Sangyun Lim

Low-defect, purified, narrowly (n,m)-dispersed single-walled carbon nanotubes grown from cobalt-incorporated MCM-41.

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.

Synthesis and characterization of Pt/MCM-41 catalysts

Abstract The preparation of Pt/MCM-41 catalysts was studied. Three different precursors were used: platinum acetyl acetonate Pt(AcAc) 2 , tetraamine platinum (II) nitrate Pt(NH 3 ) 4 (NO 3 ) 2 , and hydrogen hexachloroplatinate (IV) hydrate H 2 PtCl 6 . With these precursors, the catalysts were prepared by three different methods: equilibrium adsorption, ion exchange, and a new method, which we call vacuum evaporation impregnation (VEI). Through the characterizations by XRD, physisorption, chemisorption, XAFS, and XANES-TPR, it was demonstrated that a structured, high loading (0.5–2 wt.%) and high dispersion (>1.0 calculated from CO and/or H 2 chemisorption) Pt/MCM-41 catalysts was obtained by the new preparation method VEI.

Preparation of highly structured V-MCM-41 and determination of its acidic properties

Vanadium substituted mesoporous molecular sieves (MCM-41) were prepared and the effects of water: Si ratio and anti-foaming agent addition to synthesis solution were investigated. The anti-foaming agent was very effective in improving the reproductibility of sample structure. The amount of V substitution into the silica framework was increased with increasing water amount and surfactant chain length. All of the incorporated V was tetrahedrally coordinated in the silica framework. The density of Lewis acid sites was constant for all samples but exceeds that in a pure silica sample.