[show abstract][hide abstract] ABSTRACT: High-quality single-walled carbon nanotubes (SWNT) with high yield were produced by using small-pore Co-MCM-41 catalyst, templated by a C10 surfactant and containing 3 wt % Co. A complete incorporation of Co ions in the silica matrix without formation of surface Co oxides and the contact time of the reaction, in the catalyst synthesis and the SWNT production, respectively, were the most critical factors to be considered. By controlling the reduction temperature and contact time in the reaction, the carbon yield could reach 34 wt % or higher with a selectivity of 96 wt % to SWNT. The metal content after purification of SWNT by base−acid treatments was 0.7 wt %, and the surface area was as high as 1800 m2/g. The metal surface occlusion effect by amorphous silica might play a key role in the stabilization of the completely reduced Co metallic clusters in the SWNT synthesis procedure, using small-pore C10 Co-MCM-41.
The Journal of Physical Chemistry C 07/2008; · 4.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: A mild, four-step purification procedure using NaOH reflux, HCl wash, and oxidation by 4 mol % molecular oxygen at 500 degrees C was developed to purify single-walled carbon nanotubes (SWCNTs) with narrow semiconducting (n,m) distribution produced from cobalt-incorporated MCM-41 (Co-MCM-41) in order to obtain bulk low-defect-density nanotubes. Three key features of Co-MCM-41 allow this mild purification technique: (1) ultrathin silica walls versus dense silica or other crystalline oxide supports are soluble in dilute NaOH aqueous solution, which avoids the damage to SWCNTs usually caused by using HF treatment to remove catalytic supports; (2) the small metallic particles are easily dissolved in HCl, a significantly milder chemical treatment compared to HF or HNO(3); (3) the high selectivity to SWCNTs with negligible multiwalled carbon nanotubes or graphite, which facilitates the removal of undesired carbon species by selective oxidation. The effectiveness of this purification procedure was evaluated by high-resolution transmission electron microscopy, scanning electron microscopy, Raman, UV-vis-NIR, and fluorescence spectroscopy, solution redox chemistry on fractionated (6,5) tubes, and SWCNT-based field effect transistor device performance. The results demonstrate that Co-MCM-41 catalyst not only provides tubes with narrow semiconducting (n,m) distribution but also allows a mild purification procedure and, therefore, produces SWCNTs with fewer defects.