A simple pyrolysis route to synthesize leaf-like carbon sheets

Leaf-like carbon sheets have been obtained by the pyrolysis of dichloromethane and ferrocene in an autoclave in 300-600 °C on Cu ribbons for 90 min. The thickness of the sheets could be controlled from 50 to 200 nm by adjusting the experimental parameters. The formation process was studied by observing product-evolution utilizing the real-time imaging capabilities of emission scanning electron microscope, and it is considered that Diffusion-Limited Aggregation mechanism could be responsible for their growth. Thermo-gravimetric analysis curves show that the initial thermal decomposition temperature of the carbon sheets increases from 300 to 420 °C with the increasing preparation temperature. The Brunauer-Emmett-Teller specific surface area was 398 m²/g and with a narrow pore distribution in the range of 2-5 nm. By changing the carbon sources, solid carbon spheres as well as chain-like solid carbon spheres (3-5 μm) could be selectively prepared using one-pot reactions.     

Wet-etched Ni foils as active catalysts towards carbon nanofiber growth

A study of wet-chemical etching treatments for nickel foils and the growth parameters for carbon nanostructures on them using hot-filament chemical vapour deposition (CVD) is described. Catalytically-active protrusions were produced on the Ni foils with sizes and densities in the range ∼24-42 nm and ∼202-314 P μm⁻², respectively. These protrusions are found to have a key role in the growth process as they determine the yield and morphology of the carbon deposits. It is shown that well-shaped, nano-sized protrusions are required to achieve high yield growth of hollow-herringbone carbon nanofibers (CNFs) with an in-plane crystallite size of ∼23 nm. Good correlation was seen between the statistical distributions of the protrusion size (sp) and the CNF diameters (df) depicting sp/df ratios close to unity. This work sheds light on the mechanisms behind CVD growth on metal foils.     

Synthesis of magnetically separable adsorbents through the incorporation of protected nickel nanoparticles in an activated carbon

We present a simple and versatile route to prepare magnetically separable porous carbons from commercial activated carbons. The magnetic properties of the composite are provided by nickel nanoparticles (around 8-15 nm), which are produced within the porous network by means of the thermal treatment at 600 °C of an activated carbon impregnated with a nickel salt and sucrose. This synthetic strategy allows the magnetic nanoparticles to be protected against acid attack. The magnetic composite thus obtained exhibits a large surface area and a high pore volume. An important advantage of this composite is that exhibits, at room temperature, low coercivity (∼0.1 kOe), allowing it to be easily manipulated by means of low external magnetic fields.     

Synthesis and properties of highly stable nickel/carbon core/shell nanostructures

A simple and cost effective technique for obtaining highly stable carbon coated nickel nanostructures at relatively low reaction temperatures is reported. Thermogravimetric analysis was carried out to optimize the annealing temperatures. The powder X-ray diffraction pattern reveals peaks corresponding to face centered cubic nickel. High resolution transmission electron micrograph shows the formation of nickel nanostructures with ∼5 nm thick carbon coating. This is confirmed by Raman spectroscopy. The nickel/carbon core/shell nanostructures exhibited a shelf life of more than a year, with high thermal stability and excellent magnetic properties. This synthesis route provides scope for large scale production of nickel/carbon nanostructures.     

Amphiphilic chitosan nanospheres: Factors to control nanosphere formation and its consequent pH responsive performance

Chitosan grafted with hydrophobic and hydrophilic groups initiates the formation of amphiphilic chitosan nanospheres. The molecular weight of mPEG plays an important role to control the particle size. As compared to mPEG 2000, which gives a bimodal nanosphere (∼200, and ∼300 nm), mPEG 5000 initiates a monodispersed nanosphere with the smaller size (150 nm). In aqueous solution, the nanosphere surface is negatively charged resulting in a well dispersion in neutral to high pH but a significant precipitation in low pH. A model drug incorporation using lidocaine is successful when amphiphilic chitosan nanospheres were dissolved in good solvent followed by allowing mixing with drug solution before dialysis. The particle size of the drug incorporated chitosan is significantly increased, that is, from 100-150 nm to approximately 400-500 nm when the amount of incorporated lidocaine was about 0.68 mg per mg of lidocaine-loaded nanosphere.     

Liquid-phase synthesized mesoporous electrochemical supercapacitors of nickel hydroxide

Electrochemical supercapacitive (ES) properties of liquid-phase synthesized mesoporous (pore size distribution centered ∼12 nm) and of 120 m²/g surface area nickel hydroxide film electrodes onto tin-doped indium oxide substrate are discussed. The amounts of inner and outer charges are calculated to investigate the contribution of mesoporous structure on charge storage where relatively higher contribution of inner charge infers good ion diffusion into matrix of nickel hydroxide. Effect of different electrolytes, electrolyte concentrations, deposit mass and scan rates on the current-voltage profile in terms of the shape and enclosed area is investigated. Specific capacitance of ∼85 F/g at a constant current density of 0.03 A/g is obtained from the discharge curve.     

Fabrication and characteristics of Pd nanoparticles/nanofilms on ceramics toward catalytic electrodes

We report an approach of fabricating various palladium nanostructures with tailored morphologies in nanoparticles (Ø80-300 nm), nanoporous films (Ø50-200 nm), and integrated nanotubules arrays (Ø300 nm and 5 μm long) on different ceramic materials. Microporous titanate ceramics or nanoporous alumina films were first prepared through a solid-state synthesis or an anodic oxidization of aluminum sheets. The micro- and nanoporous ceramics were then used as supporting materials in an electroless deposition to deposit Pd nanoparticles or nanofilms over the porous substrates, thus leading to various Pd nanostructures with large surface areas and high corrosion resistance for many applications. EDX and EPMA analysis disclosed that the phosphor co-deposition in 5-11 at.% P occurred in the palladium electroless deposition. XRD analysis showed that the as-deposited Pd-P alloys were polycrystalline with a preferential orientation of (1 1 1) facet. The phosphor included in the Pd-P alloy films existed as a solid solution form, rendering as a single phase Pd-P alloy with nanocrystals (∼5 nm across) of cubic palladium.     

Synchrotron SAXS 〈in situ〉 identification of three different size modes for soot nanoparticles in a diffusion flame

The high photon flux (10¹⁴ photons/s) and high spatial resolution (∼100 μm) of synchrotron radiation available at ID09b/ESRF facility has been exploited in an in situ investigation of the early stages of soot formation in an ethylene-air diffusion flame. SAXS data demonstrate in situ evidence that the size distribution of soot nanoparticles within the flame exhibits three distinct modes at different heights above the burner z’s. In particular, at z ∼ 3 mm, small particles (4-6 nm size), called sub-primary particles, are observed to come into existence. The corresponding monomodal distribution is observed to evolve to bimodal one at z > 5 mm, with the sub-primary particle mode being progressively depleted in favor of the growth of a mode corresponding to larger primary particles (10-12 nm size). The sub-primary peak vanishes completely at about z ∼ 20 mm where distribution is again single mode about 12 nm diameter. Porod’s plots show that the sub-primaries are born as configurational flat entities similar to discs or lamellae with a small aspect ratio (Porod’s exponent about 2), and upon going to higher z’s, they approach a spherical form with a smooth surface (Porod’s exponent about 4). Moreover, the careful use of Kratky plots has allowed to demonstrate the presence within the flame of very small nuclei, sized about 1.5-2 nm, which have a nucleation burst at about z ∼ 5 mm, whose number concentration progressively decreases at larger z, finally disappearing around z ∼ 15 mm. The relative increase of primary particles (size larger than 12 nm) is found to correspond to the progressive decrease of these very small nuclei (∼2 nm) concentration. At heights larger than 15 mm a strong ionization signal is observed that increases with height. These findings are in agreement with previous experimental works in the literature performed by Transmission Electron Microscopes and Differential Mobility Analyzers as well as with theoretical studies of dimer-dominated stochastic coagulation.     

Microstructure and optical properties of electrodeposited Al-doped ZnO nanosheets

This study grew A1-doped ZnO nanosheets on polycrystalline zinc foils using cathodic electrodeposition in an aqueous solution consisting of 0.02 M Zn(NO₃)₂ and 0.001 M Al(NO₃)₃ at 90 °C. The effects of the electrodepositing potential and thermal annealing on the physical properties of the Al-doped ZnO sheets were investigated. This study observed a high quality sheet-like structure of the electrodeposited Al-doped ZnO for the applied potential larger than −1.1 V, and the sheets were interconnected over the area of interest. The X-ray diffraction patterns showed that the intensity of the Bragg reflections of the electrodeposited Al-doped ZnO sheets increases with the electrodepositing potential because a larger applied potential results in the Al-doped ZnO sheets having a larger lateral dimension and thickness. However, the appearance of the Al-doped ZnO sheets becomes coarse and rough after thermal annealing at 400 °C in ambient air for 4 h. The intensity of the Bragg reflections of the Al-doped ZnO sheets was markedly increased through the thermal annealing due to the improvement of the crystalline quality of the annealed Al-doped ZnO sheets. Annealing caused a large decrease in structural defects of the Al-doped ZnO sheets electrodeposited at −1.3 V causing the sheets to exhibit a sharp photoluminescence peak at ∼380 nm.     

Raman scattering study of the thermal conversion of bundled carbon nanotubes into graphitic nanoribbons

Raman scattering is used to study the temperature-driven structural transformations of bundled single-walled carbon nanotubes (SWCNTs) observed in HiPCO and ARC synthesis by electron microscopy, i.e., tube-tube coalescence ∼1300-1400 °C, coalesced tubes to multi-walled tubes (MWCNT) at ∼1600-1800 °C and finally (only ARC tubes) MWCNT to graphitic nanoribbons (GNRs) at ∼1800 °C. All these transformations occurred in vacuum. Here, we present the details of these transformations as seen through the “eyes” of Raman scattering via changes in the radial (R) SWCNT band, the G-band (and its substructure) and the relative intensity of the disorder-induced D- and D′-band scattering. The Raman spectrum of GNRs is also discussed in detail. For 514.5 nm laser excitation, five relatively broad GNR Raman bands are observed: 1350, 1580, 1620, 2702 and 3250 cm⁻¹. A Knight plot is used to estimate the GNR width and we find w ∼ 9 nm, which is in reasonable agreement with the estimate of 7.6 nm based on TEM and the model that a GNR is a collapsed MWCNT.     

Tin oxide nanosensor fabrication using AC dielectrophoretic manipulation of nanobelts

Nanobelts are a new class of semiconducting metal oxide nanowires. The ribbon-like nanobelts are chemically pure and structurally uniform single crystals, with clean, sharp, smooth surfaces, and rectangular cross-sections. Positive and negative dielectrophoresis (DEP) was demonstrated for the first time on semiconducting oxide nanobelts. This effect was then used for the fabrication of a nanodevice, which consisted of SnO₂ nanobelts attached to castellated gold electrodes defined on a glass substrate, and covered by a microchannel. The SnO₂ nanobelts (width ∼ 100-300 nm, thickness ∼ 30-40 nm) were suspended in ethanol and introduced into the microchannel. An alternating (AC) voltage of ∼9.8 V peak to peak, with variable frequency, was applied between the electrodes (minimum electrode gap ∼ 20 μm), which corresponds to an average electric field strength of less than 2.5 × 10⁵ V/m. In the 10 Hz-1 kHz range, repulsion between the nanobelts and the electrodes occurred, while in the 1-10 MHz range, attraction was observed. Once the nanobelts touched the electrodes, those that were sufficiently long bridged the electrode gaps. The device was characterized and can potentially be used as a nanosensor.     

Catalytic synthesis of carbon nanotubes using Ni- and Co-doped calcium tartrates

Calcium tartrate doped with Ni and/or Co has been used as a catalyst source in the chemical vapor deposition synthesis of carbon nanotubes (CNTs). Thermolysis of doped calcium tartrate in an inert atmosphere was shown to yield Ni, Co or Ni-Co nanoparticles ∼6 nm in diameter dispersed in a calcium oxide matrix. The CNT synthesis was carried out by ethanol vapor decomposition at 800 °C. The structure of the products was characterized by transmission electron microscopy and Raman spectroscopy. It was found that Ni nanoparticles embedded in CaO provide the narrowest diameter distribution of CNTs, while the bimetallic Ni-Co catalyst allows the formation of the thinnest CNTs with the outer diameter of ∼2 nm. This type of CNT is more likely to be responsible for the lowest value of the turn-on field (∼1.8 V/μm) for the emission current detected for the latter sample.     

Magnetic properties of carbon nano-particles produced by a pulsed arc submerged in ethanol

Carbon powder was produced by a pulsed arc ignited between two carbon electrodes submerged in ethanol, and was comprised of both micro- and nano-particles. The measured magnetic properties of the mixed “raw” powder at 20 and 300 K were: saturation magnetization M_s ∼ 0.90-0.93 emu/g, residual magnetization M_r = 0.022 and 0.018 emu/g, and coercive force H_c = 11 and 8 Oe, respectively. The data lead to conclusion that the powder consisted of ferromagnetic particles with a critical temperature much higher than 300 K. Magnetic particles in solution were separated by means of bio-ferrography. It was found that the magnetically separated particles included chains of ∼30-50 nm diameter spheres, and nanotubes and nanorods with lengths of 50-250 nm and diameters of 20-30 nm. In contrast, the residual particles which passed through the bio-ferrograph consisted of 1 μm and larger micro-particles, and nano-particles without any definite shape.     

Synthesis of nitrogen-doped horn-shaped carbon nanotubes by reduction of pentachloropyridine with metallic sodium

Nitrogen-doped horn-shaped carbon nanotubes (CNTs) have successfully been prepared by reducing pentachloropyridine with metallic sodium at 350 °C. A typical CNT has an open-end diameter of ∼2 μm, a close-end diameter of ∼0.3 μm, a wall thickness of ∼30 nm, and a length up to 8 μm. TEM observation indicates that the CNTs account for ∼30% of the products, and the rest is solid and hollow carbon nanospheres (CNSs) with a diameter of about 50-290 nm. Elemental analysis shows that the N/C atomic ratio of the carbon nanostructures is about 0.0208. XRD and HRTEM measurements reveal that the CNTs are amorphous. To understand the growth process and refine the growth condition, various control experiments have been finished. At last, a sodium-catalysis-reduction solid-liquid-solid growth mechanism of the CNTs has been suggested on the basis of the experiments.     

Functionalized organic nanoparticles from core-crosslinked poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer micelles

Surface-functionalized polymeric nanoparticles were prepared by: a) self-assembly of poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer (PVBCB-b-PB) to form spherical micelles (diameter: 15-48 nm) in decane, a selective solvent for PB, b) crosslinking of the PVBCB core through thermal dimerization at 200-240 °C, and c) cleavage of the PB corona via ozonolysis and addition of dimethyl sulfide to afford aldehyde-functionalized nanoparticles (diameter: ∼16-20 nm), along with agglomerated nanoparticles ranging from ∼30 to ∼100 nm in diameter. The characterization of the diblock copolymer precursors, the intermediate micelles and the final surface-functionalized crosslinked nanoparticles was carried out by a combination of size exclusion chromatography, static and dynamic light scattering, viscometry, thermogravimetric analysis, ¹H NMR and FTIR spectroscopy and transmission electron microscopy.     

Nanoscale fine-tuning of porosity of carbide-derived carbon prepared from molybdenum carbide

Micro- and mesoporous carbide-derived carbon (CDC) was synthesised from molybdenum carbide (Mo₂C) powder by gas phase chlorination in the temperature range from 400 to 1200 °C. Analysis of XRD results show that C(Mo₂C), chlorinated at 1200 °C, consist mainly on graphitic crystallites of mean size, L_a = 9 nm and L_c = 7.5 nm. The first-order Raman spectra showed the graphite-like absorption peak at ∼1587 cm⁻¹ and the disorder-induced (D) peak at ∼1348 cm⁻¹. The low-temperature N₂ adsorption experiments were performed and a specific surface area up to 1855 m² g⁻¹ and total pore volume up to 1.399 cm³ g⁻¹ were obtained. Sorption measurements showed the presence of both micro- and mesopores after chlorination at 400-900 °C and only mesopores after chlorination at 1000°-1200 °C. Stepwise formation of micro- and mesopores was achieved and the peak pore size can be shifted from 0.8 nm up to 4 nm by increasing the chlorination temperature.     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia by the oleate complex route

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder has been synthesized by the oleate complex route. Oleate complexes of zirconium and yttrium were formed in the hexane rich layer by the reaction of sodium oleate with zirconyl chloride and yttrium chloride at the interface of the two ternary solutions in water–ethanol–hexane system. The zirconyl oletae and yttrium oleate complexes on heating decomposed to oxide through the formation of carbonate intermediates. The powder obtained by calcination at 600 °C for 2 h was cubic YSZ with surface area of 42 m²/g. The YSZ powder contained primary particles of ∼300 nm size and the primary particles were aggregate of crystallites of 5–10 nm. The compacts prepared from the YSZ powder were sintered to ∼99% TD (theoretical density) at 1400 °C. The sintered YSZ had a low average grain size of 0.73 μm.     

Carbon nanotubes and onions from carbon monoxide using Ni(acac)2 and Cu(acac)2 as catalyst precursors

New catalyst precursors (copper and nickel acetylacetonates) have been used successfully for the synthesis of carbon nanotubes and onion particles from carbon monoxide. Catalyst nanoparticles and carbon products were produced by metal-organic precursor vapour decomposition and catalytic disproportionation of carbon monoxide in a laminar flow reactor at temperatures between 705 and 1216 °C. Carbon nanotubes (CNTs) were formed in the presence of nickel particles at 923-1216 °C. The CNTs were single-walled, 1-3 nm in diameter and up to 90 nm long. Hollow carbon onion particles (COPs) were produced in the presence of copper particles at 1216 °C. The COPs were from 5 to 30 nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The results of computational fluid dynamics calculations to determine the temperature and velocity profiles and mixing conditions of the species in the reactor are presented. The mechanisms for the formation of both CNTs and COPs are discussed on the basis of the experimental and computational results.     

Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles

The TiO₂ nanofibers and nanoparticles are prepared by electrospinning and molten salt method, respectively. The materials are characterized by X-ray diffraction scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and a thermal analysis. The SEM and TEM studies showed that fibers were of average diameter ∼100 nm and composed of nanocrystallites of size 10-20 nm. Electrochemical properties of the materials are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Cyclic voltammetric studies show a hysteresis (ΔV) between the cathodic and the anodic peak potentials for TiO₂ nanofibers and nanoparticles (sizes ∼15-30 nm) are in the range, 0.23-0.30 V and a redox couple Ti^4+/3+ around ∼1.74/2.0 V. Electrochemical cycling results revealed that the TiO₂ nanofibers have lower capacity fading compared to that of the nanoparticles. The capacity fading for 2-50 cycles was ∼23% for nanofibers, which was nearly one-third of that of corresponding nanoparticles (∼63%). We discussed the effect of particle size on hysteresis and cycling performance of TiO₂ nanoparticles. Impedance analysis of TiO₂ nanofibers and nanoparticles during first discharge cycle is analyzed and interpreted.     

Rapid microwave-assisted synthesis of graphene nanosheet/Co3O4 composite for supercapacitors

Graphene nanosheet (GNS)/Co₃O₄ composite has been rapidly synthesized by microwave-assisted method. Field emission scanning electron microscopy and transmission electron microscopy observation reveals the homogeneous distribution of Co₃O₄ nanoparticles (3-5 nm in size) on graphene sheets. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 243.2 F g⁻¹ has been obtained at a scan rate of 10 mV s⁻¹ in 6 M KOH aqueous solution for GNS/Co₃O₄ composite. Furthermore, the composite exhibits excellent long cycle life along with ∼95.6% specific capacitance retained after 2000 cycle tests.