High-Strength Epoxy Nanocomposites Reinforced with Photochemically Treated CNTs.

A carbon nanotube (CNT)/epoxy nanocomposite was prepared using a photochemical surface modification process of CNTs. The vacuum ultraviolet (VUV)-excimer lamp treatment created reactive sites on the CNT surface. Increasing the irradiation time increased the oxygen functional groups and changed the oxygen bonding state such as C=O, C-O, and -COOH. By the VUV-excimer irradiation on CNTs, the epoxy infiltrated well between the CNT bundles and formed a strong chemical bond between CNT and epoxy. The tensile strength and elastic modulus of the nanocomposites with VUV-excimer irradiated sample during 30 min (R30) were found to increase by 30 and 68% compared to using pristine CNT, respectively. R30 was not pulled out and remained embedded in the matrix until the fracture occurred. The VUV-excimer irradiation is an effective surface modification and functionalization method for improving the mechanical properties of CNT nanocomposite materials.

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition.

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst's exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (−OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1'-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1'-diacetylferrocene has more sulfate (SO42−) than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal−sulfur bonds (such as S2− and Sn2−). The hydroxyl group (−OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

Tunable Synthesis of Predominant Semi-Ionic and Covalent Fluorine Bonding States on a Graphene Surface.

In this study, fluorinated graphene (FG) was synthesized via a hydrothermal reaction. Graphene oxides (GOs) with different oxygen bonding states and oxygen contents (GO(F), GO(P), and GO(HU)) were used as starting materials. GO(F) and GO(P) are commercial-type GOs from Grapheneall. GO(HU) was prepared using a modified Hummers method. The synthesized FGs from GO(F), GO(P), and GO(HU) are denoted as FG(F), FG(P), and FG(HU), respectively. The F atoms were bound to the graphene surface with predominantly semi-ionic or covalent bonding depending on the GO oxygen state. FG(F) and FG(HU) exhibited less extensive fluorination than FG(P) despite the same or higher oxygen contents compared with that in FG(P). This difference was attributed to the difference in the C=O content of GOs because the C=O bonds in GO primarily produce covalent C-F bonds. Thus, FG(F) and FG(HU) mainly exhibited semi-ionic C-F bonds. The doped F atoms were used to tune the electronic properties and surface chemistry of graphene. The fluorination reaction also improved the extent of reduction of GO.

Graphene Encapsulated Al Particles for Improvement of Thermal Conductivity in Composites.

Graphene reinforced aluminum matrix composites (GRAMCs) with improved thermal conductivity were prepared via a pH-controlled self-assembly process that involved adjusting the concentration of dispersed graphene oxide (GO) solutions. Uniform dispersion was achieved using GO coating on the aluminum (Al) surfaces. Graphene encapsulated Al powders (Al/GO) were sintered through spark plasma sintering (SPS) to prepare bulk composites, these were then analyzed to determine the thermal and mechanical properties. The density of the Al/GO composites was determined to be 99% or more compared to the theoretical density of pure Al. The Vicker's hardness and thermal conductivity increased by about 47% and 15% more than the pristine Al bulks. These processes can improve properties of the thermal interface between GO and Al, enabling uniform coating without a crosslinking agent. An Al/GO composite, fabricated through the pH-controlled self-assembly process, should be useful for various applications requiring to high thermal conductivity.

Chirality control for predominant metallic or semiconducting single-walled carbon nanotubes prepared using a mild etchant.

Highly oriented metallic and semiconducting SWCNTs were synthesized with different carrier gas compositions and etchants by the floating catalyst chemical vapor deposition method. The addition of acetone as an etchant resulted in metallic nanotubes. The acetone acted as both an additional carbon source and etching agent for carbon nanotube nucleation.

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality.

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH4 , C2 H4 , C2 H2 , C3 H6 , and C4 H10 whereas monometallic catalysts generate only CH4 and C2 H4 on decomposition. CNT fiber formation with Fe1 Ni0 begins about 400 mm from the reactor entrance, whereas CNT formation with Fe0.8 Ni0.2 and Fe0.5 Ni0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.

Influence of the Sulfur Content Catalyst on the Packing Density of Carbon Nanotube Forests.

For the fabrication of high-performance carbon nanotube (CNT) composites with practical applicability, the development of new methods for the controlled growth of high-aspect-ratio CNTs still constitutes a challenge. With the aim of gaining a deeper understanding of the catalytic CNT growth, in this study, the effect of the catalyst composition is investigated using different mixtures of Fe2(SO4)3 and FeCl2 as catalysts. The relationship between the catalyst chemical state and the growth behavior of CNT forests is demonstrated by evaluating the alignment, diameter, length, and areal density of the CNT forests. When the Fe2(SO4)3 content is increased, the area density, the IG/ID ratio, and the crystallite size of the CNTs increase. Additionally, the obtained CNT forests exhibit good spinnability with increasing the sulfur content.

Structure transformation by sp2 hydrocarbon assisted carbon nanotube growth.

In this study, we investigated the effect of hydrocarbon species composition on carbon nanotube (CNT) growth using an iron catalyst by chemical vapor deposition. The atomic hydrogen and active carbon species from hydrocarbon affect to the nucleation and growth of CNT arrays. With increasing atomic hydrogen content, the interface layer distance of the CNTs decreased from 3.7 to 3.4 Å. The shifts in the G-band in the Raman spectra of the CNTs indicated that the hydrogen atoms affected the generation of C-C bonds in graphene layers.

Fabrication of single-phase titanium carbide layers from MWCNTs using high DC pulse.

Single-phase layered titanium carbide (TiC) was successfully synthesized by reacting carbon nanotubes (CNTs) and titanium dioxide (TiO2) under a high direct current (DC) pulse. Single-phase TiC layer fabrication is confirmed as the transformation of multi-layered graphene from MWCNTs. Therefore its thickness and width is almost identical to those of transformed graphene layers. This is the first report on the formation of single-phase layered nano-TiC. Scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM) were used for the characteristic analysis of single-phase layered TiC structures.