Optical absorption spectroscopy for determining carbon nanotube concentration in solution

A simple method of determining concentration of carbon nanotubes in solution was provided by using optical absorption spectroscopy. The extinction coefficient of single-walled carbon nanotubes in Beer's law was determined after subtraction of the plasmon background. We found that the extinction coefficient was strongly dependent on the wavelength in the resonant region, whereas this was independent of wavelength in the non-resonant region after plasmon subtraction. This work demonstrates that the concentration of unknown carbon nanotubes dispersed in aqueous solution can be easily determined by simply measuring absorbance, once the extinction coefficient of the material is determined in advance.