Supapan Seraphin

Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants.

Nitrogen-doped TiO(2) was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO(2) prepared by the sol-gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO(2) properties, such as absorption ability in the UV-visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO(2) with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO(2) can be arranged in the following order: TiO(2)/diethanolamine>TiO(2)/triethylamine>TiO(2)/urea>un-doped TiO(2). The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO(2) with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 x 10(-2)min(-1) with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.

Preparation and properties of ferromagnetic carbon‐coated Fe, Co, and Ni nanoparticles

Carbon‐coated iron, cobalt, and nickel particles were produced by an arc discharge process modified in the geometry of the anode and the flow pattern of helium gas. Field emission scanning electron microscopy shows that the resulting material consists of only carbon‐coated metal particles without any nanotubes or other unwanted carbon formations present. The diameters of iron, cobalt, and nickel particles range predominantly from 32 to 81 nm, 22 to 64 nm, and 16 to 51 nm, respectively. X‐ray diffraction analysis confirmed that the as‐made particles are carbon‐coated elements rather than metal carbides. High resolution transmission electron microscopy reveals that the as‐made cobalt and nickel particles are covered by 1–2 graphitic layers, while iron particles are surrounded by amorphous carbon. When the samples were treated by annealing or immersion into nitric acid, particles completely coated by carbon resisted both postdeposition treatments. However, further graphitization of the carbon coating by eith...

Single‐walled carbon nanotubes produced at high yield by mixed catalysts

We report here on the high‐density preparation of single‐wall tubes in the presence of mixed catalysts of the types Fe/Ni and Co/Ni, in the soot as well as in the weblike deposits forming in the chamber. The yield is much higher than previously reported, and gram quantities can be obtained. Diameters cover the range from 0.9 to 3.1 nm, larger than previously reported, with the histogram showing only one peak at 1.7 nm. Evidence of an epitaxial action between C60 and single‐walled nanotubes is presented. Results from the mixed catalysts Co/Cu, Ni/Mg, and Ni/Ti are also reported.

Carbon encapsulated nanoparticles of Ni, Co, Cu, and Ti

Despite intensive research on the encapsulation of metal nanoparticles into carbon clusters deposited by arc discharge, the detailed pathways of the formation of these novel forms of materials remain unclear. The growth of a rich variety of morphologies is not well understood. Studies are reported here on the growth phenomena of different metals encapsulated into carbon cages that emphasize the effect of carbon and metal supply on the size of particles. Post-deposition annealing was introduced as a process that induces structural rearrangements, and thus enables changes in morphologies. A set of carbon encapsulated Ni, Co, Cu, and Ti particles were prepared by an arc discharge process modified in the geometry of the anode and flow pattern of helium or methane gas. The samples were then annealed under flowing argon gas. Three annealing temperatures were used (600, 900, and 1100 °C). Samples were characterized by transmission and scanning electron microscopy. Particles made under the same experimental conditions are of roughly the same size. When the supply of metal in the reactor space was increased by using a larger diameter of the metal pool, the average diameter of the particles is bigger than those of produced from the smaller metal pool. The thickness of the carbon cages of Ni and Co particles increased during the annealing. The carbon cages of Cu particles, however, did not change their thickness, while some carbon coatings of Ti particles disappeared under annealing. This suggests that the addition of layers for the Ni and Co cages results from a precipitation of carbon previously dissolved in the metal, while the much lower solubility of C in Cu prevents this possibility. The Ti of high reactivity, on the other hand, may further react with the available carbon under annealing to form TiC. It is suggested that annealing provides additional thermal energy that makes structural re-arrangement possible long after the initial deposition process was terminated. This may explain the rich variety of morphologies of deposit obtained at different locations of the reaction chamber.

Complex branching phenomena in the growth of carbon nanotubes

Abstract We report here the experimental observation of complex branching phenomena in the growth of carbon nanotubes produced under specific arc-discharge conditions. High-resolution transmission electron microscopy (HRTEM) images demonstrate that two or three carbon nanotubes can join together under specific angles in L, Y, and T patterns with saddle surfaces at the junction. Adding to the observation of negative curvature surface in straight-line tubes that change their diameters, we report here negative curved areas that support the topography of a branching structure.

Dendron-controlled nucleation and growth of gold nanoparticles

Passivation of the metal surface by dendrons bearing a focal 4-pyridone functionality (the second-generation dendron is shown; C: gray, N: blue, O: red) allows controlled nucleation and growth of gold nanoclusters. The particle size is a direct function of the generation number of the dendritic ligands, with higher generation dendron producing larger particles.

SINGLE-WALLED CARBON NANOTUBES GROWING RADIALLY FROM YC2 PARTICLES

In the primary soot produced by arc discharge using an yttrium carbide loaded anode, bundles of single‐walled carbon nanotubes (SWT) are observed, protruding radially from YC2 particles coated with graphitic multilayers. The graphitic cages separating YC2 particle and SWT bundles fall into the narrow range of 10–20 layers. The morphology of the clusters suggests a two‐step growth model: The radial SWT growth pattern is first initiated by catalytic action between the YC2 droplet and the carbon in the gas phase. Second, and upon cooling, the graphitic cage starts by segregating excess carbon from the YC2 bulk, arresting further growth of SWT.

Filling the carbon nanocages

Twenty elements were codeposited with carbon in an arc discharge between graphite electrodes. The majority of them were evaporated from composite anodes that contained the elements or their oxides stuffed into central bores in the graphite rods. The deposits, found in the soot at the reactor walls or as slag at the cathode, were characterized using scanning and transmission electron microscopy, electron energy loss spectroscopy, and x‐ray diffraction. The products fall into four categories: (1) elements that can be encapsulated in the form of their carbides (B, V, Cr, Mn, Y, Zr, Nb, Mo); (2) elements that are not encapsulated but tolerate the formation of graphitic carbon cages (Cu, Zn, Pd, Ag, Pt); (3) elements that form stable carbides, competing with and pre‐empting the carbon supply for the graphitic cage formation (Al, Si, Ti, W); and (4) the iron‐group metals (Fe, Co, Ni) that stimulate the formation of single‐walled tubes and strings of nanobeads in the conventional arc discharge condition, and pro...

Production of silicon carbide whiskers from carbon nanoclusters

Abstract We report on a method to produce SiC whiskers without the presence of metal catalysts by reacting carbon nanoclusters with SiO at 1700°C. The dark carbon nanotubes with hollow cores are converted to solid greenish SiC whiskers. Electron diffraction and EDX confirm that the product is SiC with a single crystalline hexagonal phase. TEM reveals the lattice image of the whisker with numerous defects. The formation of SiC whiskers produced from carbon nanotubes without using metal catalyst strongly suggests that the reactivity and atomic configuration of carbon nanotubes are crucial to the formation of whiskers.

Selective encapsulation of the carbides of yttrium and titanium into carbon nanoclusters

Characterization of the arc‐discharge deposits at the cathode from anodes containing yttrium oxide and titanium by transmission electron microscopy and x‐ray diffraction shows different results with respect to an encapsulation of the metal carbides into carbon clusters. Yttrium carbide is encapsulated into carbon nanoclusters in a crystalline phase. The formation of titanium carbide, on the other hand, preempts the formation of the carbon—carbon bonds necessary to form the carbon cages, so that only titanium carbide clusters are observed. Thermodynamic data support the interpretation of the results.