Effects of high temperature treatment of carbon nanotube arrays on graphite: increased crystallinity, anchoring and inter-tube bonding

Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 °C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young's modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 °C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.

Functionalized Carbon Nanostructures Versus Drug Resistance: Promising Scenarios in Cancer Treatment

Carbon nanostructures (CN) are emerging valuable materials for the assembly of highly engineered multifunctional nanovehicles for cancer therapy, in particular for counteracting the insurgence of multi-drug resistance (MDR). In this regard, carbon nanotubes (CNT), graphene oxide (GO), and fullerenes (F) have been proposed as promising materials due to their superior physical, chemical, and biological features. The possibility to easily modify their surface, conferring tailored properties, allows different CN derivatives to be synthesized. Although many studies have explored this topic, a comprehensive review evaluating the beneficial use of functionalized CNT vs G or F is still missing. Within this paper, the most relevant examples of CN-based nanosystems proposed for MDR reversal are reviewed, taking into consideration the functionalization routes, as well as the biological mechanisms involved and the possible toxicity concerns. The main aim is to understand which functional CN represents the most promising strategy to be further investigated for overcoming MDR in cancer.

Precise control of versatile microstructure and properties of graphene aerogel via freezing manipulation

A deep understanding of the shaping technique is urgently required to precisely tailor the pore structure of a graphene aerogel (GA) in order to fit versatile application backgrounds. In the present study, the microstructure and properties of GA were regulated by freeze-casting using an ice crystal template frozen from -10 °C to -196 °C. The phase field simulation method was applied to probe the microstructural evolution of the graphene-H2O system during freezing. Both the experimental and simulation results suggested that the undercooling degree was fundamental to the nucleation and growth of ice crystals and dominated the derived morphology of GA. The pore size of GA was largely regulated from 240 to 6 μm via decreasing the freezing temperature from -10 °C to -196 °C but with a constant density of 8.3 mg cm-3. Rapid freeze casting endowed GA with a refined pore structure and therefore better thermal, electrical, and compressive properties, whereas the GA frozen slowly had superior absorption properties owing to the continuous and tube-like graphene lamellae. The GA frozen at -196 °C exhibited the highest Young's modulus of 327 kPa with similar densities to those reported in the literature. These findings demonstrate the diverse potential applications of GA with regulated pore morphologies and also contribute to cryogenic-induced phase separation methods.

Graphene nanosheet-grafted double-walled carbon nanotube hybrid nanostructures by two-step chemical vapor deposition and their application for ethanol detection

Here, we present a facile technique for synthesis of graphene nanosheet (GNS)-grafted double-walled carbon nanotube (DWCNT) hybrid carbon nanostructures (here after referred to as G-DWCNTs) by directly growing GNSs along the sidewalls of DWCNTs using a two-step chemical vapor deposition (CVD). DWCNTs were synthesized by floating catalyst CVD at 1300 °C using ferrocene and thiophene dissolved in ethanol. Then, GNSs were grafted onto the synthesized DWCNT bundles by thermal CVD at 1300 °C using ethanol. The sharp-edged petal-like structure of GNSs were grown along the sidewalls of DWCNT bundles while maintaining the one-dimensional structure of DWCNT. Next, DWCNTs and G-DWCNTs were dispersed in ethanol, then deposited on the paper using vacuum filtration method and used for ethanol detection. G-DWCNTs sensor exhibited a 3-fold improvement in the response to ethanol vapor compared to the DWCNTs sensor. The sensing mechanism of DWCNTs and G-DWCNTs can be described in terms of charge transfer between the gas molecules and sensing material. These results demonstrate that the facile technique by two-step CVD method provides a promising approach for simple and low-cost technique to synthesize the hybrid nanostructure of GNSs and DWCNTs. The new hybrid carbon nanostructures are attractive for gas sensing application.

Nickel skeleton three-dimensional nitrogen doped graphene nanosheets/nanoscrolls as promising supercapacitor electrodes

A novel nickel skeleton 3D nitrogen doped graphene (N-GR/NF) superstructure with interconnected graphene nanosheets and nanoscrolls was synthesized using a facile two-step method. By varying the precursor concentration, the assembly of a graphene aerogel can be easily regulated, yielding different micro-structures and morphologies which accelerate the fast electron/ion transportation. The N-GR/NF composites demonstrate enhanced capacitance of 250 F g^-1 at 5 A g^-1, good rate performance (237 F g^-1 at the current density of 12 A g^-1) and cycle stability (90.9% retention after 5000 cycles) in 1 M KOH electrolyte. This study provides a new strategy for the microporous engineering of graphene gel, promising for further exploitation in various other applications.

In situ mechanical investigation of carbon nanotube-graphene junction in three-dimensional carbon nanostructures

Hierarchically organized three-dimensional (3D) carbon nanotubes/graphene (CNTs/graphene) hybrid nanostructures hold great promises in composite and battery applications. Understanding the junction strength between CNTs and graphene is crucial for utilizing such special nanostructures. Here, in situ pulling an individual CNT bundle out of graphene is carried out for the first time using a nanomechanical tester developed in-house, and the measured junction strength of CNTs/graphene is 2.23 ± 0.56 GPa. The post transmission electron microscopy (TEM) analysis of remained graphene after peeling off CNT forest confirms that the failure during pull-out test occurs at the CNT-graphene junction. Such a carefully designed study makes it possible to better understand the interfacial interactions between CNTs and graphene in the 3D CNTs/graphene nanostructures. The coupled experimental and computational effort suggests that the junction between the CNTs and the graphene layer is likely to be chemically bonded, or at least consisting of a mixture of chemical bonding and van der Waals interactions.

Enhanced electrochemical performance of a lead–acid battery by a surface modified negative grid with multiwall carbon nanotube coating

High-performance lead–acid battery (LAB) negative grids have been prepared using a simple carbon nanotube (CNT) coating method.

Enhanced electron transfer kinetics through hybrid graphene-carbon nanotube films

We report the first study of the electrochemical reactivity of a graphenated carbon nanotube (g-CNT) film. The electron transfer kinetics of the ferri-ferrocyanide couple were examined for a g-CNT film and compared to the kinetics to standard carbon nanotubes (CNTs). The g-CNT film exhibited much higher catalytic activity, with a heterogeneous electron-transfer rate constant, k0, approximately two orders of magnitude higher than for standard CNTs. Scanning electron microscopy and Raman spectroscopy were used to correlate the higher electron transfer kinetics with the higher edge-density of the g-CNT film.