Tayloring of Reduction Potential of Carbon Nanotubes Hybrid Compound By Substrate Interaction Probed By Metal Deposition

Abstract

The determination or alteration of oxi-reduction potentials and Fermi level (EF) of single-walled carbon nanotubes is a relevant issue in the science of carbon nanotubes (CNTs) because many of the envisaged applications may involve charge transfer. So far, it is well known that redox potential and EF of single-walled carbon nanotubes are correlated to inverse of diameter and chiral angle. The reduction potential or the conduction band bottom energy of SWCNTs is in the range of 3.7 to 4.7 V vs. vacuum1,2. Nevertheless, in many electrochemical devices the CNTs is found on surface of other materials as oxides, carbons, metals, for instance. CNTs can also be directly grown on surface of several micrometric granules, fiber, thin films resulting, indeed, in hybrid compounds whose physical-chemical properties appears often correlated with amount and/or eventual electronic interaction of constituents. Herein, we investigate the eventual influence of a micrometric substrate on reduction potential of CNTs grown on its surface. Particularly, several carbonaceous materials and TiO2 were studied and the CNTs were vertically grown on surface of these micrometric substrates by chemical vapor deposition using the same CNTs growth protocol. In order to access the reduction potential of CNTs, the CNT/micrometric compounds were dipped into solutions of Ag, Cu, Al, Pd salts. The CNTs extracted from substrate by mechanical treatment were also dipped in same solutions. Afterwards, the obtained samples were analyzed in scanning electron microscopy, EDS and XPS after washed in deionized water. Interestingly the presence of metal nanoparticles was detected only in some types of CNT/micrometric substrate compounds. The mechanism of reduction of metals on surface of CNTs seems to be correlated with the participation of counter ions or presence of acids which can functionalize the surface of CNTs with COOH, COH, C=O groups. However, the main finding was the detection of an electronic coupling between CNT network-substrate which can modify the reduction potential of CNTs bear on its surface. Therefore, the CNTs growth on a micrometric substrate can lead to production of hierarchical hybrid compounds with unique redox potential. [1] Hirana, Y. et al. Empirical Prediction of Electronic Potentials of Single-Walled Carbon Nanotubes With a Specific Chirality (n,m). Sci. Rep. 3, 2959; (2013). [2] Kim, K. Ki et al.Doping strategy of carbon nanotubes with redox chemistry. New J.Chem.34, 2183; (2010).