Browsing by Author "Yang, XS"

Now showing 1 - 7 of 7
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    Facile preparation of free-standing carbon nanotube arrays produced using two-step floating-ferrocene chemical vapor deposition
    (American Chemical Society, 2012-03-01) Yang, XS; Yuan, LX; Peterson, VK; Minett, AI; Yin, YB; Harris, AT
    A two-step floating-ferrocene chemical vapor deposition method has been devised for the preparation of single-layered aligned carbon nanotube (CNT) arrays. In the first step, uniform Fe catalysts are in situ produced and coated on a Si substrate from ferrocene; single-layered CNT arrays are prepared on these catalysts from ethylene in the second step. The effect of ferrocene loading on the distribution of Fe catalysts, as well as the morphology, diameter, and height of the CNT arrays, was investigated. A novel vacuum extraction process was employed to release the as-prepared CNT array from the Si wafer after water etching at 750 degrees C. The structural integrity of the free-standing arrays was preserved after the detachment process. The interface between the substrate and the as-grown CNT array was examined. The Fe catalyst distribution on the Si substrate remained homogeneous when the CNT array was removed, and the tops and bottoms of the arrays had different structures, suggesting that the arrays were formed predominantly by a base-growth mode. These free-standing arrays could potentially be applied in membrane or electronic applications. © 2011 American Chemical Society.
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    Interaction between a bimetallic Ni-Co catalyst and micrometer-sized CaO for enhanced H2 production during cellulose decomposition
    (Elsevier, 2011-01-01) Zhao, M; Yang, XS; Church, TL; Harris, AT
    An SBA-15 supported Ni–Co catalyst and micrometer-sized CaO were used as additives in cellulose decomposition in the presence and absence of injected H2O. A thermogravimetric analyser coupled to a mass spectrometer (TG-MS) was used to examine the different roles of the Ni–Co catalyst and CaO in tuning the kinetics of decomposition and the distribution of the gaseous products. There existed optimal additive/cellulose ratios beyond which H2 generation could not be enhanced by using more of a single additive. However, the combination of both the additives dramatically promoted selective H2 generation. The mechanism of their interaction is discussed. When the catalyst, CaO, and 1 vol.% H2O were present, a stable sustained (interval of >150 °C) high-rate (max >80 vol.%) H2 output resulted. The cumulative H2 yield (250–550 °C) reached 688 ml/g cellulose and the H2 selectivity during this period was nearly 70 vol.%. The char yield was also minimized, at 5.2%. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd.
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    Novel CaO-SiO2 sorbent and bifunctional Ni/Co-CaO/SiO2 complex for selective H-2 synthesis from cellulose
    (American Chemical Society, 2012-01-17) Zhao, MW; Yang, XS; Church, TL; Harris, AT
    Catalysis- and sorption-enhanced biomass gasification is a promising route to high-purity hydrogen (H-2); however, most CaO-based sorbents for CO2 capture have poor surface area and mechanical properties, lose carrying capacity over multiple uses, and have insufficient porosity to accommodate extra catalyst sites. We aimed to develop a high-surface-area CaO-SiO2 framework onto which catalysts could be grafted. The best CaO-SiO2 sorbent (n(Ca)/n(Si) = 2:1) maintained a Cao conversion of 65% even after 50 carbonation-decarbonation cycles, better than commercial micrometer-sized CaO or tailored CaO, because of stabilization via Ca-O-Si interactions and an ordered porous structure. Bimetallic catalyst grains (Ni/Co alloy, <20 nm) could be evenly loaded onto this structure by impregnation. The resulting bifunctional complex produced H-2 at nearly the same rate as a mixture of catalyst and commercial CaO while using less total sorbent/catalyst. Furthermore, this complex was much more durable due to its higher coking resistance and stable structure. After 25 carbonation decarbonation cycles, the new catalyst sorbent complex enhanced the H-2 yield from cellulose far more than a mixture of catalyst and commercial CaO did following the same treatment. © 2012, American Chemical Society.
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    Open-ended aligned carbon nanotube arrays produced sing CO(2)-assisted floating-ferrocene chemical vapor deposition
    (American Chemical Society, 2011-07-28) Yang, XS; Yuan, LX; Peterson, VK; Yin, YB; Minett, AI; Harris, AT
    The influence of CO2, in concentrations of up to 7600 ppm, on the preparation of aligned carbon nanotube (CNT) arrays from ethylene using floating-ferrocene chemical vapor deposition (CVD) at 750 °C was investigated. The CO2-assisted floating-ferrocene CVD method facilitates the well-controlled growth of aligned CNT arrays; the quality of the aligned CNT arrays was significantly improved in the presence of CO2, as demonstrated by improved alignment and crystallinity. Under the assistance of CO2, CNT arrays were linear and vertical. CNTs grown with CO2 were also higher than those grown in the absence of CO2, with the optimum CO2 concentration of 760 ppm producing a 50% enhancement in CNT height. Varying the concentration of CO2 also controlled the diameter and wall numbers of the aligned CNTs. CNTs synthesized in the presence of 7600 ppm CO2 had a diameter of 8.0 ± 1.6 nm, and an average wall number of 4 ± 1. In particular, both open-ended and triple-walled CNTs were clearly observed. © 2011, American Chemical Society
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    Pretreatment control of carbon nanotube array growth for gas separation: alignment and growth studied using microscopy and small-angle x-ray scattering
    (Americal Chemical Society, 2013-04-24) Yang, XS; Yuan, LX; Peterson, VK; Minett, AI; Zhao, MW; Kirby, N; Mudie, ST; Harris, AT
    Aligned multiwalled carbon nanotube (CNT) arrays were prepared using chemical vapor deposition of C2H4 on Fe catalyst at 750 degrees C. CNT array height and alignment depends strongly on the duration of H-2 pretreatment, with optimal height and alignment achieved using 10-15 min pretreatment. Small-angle X-ray scattering (SAXS) was used to quantify the alignment, distribution, and size of the CNTs in arrays produced from varying pretreatment times and the results correlated with microscopy measurements. SAXS analysis revealed that the higher section of the CNT arrays exhibited better alignment than the lower section. Combining these insights with transmission electron microscopy measurements of the CNT defects within each array enable a mechanism for the CNT growth to be proposed, where the loss of alignment arises from deformation of the CNTs during their growth. Gas permeation test across densified CNT arrays indicated that the alignment of the CNT array plays an important role in the gas transport, and that the gas diffusion across the well-aligned CNT arrays was enhanced by a factor of 45, which is much more than that across the poorly aligned CNT arrays, with an enhancement factor of similar to 8. © 2013, American Chemical Society.
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    Removal of natural organic matter in water using functionalised carbon nanotube buckypaper
    (Elsevier, 2013-08-01) Yang, XS; Lee, J; Yuan, LX; Chae, SR; Peterson, VK; Minett, AI; Yin, YB; Harris, AT
    A simple, surfactant-free assembly process was used to prepare multi-wall carbon nanotube (CNT) buckypapers using a highly efficient purification, sonication, and filtration process. To achieve effective dispersion of CNT into ethanol, a minimum 5-min sonication time was required. Here, we fabricated a buckypaper with pore size of 41 +/- 10 nm and porosity of 72.9% with a 10-min sonication. The as-prepared buckypaper was used as a membrane for humic acid (HA) removal from water. During purification process, carboxylic and hydroxylic functional groups were introduced onto the CNT surface. The functional groups increased the hydrophilicity of the CNTs and improved the removal efficiency of HA by the buckypaper. The buckypaper prepared from purified CNTs exhibited excellent removal of HA (>93%) and a long lifetime for filtration. © 2013 Elsevier Ltd.
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    Synthesis of vertically aligned carbon nanotube arrays on polyhedral Fe/Al2O3 catalysts
    (Royal Society of Chemistry, 2011-06-14) Liu, J; Yuan, LX; Yang, XS; Elbert, A; Harris, AT
    Polyhedral Fe/Al(2)O(3) catalysts prepared by an impregnation method were used for the synthesis of vertically aligned carbon nanotube (CNT) arrays from the pyrolysis of ethylene at 800 degrees C. © 2011 Royal Society of Chemistry