Adsorption of surfactant peptides on single-walled carbon nanotubes: Towards tailoring the electronic properties of carbon nanotubes.

摘要

Single-walled carbon nanotubes (SWCNTs) are one of the most researched materials in nanotechnology due to their unique structural, electronic, and mechanical properties. Although this material has many potential applications, SWCNTs suffer from several inherent challenges including self-association and insolubility in most solvents. Surface functionalization of SWCNTs is an area of immense interest since it not only reduces inter-tube interactions and enhances the solubility of SWCNTs in different media, but it can also be used to modify the intrinsic properties of SWCNTs to widen their applicability.;Our study focuses on the preparation of stable, aqueous dispersions of SWCNTs using amphiphilic surfactant peptides with varied aromatic moieties to investigate how the aromatic moieties affect the peptide/SWCNT interaction. We also examine the modulation of SWCNT electronic structure that occurs upon the adsorption of peptide molecules in order to gain a better understanding for potential nanoelectronic applications of peptide/SWCNT composites.;The selected aromatic functional groups are of diverse character having (i) exocyclic electron-donor substituents, including amine, dimethylamine, and hydroxyl groups, (ii) nitrogen (N)-containing heterocycles, such as indole and pyridine, or (iii) extended π-conjugated systems, including naphthalene and pyrene. Using scanning tunneling spectroscopy dI/dV plots and Raman spectroscopy G-band peak shifts, we show that the surfactant peptides containing exocyclic electron-donor substituents and N-containing heterocycles cause n-type doping of the SWCNTs. Moreover, our data reveal that the location of the heteroatom on the aromatic ring contributes significantly to the peptide/SWCNT interaction. We also find that the influence of extended π-conjugated systems on SWCNT electronic properties is minimal. Experimental data suggest that the pyrene moiety, with its large extended π-conjugated system, does not necessarily result in a better dispersal agent. Molecular dynamics simulation studies further show that the surfactant peptides containing pyrene moieties form relatively large peptide clusters as compared to the other peptides, indicating their tendency to self-aggregate. However, the dimerization and the adsorption free energy profiles determined for the peptides do not exhibit a clear trend or direct evidence for the affinity of pyrene-containing peptides to associate more strongly or adsorb onto SWCNTs less favorably than naphthalene-containing peptides.