Single-walled Nanohorns Research Articles

Carbon nanohorn improved durable PVDF membranes - The future of membrane distillation and desalination

Novel durable, hybrid separation materials based on the PVDF support and single walled nanohorn (SWCNH) were generated by a facile and efficient method. Three types of SWCNH, pristine, treated with ultrasounds, and oxidized, were applied to cover the PVDF-material. The extended characterization of the produced materials provided a broad spectrum of data including morphology, textural properties, surface ζ potential and wettability features. For the first time, the defined materials were finally tested in the air gap membrane distillation process for desalination, and the improvement was observed comparing to the PVDF. It was revealed that via the simple pretreatment method of SWCNH, it was possible to control wettability and material performance. Very important finding was that the hybrid membranes exhibited the improved permeate flux for hybrids. The enhancement was in the range of 14–27% for materials with pristine and ultrasound treated SWCNH. However, for hybrids with oxidized SWCNH 23%-improvement in transport was observed. Owing to the significantly differentiated character of pristine and oxidized SWCNH and the presence of hydrophobic support inside the structure of hybrids, separation materials with the external layer ranging from hydrophilic (contact angle 6°) to superhydrophobic (contact angle 165°) features were created.

Carbon Nanohorn-Derived Graphene Nanotubes as a Platinum-Free Fuel Cell Cathode.

Current low-temperature fuel cell research mainly focuses on the development of efficient nonprecious electrocatalysts for the reduction of dioxygen molecule due to the reasons like exorbitant cost and scarcity of the current state-of-the-art Pt-based catalysts. As a potential alternative to such costly electrocatalysts, we report here the preparation of an efficient graphene nanotube based oxygen reduction electrocatalyst which has been derived from single walled nanohorns, comprising a thin layer of graphene nanotubes and encapsulated iron oxide nanoparticles (FeGNT). FeGNT shows a surface area of 750 m(2)/g, which is the highest ever reported among the metal encapsulated nanotubes. Moreover, the graphene protected iron oxide nanoparticles assist the system to attain efficient distribution of Fe-Nx and quaternary nitrogen based active reaction centers, which provides better activity and stability toward the oxygen reduction reaction (ORR) in acidic as well as alkaline conditions. Single cell performance of a proton exchange membrane fuel cell by using FeGNT as the cathode catalyst delivered a maximum power density of 200 mW cm(-2) with Nafion as the proton exchange membrane at 60 °C. The facile synthesis strategy with iron oxide encapsulated graphitic carbon morphology opens up a new horizon of hope toward developing Pt-free fuel cells and metal-air batteries along with its applicability in other energy conversion and storage devices.

Single-walled nanohorns and other nanocarbons generated by submerged arc discharge between carbon electrodes in liquid argon and other media

Arc discharge between two graphite electrodes submerged in different liquid media yields various dimensional nanocarbon structures such as 1D carbon nanotubes and 2D graphene. Single-walled carbon nanohorns (SWNHs) prepared by submerged arc discharge in liquid nitrogen medium are found to have nitrogen impurities. Here, we report the structure and properties of pure and nitrogen-doped SWNHs obtained by submerged arc discharge in a liquid argon medium. The absence of an XPS N 1s signal, which is present in nanohorns obtained in liquid nitrogen, indicate that the nanohorns are free from nitrogen impurities. Raman spectra show a strong defect-induced D band and current–voltage characteristics show a slight nonlinear behavior. N2 adsorption of pure SWNHs shows type-IV isotherms with a surface area of 300 m2 g−1. Adsorption of CO2 and H2 in pure SWNHs has also been measured. Arc discharge in other liquid media such as water, ethanol, dimethylformamide (DMF), n-methyl pyrrolidone (NMP), formamide, benzene, heptane and acetone yields different nanocarbon structures including multi-walled carbon nanotubes (MWNTs), few-layer graphene, carbon onions and carbon nanoparticles.

Synthesis, Characterization and Properties of Single-Walled Carbon Nanohorns

Single-walled nanohorns (SWNHs) have been prepared by sub-merged arc discharge of graphite electrodes in liquid nitrogen. The samples were examined by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Nitrogen and boron doped SWNHs have been prepared by the sub-merged arc discharge method using melamine and elemental boron as precursors. Intensification of Raman D-band and stiffening of G-band has been observed in the doped samples. The electrical resistance of the SWNHs varies in opposite directions with nitrogen and boron doping. Functionalization of SWNHs through amidation has been carried out for solubilizing them in non-polar solvents. Water-soluble SWNHs have been produced by acid treatment and non-covalent functionalization with a coronene salt. SWNHs have been decorated with nanoparticles of Au, Ag and Pt. Interaction of electron donor (tetrathiafulvalene, TTF) and acceptor molecules (tetracyanoethylene, TCNE) with SWNHs has been investigated by Raman spectroscopy. Progressive softening and stiffening of Raman G-band has been observed respectively with increase in the concentration of TTF and TCNE.

3D viability imaging of tumor phantoms treated with single-walled carbon nanohorns and photothermal therapy

A new image analysis method called the spatial phantom evaluation of cellular thermal response in layers (SPECTRL) is presented for assessing spatial viability response to nanoparticle enhanced photothermal therapy in tissue representative phantoms. Sodium alginate phantoms seeded with MDA-MB-231 breast cancer cells and single-walled nanohorns were laser irradiated with an ytterbium fiber laser at a wavelength of 1064 nm and irradiance of 3.8 W cm−2 for 10–80 s. SPECTRL quantitatively assessed and correlated 3D viability with spatiotemporal temperature. Based on this analysis, kill and transition zones increased from 3.7 mm3 and 13 mm3 respectively to 44.5 mm3 and 44.3 mm3 as duration was increased from 10 to 80 s. SPECTRL provides a quantitative tool for measuring precise spatial treatment regions, providing information necessary to tailor therapy protocols.

Separation of CO2–CH4 mixtures on defective single walled carbon nanohorns – tip does matter

Using realistic models of single-walled carbon nanohorns and their single-walled carbon nanotube counterparts, we study the equilibrium separation of CO2-CH4 mixtures near ambient operating conditions by using molecular simulations. We show that regardless of the studied operating conditions (i.e., total CO2-CH4 mixture pressures and mole fractions of mixture components in the bulk phase), single-walled carbon nanohorns maximize the CO2-CH4 equilibrium separation factor. Optimized samples of single-walled carbon nanohorns consisting of narrow tubular parts capped with horn-shaped tips show highly selective adsorption of CO2 over the CH4 mixture component, with the CO2-CH4 equilibrium separation factor of ~8-12. A large surface-to-volume ratio (i.e., enhanced surface forces) and unique defective morphology (i.e., packing of adsorbed molecules in quasi-one/quasi-zero dimensional nanospaces) of single-walled carbon nanohorns are their key structural properties responsible for the excellent separation performance. Our theoretical simulation results are in quantitative agreement with a recent experimental/theoretical study of the CO2-CH4 adsorption and separation on oxidized single-walled carbon nanohorns [Ohba et al., Chem. Lett., 40, 2011, 1089]. Both experiment and theory showed that the CO2-CH4 equilibrium separation factor of oxidized samples of single-walled nanohorns measured near ambient operating conditions is ~2-5. This reduction in the separation efficiency as compared to optimized samples of single-walled carbon nanohorns is theoretically justified by their lower surface-to-volume ratio (i.e., larger diameters of tubular parts and horn-shaped tips).

Single wall nanohorns as electrocatalyst support for vapour phase high temperature DMFC

The use of single wall nanohorns (SWNH) as electrocatalyst support has proved to increase the performance of polymer electrolyte membrane-based fuel cells. In order to investigate in more detail such behavior, the electrochemical characterization of SWNH based electrodes was performed. The use of SWNH in vapour phase high temperature direct methanol fuel cells (HT-DMFC) was also addressed. Cyclic voltammetry experiments have indicated a higher electrochemical activity towards methanol electro-oxidation and a higher tolerance to carbonaceous species accumulation for a SWNH based electrode than for carbon black and commercial corresponding ones. Carbon black electrode presented a better performance than SWNH one for oxygen reduction reaction at low current densities while, at higher overvoltages, SWNH electrode performed better. The exact role of the improved performance of SWNH based electrodes is yet not clear but may be related to a higher water vapour adsorption or electrode morphology. Vapour phase HT-DMFC operation showed the improved performance of the SWNH electrode in agreement with previous works and with the electrochemical characterization performed during this work; despite the higher ohmic resistance observed in comparison with the carbon black based electrode. Moreover, SWNH based electrode showed improved fuel cell stability during longer operation times.

Electrostatically mediated adsorption by nanodiamond and nanocarbon particles

Nanodiamond (ND) and other nanocarbon particles are popular platforms for the immobilization of molecular species. In the present research, factors affecting adsorption and desorption of propidium iodide (PI) dye, chosen as a charged molecule model, on ND and sp 2 carbon nanoparticles were studied, with a size ranging from 75 to 4,305 nm. It was found that adsorption of PI molecules, as characterized by ultra- violet-visible spectroscopy, on ND particles is strongly influenced by sorbent-sorbate electrostatic interactions. Different types of NDs with a negative zeta potential were found to adsorb positively charged PI molecules, while no PI adsorption was observed for NDs with a positive zeta potential. The type and density of surface groups of negatively charged NDs greatly influenced the degree and capacity of the PI adsorbed. Ozone-purified NDs had the highest capacity for PI adsorption, due to its greater density of oxygen containing groups, i.e., acid anhydrides and carboxyls, as assessed by TDMS and TOF-SIMS. Single wall nanohorns and carbon onion particles were found to adsorb PI regardless of their zeta potential; this is likely due to p bonding between the aromatic rings of PI and the graphitic surface of the materials and the internal cavity of the horns.

Single-Wall Nanohorns as Electrocatalyst Support for High Temperature PEM Fuel Cells

This work compares the performance of electrodes prepared with electrocatalysts based on platinum supported in single-wall carbon nanohorns (Pt-SWNHs) and in carbon black (Pt-carbon black) for high temperature fuel cells. Membrane electrode assemblies (MEAs) assembled with phosphoric acid doped polybenzimidazole (PBI/H3PO4) membrane were characterized by polarization curves, ac impedance spectroscopy and cyclic voltammetry (CV), at 160°C. A similar power density peak was obtained for both MEAs, at 160°C and 1.0% relative humidity. The electrochemical characterization showed a higher ohmic resistance for the Pt-SWNH compared to carbon black-based MEA, due to the higher hydrophobic character of the SWNH carbon support. Furthermore, the Pt-SWNH anode presented a lower charge transfer resistance than the correspondent carbon black but similar cathode charge transfer resistance.

Synthesis of Nickel-Carbon Nanohorn Composite Films by an Electrodeposition Technique

In this work, electrodeposition of nickel-single walled carbon nanohorns composite is obtained from a sulfamate bath. Electrodeposition of nickel-nanohorn composites is carried out from a sulfamate bath containing up to 2 g/l of dispersed single walled nanohorns with diameter 30 to 50 nm. Deposits with embedded nanohorns, homogeneously dispersed in metal matrix, are obtained. Structure of the deposits and contents of carbon nanohorns particles in these layers were investigated with respect to the possibility of agglomeration of SWNH particles and bath composition (concentration of SWNH in the electrolyte). Morphology of the coatings and the effects of codeposited particles on metal matrix structure are also reported. Microhardness of the composites has been investigated: Martens hardness is highly influenced by the incorporation of particles.

Improvement of DMFC Electrode Kinetics by Using Nanohorns Catalyst Support

One of the factors limiting direct methanol fuel cells (DMFC) performance is the slow kinetics of methanol oxidation at the anode. The importance of the catalyst support for fuel cells has been recognized and different forms of carbon have been suggested. Single wall nanohorns (SWNH) are a new class of carbon with a similar graphitic structure of carbon nanotubes. They are self-assembling materials that produce aggregates of about 100 nm. In the present study, the comparison of the performance of a DMFC equipped with electrocatalysts supported on a commercial carbon black and on SWNH was carried out. The SWNH were synthesized by the arc discharge method in air. The deposition of the Pt and Pt/Ru catalysts on the carbon supports was accomplished by using ethylene glycol as reducing agent. The synthesized catalyst nanoparticles have a very small diameter size (ca. 2.5 nm) and they are uniformly distributed on both carbon supports. The supported electrode catalysts were tested in a DMFC and results indicate that employing SWNH is very promising showing catalytic activities 60 % higher.

Carbon Nanostructures Produced by an AC Arc Discharge

Carbon nanostructures are under deep investigation due their peculiar properties and possible applications. In particular, development of new methods for the synthesis of these materials and their mechanism of formation represent interesting research fields. Arc discharge allows to produce different forms of carbon nanostructures. The parameters involved in the process, voltage, current density, type and pressure of the surrounding gas can be controlled especially for achieving high quantity of material with enhanced characteristics in terms of purity while the use of transition metal-graphite mixtures has been used to produce single wall structures. Moreover direct current (DC) and alternating current (AC) are suitable for producing carbon nano-materials, but different results can be obtained. In this work the effect of the power frequency in an AC arc discharge technique on the synthesis of carbon nanostructures is reported. Pure graphite electrodes have been arched in air in an homemade apparatus where the material can be collected directly on a cylindrical collector fixed near the arc. In order to avoid the formation of deposits under the arc a symmetrical configuration of the electrodes has been set. The production of carbon soot containing Single Wall Nanohorns (SWNH) and highly convoluted graphene sheets is optimized. The range of power frequencies 32-1000Hz has been investigated and the arcs have been ignited fixing the voltage at 28 V. The materials has been analyzed by field emission scanning electron microscope and high resolution transmission electron microscope. The microstructure of the material synthesized by this apparatus is affected by the power frequency, as the experimental results demonstrate. The samples produced at low frequency presented high amounts of single wall structures, SWNH-type. More compact structures, similar to large onion-like structures, have been found in samples synthesized at high frequency values.

Photoinduced electron transfer in zinc phthalocyanine loaded on single-walled carbon nanohorns in aqueous solution.

Notable electronic communication within ZnPc-SWNHox nanoensembles, where ZnPc is zinc phthalocyanine and SWNHox is an oxidized single-walled nanohorn, in both the ground and excited states is revealed by steady-state absorption and fluorescence spectroscopy measurements. The details of electron transfer reported here with time-resolved absorption and fluorescence measurements may broaden the use of SWNHox nanoensembles in photochemistry and photobiology.

Fluorescent dye adsorption on nanocarbon substrates through electrostatic interactions

Nanodiamonds (NDs) with modified surface functional groups and surface characteristics are an attractive model to understand adsorption mechanisms of molecules on substrates. The research described in this paper illustrates the binding mechanisms of fluorescent dyes to ND surfaces as these interactions are extremely useful in many biomedical ND applications. A thorough study of binding and release mechanisms was completed using an assortment of carbon based nanoparticles, including NDs, onion-like carbon, and single-wall nanohorns. Surface charge interactions were studied in combination with surface areas, configurations, and modifications in order to determine which is responsible for the largest adsorption capacity and strongest binding. Adsorption studies were carried out using UV–Vis measurements followed by maximum binding capacity determination using the Langmuir isotherm and related transform equations. Langmuir and transform calculations further reveal the specific surface area covered by adsorbents for select nanocarbon materials. In addition, cyclic voltammetry measurements confirm that dye adsorbed onto NDs exhibits equal electrochemical properties as in its unbound state.

Cumulative and continuous laser vaporization synthesis of single wall carbon nanotubes and nanohorns

The conditions for the scaled synthesis of single wall carbon nanotubes (SWNTs) and single wall carbon nanohorns (SWNHs) by laser vaporization at high temperatures are investigated and compared using in situ diagnostics. An industrial Nd:YAG laser (600 W, 1–500 Hz repetition rate) with tunable pulse widths (0.5–50 ms) is utilized to explore conditions for high-yield production. High-speed videography (50000 frames/s) of the laser plume and pyrometry of the target surface are correlated with ex situ high resolution transmission electron microscopy analysis of the products for pure carbon targets and carbon/catalyst targets to understand the effects of the processing conditions on the resulting nanostructures. Carbon is shown to self-assemble into single-wall nanohorn structures at rates of ∼1 nm/ms, which is comparable to the catalyst-assisted SWNT growth rates. Two regimes of laser ablation, cumulative ablation by multiple pulses and continuous ablation by individual pulses, were explored. Cumulative ablation with spatially overlapping 0.5-ms pulses is favorable for the high yield and production rate of SWNTs at ∼6 g/h while continuous ablation by individual long laser pulses (∼20 ms) at high temperatures results in the highest yield of SWNHs at ∼10 g/h. Adjustment of the laser pulse width is shown to control SWNH morphology.

AC arc discharge synthesis of single-walled nanohorns and highly convoluted graphenesheets

In this paper we report the synthesis of single-walled carbon nanohorns (SWNHs)and highly convoluted graphene sheets by AC powered arc discharge in air. Theexperimental strategy was based on the design of an experimental set-up able toenhance the synthesis of these compounds at the expense of the usually foundcathode crust where multi-walled nanotubes are often found. In this set-up the arcdischarge is ignited between pure graphite electrodes experiencing a symmetricalsituation as far as the heat generation by the arc and the heat dissipation atthe heat sinks is concerned. This is achieved by AC powering two electrodes ofthe same size and length. A cylindrical steel collector able to control the heatexchange with the surroundings completes the experimental set-up. The yieldof the device, in terms of synthesis rate and of fraction of sublimated carbonconverted to nanostructures, has been evaluated, and it resulted in being particularlyhigh, indicating that AC powering can represent a key factor in the large-scalesynthesis of SWNHs and highly convoluted graphene sheets by arc discharge. Thestructure of the synthesized powder has been determined by transmission electronmicroscopy.

Selective deposition of a gadolinium(III) cluster in a hole opening of single-wall carbon nanohorn.

Selective synthesis of particles of angstrom to nanometer size consisting of one to many metal atoms is instrumental in various applications, but it has been hampered by the tendency of the metal atom to form large clusters. We found, as studied by the state-of-the-art electron microscopic technique, a strategy to produce metal-containing nanoparticles isolated from each other by depositing metal atoms in a hydrophilic hole on or in the interior of a carbon nanotube as demonstrated by the reaction of Gd(OAc)(3) with oxidized single-wall nanohorns. Besides the potential utilities of the deposited metal clusters, the metal deposition protocol provides a method to control permeation of molecules through such openings.