Browsing by Author "Xu, Ya-Qiong"

Now showing 1 - 6 of 6
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    Carbon nanotube diameter selection by pretreatment of metal catalysts on surfaces
    (2012-02-28) Hauge, Robert H.; Xu, Ya-Qiong; Shan, Hongwei; Nicholas, Nolan Walker; Kim, Myung Jong; Schmidt, Howard K.; Kittrell, Carter W.; Rice University; United States Patent and Trademark Office
    A new and useful nanotube growth substrate conditioning processes is herein disclosed that allows the growth of vertical arrays of carbon nanotubes where the average diameter of the nanotubes can be selected and/or controlled as compared to the prior art.
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    Controlled multi-step purification of single-walled carbon nanotubes
    (2005) Xu, Ya-Qiong; Smalley, Richard E.
    A controlled and scalable multi-step purification method has been developed to remove iron impurity and non-nanotube carbon materials from raw single-walled carbon nanotubes produced in the HiPco (high pressure CO) process. In this study, iron nanoparticles, coated by carbon, are exposed and oxidized by multiple step oxidation at increasing temperatures. To avoid catalytic oxidation by iron oxide of carbon nanotubes, the exposed and oxidized iron oxide is deactivated by reaction with C2H2F4 or SF6. The iron fluorides are removed by a soxhlet extraction with a 6M HCl solution. The purity and quality of each sample were determined by thermo-gravimetric analysis (TGA), Raman spectrometry, ultraviolet-visible-near-IR (UV-vis-near-IR) spectrometry, fluorescence spectrometry and transmission electron microscope (TEM) spectroscopy. The purity and yield of SWNT are improved due to reduced catalytic activity of the iron oxide. Greater iron oxide removal also resulted from oxidation at higher temperatures.
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    Multi-step purification of single-wall carbon nanotubes
    (2010-03-02) Hauge, Robert H.; Xu, Ya-Qiong; Peng, Haiqing; Smalley, Richard E.; Marek, Irene Morin; Rice University; United States Patent and Trademark Office
    The present invention relates to processes for the purification of single-wall carbon nanotubes (SWNTs). Known methods of single-wall carbon nanotube production result in a single-wall carbon nanotube product that contains single-wall carbon nanotubes in addition to impurities including residual metal catalyst particles and amounts of small amorphous carbon sheets that surround the catalyst particles and appear on the side of the single-wall carbon nanotubes. The present purification processes remove the extraneous carbon as well as metal-containing residual catalyst particles.
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    Production of single-walled carbon nanotube grids
    (2013-12-03) Hauge, Robert H.; Xu, Ya-Qiong; Pheasant, Sean; Rice University; United States Patent and Trademark Office
    A method of forming a nanotube grid includes placing a plurality of catalyst nanoparticles on a grid framework, contacting the catalyst nanoparticles with a gas mixture that includes hydrogen and a carbon source in a reaction chamber, forming an activated gas from the gas mixture, heating the grid framework and activated gas, and controlling a growth time to generate a single-wall carbon nanotube array radially about the grid framework. A filter membrane may be produced by this method.
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    Production of vertical arrays of small diameter single-walled carbon nanotubes
    (2013-08-13) Hauge, Robert H.; Xu, Ya-Qiong; Rice University; United States Patent and Trademark Office
    A hot filament chemical vapor deposition method has been developed to grow at least one vertical single-walled carbon nanotube (SWNT). In general, various embodiments of the present invention disclose novel processes for growing and/or producing enhanced nanotube carpets with decreased diameters as compared to the prior art.
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    Study of purification and growth of single-walled carbon nanotubes
    (2006) Xu, Ya-Qiong; Hauge, Robert H.; Smalley, Richard E.
    Single-walled carbon nanotubes (SWNTs) have been intensively studied because of their many potential applications. However, all known processes for formation of SWNTs involve transition-metal catalysts, residues of which are invariably present in the as-produced SWNT material. To truly realize the full potential of SWNTs, a controlled and scalable multi-step purification method has been developed to remove iron impurities and non-nanotube carbon materials from raw SWNTs produced in the high pressure CO (HiPco) process. Here, iron nanoparticles, coated by carbon, are exposed and oxidized by multiple step oxidation at increasing temperatures. To avoid catalytic oxidation by iron oxide of carbon nanotubes, the exposed and oxidized iron oxide is deactivated by reaction with C2H2F4 or SF6. The iron fluorides are removed by a soxhlet extraction with a 6M HCl solution. Iron content of approximately 1 wt% with approximately 70% SWNT yield has been achieved by this method. Furthermore, a hot filament chemical vapor deposition (HFCVD) method has been developed to grow vertically aligned single-walled carbon nanotubes (VA-SWNTs). Silicon substrates decorated with islands of iron were rapidly inserted into a preheated furnace in which a hot filament (temperature greater than 2000°C) is activating the gas. Characterization of VA-SWNTs by using Raman spectroscopy, fluorescence spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM) clearly shows that the VA-SWNTs have diameters ranging from 0.78 to 1.6 nm. Finally, HFCVD method has been used to investigate the effect of atomic hydrogen on the growth of VA-SWNTs. It is obvious that rapid heating of the substrate in the presence of atomic hydrogen facilitates the nucleation and growth of SWNTs before the aggregation of catalyst occurs. By comparing the Raman shifts of SWNTs synthesized from a mixture of isotopic methane (13CH 4) and normal acetylene (12C2H2), we found that SWNT growth occurs with addition of acetylene and ethylene that are formed by methane decomposition on the hot filament.