Temperature modification of oxidized multiwall carbon nanotubes studied by electron spectroscopy methods

Abstract

AbstractCarbon nanotubes (CNTs) offer interesting applications in nanotechnology, biochemistry, biomedicine, catalysis, electronics, optoelectronics, electrochemistry, and sensor technologies. They could also be used as a filler for metallic nanoparticle composites prepared at elevated temperatures by sintering. In the present work the oxidized multiwall carbon nanotubes (ox‐MWCNTs) are investigated. The aim is their characterization after oxidation reaction, investigation of their temperature stability and the influence of temperature modification on the structural and chemical changes in the atomic bonding state during annealing. The ox‐MWCNTs are studied in the temperature range from RT (25 °C) to 150 °C by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES), elastic peak electron spectroscopy (EPES), quadrupole mass spectroscopy (QMS), transmission electron microscopy (TEM), Fourier transform infra‐red spectroscopy (FTIR) methods. The FTIR and XPS results indicate the presence of water, carboxyl, hydroxyl, carbonyl, ester, and acid anhydride groups in the bulk and at the surface. Annealing decreases the oxygen content (from 12.4 to 9.8 at.%), accompanied by increasing amount of C sp2 groups (from 63 to 74%), indicating the reconstruction of C bonds. For the applied temperature range increasing content of water is observed, whereas decreasing content of other carbon–oxygen groups, i.e., carbonyl, carboxyl, hydroxyl, ester, and acid anhydride. This decrease undergoes with different rate. The QMS at 150 °C showing the largest contribution of CO2, indicates major desorption of oxygen groups from the edges of ox‐MWCNTs, whereas desorption of oxygen from the bridges visible as CO is minor. The surface structural changes in EPES spectra at the temperature of 150 °C confirm increasing surface imperfection. The proposed method of chemical oxidation also results in significant elimination of amorphous carbon and metallic residues from as prepared MWCNTs.magnified image The TEM image of ox‐MWCNTs.