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.     

Capacitive and Charge Transfer Effects of Single-Walled Carbon Nanotubes in TiO2 Electrodes

The transfer of nanoscale properties from single-walled carbon nanotubes (SWCNTs) to macroscopic systems is a topic of intense research. In particular, inorganic composites of SWCNTs and metal oxide semiconductors are being investigated for applications in electronics, energy devices, photocatalysis, and electroanalysis. In this work, a commercial SWCNT material is separated into fractions containing different conformations. The liquid fractions show clear variations in their optical absorbance spectra, indicating differences in the metallic/semiconducting character and the diameter of the SWCNTs. Also, changes in the surface chemistry and the electrical resistance are evidenced in SWCNT solid films. The starting SWCNT sample and the fractions as well are used to prepare hybrid electrodes with titanium dioxide (SWCNT/TiO₂). Raman spectroscopy reflects the optoelectronic properties of SWCNTs in the SWCNT/TiO₂ electrodes, while the electrochemical behavior is studied by cyclic voltammetry. A selective development of charge transfer characteristics and double-layer behavior is achieved through the suitable choice of SWCNT fractions.     

On the applicability of cluster models to study the chemical reactivity of carbon nanotubes

We have performed a comparative study on the reactivity of metallic and semiconducting nanotubes using infinite and finite models. Infinite models were created using periodic boundary conditions while finite ones were constructed by means of hydrogen terminated nanotubes sections. Cluster models systematically underestimate the reactivity of metallic single wall carbon nanotube (SWCNT)s. We have confirmed that metallic nanotubes are more reactive than semiconducting species, in disagreement with previous works. The differences can be attributed to the presence of an instability in the singlet ground state of the wavefunction corresponding to semiconducting nanotubes clusters. When lower electronic states of the pristine cluster are considered, semiconducting nanotubes become less reactive as compared with metallic SWCNTs. Particularly, if an antiferromagnetic solution is considered for the semiconducting (10,0) SWCNT cluster, it becomes less reactive than the (5,5) SWCNT, as observed for infinite models. Because semiconducting nanotubes are less reactive than metallic counterparts, their reaction energies converge faster to the values observed for graphene. For a 1.6-nm diameter semiconducting nanotube, the addition energy is comparable with graphene. Thus, semiconducting nanotubes with diameters larger than 1.6 nm are going to be as reactive as graphene and the effects of curvature will be unimportant.     

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.     

Structure-dependent reactivity of semiconducting single-walled carbon nanotubes with benzenediazonium salts

The addition of diazonium salts to single-walled carbon nanotubes (SWCNTs) in aqueous surfactant suspensions quenches the intrinsic near-infrared fluorescence of semiconducting SWCNTs through sidewall chemical reactions. Spectrally resolved fluorescence spectroscopy of mixed SWCNT samples has been used to measure structure-dependent relative reactivities in the initial stages of these reactions. For several 4-substituted benzenediazonium salts, Ar-R (Ar = N 2 (+)-C 6H 4 and R = Cl, NO 2, OMe), reactivities at pH 10 were found to be greatest for SWCNTs having the largest band gaps. The magnitude of this band gap dependence varies according to the R-group of the salt, with R = OMe showing the strongest variation. For R = OH, acidification of the sample to pH 5.5 results in reversal of the structural trend, as smaller band gap SWCNTs show slightly greater reactivities. The derivatization reactions observed here proceed concurrently, although at different rates, for semiconducting and metallic SWCNT species. These results therefore provide insight into the difficulties of separating metallic and semiconducting SWCNTs through selective reaction schemes and underscore the need for fluorescence spectroscopy to be used in assessing semiconducting SWCNT reactions.     

Residual Metal Impurity Aids Facile In Situ Electrochemical Surface Derivatization of Single‐Walled Carbon Nanotubes

Residual metal impurities were exploited as reactants in the functionalization of the surface of single‐walled carbon nanotubes (SWCNT) with nickel hexacyanoferrate (NiHCF) by simple electrochemical cycling in ferricyanide solutions. This facile in situ electrochemical modification process provides intimate contact between NiHCF and SWCNTs that improves the stability of the redox property and reactivity of NiHCF. The characteristic redox behavior of NiHCF on SWCNT surfaces can be used as an electrochemical probe to access qualitative and quantitative information on unknown electroactive metal impurities in SWCNTs. Significantly, the NiHCF‐modified SWCNTs exhibit pseudocapacitive behavior, and the calculated specific capacitances are 710 and 36 F g^?1 for NiHCF‐SWCNTs and SWCNTs respectively. Furthermore, NiHCF‐SWCNTs were transformed into Ni(OH)₂/SWCNTs and used for enzymeless glucose oxidation.     

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.     

Sexithiophene Encapsulated in a Single‐Walled Carbon Nanotube: An In Situ Raman Spectroelectrochemical Study of a Peapod Structure

The interaction of single‐walled carbon nanotubes (SWCNTs) and α‐sexithiophene (6T) was studied by Raman spectroscopy and by in situ Raman spectroelectrochemistry. The encapsulation of 6T in SWCNT and its interaction causes a bleaching of its photoluminescence, and also small shifts of its Raman bands. The Raman features of the SWCNT with embedded 6T (6T‐peapods) change in both intensity and frequency compared to those of pristine SWCNT, which is a consequence of a change of the resonant condition. Electrochemical doping demonstrated that the electrode potential applied to the SWCNT wall causes changes in the embedded 6T. The effects of electrochemical charging on the Raman features of pristine SWCNT and 6T@SWCNT were compared. It is shown that the interaction of SWCNT with 6T also changes the electronic structure of SWCNT in its charged state. This change of electronic structure is demonstrated both for semiconducting and metallic tubes.     

Synthesis and characterization of polyethylene chains grafted onto the sidewalls of single‐walled carbon nanotubes via copolymerization

Polyethylene (PE) chains grafted onto the sidewalls of SWCNTs (SWCNT‐g‐PE) were successfully synthesized via ethylene copolymerization with functionalized single‐walled carbon nanotubes (f‐SWCNTs) catalyzed by rac‐(en)(THInd)₂ZrCl₂/MAO. Here f‐SWCNTs, in which α‐alkene groups were chemically linked on the sidewalls of SWCNTs, were synthesized by Prato reaction. The composition and microstructure of SWCNT‐g‐PE were characterized by means of ¹H NMR, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyses (TGA), field‐emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Nanosized cable‐like structure was formed in the SWCNT‐g‐PE, in which the PE formed a tubular shell and several SWCNTs bundles existed as core. The formation of the above morphology in the SWCNT‐g‐PE resulted from successfully grafting of PE chains onto the surface of SWCNTs via copolymerization. The grown PE chains grafted onto the sidewall of the f‐SWCNTs promoted the exfoliation of the mass nanotubes. Comparing with pure PE, the physical mixture of PE/f‐SWCNTs and in situ PE/SWCNTs mixture, thermal stability, and mechanical properties of SWCNT‐g‐PE were higher because of the chemical bonding between the f‐SWCNTs and PE chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5459–5469, 2007     

Two‐Photon Chemistry in Ruthenium 2,2′‐Bipyridyl‐Functionalized Single‐Wall Carbon Nanotubes

Ruthenium polypyridyl complexes are widely used as light harvesters in dye‐sensitized solar cells. Since one of the potential applications of single‐wall carbon nanotubes (SWCNTs) and their derived materials is their use as active components in organic and hybrid solar cells, the study of the photochemistry of SWCNTs with tethered ruthenium polypyridyl complexes is important. A water‐soluble ruthenium tris(bipyridyl) complex linked through peptidic bonds to SWCNTs (Ru‐SWCNTs) was prepared by radical addition of thiol‐terminated SWCNT to a terminal C?C double bond of a bipyridyl ligand of the ruthenium tris(bipyridyl) complex. The resulting macromolecular Ru‐SWCNT (≈500 nm, 15.6 % ruthenium complex content) was water‐soluble and was characterized by using TEM, thermogravimetric analysis, chemical analysis, and optical spectroscopy. The emission of Ru‐SWCNT is 1.6 times weaker than that of a mixture of [Ru(bpy)₃]²⁺ and SWCNT of similar concentration. Time‐resolved absorption optical spectroscopy allows the detection of the [Ru(bpy)₃]²⁺‐excited triplet and [Ru(bpy)₃]⁺. The laser flash studies reveal that Ru‐SWCNT exhibits an unprecedented two‐photon process that is enabled by the semiconducting properties of the SWCNT. Thus, the effect of the excitation wavelength and laser power on the transient spectra indicate that upon excitation of two [Ru(bpy)₃]²⁺ complexes of Ru‐SWCNT, a disproportionation process occurs leading to delayed formation of [Ru(bpy)₃]⁺ and the performance of the SWCNT as a semiconductor. This two‐photon delayed [Ru(bpy)₃]⁺ generation is not observed in the photolysis of [Ru(bpy)₃]³⁺; SWCNT acts as an electron wire or electron relay in the disproportionation of two [Ru(bpy)₃]²⁺ triplets in a process that illustrates that the SWCNT plays a key role in the process. We propose a mechanism for this two‐photon disproportionation compatible with i) the need for high laser flux, ii) the long lifetime of the [Ru(bpy)₃]²⁺ triplets, iii) the semiconducting properties of the SWNT, and iv) the energy of the HOMO/LUMO levels involved.     

Diameter‐Sorted SWCNT–Porphyrin and SWCNT–Phthalocyanine Conjugates for Light‐Energy Harvesting

A non‐covalent double‐decker binding strategy is employed to construct functional supramolecular single‐wall carbon nanotubes (SWCNT)–tetrapyrrole hybrids capable of undergoing photoinduced electron transfer and performing direct conversion of light into electricity. To accomplish this, two semiconducting SWCNTs of different diameters (6,5 and 7,6) were modified via π–π stacking of pyrene functionalized with an alkyl ammonium cation (PyrNH₃⁺). Such modified nanotubes were subsequently assembled via dipole–cation binding of zinc porphyrin with one ( 1 ) or four benzo‐18‐crown‐6 cavities ( 2 ) or phthalocyanine with four benzo‐18‐crown‐6 cavities at the ring periphery ( 3 ), employed as visible‐light photosensitizers. Upon charactering the conjugates using TEM and optical techniques, electron transfer via photoexcited zinc porphyrin and phthalocyanine was investigated using time‐resolved emission and transient absorption techniques. Higher charge‐separation efficiency is established for SWCNT(7,6) with a narrow band gap than the thin SWCNT(6,5) with a wide band gap. Photoelectrochemical studies using FTO/SnO₂ electrodes modified with these donor–acceptor conjugates unanimously demonstrated the ability of these conjugates to convert light energy into electricity. The photocurrent generation followed the trend observed for charge separation, that is, incident‐photon‐to‐current efficiency (IPCE) of a maximum of 12 % is achieved for photocells with FTO/SnO₂/SWCNT(7,6)/PyrNH₃⁺: 1 .     

Unraveling the 13C NMR chemical shifts in single-walled carbon nanotubes: dependence on diameter and electronic structure

The atomic specificity afforded by nuclear magnetic resonance (NMR) spectroscopy could enable detailed mechanistic information about single-walled carbon nanotube (SWCNT) functionalization as well as the noncovalent molecular interactions that dictate ground-state charge transfer and separation by electronic structure and diameter. However, to date, the polydispersity present in as-synthesized SWCNT populations has obscured the dependence of the SWCNT (13)C chemical shift on intrinsic parameters such as diameter and electronic structure, meaning that no information is gleaned for specific SWCNTs with unique chiral indices. In this article, we utilize a combination of (13)C labeling and density gradient ultracentrifugation (DGU) to produce an array of (13)C-labeled SWCNT populations with varying diameter, electronic structure, and chiral angle. We find that the SWCNT isotropic (13)C chemical shift decreases systematically with increasing diameter for semiconducting SWCNTs, in agreement with recent theoretical predictions that have heretofore gone unaddressed. Furthermore, we find that the (13)C chemical shifts for small diameter metallic and semiconducting SWCNTs differ significantly, and that the full-width of the isotropic peak for metallic SWCNTs is much larger than that of semiconducting nanotubes, irrespective of diameter.     

Bioelectrocatalysis of Dopamine Using Adsorbed Tyrosinase on Single-Walled Carbon Nanotubes

Abstract

A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on a suitable electrode surface. Here, we describe a method for the performance of a tyrosinase/single-walled carbon nanotubes/glassy carbon (Tyr/SWCNTs/GC) electrode, prepared by the modification of GC electrode surface by SWCNTs and adsorption of tyrosinase on the SWCNT surfaces. SWCNTs were studied with the help of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The dimensions of SWCNTs make them ideal candidates for the adsorption of proteins. The copper-containing enzyme, tyrosinase, exhibited an electrical contact with the electrode, because of the structural alignment of the enzyme on the SWCNT surfaces. The apparent Michaelis–Menten constant (K _m) for dopamine (DA) and the stability of the enzyme electrode were estimated. This method could be suitable for applications to nanofabricated devices.     

Effect of substitutionally boron‐doped single‐walled semiconducting zigzag carbon nanotubes on ammonia adsorption

We investigate the binding of ammonia on intrinsic and substitutionally doped semiconducting single‐walled carbon nanotubes (SWCNTs) on the side walls using density functional calculations. Ammonia is found to be weakly physisorbed on intrinsic semiconducting nanotubes while on substitutional doping with boron its affinity is enhanced considerably reflected with increase in binding energies and charge transfer. This is attributed to the strong chemical interaction between electron rich nitrogen of ammonia and electron deficient boron of the doped SWCNT. On doping, the density of states are changed compared to the intrinsic case and additional levels are formed near the Fermi level leading to overlap of levels with that of ammonia indicating charge transfer. The doped SWCNTs thus are expected to be a potential candidate for detecting ammonia. © 2014 Wiley Periodicals, Inc.     

The 1,3 dipolar cycloaddition of azomethine ylides to graphene,single wall carbon nanotubes,and C60

Herein, we perform a comparative study on the addition of azomethine ylides to graphene, carbon nanotubes, C₆₀, ethene, pyrene and a C₄₈H₁₈ hydrocarbon. The calculated binding energies and free energy corrections suggest that the addition of azomethine ylide to perfect graphene is not spontaneous (ΔG > 0). However, the presence of Stones–Wales defects significantly increases reactivity: the binding energy between SW‐defective graphene and the azomethine ylide is 0.83 eV, close to that determined for a (5,5) SWCNT. The electronic properties of the sheet are not modified by the 1,3 cycloaddition. The binding energies determined for the addition of an azomethine ylide to a (5,5) SWCNT are significantly lower than previously reported. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Poly(γ‐benzyl‐L‐glutamate)‐functionalized single‐walled carbon nanotubes from surface‐initiated ring‐opening polymerizations of N‐carboxylanhydride

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate) (PBLG) by ring‐opening polymerizations of γ‐benzyl‐L ‐glutamic acid‐based N‐carboxylanhydrides (NCA‐BLG) using amino‐functionalized SWCNTs (SWCNT‐NH₂) as initiators. The SWCNT functionalization has been verified by FTIR spectroscopy and transmission electron microscopy. The FTIR study reveals that surface‐attached PBLGs adopt random‐coil conformations in contrast to the physically absorbed or bulk PBLGs, which exhibit α‐helical conformations. Raman spectroscopic analysis reveals a significant alteration of the electronic structure of SWCNTs as a result of PBLG functionalization. The PBLG‐functionalized SWCNTs (SWCNT‐PBLG) exhibit enhanced solubility in DMF. Stable DMF solutions of SWCNT‐PBLG/PBLG with a maximum SWCNTs concentration of 259 mg L^?1 can be readily obtained. SWCNT‐PBLG/PBLG solid composites have been characterized by differential scanning calorimetry, thermogravimetric analysis, wide/small‐angle X‐ray scattering (W/SAXS), scanning electron microscopy, and polarized optical microscopy for their thermal or morphological properties. Microfibers containing SWCNT‐PBLG and PBLG can also be prepared via electrospinning. WAXS characterization reveals that SWCNTs are evenly distributed among PBLG rods in solution and in the solid state where PBLGs form a short‐range nematic phase interspersed with amorphous domains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2340–2350, 2010     

Structural,Vibrational and Electronic Properties of Defective Single‐Walled Carbon Nanotubes Functionalised with Carboxyl Groups: Theoretical Studies

Covalent sidewall functionalisation of defective zigzag single‐walled carbon nanotubes [SWCNTs(10,0)] with COOH groups is investigated by using DFT. Four types of point defects are considered: vacancy (V), divacancy [V₂(5‐8‐5), V₂(555‐777)], adatom (AA) and Stone–Wales (SW). The energetic, structural, electronic and vibrational properties of these systems are analysed. Decreasing reactivity is observed in the following order: AA>V>V₂(555‐777)>V₂(5‐8‐5)>SW. These studies also demonstrate that the position in which a carboxyl group is attached to a defective SWCNT is of primary importance. Saturation of two‐coordinate carbon atoms in systems with the vacancy V‐7 and with the adatom AA‐1(2) is 3.5–4 times more energetically favourable than saturation of three‐coordinate carbon atoms for all studied systems. Vibrational analysis for these two systems shows significant redshifts of the ν(C?O) stretching vibration of 96 and 123 cm^?1 compared to that for carboxylated pristine systems. Detailed electronic‐structure analysis of the most stable carboxylated systems is also presented.     

Piezoresistive characteristics of single wall carbon nanotube/polyimide nanocomposites

A systematic study of the effect of single wall carbon nanotubes (SWCNTs) on the enhanced piezoresistive sensitivity of polyimide nanocomposites from below to above percolation was accomplished. The maximum piezoresistive stress coefficient (Π) of 1.52 × 10^?3 MPa^?1 was noted at just above the percolation threshold concentration (Φ ～ 0.05 wt %) of SWCNT. This coefficient value exceeds those of metallic piezoresistive materials by two orders of magnitude (4.25 × 10^?5 MPa^?1 for aluminum). The high piezoresistive characteristics appear to originate from a change in the intrinsic resistivity of the composite caused by the variation of the tunneling distance between conducting inclusions (SWCNTs) under compression or tension. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 994–1003, 2009     

Electrochemical Behavior and Determination of L‐Tyrosine at Single‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

Based on single‐walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE/SWCNTs), a novel method was presented for the determination of L ‐tyrosine. The GCE/SWCNTs exhibited remarkable catalytic and enhanced effects on the oxidation of L ‐tyrosine. In 0.10 mol/L citric acid‐sodium citrate buffer solution, the oxidation potential of L ‐tyrosine shifted negatively from +1.23 V at bare GCE to +0.76 V at GCE/SWCNTs. Under the optimized experimental conditions, the linear range of the modified electrode to the concentration of L ‐tyrosine was 5.0×10^?6–2.0×10^?5 mol/L (R₁=0.9952) and 2.7×10^?5–2.6×10^?4 mol/L (R₂=0.9998) with a detection limit of 9.3×10^?8 mol/L. The kinetic parameters such as α (charge transfer coefficient) and D (diffusion coefficient) were evaluated to be 0.66, 9.82×10^?5 cm² s^?1, respectively. And the electrochemical mechanism of L ‐tyrosine was also discussed.