Experimental studies on carbon nanotubes and graphene functionalized via physical adsorption with cellulose and avidin

Abstract

In this Thesis I have experimentally studied structural, electronic, and optical properties of hybrids of nanocarbon materials, carbon nanotubes (CNT) and graphene, and certain biomacromolecules. The latter are especially xylan, a type of hemicellulose, and avidin, an important protein.

Complexes of CNT with hemicellulose are attractive because the hybrid material is soluble in water. The conductive transport properties of thin films of CNT /hemicellulose have been systematically studied with different experimental tools. These are low temperature DC conduction measurements, Kelvin probe microscopy, and optical conductivity measurements at terahertz frequencies. The results clearly indicate that the CNT/CNT junctions rather than the defects along the CNTs play the key role in the CNT/hc transport mechanism of the thin films. Furthermore, we tested one application of the CNT/hc thin films as transparent conductive thin film (TCF), which combine high conductivity with low adsorption in the visible light region. The results are quite close to the best pure CNT thin films, but still well below the figure of merit of the indium tin oxide which is the most widely used TCF material.

The other major research topic in the Thesis is on structural properties of proteins physically adsorbed on carbon nanomaterials. We have experimented with physical adsorption of chimeric avidin on different surfaces, such as silicon, highly oriented pyrolytic graphite, graphene, and suspended multiwalled CNTs. The deposition results are dramatically different between silicon and nanocarbon materials. We observed that the topography difference between graphite (or graphene) and CNTs have significant effect on chi-avidin deposition. Furthermore, we investigated the functionality of avidin after surface adsorption, with respect to its excellent binding capability in the solution phase of biotin.