Time dependent thermal treatment of oxidized MWCNTs studied by the electron and mass spectroscopy methods

• DOI: 10.1016/j.apsusc.2012.04.127
• Publication Date: 2012-04-28T14:50:17Z
• Authors: L. Stobinski; B. Lesiak; J. Zemek; P. Jiricek
• Keywords: 13. Climate action; 01 natural sciences; 0104 chemical sciences

Abstract Purified and functionalized in boiling concentrated (68%) HNO 3 acid the oxidized multiwall carbon nanotubes (ox-MWCNTs) under thermal treatment from RT to 630 °C and at 350 °C time dependent (1–4 h) were investigated using the surface sensitive electron and mass spectroscopy methods. Mass spectroscopy indicates significant desorption of H 2 and H 2 O to about 300 °C. Higher H 2 desorption rate from RT up to about 100 °C is most likely caused by decomposition of organic acid impurities included within a bundle and in channels of the ox-MWCNTs after their functionalization by HNO 3. In the range of 100–300 °C part of the detected H 2 , accompanied by desorption of CO 2 , may origin from desorbed water. Above 300 °C, the small amount of desorbing H 2 O may result from transformation of carboxylic groups into carboxylic acid anhydride. Significant desorption of CO 2 starting from 150 °C may result from decomposition of carboxylic groups, whereas desorption of CO starting at about 300 °C from decomposition of acid anhydride groups created from carboxylic groups during thermal dehydration. Desorption of CO and CO 2 at about 470 °C may be due to decomposition of hydroxyl O H and carbonyl C O groups. Above 600 °C mainly decomposition of C O groups takes place and results in small desorption of CO. Time dependent (1–4 h) thermal treatment of ox-MWCNTs at 350 °C shows in XPS spectra decreasing amount of C O in carboxyl groups and increasing amount of C O in carbonyl and acid anhydride groups arising from carboxyl groups decomposition. Between 350 °C and 470 °C the higher desorption rate of CO 2 than CO indicates significant decomposition of carboxyl and carboxyl anhydride groups. At 350 °C the dynamic changes are indicated by the energy, intensity and full width at half maximum (FWHM) of the π → π * interband transition and π loss peak, and quasi-elastic peak FWHM. During 4 h at 350 °C no C sp 2 reconstruction is observed. For the applied procedure of MWCNTs oxidation, large amount of water and some organic acid impurities, resulting from the MWCNTs oxidation, remain in the CNTs channels, interstitial channels between tubes and at nanotubes surface.