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     

Shear piezoelectricity in single‐wall carbon nanotube/poly(γ‐benzyl‐L‐glutamate) composites

Single‐wall carbon nanotubes (SWCNTs) have been added to high molecular weight poly(γ‐benzyl‐L ‐glutamate), or PBLG, to evaluate their effects on the polymer's shear piezoelectricity. While the addition of SWCNTs increased various PBLG physical properties such as electrical conductivity, dielectric constant, several mechanical properties, and electrostriction coefficient, the shear piezoelectricity remained constant up to a 0.3 wt % SWCNT concentration. The composite crystallinity, orientation, and SWCNT alignment (measured by X‐ray diffraction, birefringence, and polarized Raman spectroscopy, respectively) were found to be constant up to this same concentration, corroborating the shear piezoelectric findings. PBLG composites made with acid‐treated (and therefore less electrically conductive) SWCNTs exhibited similar shear piezoelectric behavior, indicating that neither the SWCNT type, concentration (up to the percolation threshold), nor electrical conductivity influences PBLG shear piezoelectricity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Double‐Wall Carbon Nanotube–Porphyrin Supramolecular Hybrid: Synthesis and Photophysical Studies

Double‐wall carbon nanotubes (DWCNTs) with pyridyl units covalently attached to the external wall through isoxazolino linkers and carboxylic groups that have been esterified by pentyl chains are synthesized. The properties of these modified DWCNTs are then compared with an analogous sample based on single‐wall carbon nanotubes (SWCNTs). Raman spectroscopy shows the presence of characteristic radial breathing mode vibrations, confirming that the samples partly retain the integrity of the nanotubes in the case of DWCNTs, including the internal and external nanotubes. Quantification of the pyridyl content for both samples (DWCNT and SWCNT derivatives) is based on X‐ray photoelectron spectroscopy and thermogravimetric profiles, showing very similar substituent load. Both pyridyl‐containing nanotubes (DWCNTs and SWCNTs) form a complex with zinc porphyrin (ZnP), as evidenced by the presence of two isosbestic points in the absorption spectra of the porphyrin upon addition of the pyridyl‐functionalized nanotubes. Supramolecular complexes based on pyridyl‐substituted DWCNTs and SWCNTs quench the emission and the triplet excited state identically, through an energy‐transfer mechanism based on pre‐assembly of the ground state. Thus, the presence of the intact inner wall in DWCNTs does not influence the quenching behavior, with respect to SWCNTs, for energy‐transfer quenching with excited ZnP. These results sharply contrast with previous ones referring to electron‐transfer quenching, in which the double‐wall morphology of the nanotubes has been shown to considerably reduce the lifetime of charge separation, owing to faster electron mobility in DWCNTs compared to SWCNTs.     

Arginine Side Chains as a Dispersant for Individual Single‐Wall Carbon Nanotubes

Charged peptides and proteins disperse single‐wall carbon nanotubes (SWCNTs) in aqueous solutions. However, little is known about the role of their side chains in their interactions with SWCNTs. Homopolypeptide–SWCNT systems are ideal for investigating the mechanisms of such interactions. In this study, we demonstrate that SWCNTs are individually dispersed by poly‐L ‐arginine (PLA). The debundled SWCNTs exhibited a distinct fluorescence. The dispersibility of SWCNTs with PLA was greater than that of SWCNTs with poly‐L ‐lysine (PLL). Molecular dynamics simulations suggest that the side chains of PLA have stronger interactions with the sidewalls of SWCNTs compared with those of PLL. The guanidinium group at the end of the side chain of an arginine residue plays an important role in the interaction with SWCNTs, likely through hydrophobic, van der Waals, and π–π interactions. PLA can be useful as a tool for the dispersion of SWCNTs and can be used to non‐covalently anchor materials to SWCNTs with strong binding.     

Synthesis and characterization of water‐dispersible,superparamagnetic single‐wall carbon nanotubes decorated with iron oxide nanoparticles and well‐defined chelating diblock copolymers

A novel approach for the fabrication of magneto‐active carbon nanotubes (CNTs) stabilized in aqueous media, involving the combination of carboxylated single‐wall carbon nanotubes (SWCNTs) with a new class of methacrylate‐based chelating diblock copolymers, is described. More precisely, a well‐defined diblock copolymer consisting of hexa(ethylene glycol) methyl ether methacrylate (hydrophilic and thermo‐responsive) and 2‐(acetoacetoxy)ethyl methacrylate (hydrophobic and metal‐chelating) synthesized by reversible addition‐fragmentation chain transfer polymerization has been used to prepare polymer‐coated magneto‐active SWCNTs decorated with iron oxide nanoparticles. Further to the characterization of the compositional and thermal properties using transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction spectroscopy and thermal gravimetric analysis, assessment of the magnetic characteristics by vibrational sample magnetometry disclosed superparamagnetic behavior at room temperature. The latter, combined with the thermo‐responsive properties of the polymeric coating and the unique, inherent properties of the carbon nanotubes may allow for their future exploitation in the biomedical field. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1389–1396, 2011     

An Amino‐Acid‐Based Self‐Healing Hydrogel: Modulation of the Self‐Healing Properties by Incorporating Carbon‐Based Nanomaterials

An amino‐acid‐based (11‐(4‐(pyrene‐1‐yl)butanamido)undecanoic acid) self‐repairing hydrogel is reported. The native hydrogel, as well as hybrid hydrogels, have been thoroughly characterized by using various microscopic techniques, including transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, fluorescence spectroscopy, FTIR spectroscopy, X‐ray diffraction, and by using rheological experiments. The native hydrogel exhibited interesting fluorescence properties, as well as a self‐healing property. Interestingly, the self‐healing, thixotropy, and stiffness of the native hydrogel can be successfully modulated by incorporating carbon‐based nanomaterials, including graphene, pristine single‐walled carbon nanotubes (Pr‐SWCNTs), and both graphene and Pr‐SWCNTs, within the native gel system. The self‐recovery time of the gel was shortened by the inclusion of reduced graphene oxide (RGO), Pr‐SWCNTs, or both RGO and Pr‐SWCNTs. Moreover, hybrid gels that contained RGO and/or Pr‐SWCNTs exhibited interesting semiconducting behavior.     

Synthesis,stereocomplex crystallization and properties of poly(l‐lactide)/four‐armed star poly(d‐lactide) functionalized carbon nanotubes nanocomposites

Functionalized carbon nanotubes (F‐CNTs) were synthesized through the nucleophilic substitution reaction between four‐armed star poly(d ‐lactide) (4PDLA) and acryl chloride of carbon nanotubes and were characterized using Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy and thermogravimetric analysis. The results indicated that the 4PDLA was successfully grafted onto carbon nanotubes, and it contained 45.5 wt% of 4PDLA. Poly(l ‐lactide) (PLLA) nanocomposites with different F‐CNTs content were prepared by solution casting. Optical microscopy and scanning electron microscopy results showed that F‐CNTs were uniformly dispersed in the nanocomposites. Crystallization behavior and crystal structure of PLLA nanocomposites were investigated using differential scanning calorimetry, polarizing microscope and X‐ray diffraction. The results found that poly(lactide) stereocomplex crystal could be formed between PLLA and F‐CNTs. F‐CNTs played different roles in the process of solution casting and melting crystallization. Polarizing microscope also revealed that crystallization temperature had a significant effect on the nucleation and spherulites growth of PLLA. Thermal stability and mechanical properties of the nanocomposites were also investigated by thermogravimetric analysis, dynamic mechanical analysis and tensile testing. These results demonstrated that the addition of F‐CNTs obviously improved thermal stability and tensile strength of PLLA. The results showed that PLLA/F‐CNTs would have potential values in engineering fields. Copyright © 2015 John Wiley & Sons, Ltd.     

Modified SWCNTs with Amphoteric Redox and Solubilizing Properties

A complementary double‐covalent functionalization of single‐wall carbon nanotubes (SWCNTs) that involves both solubilizing ionic liquids and electroactive moieties is reported. Our strategy is a simple and efficient methodology based on the stepwise functionalization of the nanotube surface with two different organic moieties. In a first instance, oxidized SWCNTs are amidated with ionic liquid precursors, and further treated with n‐butyl bromide to afford SWCNTs functionalized with 1‐butylimidazolium bromide. This approach allows tuneable polarity induced by anion exchange, which has an effect on the relative solubility of the modified SWCNTs in water. Subsequently, a 1,3‐dipolar cycloaddition reaction was performed to introduce the electron‐acceptor 11,11,12,12‐tetracyano‐9,10‐anthra‐para‐quinodimethane (TCAQ) unit on the SWCNTs. Furthermore, to evaluate the influence of the functional group position, the TCAQ electroactive molecule was anchored through an esterification reaction onto previously oxidized SWCNTs, followed by the Tour reaction to introduce the ionic liquid functions. IR and Raman spectroscopies, thermogravimetric analysis (TGA), UV/Vis/NIR spectroscopy, transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) were employed and clearly confirmed the double‐covalent functionalization of the SWCNTs.     

Thermoreversible gelation of helical polypeptide/single‐walled carbon nanotubes and their solid‐state structures

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate)s (PBLGs) having well‐defined polymer molecular weight (M_n = 7.5–21.1 kg·mol^?1) and molecular weight distribution (PDI = 1.05–1.20) by a graft‐to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG‐functionalized SWCNTs (PBLG‐SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (ΔH_m) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG‐SWCNTs. Small‐angle X‐ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG‐SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG‐SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG‐SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A comparative study of single-walled carbon nanotube purification techniques using Raman spectroscopy

Raman spectroscopy has been utilized to show the increase of single-walled carbon nanotubes (SWCNTs) content in commercial grade samples synthesized by the chemical vapour deposition (CVD) technique with a minimization of impurities using both hydrochloric acid treatment and surfactant purification. Surfactant purification methods proved to be the most effective, resulting in a three-fold increase in the percentage of SWCNTs present in the purified product as determined by Raman spectroscopy.     

Selective and Scalable Chemical Removal of Thin Single‐Walled Carbon Nanotubes from their Mixtures with Double‐Walled Carbon Nanotubes

Double‐walled carbon nanotubes (DWCNTs) are materials in high demand due to their superior properties. However, it is very challenging to prepare DWCNTs samples of high purity. In particular, the removal of single‐walled carbon nanotubes (SWCNTs) contaminants is a major problem. Here, a procedure for a selective removal of thin‐diameter SWCNTs from their mixtures with DWCNTs by lithium vapor treatment is investigated. The results are evaluated by Raman spectroscopy and in situ Raman spectroelectrochemistry. It is shown that the amount of SWCNTs was reduced by about 35 % after lithium vapor treatment of the studied SWCNTs–DWCNTs mixture.     

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.     

单壁纳米碳管的纯化及表征

利用微孔膜及空气氧化法逐步除去电弧放电法制备的单壁纳米碳管(SWCNTs)中的金属催化剂粒子、碳纳米粒子、无定形碳等杂质,并利用热重分析（TGA）、高分辨透射电子显微镜（HRTEM）及拉曼（Raman）光谱,对每一步得到的产物进行分析表征.实验证明,该方法对单壁纳米碳管的纯化是比较有效的,可以得到纯度在90％以上的单壁纳米碳管.     

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.     

Preparation of Hydroxypropyl-β-cyclodextrin Cross-linked Multi-walled Carbon Nanotubes and Their Application in Enantioseparation of Clenbuterol

A method of cross‐linking multi‐walled carbon nanotubes by a nucleophilic substitution of brominated multi‐walled carbon nanotubes using hydroxypropyl‐β‐cyclodextrin anions was studied. The modified multi‐walled carbon nanotube samples were characterized using thermogravimetric analysis, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The hydroxypropyl‐β‐cyclodextrin modified multi‐walled carbon nanotubes were used as a chiral stationary phase additive for thin‐layer chromatography to separate clenbuterol enantiomers, and the chiral separation factor was increased.     

Deposition and characterization of Langmuir‐Blodgett films of cadmium arachidate/SWCNTs composites

The incorporation of single‐wall carbon nanotubes (SWCNTs) in cadmium arachidate film by means of the Langmuir‐Blodgett (LB) technique was investigated as a function of arachidic acid/SWCNT mass ratio at the air/water interface and in Langmuir‐Blodgett films. The behaviour at the air/water interface shows that SWCNTs act as an independent phase with respect to the cadmium arachidate. Deposition conditions are optimized when the weight ratio between the arachidic acid (AA) and SWCNTs is in the range 0.018:1 to 1:1. The general order of the LB multilayered structure was destroyed by the progressive density increase in SWCNT quantity as evidenced by X‐ray reflectivity (XRR) analysis. Scanning electron microscopy images indicated that when a multilayered structure was formed its layers consisted of SWCNT bundles stacked one over the other. Copyright © 2006 John Wiley & Sons, Ltd.     

Selective oxidation of metallic single-walled carbon nanotubes

In this work we present a simple and non-invasive approach to the preparation of semi-conducting single-walled carbon nanotubes (SWCNTs) through selective destruction of the metallic counterparts present in the starting material. Most separation techniques require chemical treatment, the application of ultrasound, or the addition of auxiliary molecules, which lead to the introduction of defects and impurities. In this contribution, laser ablation SWCNTs were selectively oxidised via long-term heating leading to the enrichment of semi-conductive nanotubes. Spectroscopic analysis demonstrates that the selective character of oxidation occurs only in the optimal temperature range, determined by thermo-gravimetric analysis. By tuning the process parameters, one can obtain a sample exhibiting different purity (up to 95 % of semi-conducting nanotubes) and separation efficiency. The samples’ quality and yield of separation were determined by UV-VIS-NIR spectroscopy, Raman spectroscopy, and TG analysis. The approach presented is readily scaleable.     

In Vivo Monitoring of the Thiols in Rat Striatum by Liquid Chromatography with Amperometric Detection at a Functionalized Multi‐Wall Carbon Nanotubes Modified Electrode

A new chemically modified electrode (CME) was fabricated, which was based on the immobilization of multi‐wall carbon nanotubes fuctionalized with carboxylic group (MWNT‐COOH). The results indicated that the CME exhibited efficiently electrocatalytic oxidation for L ‐cysteine and glutathione with relatively high sensitivity, stability and long‐life. Coupled with HPLC, the MWNT‐COOH CME was utilized for amperometric detection of the thiols. The peak currents of L ‐cysteine and glutathione were linear to their concentrations ranging from 3.0×10^?7 to 1.0×10^?3 mol/L with the calculated detection limit (S/N=3) of 1.2×10^?7, 2.2×10^?7 mol/L, respectively. The method had been successfully applied to assess the contents of L ‐cysteine and glutathione in rat striatal microdialysates.     

Correlation between the O 2p Orbital and Redox Reaction in LiMn0.6Fe0.4PO4 Nanowires Studied by Soft X‐ray Absorption

The changes in the electronic structure of LiMn_0.6Fe_0.4PO₄ nanowires during discharge processes were investigated by using ex situ soft X‐ray absorption spectroscopy. The Fe L ‐edge X‐ray absorption spectrum attributes the potential plateau at 3.45 V versus Li/Li⁺ of the discharge curve to a reduction of Fe³⁺ to Fe²⁺. The Mn L ‐edge X‐ray absorption spectra exhibit the Mn²⁺ multiplet structure throughout the discharge process, and the crystal‐field splitting was slightly enhanced upon full discharge. The configuration‐interaction full‐multiplet calculation for the X‐ray absorption spectra reveals that the charge‐transfer effect from O 2p to Mn 3d orbitals should be considerably small, unlike that from the O 2p to Fe 3d orbitals. Instead, the O K‐edge X‐ray absorption spectrum shows a clear spectral change during the discharge process, suggesting that the hybridization of O 2p orbitals with Fe 3d orbitals contributes essentially to the reduction.     

Metallic Li in carbonaceous nanotubes grown by metalorganic chemical vapor deposition from a metalorganic precursor

Metallic Li in carbonaceous nanostructures was obtained in high concentration (as much as 33.4%) through metalorganic chemical vapor deposition involving certain lithium–aminoalkyl moieties, which are formed in situ , by decomposition of a precursor containing both cobalt and lithium. The bimetallic complex containing both lithium and cobalt was characterized by IR spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis and thermogravimetric analysis. X‐ray photoelectron spectroscopy measurements performed on the as‐grown films demonstrate that lithium can be stable in metallic form in such a film. Results of X‐ray photoelectron spectroscopic analysis of the as‐grown films are presented as direct evidence of the formation and stabilization of metallic lithium in carbon nanotubes. Carbon nanotubes, encapsulating metallic lithium, can potentially act as a miniaturized nanobattery. Such a battery would be potentially useful in the next generation of communication and remote sensing devices, where a pulse of current is required for their operation. In addition, with metallic lithium, having an effective nuclear magnetic moment, such materials can be envisioned to show potential applications in devices based on nuclear magnetic resonances. Copyright © 2008 John Wiley & Sons, Ltd.