Tuning the energy barrier of water exchange reactions on Al(III) by interaction with the single-walled carbon nanotubes

The limiting dissociative (D) and interchange dissociative (I(d)) water exchange pathways on Al(III) inside and outside single-walled carbon nanotubes (SWCNTs) were modelled using ONIOM calculations with density functional theory, and the influence of SWCNTs on both D and I(d) pathways was examined. The interchange dissociative water exchange pathway was revealed, in which the zigzag SWCNTs (13,0), (14,0) and (15,0) with the same length were modelled for interaction. The results indicate that the confinement effect of SWCNTs on the energy barriers is strong when the reaction takes place inside SWCNTs with small diameter relative to reaction complexes, and varies heavily along with the change of diameters of SWCNTs. The results also indicate that SWCNTs act as trans-activating ligand to effectively lower the energy barriers of both D and I(d) pathways outside SWCNTs. The interaction between aluminium-water complexes and SWCNTs can effectively lower the energy barriers in general and may accelerate the reaction rates, which has great importance for the influence of carbon nanotubes on dissolution and transformation rates of minerals such as aluminium (hydr)oxide.     

The catalytic performance of metal-free defected carbon catalyst towards acetylene hydrochlorination revealed from first-principles calculation

Defected carbon materials as a metal-free catalyst have shown superior stability and catalytic performance in the acetylene hydrochlorination reaction. Through density functional theory (DFT) calculations, for the first time, several different defected configurations comprising mono and divacancies and Stone Wales defect on single-walled carbon nanotubes (SWCNTs) have been used as a direct catalyst for acetylene hydrochlorination reaction. These defective sites on SWCNTs are the most active site for acetylene hydrochlorination reaction compare to pristine SWCNT. The different configurations of defects have different electronic structures, which specify that monovacancy defects have more states adjacent to the Fermi level. The reactant acetylene (C₂H₂) adsorbed strongly compared to hydrogen chloride (HCl) and expected to be the initial step of the reaction. Acetylene adsorbed strongly at monovacancy defected SWCNT compared to other investigated defects. Reaction pathway analysis revealed that mono- and divacancy defected SWCNTs have minimum energy barriers and show extraordinary performance toward acetylene hydrochlorination. This work suggests the potential of metal-free defected carbon in catalyzing acetylene hydrochlorination and provides a solid base for future developments in acetylene hydrochlorination.     

Probing the Chemical Functionalization of Single‐Walled Carbon Nanotubes with Multiple Carbon Ad‐Dimer Defects

Drying‐tube‐shaped single‐walled carbon nanotubes (SWCNTs) with multiple carbon ad‐dimer (CD) defects are obtained from armchair (n,n,m) SWCNTs (n=4, 5, 6, 7, 8; m=7, 13). According to the isolated‐pentagon rule (IPR) the drying‐tube‐shaped SWCNTs are unstable non‐IPR species, and their hydrogenated, fluorinated, and chlorinated derivatives are investigated. Interestingly, chemisorptions of hydrogen, fluorine, and chlorine atoms on the drying tube‐shaped SWCNTs are exothermic processes. Compared to the reaction energies for binding of H, F, and Cl atoms to perfect and Stone–Wales‐defective armchair (5,5) nanotubes, binding of F with the multiply CD defective SWCNTs is stronger than with perfect and Stone–Wales‐defective nanotubes. The reaction energy for per F₂ addition is between 85 and 88 kcal mol^?1 more negative than that per H₂ addition. Electronic structure analysis of their energy gaps shows that the CD defects have a tendency to decrease the energy gap from 1.98–2.52 to 0.80–1.17 eV. After hydrogenation, fluorination, and chlorination, the energy gaps of the drying‐tube‐shaped SWCNTs with multiple CD defects are substantially increased to 1.65–3.85 eV. Furthermore, analyses of thermodynamic stability and nucleus‐independent chemical shifts (NICS) are performed to analyze the stability of these molecules.     

Reactivity of Single‐Walled Carbon Nanotubes in the Diels–Alder Cycloaddition Reaction: Distortion–Interaction Analysis along the Reaction Pathway

Diels–Alder cycloaddition is one of the most powerful tools for the functionalization of single‐walled carbon nanotubes (SWCNTs). Density functional theory at the B3‐LYP level of theory has been used to investigate the reactivity of different‐diameter SWCNTs (4–9,5) in Diels–Alder reactions with 1,3‐butadiene; the reactivity was found to decrease with increasing SWCNT diameter. Distortion/interaction analysis along the whole reaction pathway was found to be a better way to explore the reactivity of this type of reaction. The difference in interaction energy along the reaction pathway is larger than that of the corresponding distortion energy. However, the distortion energy plots for these reactions show the same trend. Therefore, the formation of the transition state can be determined from the interaction energy. A lower interaction energy leads to an earlier transition state, which indicates a lower activation energy. The computational results also indicate that the original distortion of the SWCNTs leads to an increase in the reactivity of the SWCNTs.     

Surface-enhanced Raman scattering of single-walled carbon nanotubes on silver-coated and gold-coated filter paper

Surface-enhanced Raman scattering (SERS) spectra of single-walled carbon nanotubes (SWCNTs) on metal-coated filter paper are reported for the first time. Experimental results show that the metal-coated filter paper is very effective and active. The SERS spectrum not only shows that all Raman bands of SWCNTs in normal Raman scattering have been generally enhanced, but also shows many new bands, which characterize the structure of SWCNTs and the interaction between SWCNTs and silver/gold nanoparticles, arising from symmetry lowering and selection rule relaxing of SWCNTs induced by the silver/gold surface. In our case, it is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The analysis shows that the SERS spectra of SWCNTs on the metal-coated filter paper provide convenience for probing the sample molecules with fine structures related to defects of SWCNTs, the diameter of SWCNTs, and the SERS mechanism of SWCNTs deposited on metal-coated filter paper. Moreover, this can be used as a probe technique for monitoring the synthesis quality of SWCNTs with significant higher sensitivity than other methods, which has promise of being a new technique for monitoring synthesis quality of SWCNTs.     

Regulatory Peptides Are Susceptible to Oxidation by Metallic Impurities within Carbon Nanotubes

In this article, we show that the redox properties of the regulatory peptide L ‐glutathione are affected by the presence of nickel oxide impurities within single‐walled carbon nanotubes (SWCNTs). Glutathione is a powerful antioxidant that protects cells from oxidative stress by removing free radicals and peroxides. We show that the L ‐cysteine moiety in L ‐glutathione is responsible for the susceptibility to oxidation by metallic impurities present in the carbon nanotubes. These results have great significance for assessing the toxicity of carbon‐nanotube materials. The SWCNTs were characterized by Raman spectroscopy, high‐resolution X‐ray photoelectron spectroscopy, transmission electron microscopy, and energy dispersive X‐ray spectroscopy.     

The role of vacancy defects and holes in the fracture of carbon nanotubes

We present quantum mechanical calculations using density functional theory and semiempirical methods, and molecular mechanics (MM) calculations with a Tersoff–Brenner potential that explore the role of vacancy defects in the fracture of carbon nanotubes under axial tension. These methods show reasonable agreement, although the MM scheme systematically underestimates fracture strengths. One- and two-atom vacancy defects are observed to reduce failure stresses by as much as 26% and markedly reduce failure strains. Large holes – such as might be introduced via oxidative purification processes – greatly reduce strength, and this provides an explanation for the extant theoretical–experimental discrepancies.     

Nerve agents interacting with single wall carbon nanotubes: Density functional calculations

First-principles calculations based on density functional theory (DFT) method are used to investigate the adsorption properties of nerve agent DMMP on typical zigzag (semiconducting) and armchair (metallic) single wall carbon nanotubes (SWCNTs). The adsorption energies for DMMP molecule on different adsorption sites on SWCNTs are obtained. The results indicate that DMMP is weakly bound to the outer surface of both the considered SWCNTs and the obtained adsorption energy values and binding distances are typical for the physisorption. We find that DMMP adsorptive capability of metallic CNTs is about twofold that of semiconducting one. The adsorption of DMMP on the higher chiral angle nanotubes was also investigated and the results indicate that nanotube’s chirality increases the adsorption capability of the tube but however the adsorption characteristic is typical for the physisorption. Furthermore, co-adsorption of two DMMP molecules on the SWCNTs as a single-layer/bi-layer of adsorbed molecules as well as the adsorption of one DMMP molecule on the CNT bundles consisting of three SWCNTs has also been examined. The obtained results reveal that for both the considered systems the binding energy was increased for the DMMP adsorption but it’s still typical for the physisorption, consistent with the recent experimental result. The study of the electronic structures and charge analysis indicate that no significant hybridization between the respective orbital takes place and the small interaction obtained quantitatively in terms of binding energies.     

Tight-binding molecular dynamics study of the role of defects on carbon nanotube moduli and failure

We performed tight-binding molecular dynamics on single-walled carbon nanotubes with and without a variety of defects to study their effect on the nanotube modulus and failure through bond rupture. For a pristine (5,5) nanotube, Young's modulus was calculated to be approximately 1.1 TPa, and brittle rupture occurred at a strain of 17% under quasistatic loading. The predicted modulus is consistent with values from experimentally derived thermal vibration and pull test measurements. The defects studied consist of moving or removing one or two carbon atoms, and correspond to a 1.4% defect density. The occurrence of a Stone-Wales defect does not significantly affect Young's modulus, but failure occurs at 15% strain. The occurrence of a pair of separated vacancy defects lowers Young's modulus by approximately 160 GPa and the critical or rupture strain to 13%. These defects apparently act independently, since one of these defects alone was independently determined to lower Young's modulus by approximately 90 GPa, also with a critical strain of 13%. When the pair of vacancy defects adjacent, however, Young's modulus is lowered by only approximately 100 GPa, but with a lower critical strain of 11%. In all cases, there is noticeable strain softening, for instance, leading to an approximately 250 GPa drop in the apparent secant modulus at 10% strain. When a chiral (10,5) nanotube with a vacancy defect was subjected to tensile strain, failure occurred through a continuous spiral-tearing mechanism that maintained a high level of stress (2.5 GPa) even as the nanotube unraveled. Since the statistical likelihood of defects occurring near each other increases with nanotube length, these studies may have important implications for interpreting the experimental distribution of moduli and critical strains.     

Interaction of Na, Mg, Al, Si with carbon nanotube (CNT): NMR and IR study

A Quantum Mechanics (QM) is used for investigated the nature of metals transport and interaction with single-walled carbon nanotubes (SWCNTs) inter membranes. Metal species can be transported actively by a combination of SWCNT-membranes conducting channels that have been used for bio-molecular and detection. This study is based on the interaction of Na, Mg, Al, and Si with the structural features of SWCNTs in the ground state ab initio, HF theory and DFT calculation have been performed with the program Gaussian A7 package suite of programs. We used HF and DFT (B3LYP) method for calculation energy, chemical shift nucleus magnetic resonance and proportion thermodynamic by DFT-IR and DFT-NMR for RWCNT in absence and presence metals. The basis set used 6-31G and 6-31G* that increasing electronegativity metals increased the total energy. The proportion SWCNTs were changed by them. In this study presented a comprehensive on effects of metals on SWCNTs, which are on theirs electronic structure, and transfer of charge from metal to SWCNTs. The results are presented for T = 310 K, the temperature of human’s body.