Determining the percentages of semi-conducting and metallic single-walled carbon nanotubes in bulk soot

A procedure is presented to determine the percentages of metallic and semi-conducting single-walled carbon nanotubes (SWCNTs) in as-produced soot synthesized by a cobalt/molybdenum-catalyzed chemical vapor deposition (CVD) process. The procedure involves the acquisition of UV–Vis–NIR absorption spectra of solvent-suspended soot samples, and the key aspect is the use of a physically-based subtraction of the π-plasmon absorbance from the overall absorbance to ensure that the percentage of semi-conducting SWCNTs is not overstated. The improvement in accuracy using the procedure is demonstrated using two lots of soot with different amounts of non-tubular carbon (NTC) contaminants. The semi-conducting SWCNT percentage of the soot containing low NTC levels was 82 ± 3%, and this mean was overestimated by 4% when the π-plasmon absorbance was not subtracted. The semi-conducting SWCNT percentage of the soot containing higher NTC levels was 76 ± 9%, and this mean was overestimated by 6% without subtraction of the π-plasmon absorbance.