Effect of different acid oxidation on morphology, dispersion and optical band-gap of multi-walled carbon nanotubes

Abstract

In this paper the effect of different acid oxidation on morphology, dispersion and optical band gap of multi-walled carbon nanotubes (CNTs) is reported. Oxidation of CVD synthesized MWCNTs were carried out in 8M HNO3, 8M H2SO4, 8M HNO3/H2O2 and 8M H2SO4/HNO3. Oxidized nanotubes sample were characterized by XRD, SEM, FT-IR, TGA, UV-Vis spectroscopy and Raman analysis. Oxidized-nanotubes show a lower shift in XRD peak and an increase in d-spacing, which implies deterioration of MWNTs. New peaks in FT-IR spectra of oxidized-nanotube samples at around 1742 cm−1 confirms the presence of carbonyl groups. Optical bandgap, molar absorptivity coefficient is estimated for pristine and oxidized nanotubes sample using UV-Vis spectroscopy data and Tauc plot. It is observed that optical bandgap decreases on oxidation and lowest bandgap 2.92 eV is observed for H2SO4 treated MWNTs. The information on the optical bandgap of the MWNTs is of great importance for the development of optoelectronic devices.