Effect of reaction temperature in the selective synthesis of single wall carbon nanotubes (SWNT) on a bimetallic CoCr-MCM-41 catalyst

Abstract

Synthesis of single wall carbon nanotubes (SWNT) on a CoCr-MCM-41 bimetallic catalyst by CO disproportionation has been carried out at five different temperatures between 500 and 900 °C. A series of methods have been employed for a comprehensive assessment effect of temperature on the size-controllability of the catalyst particles and the morphology of the resultant SWNT. By extended fine structure X-ray absorption, thermogravimetric analysis, resonance Raman spectroscopy, photoluminescence excitation (PLE) mapping and transmission electron microscopy we found an optimal synthesis temperature window between 600 and 800 °C. In this window, modifying the reaction temperature leads to significant changes in the SWNT yield, diameter and chirality distribution. Decrease in reaction temperature favored the selective synthesis of very small diameter carbon nanotubes (as low as 0.6 nm). Chirality dependence of SWNT on temperature has been measured by PLE. A progressive suppression of larger diameter SWNT identities in the measured SWNT population was noted when reaction temperature decreased. In the measured PL maps, two near armchair structures (6,5) and (7,3) were dominant at 600 and 700 °C.