Additional SEM and TEM images. from Revisiting behaviour of monometallic catalysts in chemical vapour deposition synthesis of single-walled carbon nanotubes

Figure S1 Original SEM image of SWNTs grown from Co catalyst on TEM grid; Figure S2 Original TEM images of Ni catalyst before and after growth; Figure S3 Original SEM image of SWNTs grown from Fe catalyst on suspended SiO2; Figure S4 Original TEM image of SWNTs grown from Fe catalyst on suspended SiO2; Figure S5 Original TEM images of Cu catalyst after SWNT growth; Figure S6 Original TEM images of Pd catalyst after reduction

Twofold Effects of Zirconium Doping into TiN on Durability and Oxygen Reduction Reactivity in an Acidic Environment

Carbon-support-free TiN-based catalysts have recently been developed to avoid both carbon oxidation and the use of scarce platinum group metals in acidic polymer electrolyte fuel cell cathodes. However, providing sufficient durability at high potentials above 1.0 V remains a challenge. Herein, zirconium doping is revealed as a new route that enhances catalyst activity and selectivity toward the four-electron oxygen reduction reaction (ORR) in an acidic environment. The TiN surface is oxidized to form rutile TiO2 layers, and some zirconium atoms are dissolved into both the bulk TiN and the surface rutile layers. The zirconium atoms distort the rutile lattice to increase the number of oxygen vacancies which are critical for the ORR, whereas some others segregate to form monoclinic and tetragonal ZrO2 phases to inhibit the TiN crystallite growth. The optimized Ti0.8Zr0.2OxNy catalysts exhibit excellent durability during 5000 start-up and shut-down cycles between 1.0 and 1.5 V versus the reversible hydrogen electrode in 0.1 mol dm–3 H2SO4 solution. The decrease in the halfwave potential during the 5000 cycles is only 0.04 V, which is half that of the previous best phosphorus-doped TiN catalyst

Controllable Expansion of Single-Walled Carbon Nanotube Dispersions Using Density Gradient Ultracentrifugation

We present a protocol to selectively isolate single-walled carbon nanotubes (SWNTs) with different chiralities in a full-colored “rainbow” expansion using density gradient ultracentrifugation (DGU). Starting with SWNTs synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) method, we used sodium deoxycholate (DOC) and sodium dodecyl sulfate (SDS) as cosurfactant encapsulating agents to form a DOC-restricted SDS wrapping morphology around the SWNTs. This enhances the density differences between nanotubes of different diameters, which leads to efficient chirality redistribution when combined with an appropriate density gradient profile. UV−vis-NIR absorbance spectra and photoluminescence excitation (PLE) maps show the optical properties of each fraction, and 97% pure isolation of (6,5) SWNTs achieved from the rainbow is also reported

Zeolite Surface As a Catalyst Support Material for Synthesis of Single-Walled Carbon Nanotubes

Preparation of single-walled carbon nanotubes (SWNTs) has been advanced by controlling several parameters including the catalyst and the catalyst support material. Although zeolite has been frequently used as a catalyst support material for the synthesis of SWNTs, detailed surface properties of previously employed zeolites and thus their role as a catalyst support material have not been sufficiently clarified yet. In this study, a clean b-plane surface of silicalite-1, which is a siliceous MFI-type zeolite, was used as a model substrate for the synthesis of SWNTs. The amount of active cobalt used for SWNT generation was smaller than the initially sputtered amount, and XPS measurements revealed diffusion of cobalt into the zeolite framework. The diffused cobalt was found to interact strongly with the silica framework of zeolite. The diffusion coefficient of cobalt in silicalite-1 zeolite was larger than that in thermally oxidized SiO2 formed on a Si substrate. This difference was ascribed to the microporous structure and lower density of zeolite. In this study, the state of the cobalt catalyst and the interaction between cobalt and the crystalline zeolite substrate is presented and discussed

Acetylene-Accelerated Alcohol Catalytic Chemical Vapor Deposition Growth of Vertically Aligned Single-Walled Carbon Nanotubes

Addition of only 1% acetylene into ethanol was found to enhance the growth rate of single-walled carbon nanotubes (SWNTs) by up to 10-fold. This accelerated growth, however, only occurred in the presence of ethanol, whereas pure acetylene at the same partial pressure resulted in negligible growth and quickly deactivated the catalyst. The dormant catalyst could be revived by reintroduction of ethanol, indicating that catalyst deactivation is divided into reversible and irreversible stages. Since the thermal decomposition of ethanol also yields some amount of acetylene, the possible contribution to the formation of SWNTs from these decomposed gases is also discussed

Growth Mechanism of Single-Walled Carbon Nanotube from Catalytic Reaction Inside Carbon Nanotube Template

We report a numerical investigation on the catalytic growth mechanism of a single-walled carbon nanotube (SWNT) inside a template SWNT, that is, formation of a double-walled carbon nanotube (DWNT). The molecular dynamics simulations together with complementary ab inito calculations suggest that the DWNT formation from thermally annealed metallocene-encapsulating SWNT goes through formation of metal catalyst cluster, followed by SWNT precipitation at the root. The diameter of the inner SWNT is determined by the carbon/metal layered structure of the catalyst cluster, which gives rise to a DWNT interlayer distance significantly different from the van der Waals distance

Influence of Zeolite Catalyst Supports on the Synthesis of Single-Walled Carbon Nanotubes: Framework Structures and Si/Al Ratios

Choice of the catalyst support is an important factor for the synthesis of single-walled carbon nanotubes (SWNTs) by the catalytic chemical vapor deposition (CCVD) method. Zeolites, which are a class of microporous crystalline material, have also been known as the catalyst support for the synthesis of SWNTs. However, detailed influences of their porous framework and framework composition have not been clarified yet. In this study, we have investigated zeolites as catalyst supports on the SWNTs synthesis. Various zeolites possessing different Si/Al ratios and framework types, FAU, *BEA, and MFI-type, were used as catalyst supports. Both properties influenced the SWNT growth, and the results are explained by the diffusion of catalyst metal atoms into the zeolite framework and the stabilization of the diffused atoms at ion-exchange sites in the crystals. By tuning these properties, zeolites could be convenient catalyst supports that can impart a relatively wide effective loading range to the metal catalyst for the CCVD growth of SWNTs

Anomalous Thermal Conduction Characteristics of Phase Change Composites with Single-Walled Carbon Nanotube Inclusions

We report strikingly large contrasts in the thermal conductivity enhancement of phase change alkane in liquid and solid state with single-walled carbon nanotube (SWCNT) inclusions. With a small SWCNT loading of 0.25 wt % a strikingly high, 250% enhancement is achieved in the solid state and a nominal enhancement of 10% is achieved in the liquid state. The thermal conductivity contrast between solid and liquid state was found to increase with increasing SWCNT loading. The thermal conductivity contrast was more pronounced in the presence of SWCNTs compared to the presence of exfoliated graphite nanoplatelets reported in the literature

Tunable Electrical and Thermal Transport in Ice-Templated Multilayer Graphene Nanocomposites through Freezing Rate Control

We demonstrate tunable electrical and thermal conductivities through freezing rate control in solution-based nanocomposites. For a prototypical suspension of 1 vol % multilayer graphene suspended in hexadecane, the solid–liquid electrical conductivity contrast ratio can be tuned from 1 to 4.5 orders of magnitude for freezing rates between 10² and 10^–3 °C/min. We hypothesize that this dramatic variation stems from ice-templating, whereby crystal growth drives nanoparticles into concentrated intercrystal regions, increasing the percolation pathways and reducing the internanoparticle electrical resistance. Optical microscopy supports the ice-templating hypothesis, as these dramatic property changes coincide with changing crystal size. Under the same range of freezing rates, the nanocomposite solid–liquid thermal conductivity contrast ratio varies between 2.3 and 3.0, while pure hexadecane’s varies between 2.1 and 2.6. The nanocomposite’s thermal conductivity contrast ratios and solid phase enhancements are greater than effective medium theory predictions. We suggest this is due to ice-templating, consistent with our electrical measurements, as well as nanoparticle-induced molecular alignment of alkanes

An Analytical System for Single Nanomaterials: Combination of Capillary Electrophoresis with Raman Spectroscopy or with Scanning Probe Microscopy for Individual Single-Walled Carbon Nanotube Analysis

Nanomaterials continue to attract widespread attention in many scientific and technological fields. The sizes and shapes of nanomaterials determine their physical and chemical properties. We have developed an analytical system for single nanomaterials that combines capillary electrophoresis (CE) with a highly sensitive detection method. In this manuscript, we combined CE with Raman spectroscopy or with scanning probe microscopy (SPM) for the analysis of individual single-walled carbon nanotubes (SWNTs). To combine CE with these detection techniques, we fabricated a fraction collection system that can collect droplets of small volume (<300 nL) in a small hydrophilic spot on a fractionation glass plate. The CE-separated fractions were concentrated by the evaporation of effluent, thus increasing the sensitivity by more than a factor of 10 in the case of Raman spectroscopic analysis. We characterized the fractionated SWNTs by means of Raman spectroscopy and SPM, both of which detected single SWNTs. Raman analysis enabled us to recognize a diameter difference of only 0.02 nm between SWNTs, and it was supposed that the separation by CE occurred based on the diameters of the SWNTs. We also observed a fibrous SWNT structure 1 nm high via SPM, and this structure was thought to be a single SWNT. These combined analytical systems enable the precise separation and characterization of individual SWNTs. We expect that methods developed herein can be applied to the analysis of many nanomaterials, because these methods offer separation and analysis with nanometer-scale precision. The characterization of nanomaterials at the single-compound level will be a necessity as the field of nanomaterials continues to evolve, and these combined methods may become indispensable techniques for the analysis of widely available nanomaterials