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a b s t r a c tThe pyrolysis of cyclohexane at low pressure (40 mbar) was studied in a plug flow reactor from 950 to 1520 K by synchrotron VUV photoionization mass spectrometry. More than 30 species were identified by measurement of photoionization efficiency (PIE) spectra, including some radicals like methyl, propargyl, allyl and cyclopentadienyl radicals, and stable products (e.g., 1-hexene, benzene and some aromatics). Among all the products, 1-hexene is formed at the lowest temperature, indicating that the isomerization of cyclohexane to 1-hexene is the dominant initial decomposition channel under the condition of our experiment. We built a kinetic model including 148 species and 557 reactions to simulate the experimental results. The model satisfactorily reproduced the mole fraction profiles of most pyrolysis products. The rate of production (ROP) analysis at 1360 and 1520 K shows that cyclohexane is consumed mainly through two reaction sequences: cyclohexane ? 1-hexene ? allyl radical + n-propyl radical, and cyclohexane ? cyclohexyl radical ? hex-5-en-1-yl radical that further decomposes to 1,3-butadiene via hex-1-en-3-yl and but-3-en-1-yl radicals.

Semiconducting single-walled carbon nanotubes (s-SWNTs) have emerged as a promising class of electronic materials, but the metallic (m)-SWNTs present in all as-synthesized nanotube samples must be removed for many applications. A high selectivity and high yield separation method has remained elusive. A separation process based on selective chemistry appears to be an attractive route since it is usually relatively simple, but more effective chemicals are needed. Here we demonstrate the first example of a new class of dual selective compounds based on polycyclic aromatic azo compounds, specifically Direct Blue 71 (I), for high-purity separation of s-SWNTs at high yield. Highly enriched (~93% purity) s-SWNTs are produced through the simple process of standing arc-discharge SWNTs with I followed by centrifugation. The s-SWNTs total yield is up to 41%, the highest yet reported for a solution-based separation technique that demonstrates applicability in actual transistors. 91% of transistor devices fabricated with these s-SWNTs exhibited on/off ratios of 10(3) to 10(5) with the best devices showing mobility as high as 21.8 cm(2)/V s with on/off ratio of 10(4). Raman and X-ray photoelectron spectroscopic shifts and ultraviolet-visible-near-infrared (UV-vis-NIR) show that I preferentially complexes with s-SWNTs and preferentially suspends them. Preferential reaction of naphthyl radicals (generated from I with ultrasonication) with m-SWNTs is confirmed by changes in the D-band in the Raman spectroscopy, matrix-assisted desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and molecular simulation results. The high selectivity of I stems from its unique dual action as both a selective dispersion agent and the generator of radicals which preferentially attack unwanted metallic species.

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