Determination of glyphosate mono-isopropylamine salt in process samples using flow injection analysis with tris(2,2`-bipyridyl)ruthenium(II) chemiluminescence detection

The mono-isopropylamine salt of glyphosate was selectively determined directly in industrial and commercial formulations using flow injection analysis with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection without the need for separation. Glyphosate and its mono-isopropylamine salt furnished detection limits of 7×10⁻⁹ and 3.5×10⁻¹⁰ M and relative standard deviations of 0.4% at 1×10⁻⁷ M and 0.8% at 5×10⁻⁸ M, respectively. The methodology is robust and reliable with samples subjected only to aqueous dilution prior to analysis.

Chemistry of carbon nanotubes

Judicious application of site-selective reactions to non-aligned and aligned carbon nanotubes has opened a rich field of carbon nanotube chemistry. In order to meet specific requirements demanded by particular applications (e.g. biocompatibility for nanotube biosensors and interfacial strength for blending with polymers), chemical modification of carbon nanotubes is essential. The tips of carbon nanotubes are more reactive than their sidewalls, allowing a variety of chemical reagents to be attached at the nanotube tips. Recently, some interesting reactions have also been devised for chemical modification of both the inner and outer nanotube walls, though the seamless arrangement of hexagon rings renders the sidewalls relatively unreactive. This review provides a brief summary of very recent progress in the research on chemistry of carbon nanotubes.

Focused ion beam milling as a universal template technique for patterned growth of carbon nanotubes

Focused ion beam (FIB) milling system has been used to create nanosized patterns as the template for patterned growth of carbon nanotubes on Si substrate surface without predeposition of metal catalysts. Carbon nanotubes only nucleate and grow on the template under controlled pyrolysis of iron phthalocyanine at 1000 °C. The size, growth direction, and density of the patterned nanotubes can be controlled under different growth conditions and template sizes. Atomic force microscopy and electron microscopy analyses reveal that the selective growth on the FIB template is due to its special surface morphology and crystalline structure.

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000 °C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

Boron nitride nanotubes : pronounced resistance to oxidation

Boron nitride (BN) nanotubes have the same nanostructure as carbon nanotubes but are found to exhibit significant resistance to oxidation at high temperatures. Our systematic study has revealed that BN nanotubes are stable at 700 °C in air and that some thin nanotubes (diameter less than 20 nm) with perfect multiwalled cylindrical structure can survive up to 900 °C. Thermogravimetric analysis reveals an onset temperature for oxidation of BN nanotubes of 800 °C compared with only 400 °C for carbon nanotubes under the same conditions. This more pronounced resistance of BN nanotubes to oxidation is inherited from the hexagonal BN and also depends on the nanocrystalline structure. This high level of resistance to oxidation allows promising BN nanotube applications at
high temperatures

Nucleation and growth of carbon nanotubes in a mechano-thermal process

Separate nucleation and growth processes of carbon nanotubes were found in a mechano-thermal method in which carbon nanotubes are produced by first mechanical milling of graphite powder at room temperature and subsequent thermal annealing up to 1400 &deg;C. The ball-milled graphite contains nucleation structures (nanosized metal particles and deformed (0 0 2) layers containing pentagons), and disordered carbon as a free carbon atom source. The subsequent annealing activates the growth of two types of multi-walled nanotubes in the absence of carbon vapor. Thin nanotubes (diameter <20 nm) are formed via crystallization of the disordered carbon with the preferred formation of the (0 0 2) basal planes. Thick nanotubes (diameter >20 nm) are formed through a metal catalytic solution–precipitation process (solid–liquid–solid). In both cases, carbon nanotubes grew out from disordered carbon particles with closed tips.

Carbon nanotubes formed in graphite after mechanical grinding and thermal annealing

Multi-walled carbon nanotubes with cylindrical and bamboo-type structures are produced in a graphite sample after mechanical milling at ambient temperature and subsequent thermal annealing up to 1400 &deg;C. The ball milling produces a precursor structure and the thermal annealing activates the nanotube growth. Different nanotubular structures indicate different formation mechanisms: multi-wall cylindrical carbon nanotubes are probably formed upon micropores and the bamboo tubes are produced because of the metal catalysts. A two-dimensional growth governed by surface diffusion is believed to be one important factor for the nanotube growth. A potential industrial production method is demonstrated with advantages of large production quantity and low cost.

Light emission and excitonic effect of boron nitride nanotubes observed by photoluminescent spectra

Photoluminescent (PL) and optical absorption spectra of high-yield multi-wall BN nanotubes (BNNTs) were systematically investigated at room temperature in comparison with commercial hexagonal BN (h-BN) powder. The direct band gap of the BNNTs was determined to be 5.75 eV, just slightly narrower than that of h-BN powder (5.82 eV). Two Frenkel excitons with the binding energy of 1.27 and 1.35 eV were also determined. However, they were not a distinctive characteristic of the BNNTs as reported previously. Observed broad UV–visible–NIR light emission demonstrates the potential of the BNNTs as a nano light source.

Purification of boron nitride nanotubes

A purification process was developed for the first time for boron nitride (BN) nanotubes. BN nanotubes, prepared using a ball milling and annealing method, contain a high yield of nanotubes and a small amount of BN and metal catalyst particles. The metal particles can be dissolved in an HCl solution. Fine BN nanoparticles and thin layers were first converted to water soluble B₂O₃ via a partial oxidation treatment at 800 &deg;C. The oxide particles and layers can then be dissolved in hot water. Thermogravimetric analysis has been used to determine an adequate oxidation temperature at which fine BN particles were oxidized.

Demonstration of the advantages of using bamboo-like nanotubes for electrochemical biosensor applications compared with single walled carbon nanotubes

The modification of glassy carbon electrodes with random dispersions of nanotubes is currently the most popular approach to the preparation of carbon nanotube modified electrodes. The performance of glassy carbon electrodes modified with a random dispersion of bamboo type carbon nanotubes was compared with single walled carbon nanotubes modified glassy carbon electrodes and bare glassy carbon electrodes. The electrochemical performance of all three types for electrode were compared by investigating the electrochemistry with solution species and the oxidation of guanine and adenine bases of surface adsorbed DNA. The presence of edge planes of graphene at regular intervals along the walls of the bamboo nanotubes resulted in superior electrochemical performance relative to SWNT modified electrodes from two aspects. Firstly, with solution species the peak separation of the oxidation and reduction waves were smaller indicating more rapid rates of electron transfer. Secondly, a greater number of electroactive sites along the walls of the bamboo-carbon nanotubes (BCNTs) resulted in larger current signals and a broader dynamic range for the oxidation of DNA bases.

11B nuclear magnetic resonance study of boron nitride nanotubes prepared by mechano-thermal method

We reported ¹¹B nuclear magnetic resonance studies of boron nitride (BN) nanotubes prepared by mechano-thermal route. The NMR lineshape obtained at 192.493 MHz (14.7 T) was fitted with two Gaussian functions, and the ¹¹B nuclear magnetization relaxations were satisfied with the stretched–exponential function, exp[-(tlT₁)^(D+1)/6] (D: space dimension) at all temperatures. In addition, the temperature dependence of spin–lattice relaxation rates was well described by T_i^-1 = aT (a: constant, T: temperature) and could be understood in terms of direct phonon process. All the 11BNMR results were explained by considering the inhomogeneous distribution of the paramagnetic metal catalysts, such as α-Fe, Fe–N, and Fe₂ B, that were incorporated during the process of high-energy ball milling of boron powder and be synthesized during subsequent thermal annealing. X-ray powder diffraction as well as electron paramagnetic resonance (EPR) on BN nanotubes were also conducted and the results obtained supported these conclusions.

Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 &deg;C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.