Structural Tuning Using a Novel Membrane Reactor for Carbon Nanotube Synthesis
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Structural Tuning Using a Novel Membrane Reactor for Carbon Nanotube Synthesis Dane J. K. Sheppard and L. P. Felipe Chibante Applied Nanolab, Department of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
ABSTRACT Carbon nanotubes come in many varieties, with chemical, mechanical, and electrical properties depending on carbon nanotube (CNT) structural morphology. In order to provide a platform for CNT structural tuning, a membrane reactor was designed and constructed. This reactor provided more intimate gas-catalyst contact by decoupling the carbon feedstock gas from carrier gas in a chemical vapour deposition (CVD) environment using an asymmetric membrane and a macroporous membrane. Growth using this membrane reactor demonstrated normalized yield improvements of ~300% and ~1000% for the asymmetric and macroporous membrane cases, respectively, over standard CVD methods. To illustrate the possibility for control, growth variation with time was successfully demonstrated by growing vertically aligned multi-walled CNTs to heights of 0.71 mm, 1.36 mm, and 1.84 mm after growth for 15, 30, and 60 minutes in a commercial thermal CVD reactor. To demonstrate CNT diameter control via catalyst particle size, dip coating and spray coating methods were explored using ferrofluid and Fe(NO3)3 systems. CNT diameter was demonstrated to increase with increasing particle size, yielding CNT like growth with diameters ranging from 15 -150 nm. Demonstration of these dimensions of control coupled with the dramatic efficiency increases over growth in a commercialized CVD reactor establish this new reactor technology as a starting point for further research into CNT structural tuning.
INTRODUCTION Carbon nanotubes (CNTs) have generated a tremendous amount of interest since they were first described by Iijima in 1991 [1]. The wide array of remarkable properties exhibited by CNTs [2-4] has led to an equally wide array of applications across a variety of fields [5-8]. However, the various applications utilizing CNTs all require nanotubes of a particular configuration. Long multi-walled carbon nanotubes (MWCNTs) are often used in nanocomposites due to easier dispersion in a polymer matrix [7], while long single-walled carbon nanotubes (SWCNTs) are preferable for CNT yarns that harness nanotube mechanical properties [9]. CNT wire applications require conductive nanotubes in the armchair configuration, while transistor and energy storage applications use semiconductor CNTs with chiral or zigzag configurations. A number of methods are available for controlling CNT diameter, length, and electronic character [10-12], but each method tends to control a small number of characteristics, and there is no method for true fine-tuning of nanotube structure during production. The reactor design central to this body of work aims to provide a platform for structural tuning by decoupling carbon
feedstock from carrier gas to allow for intimate gas-catalyst contact in a thermal chemical vapour deposition (CVD) process. EXP
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