Ultrasound-promoted direct functionalization of multi-walled carbon nanotubes in water via Diels-Alder “click chemistry”

A facile and environmentally friendly strategy for grafting polymers onto the surface of multi-walled carbon nanotubes (CNTs) was demonstrated by Diels-Alder “click chemistry”. Firstly, the copolymers of poly(styrene-alt-maleic anhydride) (PSM) were prepared by the reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently functionalized with furfuryl amine to introduce anchoring groups. The copolymers were then grafted on CNTs via the Diels-Alder reaction in water through a conventional heating-stirring route and ultrasound-assisted method. The obtained nanocomposite materials were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. The results indicated that the reaction rate under ultrasound irradiation was accelerated about 12 times than the one under the conventional heating-stirring condition without losing the grafting efficiency. The direct functionalization of CNTs formed a stably dispersed solution in water, promising a green and effective method for industrial process.     

Modulating the diameter of carbon nanotubes in array form via floating catalyst chemical vapor deposition

Based on the analysis of catalyst particle formation and carbon nanotube (CNT) array growth process in floating catalyst chemical vapor deposition (CVD), delicately controlled gaseous carbon sources and catalyst precursors were introduced into the reactor for the controllable growth of CNT array. The low feeding rate of ferrocene was realized through low-temperature sublimation. With less ferrocene introduced into the reactor, the collision among the in situ formed iron atoms decreased, which led to the formation of smaller catalyst particles. The mean diameter of the CNT array, grown at 800^oC, decreased from 41 to 31 nm when the ferrocene-sublimed temperature reduced from 80 to 60^oC. Furthermore, low growth temperature was adopted in synthesis, through the modulation of the CNT diameter, by controlling the sintering of catalyst particles and the collision frequency. When the growth temperature was 600^oC, the as-grown CNTs in the array were with a mean diameter of 10.2 nm. If propylene was used as carbon source, the diameter can be modulated in similar trends. The diameter of CNT can be modulated by the parameter of the operation using the same substrate and catalyst precursor without other equipment or previous treatment. Those results provide the possibility for delicately controllable synthesis of CNT array via simple floating catalyst CVD.     

The use of calcination in exposing the entrapped Fe particles from multi-walled carbon nanotubes grown by chemical vapour deposition

Multi-walled carbon nanotubes (MWCNTs) were synthesized a by chemical vapour deposition method. The effect of calcination at temperatures ranging from 300 to 550°C in exposing the metal nanoparticles within the nanotube bundles was studied. The degree of degradation of the structural integrity of the MWCNTs during the thermal process was studied by Raman spectroscopy, X-ray diffraction analysis, field-emission scanning electron microscopy, and transmission electron microscopy. The thermal behaviour of the as-prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air, at 400°C for 1 h, was found to be an efficient and simple method to extract metallic impurities from the amorphous carbon shells with minimal damage to the tube walls and lengths. The nanotubes were observed to be damaged at temperatures higher than 450°C.     

Synthesis and electrochemical characterization of nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes

Nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes (N-MWCNTs and N–P-MWCNTs, respectively) were fabricated by chemical vapor deposition and characterized using scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray spectroscopy and Raman spectroscopy. The electrochemical response of N-MWCNTs and N–P-MWCNTs towards ferrocyanide/ferricyanide was initially studied. The findings exhibit weakening of electrochemical response and sensitivity of nanotubes with phosphorus doping, and thus, within the composite films tested, those consist exclusively of N-MWCNTs exhibit the greatest electrocatalytic activity. N–P-MWCNT film was further applied for individual electrochemical analysis of ascorbic acid (AA), uric acid (UA), and dopamine (DA), and lower limits of detections of 11.6, 7.8, and 1.9 μM were estimated, respectively. The findings demonstrate that AA does not interfere with UA, but considerable interference of AA in analysis of DA was observed. Thus, the simultaneous analysis of AA, UA, and DA on N–P-MWCNTs appears to be restricted.     

Laser-induced decoration of carbon nanotubes with metal nanoparticles

Hybrid nanomaterials consisting of multiwall carbon nanotubes (MWCNT) decorated with noble metal nanoparticles were produced by irradiating aqueous mixed solutions of the separate components with nanosecond lasers pulses at 248 nm. Specifically, the decoration with Au and Pd nanoparticles is discussed. No decoration of the MWCNT was observed by simple mixing with nanoparticle solutions. Hence, a photo-thermal mechanism is suggested, whereby the laser-heating of the nanoparticles induces melting, boiling and subdivision into smaller clusters and atoms, which then attach to the MWCNT.     

Hydrogen storage in multi-wall carbon nanotubes using samples up to 85 g

Hydrogen storage in carbon nanotubes (CNTs) is investigated at ambient temperature and pressures of 0–12 MPa, using 35–85 g multi-wall carbon nanotube (MWNT) samples that were synthesized in a nano-agglomerate fluidized bed reactor. The volume of hydrogen gas released by the CNTs was measured by a volumetric flow meter. The capability of H₂ storage in the CNT samples of mass of up to 85 g can be obtained with a precision of 0.01 wt.%. MWNTs with average diameters ranging from 10–30 nm and were pretreated using nitric acid or a sodium hydroxide solution wash and a high temperature treatment. The influence of the hydrogen pressure, hydrogen storage time and treatment method were studied. All data show that the amount of hydrogen released by the MWNTs at room temperature is no more than 0.30 wt.%, while hydrogen released by MWNT at 77 K can reach 2.27 wt.%. PACS 61.46.+w; 68.43.-h; 84.60.Ve     

Bundling influence on ultrafast optical nonlinearities of single-walled carbon nanotubes in suspension and composite film

Nonlinear optical characteristics of single-walled carbon nanotubes (SWCNTs) dispersed in dichlorobenzene and imbedded in polymer were investigated at 800 nm using the time-resolved optical Kerr gate technique. For systematic study of the influence of SWCNT bundling on optical nonlinearities, SWCNT solutions with different concentrations and a series of SWCNT/polymer composites deposited on glass substrates with different concentrations and thicknesses were prepared. The nonlinear response was comparable to the pulse duration of the laser used (～90 fs) both in SWCNT solutions and SWCNT/polymer composites. Over three orders of magnitude enhancement was observed in the third-order nonlinear susceptibility of SWCNT/polymer composite film compared with that of SWCNT solution. An appreciable reduction of microscopic and macroscopic nonlinearities was observed with increasing SWCNT concentrations due to stronger bundling of SWCNTs.     

Spin-orbit effects in carbon nanotubes – Analytical results

We report a study of the normal and superconducting state properties of the Ti _x V_1?x alloys for x = 0.4, 0.6, 0.7 and 0.8 with the help of dc magnetization, electrical resistivity and heat capacity measurements along with the electronic structure calculation. The superconducting transition temperature T _c of these alloys is higher than that of elemental Ti and is also higher than elemental V for x ≤ 0.7. The roles of electron density of states, electron-phonon coupling and spin fluctuations in the normal and superconducting state properties of these alloys have been investigated in detail. The experimentally observed value of T _c is found to be considerably lower than that estimated on the basis of electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys. There is some evidence as well for the preformed Cooper pair in all these Ti-V alloys in the temperature regime well above T _c . Similar to x = 0.6 [Md. Matin, L.S. Sharath Chandra, R.K. Meena, M.K. Chattopadhyay, A.K. Sinha, M.N. Singh, S.B. Roy, Physica B 436, 20 (2014)], the normal state properties of the x = 0.4 alloy showed the signature of the presence of spin fluctuations. The difference between the experimentally observed T _c and that estimated by considering electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys is attributed to the possible influence of these spin fluctuations. We show that the non-monotonous variation of T _c as a function of x in the Ti _x V_1?x alloys is due to the combined effects of the electron-phonon coupling and the spin fluctuations.     

The 1/f noise in multiwalled carbon nanotubes

The $1/f$ noise in multiwalled carbon nanotubes bundles has been investigated between the frequency range of 0.1 to 30 Hz. At room temperature the noise spectrum is standard 1/f, and its level is proportional to the square of the bias voltage. With decreasing temperature the noise level also decreases. At 4.2 K the noise level follows a non-monotonic dependence against the bias voltage, showing a peak at a certain bias voltage, meanwhile its frequency dependence also deviates from the 1/f trend. This anomalous behaviour is discussed within the picture of environmental quantum fluctuation of charge transport in the samples.     

Fast electron beam–plasma interaction in single-walled carbon nanotubes

A theoretical study on the plasmon-polariton modes coupled with a fast electron beam inside a metallic single-walled carbon nanotube is presented. The Maxwell’s equations coupled with a linearized hydrodynamic model for the nanotube’s charge oscillations are used. By considering the electron beam effects, general expression of dispersion relation of electromagnetic modes on nanotube’s surface is obtained. It is shown numerically that by considering the electron beam effects, the polariton frequency shifts to lower values.     

Intrinsic spin–orbit interaction in carbon nanotubes and curved nanoribbons

We present a theoretical study of spin–orbit interaction effects on single wall carbon nanotubes and curved graphene nanoribbons by means of a realistic multiorbital tight-binding model, which takes into account the full symmetry of the honeycomb lattice. Several effects relevant to spin–orbit interaction, namely, the importance of chirality, curvature, and a family-dependent anisotropic conduction and valence band splitting are identified. We show that chiral nanotubes and nanoribbons exhibit spin-split states. Curvature-induced orbital hybridization is crucial to understand the experimentally observed anisotropic spin–orbit splittings in carbon nanotubes. In fact, spin–orbit interaction is important in curved graphene nanoribbons, since the induced spin-splitting on the edge states gives rise to spin-filtered states.     

Studying the relative bottom contribution via heavy-quark decay electron measurements in STAR

We report measurements of the azimuthal angular correlation distribution of heavy-quark decay electrons and open charmed mesons in pp collisions at  GeV in the STAR experiment at RHIC. This measurement in combination with current theoretical model calculations allows to extract the relative bottom contribution to the heavy-quark decay electrons, which is important for the interpretation of the observed strong suppression of the high-p _T electron yield in central Au+Au collisions.     

Formation and structure of circular-disc assemblies of double-walled carbon nanotubes from a catalytic CVD reaction

A large-size circular-disc (CD) assembly of carbon nanotubes (CNTs) was formed from injection catalytic chemical vapor deposition (CVD) reactions. The CNT-CD assembly, which has an outer diameter of 830 nm, consists of closely packed rings of double-walled carbon nanotubes (DWNTs), in twenty-eight circles, and stacked in five layers. A structural interpretation suggests that the CNT-CD assembly is coiled from a “tape-like” bundle of DWNTs, whose coiling to form the CNT-CD resembles the rolling up of tape to form a disc. The large CD assembly was formed within milliseconds in the transient gas flow reactions, and the coiling of nanotubes or “nucleation” of the circular assembly was associated with shears generated by gas disturbances in the vapor phase.     

Phonon transport in isotope-disordered carbon and boron-nitride nanotubes: is localization observable?

We present an ab initio study which identifies dominant effects leading to thermal conductivity reductions in carbon and boron-nitride nanotubes with isotope disorder. Our analysis reveals that, contrary to previous speculations, localization effects cannot be observed in the thermal conductivity measurements. Observable reduction of the thermal conductivity is mostly due to diffusive scattering. Multiple scattering induced interference effects were found to be prominent for isotope concentrations > or approximately 10%; otherwise, the thermal conduction is mainly determined by independent scattering contributions of single isotopes. We give explicit predictions of the effect of isotope disorder on nanotube thermal conductivity that can be directly compared with experiments.     

On the efficiency of bile salt for stable suspension and isolation of single-walled carbon nanotubes—spectroscopic and microscopic investigations

In this contribution we present a systematic study on the dispersion of SWCNTs in a water-based solution of biocompatible detergent: sodium deoxycholate (DOC). By avoiding harsh chemical conditions, which are known to damage nanotubes structure, a stable SWCNTs suspension was created. Long term stirring of the solution led to preparation of a stable transparent solution, containing well-dispersed isolated SWCNTs. The as-prepared dispersion remained stable and clear for two months. Optical absorption spectroscopy was employed to measure SWCNTs suspension stability. Nanotube aggregation was evaluated through the tangential mode (G mode) present in the Raman spectrum. High-resolution transmission electron microscopy was employed to observe the mechanism of debundling process.     

An efficient composite growing N-doped TiO<Subscript>2</Subscript> on multi-walled carbon nanotubes through sol–gel process

High-activity, visible-light-driven photocatalysts were prepared by forming N-doped TiO₂ on multi-walled carbon nanotubes (MWCNTs). The use of MWCNTs as the support in a N-doped TiO₂ system favored electron trapping, because the recombination process could be retarded, thus promoting photocatalytic activity. The prepared photocatalysts were systematically characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunaure–Emmett–Teller (BET) spectroscopy, and UV–Vis diffuse reflectance spectroscopy (UV–Vis/DRS). The results indicated that the N-doped TiO₂ coated on MWCNTs improved the surface area and slightly modified the optical properties of the composite. The activities of the photocatalysts were probed by photodegradation of methanol in the presence of visible light irradiation. The experimental results revealed that the strong interphase linkage between the MWCNTs and the N-doped TiO₂ played a significant role in improving photocatalytic activity. However, the mechanical process for MWCNT–TiO_2-x N _x mixtures showed lower activity than just pure N-doped TiO₂. In this study, N-doped TiO₂ precursors coated with pretreated MWCNTs during a sol–gel process could effectively form a MWCNT–TiO_2-x N _x composite. The composite showed excellent activity and effectively enhanced the efficiency of N-doped TiO₂ under the visible light region.     

Vertically aligned carbon nanotubes from natural precursors by spray pyrolysis method and their field electron emission properties

Vertically aligned carbon nanotubes have been synthesized from botanical hydrocarbons: Turpentine oil and Eucalyptus oil on Si(100) substrate using Fe catalyst by simple spray pyrolysis method at 700°C and at atmospheric pressure. The as-grown carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Raman spectroscopy. It was observed that nanotubes grown from turpentine oil have better degree of graphitization and field emission performance than eucalyptus oil grown carbon nanotubes. The turpentine oil and eucalyptus oil grown carbon nanotubes indicated that the turn-on field of about 1.7 and 1.93 V/μm, respectively, at 10 μA/cm². The threshold field was observed to be about 2.13 and 2.9 V/μm at 1 mA/cm² of nanotubes grown from turpentine oil and eucalyptus oil respectively. Moreover, turpentine oil grown carbon nanotubes show higher current density in relative to eucalyptus oil grown carbon nanotubes. The maximum current density of 15.3 mA/cm² was obtained for ∼3 V/μm corresponding to the nanotubes grown from turpentine oil. The improved field emission performance was attributed to the enhanced crystallinity, fewer defects, and greater length of turpentine oil grown carbon nanotubes.