We report a systematic evaluation of the influence of the use of nitric acid at elevated temperature (80 degrees C) as purification and functionalization treatment for four different types of multi wall carbon nanotubes (MWCNTs) and for carbon microparticles upon their physico-chemical properties. We used BET, Raman spectroscopy, high resolution X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy measurements for MWCNTs characterization. We found that nitric acid treatment significantly changes physico-chemical properties of MWCNTs and that these changes vary significantly between different MWCNTs. Therefore we urge researchers to be careful when relying on the physico-chemical properties measured on different MWCNTs samples.
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Pumera et al. (2009) studied this question.