen and CNTs, we obtain the adsorption capacity of hydrogen into CNTs.

Magnetic carbon nanotubes synthesis by Fenton’s reagent method and their potential application for removal of azo dye from aqueous solution

We report a simple and easy method to fabricate magnetic carbon nanotubes (CNTs) by Fenton’s reagent method without the addition of any cations. H2O2 was added slowly into the FeSO4 solution mixed with purified CNTs, and the resulting reactants were placed into a quartz tube to undergo heat treatment under a nitrogen/hydrogen flow. Iron oxide (Fe2O3) nanoparticles were uniformly dispersed on CNTs without any pretreatment such as strong acid or covalent functionalization processes. The as-produced magnetic CNTs were usedas an adsorbent forremovalof methyl orange (MO) dye fromaqueous solutions. Adsorption experiments indicated that the magnetic CNTs have good adsorption capacity (qe) of MO (28mg/g). The Freundlich isotherm model fitted the experiment databetter than the Langmuirisothermmode. The mean energy of adsorption was calculated as 3.72kJ/mol based on the Dubinin–Radushkevich model, which suggests that theremoval process was dominated by physical adsorption. Kinetic regression results showed that the adsorption kinetics was more accurately represented by a pseudo second-order model. Intra-particle diffusionwasinvolved in the adsorption process, but it was not the only rate-controlling step. More importantly, a new photocatalytic regeneration technology can be enabled by the high nanoscale iron oxide loading (50%). The magnetic CNT adsorbents could be effectively and quickly separated by applying an external magnetic field and regenerated by UV photocatalysis. Therefore, CNTs/λ-Fe2O3 hybrid is a promising magnetic nanomaterial for preconcentration and separation of organic pollutants for environmental remediation.

The use of flake powder metallurgy to produce carbon nanotube (CNT)/aluminum composites with a homogenous CNT distribution

A strategy called flake powder metallurgy (flake PM) was used to achieve a uniform distribution of carbon nanotubes (CNTs) in CNT/Al composites and thus realize the potential of CNTs as a reinforcement. It consists of the addressing of the incompatibilities of Al powders with CNTs, uniform adsorption of CNTs onto the Al nanoflake surface by slurry blending and consolidation of as-prepared CNT/Al composite powders by hot extrusion. By changing spherical Al powders to nanoflakes and surface modifying them with a polyvinyl alcohol hydrosol, flake PM achieved high compatibilities of Al powders with CNTs, in terms of both surface properties and geometries. Thus, it essentially exploits the fact that a homogeneous and individual distribution of CNTs in Al powders can be achieved simply by direct slurry blending. Moreover, the structural integrity of the CNTs was well maintained in the final composites since CNTs were protected from high energy physics force such as ballmilling. As a consequence, a strong and ductile CNT/Al composite with tensile strength of 435MPa and plasticity of 6% was fabricated, which greatly surpasses values for materials fabricated by conventional methods.

Ultrasonication induced adsorption of carbon nanotubes onto electrospun nanofibers with improved thermal and electrical performances

Ultrasonication was employed to induce the uniform adsorption of carbon nanotubes (CNTs) onto electrospun polymer nanofiber (EPNF) surfaces. Compared with pristine CNTs, acid treated CNTs became shorter, which facilitated their decoration onto the EPNF surfaces more tightly and densely. Under ultrasonication, CNTs possessing strong energy hit the EPNF drastically, leading to the partial softening of the EPNF at the impact sites, and then the CNTs could be successfully embedded into the EPNF surface. Our study demonstrated that CNT adsorption could not be achieved by the direct immersion of the EPNF into the CNT solution, even at elevated temperatures. It was also found that the existence of surfactant in the solution could prevent the CNTs adsorbing onto the fiber surface, which suggested that it was really a surfactant-free method. After CNT adsorption, the temperature for the maximum weight loss rate of the polyurethane (PU) nanofibers increased from 360.7 °C to 397.7 °C, which was attributed to the uniform dispersion of CNTs as well as the strong interaction between the CNTs and the polymer nanofibers. The conductivity was also significantly raised to 10 S m−1, derived from the formation of a conductive percolation network. Furthermore, porous nanofiber-like CNT cages could be obtained after the removal of the polymer component by pyrolysis. This approach provides a new avenue for harvesting CNT decorated nanofiber composites with improved performances.

Two-dimensional distribution of carbon nanotubes in copper flake powders

We report an approach of flake powder metallurgy to the uniform, two-dimensional (2D)distribution of carbon nanotubes (CNTs) in Cu flake powders. It consists of thepreparation of Cu flakes by ball milling in an imidazoline derivative (IMD) aqueoussolution, surface modification of Cu flakes with polyvinyl alcohol (PVA) hydrosoland adsorption of CNTs from a CNT aqueous suspension. During ball milling, ahydrophobic monolayer of IMD is adsorbed on the surface of the Cu flakes, on top ofwhich a hydrophilic PVA film is adsorbed subsequently. This PVA film couldfurther interact with the carboxyl-group functionalized CNTs and act to lock theCNTs onto the surfaces of the Cu flakes. The CNT volume fraction is controlledeasily by adjusting the concentration/volume of CNT aqueous suspension and Cuflake thickness. The as-prepared CNT/Cu composite flakes will serve as suitablebuilding blocks for the self-assembly of CNT/Cu laminated composites that enablethe full potential of 2D distributed CNTs to achieve high thermal conductivity.

Adsorption Behavior of Carbon Nanotubes on Polystyrene Surfaces

Polystyrene (PS) was prepared using two different polymerization methods (dispersion polymerization and seed polymerization) to investigate the steric stabilizer effect during the adsorption process of carbon nanotubes (CNTs) on the surface of PS microspheres. Experiments with different microsphere diameters and difference types of CNTs were conducted to analyze the curvature effect of the spheres on the adsorption mechanism. The results showed that PS microspheres prepared through dispersion polymerization exhibited preferable adsorption behavior compared to PS spheres prepared through seed polymerization, suggesting that poly(N-vinylpyrrolidone) led to improved adsorption interactions between the CNTs and the PS microspheres in the CNTs dispersion. Additionally, the PS diameter and CNT curvature were examined with respect to the adsorption behavior between the PS microspheres and the CNTs. Multiwalled carbon nanotubes (MWCNTs) were found to be well adsorbed on the surface of PS microspheres measuring 2 microm. However, the MWCNTs were adsorbed much less on the surface of submicron-sized PS microspheres, compared with thinwalled carbon nanotubes (TWCNTs). On the other hand, TWCNTs were found to be suitable for adsorption on submicron-sized PS microspheres. These results also indicate that the curvature of the CNTs and the polymer microspheres are important to the CNT adsorption process.

Reversible positioning at submicrometre scale of carbon nanotubes mediated by pH-sensitive poly(amino-methacrylate) patterns

The selective adsorption of carbon nanotubes (CNTs) on a pH-reversible PDMAEMA patterned gold surface is presented. In acidic conditions, a selective CNTs adsorption onto the polymer brushes is obtained due to ammonium-π interactions. The reversible behavior was shown by successive treatments in both alkaline and acidic solutions with CNTs.

Effects of Surface Curvature and Surface Strength on Argon Adsorption in Carbon Nanotubes at Temperatures below the Triple Point

This paper describes an investigation of argon adsorption into carbon nanotubes at temperatures below the triple point, using a grand canonical Monte Carlo simulation to study the effects of confinement and surface strength on the 2D transition. In large pores, it was found that 2D transitions can occur in more than one layer, but are absent in higher layers for small pores. The 2D critical temperature of the first layer for a small pore (R = 1.2 nm) was found to be ca. 66 K (MWCNT) and 65 K (SWCNT), compared to 55–59 K observed experimentally for a flat graphite surface. This is because of the overlapping effects due to the surface curvature or the confinement in a carbon nanotube. Assuming a weaker carbon surface by reducing the graphene surface strength by 40% for SWCNT, the 2D critical temperature was only modestly reduced to 63 K. This suggests that the experimental data at 59 K might be attributed to other factors, other than confinement effects. An imperfect surface is suggested and, employing 5% defects on this surface, the 2D critical temperature has been determined as 58 K which is in better agreement with the experimental value of 59 K.

Entropy-driven adsorption of carbon nanotubes on (0 0 1) and (1 1 1) surfaces of CeO 2 islands grown on sapphire substrate

According to the aim to compose combinatorial material by adsorption of carbon nanotubes onto the structured CeO 2 surface the interaction of the armchair (5,5) and zigzag (8,0) nanotubes with the (0 0 1) and (1 1 1) surfaces of CeO 2 islands have been investigated by theoretical methods. The thermodynamics of the adsorption were studied at the low surface coverage region. The interaction energy between the nanotube and the different CeO 2 surfaces shows significant increase when the size of the interface reaches 7–8 unit cells of CeO 2 and it remains unchanged in the larger interface region. However, the entropy term of the adsorption is significantly high when the distances of CeO 2 islands are equal to 27 nm (adsorption of armchair (5,5) nanotube) or 32 nm (adsorption of zigzag (8,0) nanotube). This property supports adsorption of nanotubes onto CeO 2 surfaces which possesses a very specific surface morphology. A long-wave vibration of nanotubes was identified as background of this unexpected phenomenon. This observation could be applicable in the development of such procedures where the nanotube adsorption parallel to the surface is aimed to perform.

Adsorption of Single Walled Carbon Nanotubes onto Silicon Oxide Surface Gradients of 3-Aminopropyltri(ethoxysilane) Described by Polymer Adsorption Theory

Integration of single-walled carbon nanotubes (SWNT) into complex sensing and electronic devices can necessitate the selective placement of individual nanotubes from solution onto custom-prepared surfaces. Existing studies indicate carbon nanotube adsorption can be controlled by creating hydrophilic and/or hydrophobic surfaces, depending on the nanotube surface chemistry and solvent. Various recipes exist for specific conditions, but no quantitative theoretical model describing experimental observations has been developed. This work examines the adsorption behavior of SWNT functionalized with aryl hydroxyl (OH-SWNT) or aryl carboxylic acid groups (COOH-SWNT) onto 3-aminopropyltri(ethoxysilane) (APTES) concentration gradients on SiO(2) wafers. For the first time, self-consistent field polymer adsorption theory is utilized to quantitatively describe SWNT adsorption onto planar surfaces. Experimental results indicate SWNT adsorption strongly depends on three key factors: concentration of APTES molecules on the silicon oxide and the type and number of SWNT functional groups. In general, COOH-SWNT adsorb to the greatest extent, followed by OH-SWNT and P2-SWNT. The data show a distinct threshold phenomenon, with appreciable adsorption detected only when the APTES concentration exceeded 2.6 x 10(14) molecules/cm(2).

Simulation of hydrogen adsorption in carbon nanotubes

The processes of physical hydrogen adsorption by carbon nanotubes are simulated by considering the molecular dynamics. The interactions are described by the Lennard-Jones potential and quantum effects are neglected. The dependences of the relative mass content of adsorbed hydrogen on the pressure and temperature are obtained. The formation of a second adsorption layer at low temperatures is detected. This leads to a higher stored hydrogen content.

Simultaneous determination of pesticides at trace levels in water using multiwalled carbon nanotubes as solid-phase extractant and multivariate calibration

The application of solid-phase extraction with multivariate calibration for simultaneous determination of three toxic pesticides in tap and reservoir waters was presented. The proposed analytical method was used for the determination of atrazine, methidathion, and propoxur in complex water samples without the need for chromatographic separation. Among the applied multivariate calibration methods, partial least squares (PLS-1) method was found the most effective for pesticides quantification. Multiwalled carbon nanotubes (MWCNTs) adsorbent showed a perfect extraction/preconcentration of pesticides present at trace levels. The experimental factors that affect pesticides extraction by MWCNTs adsorbent such as sample volume, eluent volume, solution pH, and extraction flow rate were studied and optimized. The figures of merit of the proposed method were: limits of detection 3, 2, and 3 μg l −1 and linear ranges 5–30, 3–60, and 5–40 μg l −1 for atrazine, methidathion, and propoxur, respectively. A good precision was reported for the method, R.S.D. values were always less than 5.0%. Satisfactory results were reported for simultaneous determination of trace levels of pesticides in complex matrices. In tap water, the percent recoveries for pesticides were extended from 95 to 104% and R.S.D. from 1 to 3%, while lower recoveries were observed in reservoir water: 84–93% (R.S.D.: 1–3). Although the pesticides can be accurately quantified by SPE and liquid chromatography, SPE–PLS-1 method was found simpler and operated at lower running costs.

Sensitive determination of amide herbicides in environmental water samples by a combination of solid‐phase extraction and dispersive liquid–liquid microextraction prior to GC–MS

In this paper, solid-phase extraction (SPE) in combination with dispersive liquid-liquid microextraction (DLLME) has been developed as a sample pretreatment method with high enrichment factors for the sensitive determination of amide herbicides in water samples. In SPE-DLLME, amide herbicides were adsorbed quantitatively from a large volume of aqueous samples (100 mL) onto a multiwalled carbon nanotube adsorbent (100 mg). After elution of the target compounds from the adsorbent with acetone, the DLLME technique was performed on the resulting solution. Finally, the analytes in the extraction solvent were determined by gas chromatography-mass spectrometry. Some important extraction parameters, such as flow rate of sample, breakthrough volume, sample pH, type and volume of the elution solvent, as well as salt addition, were studied and optimized in detail. Under optimum conditions, high enrichment factors ranging from 6593 to 7873 were achieved in less than 10 min. There was linearity over the range of 0.01-10 microg/L with relative standard deviations of 2.6-8.7%. The limits of detection ranged from 0.002 to 0.006 microg/L. The proposed method was used for the analysis of water samples, and satisfactory results were achieved.

Statistical mechanical lattice models of endohedral and exohedral xenon adsorption in carbon nanotubes and comparison with Monte-Carlo simulations

Adsorption of xenon in carbon nanotubes has been investigated by Kuznetsova et al. [A. Kuznetsova, J.T. Yates Jr., J. Liu, R.E. Smalley, J. Chem. Phys. 112 (2000) 9590] and Simonyan et al. [V. Simonyan, J.K. Johnson, A Kuznetsova, J.T. Yates Jr., J. Chem. Phys. 114 (2001) 4180] where endohedral adsorption isotherms show a step-like structure. A matrix method is used for calculation of the statistical mechanics of a lattice model of xenon endohedral adsorption which reproduces the isotherm structure while exohedral adsorption is treated by mean-field theory.

Dependence of Single-Walled Carbon Nanotube Adsorption Kinetics on Temperature and Binding Energy

We present results for the isothermal adsorption kinetics of methane, hydrogen, and tetrafluoromethane on closed-ended single-walled carbon nanotubes. In these experiments, we monitor the pressure decrease as a function of time as equilibrium is approached, after a dose of gas is added to the cell containing the nanotubes. The measurements were performed at different fractional coverages limited to the first layer. The results indicate that, for a given coverage and temperature, the equilibration time is an increasing function of E/(k(B)T), where E is the binding energy of the adsorbate and k(B)T is the thermal energy. These findings are consistent with recent theoretical predictions and computer simulations results that we use to interpret the experimental measurements.

Processing of Electroactive Nanostructured Films Incorporating Carbon Nanotubes and Phthalocyanines for Sensing

The use of carbon nanotubes (CNTs) combined with other materials in nanostructured films has demonstrated their versatility in tailoring specific properties. In this study, we produced layer-by-layer (LbL) films of polyamidoamine-PAMAM-incorporating multiwalled carbon nanotubes (PAMAM-NT) alternated with nickel tetrasulfonated metallophthalocyanine (NiTsPc), in which the incorporation of CNTs enhanced the NiTsPc redox process and its electrocatalytic properties for detecting dopamine. Film growth was monitored by UV−vis spectroscopy, which pointed to an exponential growth of the multilayers, whose roughness increased with the number of bilayers according to atomic force microscopy (AFM) analysis. Strong interactions between -NH3+ terminal groups from PAMAM and -SO3− from NiTsPc were observed via infrared spectroscopy, while the micro-Raman spectra confirmed the adsorption of carbon nanotubes (CNTs) onto the LbL film containing NiTsPc. Cyclic voltammograms presented well-defined electroactivity with a redo...

Influence of quantum effects on the mechanism of adsorption and phase diagram of rare gases in carbon nanotubes

We present results of grand canonical Monte Carlo simulations of rare gases (He, Ne, Ar, Kr and Xe) adsorption in carbon nanotubes. The interaction model includes both quantum effects (via effective Feymann-Hibbs potential) and the atomic roughness of the tube. We show that the quantum contribution to interactions does not suppress the energetic corrugation of carbon nanotube but decreases only its average strength. In the case of Ne, the phase diagram and, in particular, the melting temperature for layers adsorbed on and within an individual tube does not depend on tube chirality. However, the structure of layers adsorbed on outer surface of the tube is strongly related to the atomic structure of the underlying tube.

Stability and bonding properties of finite single-walled carbon nanotubes adsorbed on Si(001)

The stability and bonding properties of capped single-walled carbon nanotubes (CNTs) adsorbed on the Si(001) surface are addressed by density-functional theory calculations. We study the armchair (5,5) and the zigzag (9,0) CNTs with a similar length of about 24Å, which are adsorbed parallel and perpendicular to the dimer direction of the reconstructed Si(001) surface. At the equilibrium geometries, both CNTs form covalent bonds with the substrates with binding energies ranging from 0.40to0.62eV per C–Si bond. These bonds only form when neighboring C and Si atoms are closer than 2.13Å. We find a preferential direction for the CNT adsorptions along the dimers where the zigzag CNT is found to be the most stable. Changes in the Si(001) band structures after the CNT adsorption are also discussed.

Immobilization of acetylcholinesterase based on the controllable adsorption of carbon nanotubes onto an alkanethiol monolayer for carbaryl sensing

A simple method to immobilize acetylcholinesterase (AChE) on the controllable adsorption of multiwalled carbon nanotubes (MWCNTs) onto an alkanethiol self-assembled monolayer (C(6)H(13)SH SAM) modified Au electrode was proposed. The surface coverage of the MWCNTs was readily controlled by adjusting the immersion time for the adsorption of the MWCNTs. Atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to monitor these controllable fabrication processes. The MWCNTs adsorbed onto the SAM surface substantially restores the heterogeneous electron transfer between the bare Au electrode and the redox system in the solution phase that is almost totally blocked by the SAM of C(6)H(13)SH, and as a result, the prepared MWCNT-SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. Due to the inherent conductive properties of MWCNTs, the immobilized AChE exhibited high affinity to its substrate and produced a detectable and fast response. Thus, a sensitive, efficient and stable amperometric sensor for quantitative determination of carbaryl was developed. The inhibition of carbaryl was proportional to its concentration ranging from 0.001 to 1 microg mL(-1) and 2 to 15 microg mL(-1), with a detection limit of 0.6 ng mL(-1). The determination of carbaryl in garlic samples showed acceptable accuracy, which provided a new promising tool for analysis of enzyme inhibitors.

Henry constant and isosteric heat at zero-loading for gas adsorption in carbon nanotubes

The Henry constant and the isosteric heat of adsorption at zero loading in a carbon nanotube bundle are studied with Monte Carlo integration for the adsorption of gases over a range of temperatures. The spacing between nanotubes in a bundle is determined from the minimization of potential energy of interaction between these tubes. We study different tube configurations with bundles of 2, 3, 4 and 7 tubes. Depending on the configuration it is found that the spacing is of between 0.31 to 0.333 nm, and this falls within the range reported in the literature. The Henry constant has been carefully defined so that it will not become negative at high temperatures. This is done with the aid of accessible volume, rather than the usual absolute void volume. We show that linearity of the van't Hoff plot for the Henry constant is not strictly followed. Furthermore the slope of this plot is not equal to the isosteric heat of adsorption at zero loading, which is found to be a strong function of temperature. From the results we find that the Henry constant and the heat of adsorption depend on the tube configuration. In general the adsorption in the cusp interstices is strongest followed by that inside the tube and finally on the outer surface. However for very small tubes adsorption occurs inside the tube first. For molecules with orientation, the behaviour is even more interesting and the shape of the isosteric heat versus temperature depends on the degree of orientation, tube configuration and the domain of adsorption (interstices, inside the tube and on the outer surface).