Browsing by Author "Yuan, LX"

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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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    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