X-ray absorption near edge spectroscopy of the electronic structure of potassium adsorbed single walled carbon nanotubes

Abstract

Carbon nanotubes (CNTs) show exceptional properties which make them extremely attractive for many applications. The electronic structure of potassium adsorbed single-walled carbon nanotubes (SWCNTs) is investigated by x-ray near edge structure (XANES) spectroscopy. Gas molecules (H 2 O, O 2 , CO 2 , CO) and potassium (K) adsorbates showed non negligible sensitivity to the geometry, thermal annealing treatment, and hybridization. The SWCNT type is shown by transmission electron microscopy (TEM) whereas an aleatory arrangement of SWCNTs and the spherical iron particles along carbon nanotubes are observed by scanning electron microscopy (SEM). XANES shows that the charge transfer effect in K-doping SWCNTs increases the conductivity to 62.7%. The adsorption study demonstrates that the adsorption mechanism to remove potassium from aqueous solutions using SWCNTs is assimilated to the ion exchange process. The functional groups OH − , C=O and C≡C are involved in the adsorption process. They are correlated to the assignment of the adsorbates given by XANES.

Sorption of metal elements by single-walled carbon nanotubes and x-ray absorption spectroscopy analysis

“…The present study addresses the sorption of metal elements by SWCNTs using XAS, and complementary techniques FTIR, EDS, SEM, and transmission electron microscopy (TEM). This paper is in the same line with the previous [34] investigating the carbon nanotube materials used for the removal of potassium from aqueous solutions. The main project concerns the study of carbon nanotubes which are used to remove pollutants from aqueous solutions with the application in wastewater purification.…”

“…The textural properties of the SWCNTs used as determined by Kamto et al [34] were surface area BET (582 m 2 g −1 ), pore volume (1.625 cm 3 g −1 ), and pore size (1.18 nm). The zero-point charge pH (pH ZPC ) was 6.79 according to [34].…”

“…The pH of the solution was adjusted daily to maintain the desired pH for each sample. After the equilibrium time, the final concentration (C f ), and corresponding final volume (V f ) of each pollutant were determined and the adsorption capacity (q) was calculated using the mass balance equation [34]:…”

“…The results of both EDS from TEM and SEM analysis agree well with a difference of 2.98, 0.98, 1, and 0.03% respectively for carbon, oxygen, iron, and sulfur. The presence of a very low concentration can be explained by the weaker interaction between sulfur and the wall of the SWCNTs [34,39]. The iron found in the raw SWCNTs may be the residue provided by the CVD synthesis method.…”

“…Generally, for the CVD process, the surface of CNTs can be covered by some impurities related to the metal particles used as catalysts [34,35]. Therefore, their characterization is necessary to better understand their properties for use in dedicated applications.…”