Pure Single-walled Carbon Nanotubes Research Articles

Modeling the interaction between anti-cancer drug penicillamine and pristine and functionalized carbon nanotubes for medical applications: density functional theory investigation and a molecular dynamics simulation

The present study focuses on the prediction and investigation of binding properties of penicillamine with pure (5,5) single-walled carbon nanotube (SWCNT) and functionalized SWCNT (f-SWCNT) through the B3LYP and M06-2X functionals using the 6-31G** basis set. The electronic and structural properties, adsorption energy and frontier molecular orbitals of various configurations are examined. Our theoretical results indicated that the interaction of the nanotubes with penicillamine molecule is weak so that the drug adsorption process is typically physisorption. Also, results of theoretical calculations show that the adsorption of the drug molecule on f-SWCNT is stronger with shorter intermolecular distances in comparison to pure SWCNT. The natural bond orbital (NBO) analysis of studied systems demonstrates that the charge is transferred from penicillamine molecule to the nanotubes. Furthermore, molecular dynamics (MD) simulation is employed to evaluate the dynamic and diffusion behavior of drug molecule on SWCNT and f-SWCNT. Energy results show that drug molecule spontaneously moves toward the carriers, and the van der Waals energy contributions in drug adsorption are more than electrostatic interaction. The obtained results from MD simulation confirm that the functionalization of SWCNT leads to increase in the solubility of the carrier in aqueous solution.Communicated by Ramaswamy H. Sarma

Stability analysis of endohedrally functionalized carbon nanotubes with pentagonal metallic nanowires: a molecular dynamics simulation approach

The endohedral functionalization of single-walled carbon nanotubes with molecular species, nanowires (NWs) and nanoparticles is of great importance for fabrication and development of nanoelecronic devices, drug delivery and energy storage applications. This research intends to explore the axial buckling behavior of the endohedrally functionalized single-walled carbon nanotubes (SWCNTs) by various metallic NWs (mNW@SWCNT), i.e. aluminum, copper, iron, sodium, nickel (AlNW, CuNW, FeNW, NaNW, NiNW), considering all possible pentagonal configurations. Employing the molecular dynamics (MD) simulations, the results demonstrate that the structurally stable radius of SWCNTs for successful endohedral functionalization of SWCNTs with pentagonal NWs are different. Considering buckling analysis of models, it is observed that NWs, solely, cannot tolerate any axial compressive load and their structure becomes dramatically unstable under mechanical force. By inserting NWs inside SWCNTs, their pentagonal structures during simulation are preserved due to Vdw interaction of NW and SWCNT until buckling occurs. Moreover, the buckling simulation results indicate that by increasing the length, the critical force of mNW@SWCNT decreases and approximately tends to that of pure SWCNTs which is more considerable for AlNWs. Also, in the particular length, the encapsulation of NWs inside the SWCNTs causes a considerable increase in the critical buckling forces particularly in smaller lengths. According to the attained results, functionalization of SWCNTs with E and S configuration of AlNWs improves the structural stability of SWCNTs more pronounced than other pentagonal NWs.

Tensile characteristics of single-walled carbon nanotubes endohedrally decorated with gold nanowires: A molecular dynamics study

Young's modulus and the fracture of gold nanowires (GNWs) encapsulated inside single-walled carbon nanotubes (SWCNTs) are studied using molecular dynamics (MD) simulations. To investigate the mechanical behavior, two important parameters, i.e. ultimate tensile force and strain, are calculated. The obtained results from aforementioned nanostructures are compared with those of pure GNWs and SWCNTs. The results illustrate that SWCNTs filled with GNWs (GNWs@SWCNTs) and pure GNWs possess lower Young's moduli than those of pure SWCNTs in a similar length. As the length increases, Young's modulus of pure GNWs and GNWs@SWCNTs is reduced. In a particular length, the highest and lowest ultimate forces belong to the multishell GNWs@SWCNTs and pure multishell GNWs, respectively. Moreover, it is found that pure SWCNTs have the highest ultimate strains. Also, by rising the length, the ultimate tensile strain increases. To study the effect of selected boundaries on the tensile characteristics, the tensile loads are applied to the boundaries of surrounding SWCNTs instead of whole configuration (B model). The obtained results demonstrated that in the similar length, Young's modulus and ultimate force for B model are higher than those of A model, i.e. the model that the whole system is under the tensile loads. By contrast, in the particular length, B model shows lower ultimate strain compared to that of A model.

Sensitivity Performance of Single Wall Carbon Nanotubes Gas Sensor on Silicon and Porous Silicon

Pure single walled carbon nanotubes (pure-SWCNTs) and Functionalized single walled nanotubes (F-SSWCNTs) have been utilized to the manufactured nitrogen dioxide gas sensor. CNTs films have been deposited on (n-type) silicon and porous silicon substrate by drop casting method. A porous silicon layer (PS) was prepared via electrochemical etching. The applied current density was 20 mA / cm2, and the typical electrochemical-etching time was chosen to be about 20 minutes. Upon exposure to fixed test gas mixing ratio (air: gas) NO2 at different operating temperatures, the sensitivity response results show that Pure single walled carbon nanotubes and Functionalized single walled nanotubes deposited on porous silicon have better performances than that deposited on silicon. At RT the F-SWCNTs/Ps sensitivity reaches to 36%, the response and recovery time is about 11 s and 26 s, whereas for SWCNTs/Ps the sensitivity 13.5%, the response and recovery time is about 13 s and 24 s.

An Efficient Method to Completely Remove Catalyst Particles from HiPCO Single Walled Carbon Nanotubes

An efficient, economic and easy method for removing 99% of catalyst particle from high pressure carbon monoxide (HiPCO) single walled carbon nanotubes (SWCNT) is reported. The experiment is carried out at low temperature followed by acid treatment. The process exploited here is oxidation of the carbon impurities to gaseous phase as CO2 and removal of oxidized catalyst debris using acid treatment. Stability of SWCNT at these temperatures does not allow any damage to the nanotubes, however, some damage is observed which can be attributed to the oxidation of catalyst particles and their removal. The purified sample showed very less/no amount of amorphous carbon and catalyst impurities. Characterization of the material was carried out using Raman spectroscopy, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Transmission electron microscope (TEM) and Energy Dispersive Spectroscopy (EDAX). The resultant SWCNT were found to be highly pure. EDAX spectroscopy showed that the purified sample had only 0.5wt% of catalyst impurities whereas the as prepared once have 9.09wt%, also, TGA curve of the treated sample showed a very significant increase in the oxidation temperature indicating less defect and less catalyst content in the sample. The non- carbonaceous residue after purification is about 0.3%. highly efficient purification of SWCNT using the proposed method. This work provides a basis on removing the catalyst particles completely.

Stepwise Aggregation of Cholate and Deoxycholate Dictates the Formation and Loss of Surface-Available Chirally Selective Binding Sites.

Bile salts are facially amphiphilic, naturally occurring chemicals that aggregate to perform numerous biochemical processes. Because of their unique intermolecular properties, bile salts have also been employed as functional materials in medicine and separation science (e.g., drug delivery, chiral solubilization, purification of single-walled carbon nanotubes). Bile micelle formation is structurally complex, and it remains a topic of considerable study. Here, the exposed functionalities on the surface of cholate and deoxycholate micelles are shown to vary from one another and with the micelle aggregation state. Collectively, data from NMR and capillary electrophoresis reveal preliminary, primary, and secondary stepwise aggregation of the salts of cholic (CA) and deoxycholic (DC) acid in basic conditions (pH 12, 298 K), and address how the surface availability of chirally selective binding sites is dependent on these sequential stages of aggregation. Prior work has demonstrated sequential CA aggregation (pH 12, 298 K) including a preliminary CMC at ca. 7 mM (no chiral selection), followed by a primary CMC at ca. 14 mM that allows chiral selection of binaphthyl enantiomers. In this work, DC is also shown to form stepwise preliminary and primary aggregates (ca. 3 mM DC and 9 mM DC, respectively, pH 12, 298 K) but the preliminary 3 mM DC aggregate is capable of chirally selective solubilization of the binaphthyl enantiomers. Higher-order, secondary bile aggregates of each of CA and DC show significantly degraded chiral selectivity. Diffusion NMR reveals that secondary micelles of CA exclude the BNDHP guests, while secondary micelles of DC accommodate guests, but with a loss of chiral selectivity. These data lead to the hypothesis that secondary aggregates of DC have an exposed binding site, possibly the 7α-edge of a bile dimeric unit, while secondary CA micelles do not present binding edges to the solution, potentially instead exposing the three alcohol groups on the hydrophilic α-face to the solution.

Polypeptides As Complexing Units

One of our research field concerns porphyrin-functionalized a-polypeptides to control the spatial organization of the chromophores and enable exciton migration through the pool of porphyrins to mimic the light harvesting antennae of the photosynthetic system.1 In the photosynthetic system, the solar energy is collected by pigment molecules attached to the light harvesting complexes, in which the chlorophylls are held in a parallel orientation by fairly short a-helical polypeptides. When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached.1 Succeeding in organizing the porphyrins in a similar way as nature does should provide information about the relation existing between the orientation of the chlorophylls and the efficiency of nature in transferring an excited state over a very long distance and with minimal loss of energy. The right-handed 310 helical conformation adopted by our poly-L-lysine functionalized with eight porphyrins induces an overlap of the chromophores (studies realized in collaboration with Prof. T. Keiderling, University of Chicago, US), which thus present sufficient electronic coupling to promote a good exciton migration within the molecular wire. The properties of our peptides with pendant porphyrins were studied extensively in collaboration with with Professor S. Fukuzumi (Univeristy of Osaka, Japan) and applications were found as organic photovoltaic cells,2 multiple photosynthetic reaction centers3 and for the successful purification of Single-Walled Carbon Nanotubes.4 Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498.T. Hasobe, K. Saito, P. V. Kamat, V. Troiani, H. Qiu, N. Solladié, K. S. Kim, J. K. Park, D. Kim, F. D'Souza, S. Fukuzumi, J. Mater. Chem. 2007, 39, 4160-4170.S. Fukuzumi, K. Saito, K. Ohkubo, V. Troiani, H. Qiu, S. Gadde, F. D’Souza and N. Solladié, Phys. Chem. Chem. Phys. 2011, 13, 17019-17022.Kenji Saito, Vincent Troiani, Hongjin Qiu, Nathalie Solladié, Takao Sakata, Hirotaro Mori, Mitsuo Ohama, Shunichi Fukuzumi, J. Phys. Chem. C 2007, 111, 1194-1199. Figure 1

The Effects of Zn Doping on the Interaction of a Single Walled Carbon Nanotube with Penicillamine Drug: A DFT Study

At the present work, we report the interaction of the penicillamine (PCA) molecule adsorbed on the pure and Zn-doped single-walled carbon nanotubes (SWCNTs) using density functional theory calculations. We conclude that the interaction of PCA on the outer surface of Zn-doped SWCNT is due to chemisorption, while its interaction with the pure SWCNT is physisorption in nature. It is undrestood that the electronic and optical structure of the Zn-doped SWCNT is more sensitive to the presence of PCA in comparison with the pure SWCNT. The Mulliken population charge analysis and the density of states analyses represent that the nature of PCA adsorption on the applied Zn-doped SWCNT is electrostatic rather than covalent.

A molecular dynamics study on the thermal conductivity of endohedrally functionalized single-walled carbon nanotubes with gold nanowires

The thermal conductivity of endohedrally functionalized single-walled carbon nanotubes (SWCNTs) with gold nanowires (GNWs) is studied by using a series of molecular dynamics (MD) simulations. The effect of geometrical parameters, i.e. length and radius of pure SWCNTs/GNWs/SWCNTs filled with GNWs on the thermal conductivity are investigated. Also, the influence of various structures of GNWs such as pentagonal and multishell-GNWs on the thermal conductivity of the system is explored. The results indicate that as the length of the system rises, the thermal conductivity increases. It is also found that the thermal conductivity of GNWs is considerably lower than that of pure SWCNTs and GNWs@SWCNTs at a constant length of SWCNT or GNWs. For long pure SWCNTs, by increasing the radii of nanotubes, the thermal conductivity increases. Moreover, the thermal conductivity of the multishell-GNWs@SWCNTs is obtained higher than that of pentagonal configurations for the same lengths of SWCNTs. Through inserting the GNWs inside the SWCNTs, by maintaining the natural properties of NWs due to endohedral functionalization, the thermal conductivity is increased. This finding can be used as a benchmark for more efficient design of NEMS based on metallic NWs.

Effect of gaseous and condensate products of ethanol decomposition on aerosol CVD synthesis of single-walled carbon nanotubes

In this study, the gaseous and condensate products of ethanol decomposition during the synthesis of single-walled carbon nanotubes (SWCNTs) by aerosol chemical vapor deposition (floating catalyst CVD) method were investigated. To determine the conditions for perfect and clean SWCNT formation the products synthesized at different temperatures and collected inside and outside the reactor were studied by transmission electron microscopy, Raman, Fourier transform infrared (FT-IR) and optical absorption spectroscopy. The individual and bundled SWCNTs of a predominantly small diameter (∼1 nm) were revealed. The obtained tubes exhibit a stable distribution of chiral indices in a wide range of the set temperature (750–1000 °C), which is promising for the development of controlled synthesis methods. The FT-IR analysis results show that the main gaseous products of thermal ethanol decomposition in our CVD system are methane and carbon monoxide. Acting as carbon source, the mixture of CO and CH4 makes possible to produce pure SWCNTs, as those obtained in the catalytic CO disproportionation method, with higher yield, taking into account twice the amount of carbon release during CH4 catalytic pyrolysis. The carbon deposit on the reactor wall is found to play important role in maintaining an optimal regime of CNT synthesis.

Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups–Birch Reduction

The Billups-Birch Reduction chemistry has been shown to functionalize single-walled carbon nanotubes (SWCNTs) without damaging the sidewalls, but has challenges in scalability. Currently published work uses a large mole ratio of Li to carbon atoms in the SWCNT (Li:C) to account for lithium amide formation, however this increases the cost and hazard of the reaction. We report here the systematic understanding of the effect of various parameters on the extent of functionalization using resonant Raman spectroscopy. Addition of 1-iodododecane yielded alkyl-functionalized SWCNTs, which were isolated by solvent extraction and evaporation, and purified by a hydrocarbon wash. The presence of SWCNT growth catalyst residue (Fe) was shown to have a strong adverse effect on SWCNT functionalization. Chlorination-based SWCNT purification reduced the amount of residual Fe, and achieve a maximum ID/IG ratio using a Li:C ratio of 6:1 in a reaction time of 30 min. This result is consistent with published literature requiring 20-fold mole equivalents of Li per mole SWCNT with a reaction time of over 12 h. This new understanding of the factors influencing the functionalization chemistry will help cut down material and process costs, and also increase the selectivity of the reaction toward the desired product.

The effect of platinum precursor concentrations on chlorine sensing characteristics of platinum nanoparticles−loaded single walled carbon nanotubes

The correlation between platinum (Pt) functionalization and chlorine (Cl2) sensing capability in single-walled carbon nanotubes (SWCNTs) was investigated. Utilizing a photoreduction technique via ultraviolet (UV) irradiation, the Pt nanoparticles (NPs) with various diameters of 7–80 nm, which were controlled by Pt precursor concentrations, were successfully functionalized on the sidewalls of SWCNTs. The discrete Pt NP−loaded SWCNTs exhibited significantly enhanced response value (−(ΔR/R0) × 100 = 33.8%) for 1 ppm Cl2 at room temperature (25 °C) compared with that (no response) of pure SWCNTs. On the other hand, in case of continuous Pt NP–loaded SWCNTs, Cl2 sensing capabilities were significantly degraded. The Cl2 sensing capabilities of fabricated sensors tended to correlate with geometric configurations of the catalytic Pt NPs on the sidewalls of SWCNTs, due to differences in the electron pathway.

Separation of Nickelocene‐Filled Single‐Walled Carbon Nanotubes by Conductivity Type and Diameter

We have performed the separation of nickelocene‐filled single‐walled carbon nanotubes (SWCNTs) with a mean diameter of 1.7 nm by conductivity type and diameter using density gradient ultracentrifugation. The separated nanotube fractions were characterized by optical absorption spectroscopy (OAS), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The OAS investigation of the separated samples showed the absence of optical absorption bands of semiconducting tubes in metallic sample and vice versa, which proved a high purity of the nanotube fractions. The XPS investigation of the separated samples showed different positions, spectral widths and asymmetry of the C 1s core level spectra. The multifrequency Raman spectroscopy investigation of the separated samples allowed performing an analysis of the diameter range of nanotubes. The demonstrated successful separation of the filled SWCNTs by conductivity type and diameter enables demanding applications of ultra pure SWCNTs with tailored properties.

Hydrodynamic phonon drift and second sound in a (20,20) single-wall carbon nanotube

Two hydrodynamic features of phonon transport, phonon drift and second sound, in a (20,20) single-wall carbon nanotube (SWCNT) are discussed using lattice dynamics calculations employing an optimized Tersoff potential for atomic interactions. We formally derive a formula for the contribution of drift motion of phonons to total heat flux at steady state. It is found that the drift motion of phonons carries more than $70%$ and $90%$ of heat at 300 and 100 K, respectively, indicating that phonon flow can be reasonably approximated as hydrodynamic if the SWCNT is long enough to avoid ballistic phonon transport. The dispersion relation of second sound is derived from the Peierls-Boltzmann transport equation with Callaway's scattering model and quantifies the speed of second sound and its relaxation. The speed of second sound is around 4000 m/s in a (20,20) SWCNT and the second sound can propagate more than 10 \textmu{}m in an isotopically pure (20,20) SWCNT for frequency around 1 GHz at 100 K.

Adsorption and Desorption of Single-Stranded DNA from Single-Walled Carbon Nanotubes.

The chemical affinity of single-stranded DNA (ssDNA) to adsorb to the surface of single-walled carbon nanotubes (SWCNTs) is used for SWCNT purification, separation and in bio-devices. Despite the popularity of research on SWCNT-ssDNA conjugates, very little work has studied the removal of adsorbed ssDNA on SWCNTs. This paper reports a comprehensive study of biological, physical and chemical treatments for the removal of ssDNA from SWCNT-ssDNA suspensions. These include enzymatic cleavage, heat treatment under vacuum up to 400 °C, chemical treatments with high or low pH, oxidizing conditions, and high-ionic-strength solvents. Complimentary characterization techniques including fluorescence from a DNA-intercalating dye (YO-PRO-1) and photoelectron spectroscopy are used to exhaustively study and compare the methods investigated. Enzyme treatment is found to remove the phosphate backbone only, leaving nucleosides adsorbed to SWCNTs. Heating in inert atmosphere is ineffective at removing ssDNA. Acid, base and oxidative treatment are found to be effective for the removal of ssDNA from SWCNTs. Where possible the mechanism of desorption is described and from the findings suggestions for "best practices" are provided.

(Invited) Polypeptides As Complexing Units

One of our research field concerns porphyrin-functionalized a-polypeptides to control the spatial organization of the chromophores and enable exciton migration through the pool of porphyrins to mimic the light harvesting antennae of the photosynthetic system.1 In the photosynthetic system, the solar energy is collected by pigment molecules attached to the light harvesting complexes, in which the chlorophylls are held in a parallel orientation by fairly short α-helical polypeptides. When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached.1 Succeeding in organizing the porphyrins in a similar way as nature does should provide information about the relation existing between the orientation of the chlorophylls and the efficiency of nature in transferring an excited state over a very long distance and with minimal loss of energy. The right-handed 310 helical conformation adopted by our poly-L-lysine functionalized with eight porphyrins induces an overlap of the chromophores (studies realized in collaboration with Prof. T. Keiderling, University of Chicago, US), which thus present sufficient electronic coupling to promote a good exciton migration within the molecular wire. The properties of our peptides with pendant porphyrins were studied extensively in collaboration with with Professor S. Fukuzumi (Univeristy of Osaka, Japan) and applications were found as organic photovoltaic cells,2 multiple photosynthetic reaction centers3 and for the successful purification of Single-Walled Carbon Nanotubes.4 Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498.T. Hasobe, K. Saito, P. V. Kamat, V. Troiani, H. Qiu, N. Solladié, K. S. Kim, J. K. Park, D. Kim, F. D'Souza, S. Fukuzumi, J. Mater. Chem. 2007, 39, 4160-4170.S. Fukuzumi, K. Saito, K. Ohkubo, V. Troiani, H. Qiu, S. Gadde, F. D’Souza and N. Solladié, Phys. Chem. Chem. Phys. 2011, 13, 17019-17022. Kenji Saito, Vincent Troiani, Hongjin Qiu, Nathalie Solladié, Takao Sakata, Hirotaro Mori, Mitsuo Ohama, Shunichi Fukuzumi, J. Phys. Chem. C 2007, 111, 1194-1199. Figure 1

Quantum Chemical Study on the adsorption of metformin drug on the surface of pristine, Si- and Al-doped (5, 5) SWCNTs

Adsorption properties of metformin (MF) drug onto pristine, Si- and Al-doped (5, 5) armchair single-wall carbon nanotubes (SWCNTs) were studied using density functional theory (DFT) calculations at the B3LYP and ωB97XD methods with the standard 6–311G** basis set. The most stable geometries of the MF drug molecule onto pristine, Si- and Al-doped (5, 5) CNTs were selected and evaluated in the gaseous and aqueous environments. We calculated the natural bond orbitals (NBO), Frontier molecular orbital (FMO), density of states (DOS) and molecular electrostatic potential (MEP) of systems upon adsorption of MF drug. It was found that the reaction of MF drug with pure SWCNT is physisorption in nature, while high chemisorption can be achieved by using Al- and Si-doped SWCNTs. Despite Al-doped SWCNT provides stronger adsorption, however the change in the energy gap of Si-doped SWCNT is more pronounced. It is predicted that MF drug incorporating Si-doped SWCNT can be extended as drug delivery system.

Filtration-guided assembly for patterning one-dimensional nanostructures

Tremendous progress has been made in synthesizing various types of one-dimensional (1D) nanostructures (NSs), such as nanotubes and nanowires, but some technical challenges still remain in the deterministic assembly of the solution-processed 1D NSs for device integration. In this work we investigate a scalable yet inexpensive nanomaterial assembly method, namely filtration-guided assembly (FGA), to place nanomaterials into desired locations as either an individual entity or ensembles, and form functional devices. FGA not only addresses the assembly challenges but also encompasses the notion of green nanomanufacturing, maximally utilizing nanomaterials and eliminating a waste stream of nanomaterials into the environment. FGA utilizes selective filtration of 1D NSs through the open windows on the nanoporous filter membrane whose surface is patterned by a polymer mask for guiding the 1D NS deposition. The modified soft-lithographic technique called blanket transfer (BT) is employed to create the various photoresist patterns of sub-10-micron resolution on the nanoporous filter membrane like mixed cellulose acetate. We use single-walled carbon nanotubes (SWCNTs) as a model 1D NS and demonstrate the fabrication of an array pattern of homogeneous 1D NS network films over an area of 20 cm2 within 10 min. The FGA-patterned SWCNT network films are transferred onto the substrate using the adhesive-based transfer technique, and show the highly uniform film thickness and resistance measurements across the entire substrate. Finally, the electrical performance of the back-gated transistors made from the FGA and transfer method of 95% pure SWCNTs is demonstrated.

Catalytic effects of calcium and potassium on a curved char surface in fuel reburning: A first-principles study on the adsorption of nitric oxide on single-wall carbon nanotubes with metal decoration

To investigate the role of a curved char surface in the nitric oxide (NO)-char reaction, single-wall carbon nanotubes (SWCNTs) were proposed as a model for simulating the curved char surface in first-principles calculations. The effect of calcium and potassium decoration on the adsorption of NO was compared for SWCNTs and graphene, the latter of which represented a flat char surface. The contribution of a curved surface to the NO-char reaction was insignificant in the absence of metals, as the binding energy of NO on pure SWCNTs was only 13% of that on pure graphene. In contrast, when calcium or potassium was present, NO adsorption on the curved surface became significant as the binding energies of NO on calcium- or potassium-decorated SWCNTs increased to 72% and 18% of those on the corresponding decorated graphene surfaces, respectively. The catalytic effect of calcium and potassium was attributed to electron transfer and backdonation between the 4s- and 3d-orbitals of the metal atoms and the NO molecule. Thus, the studies into NO adsorption on flat and curved char surfaces render it possible to determine the degree of catalytic effect of these two metals on the char surface during fuel reburning.

Establishing detection maps for carbon nanotube mass sensors: molecular versus continuum mechanics

In this work, the mass-sensing ability and the corresponding detection efficiency of a fully clamped single-walled carbon nanotube (SWCNT) are investigated through a free vibration analysis, by utilizing mainly a molecular mechanics (MM) formulation and secondarily a continuum mechanics (CM) analytical approximation. The MM method is based on representing the SWCNT as a three-dimensional (3D) finite element frame of point masses and linear springs, while the CM one is grounded on the Euler–Bernoulli beam theory. The overall effort is focused on obtaining detection maps, based on natural frequency data which are capable of leading to the straightforward identification of an unknown mass attached to the external surface of the candidate SWCNT sensor. For this reason, the SWCNT relative natural frequency shifts due to the mass addition, regarding specific modes of vibration and for a variety of mass magnitude and position combinations, are calculated beforehand. Then, the magnitude as well as the position of the added mass may be graphically found by superposing the arisen relative natural frequency shift variations in common contour diagrams. Some results from the open literature are utilized to confirm the predictive performance of the proposed MM method concerning the free vibration of pure SWCNTs, while the MM and CM established detection maps are set in contrast to examine whether a mass nanosensor may be satisfactorily treated in a continuum manner.