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Free-standing hybridized electrode consisting of double-walled carbon nanotubes (DWNTs) and activated carbon have been fabricated for flexible supercapacitor applications. The xanthan-gum, used in our methodology, showed high ability in dispersing the strongly bundled DWNTs, and was then effectively converted to activated carbon with large surface area via chemical activation. The homogeneously dispersed DWNTs within xanthan-gum derived activated carbon acted as both electrical path and mechanical support of electrode material. The hybridized film from highly dispersed DWNTs and activated carbon was mechanically strong, has high electrical conductivity, and exhibited high specific capacitance of 141.5 F/g at the current density of 100 mV/s. Our hybridized film is highly promising as electrode material for flexible supercapacitors in wearable device.

The electrochemical performance of sulfur-doped carbon nanotubes (S-CNTs) was investigated to confirm the S-doping effects and the possibility of their application as conducting agents in supercapacitor electrodes. S-CNTs were successfully synthesized via chemical vapor deposition using dimethyl disulfide as the carbon source. They were purified to obtain purified S-CNTs (P–S-CNTs) with diameters 30–50 nm and S content of 0.65 at%. The doped S atoms were removed partially from the P–S-CNTs by heat treatment in H2 atmosphere (De-P-S-CNTs). To compare the electrochemical performances of various conducting materials for supercapacitor electrodes, commercial activated carbon (MSP20) was used as the active material and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), De-P-S-CNTs, and P–S-CNTs were used as the conducting agents. The electrode with P–S-CNTs exhibited the highest specific capacitance at a high discharge current density of 100 mA cm−2 (120.2 F g−1) and the lowest charge-transfer resistance (6.19 Ω) that are significantly superior to those of Super-P (83.9 F g−1 and 15.16 Ω), MWCNTs (87.8 F g−1 and 17.02 Ω), and De-P-S-CNTs (90.1 F g−1 and 22.33 Ω). The superior electrochemical performance of P–S-CNTs can be attributed to the excellent electrical conductivity and pseudocapacitive contribution of the S-doping effect.

Linear carbon chains (LCCs) consisting of sp-hybridized carbon atoms are considered a fascinating 1D system and could be used in the fabrication of the next-generation molecular devices because of its ideal linear atomic nature. A large portion of long LCCs inside multi-walled carbon nanotubes (MWCNTs) were synthesized by atmospheric arc discharge in the presence of boron. Closed-end growth of MWCNTs in the arc process is suggested as a critical condition for the simultaneous growth of LCCs within the inner cores of carbon nanotubes. The strong Raman line around 1850 cm−1 was used to characterize the degree of filling as well as their structural stability under high temperature thermal treatments. We observed a distinctive change in the electrical conductivity of the MWCNT assembly before and after the disappearance of LCCs due to the expected strong coupling interaction between the LCCs and the innermost tube. This work demonstrates for the first time the enhanced effect of confined linear carbon chains on the overall electrical conductivity of MWCNT assemblies.

The optical properties of semiconducting carbon nanotubes respond sensitively to external conditions including the formation of chemical bonds. In order to detect the iron–3,4-dihydroxy-L-phenylalanine (DOPA) conjugation bonds with metal ions, an individually dispersed double-walled carbon nanotube (DWNT) suspension was prepared via homogeneous coating of mussel adhesive protein (MAP). MAP exhibited a high ability for individually dispersing the bundled DWNTs through strong physical interactions with the outer tubes. We demonstrated sensitively altered optical properties of the DWNT suspension upon addition of FeCl3 solution via the formation of coordinative bonds between DOPA in MAP and Fe3+ ions. The iron–DOPA bonds acted as electron acceptors and thus provided a favourable non-radiative channel for the optical depression of signal from semiconducting inner tubes in DWNT suspension. Several physical and chemical effects on the sensitively quenched photoluminescence of semiconducting inner tubes were explained based on the iron–DOPA bonds. We also observed that the DOPA groups in MAP were fully saturated at ca. 376.7 mol% of Fe3+ ions for MAP.

Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 °C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 °C that gave the stoichiometry of CF 0.20 , CF 0.30 , and CF 0.43 , respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 °C, the strong radial breathing modes (RBMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 °C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 °C were thermally treated at 1000 °C in argon. However, in the case of the DWCNTs fluorinated at 400 °C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.

Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremel...

Electrospun biopolymer-derived nanofiber webs are promising scaffolds for growing tissue and cells. However, the webs are mechanically weak and electrically insulating. We have synthesized a polyethylene oxide (PEO) nanofiber web that is pliable, tough, and electrically conductive, by incorporating optically active, DNA-wrapped, double-walled carbon nanotubes. The nanotubes were individually trapped along the length of the PEO nanofiber and acted as mechanically reinforcing filler and an electrical conductor.

Water-soluble, highly functionalized multiwalled carbon nanotubes (MWNTs) were prepared via a facile, environmentally benign method. The effectiveness of the highly functionalized MWNTs as a reinforcing filler in a water-soluble mechanically weak chitosan biopolymer was evaluated. We observed a substantial improvement in the mechanical properties of the film; the stretchability of the film was maintained when 5 wt% MWNTs was added. In addition, the biocomposite film exhibited long-term antibacterial activity. The reinforcing effect can be explained by the homogeneous dispersion of the nanotubes in the polymer matrix through the strong hydrogen bonding between the sulfonic acid groups (–SO3H) on the sidewalls of the MWNTs and the amine (–NH2) and hydroxyl (–OH) groups on the chitosan backbone. The improvement in the mechanical properties of the MWNT–chitosan biocomposite may make it suitable for many environmental and clinical applications.

Coalescing carbon nanotubes is a major challenge for designing structures with novel physical and chemical properties and for creating three-dimensional carbon networks with improved mechanical and transport properties. We have coalesced adjacent triple walled carbon nanotubes (TWNTs) covalently, using catalytic boron atoms at high temperatures. The two outermost and then the two inner nanotubes of adjacent TWNTs merged in order to create an enlarged flattened double-walled carbon nanotube which encapsulated the two innermost single-walled carbon nanotubes.