Characterization of chemically grafted carbon nanotubes by EELS spectroscopy

Abstract

The novel mechanical and electrical properties of carbon nanotubes have potential applications in a variety of fields, and their size makes them appealing for use in biosensors. However, in order to exploit their potential, carbon nanotubes must be functionalized for biologic compatibility. Sulfonated and polyanilinated multi-walled and single-walled carbon nanotubes were investigated by several spectroscopic and microscopic methods to asses their feasibility in characterization of functionalized carbon nanotubes (CNT). Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and energy-dispersive X-ray analysis (EDX) were applied to confirm the presence of heteroatoms that were not present in the parent CNTs. EELS ratio mapping, used in conjunction with bright-field TEM imaging, is an extremely powerful tool for examining functionalized nanotubes and other composites because it provides a means of showing the spatial arrangement of individual elements in a sample. This characterization approach provides clear evidence of functional group incorporation onto the CNT. Subsequent atom mapping along the vicinity of the tube structure also allowed us to illustrate the three dimensional distribution of the heteroatoms along the CNT surface. Other elemental analysis techniques can confirm and possibly quantify the presence of a particular element, but fail to illustrate its spatial distribution in a material. In this study, the presence of nitrogen and sulfur atoms along the surface of a nanotube have been confirmed and shown to be uniform by means of TEM and EELS. EDX plots have been investigated as an additional measure of functionalization.