Dye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system.

Middle infrared response on a carbon nanotube is very weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Nevertheless, a significant number of infrared phonons are predicted by the group theory. Encapsulating molecules inside nanotubes (called hybrid nanotubes in the following) is a common strategy to add new functionalities. The one-dimensional nature of single-walled carbon nanotubes (SWCNT) internal channels has been exploited here to induce a molecular order and specific interactions which are dependent of the size of the nano container (figure).Here we report the discovery of a strong dependence on the infrared response of the hybrid nanotube due to confinement effect when dimethylquaterthiophenes are encapsulated inside SWCNTs1. Results are compared to experiments performed on nanotubes where dyes are π-stacked at the outer surface. Surprisingly, the confinement properties lead to an exaltation of the infrared absorption response in the carbon nanotubes from dye molecule interactions. Thanks to the comparison between the experimental investigations and DFT calculations, we elucidate the origin of the large enhancement of this infrared absorption and demonstrate that interactions between conjugated oligomers and nanotubes can be probed.

Tuning the opto-electronic properties of hybrid nano-systems

Results and questions aboutStructural properties of molecules inside carbon nanotubes

Dye encapsulation into host single-walled carbon nanotubes is an elegant way to create hybrid nano-systems with tunable opto-electronic properties. To this aim, different kinds of molecules (either electron donor or acceptor, absorbing either in the blue or the red visible range) are encapsulated into metallic or semiconducting nanotubes displaying different diameters. Up to now, we have mainly studied encapsulated quaterthiophene derivatives (4T), tetracyanoquinodimethane (TCNQ) and phthalocyanine (MPc) molecules. In this work, we discuss the supramolecular organization of dyes inside the nanotube, the optical properties and the charge transfer for some of our hybrid systems. For instance, using Raman spectroscopy, a significant electron transfer is reported with 4T, whose magnitude strongly depends on the nanotube diameter, and on the metallic or semiconducting character. Experiments also suggest a photo-activated electron transfer for small diameter (~9 Å) semiconducting and metallic tubes. Confinement of electron donor (4T) (respectively electron acceptor (TCNQ)) into small diameter tubes leads to a red shift (blue shift) of the optical absorption energy and an increase (decrease) of the photoluminescence intensities, evidenced by the photoluminescence excitation maps.

Dye encapsulation into host single-walled carbon nanotubes is an easy way to create hybrid nano-systems with tunable opto-electronic properties. In this work, we will discuss the supramolecular organization inside the nanotube, the optical properties and the charge transfer as the function of the type of molecules, diameter and metallic or semiconducting character of the host nanotube. A significant electron transfer from encapsulated dyes to the carbon material is reported, whose magnitude strongly depends on the nanotube diameter, in good agreement with DFT calculations, and on the metallic or semiconducting character. Experiments also suggest a photo-activated electron transfer for small diameter (~9 Å) semiconducting and metallic tubes. Dye encapsulation is shown to significantly alter electron-phonon coupling into metallic nanotubes as revealed by the value of the coupling factor extracted from the Fano equation. The charge transfer is consistent with an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This charge transfer shifts the Fermi level, acting on the photoluminescence efficiency and the electron-phonon-coupling.

Single-walled carbon nanotubes are functionalized with copper hexacyanoferrate nanoparticles for the liquid-solid extraction of cesium from liquid waste and contaminated water. The functionalization process is followed mainly by x-ray photoemission spectroscopy. Indeed, determining the chemical environment around carbon or nitrogen atoms allows to evidence the formation of covalent bounding. In addition, the signatures of iron and copper ions give information on the effective growth of hexacyanoferrate nanoparticles. Furthermore, the cesium sorption mechanism is investigated by comparing the peak intensities associated to the response of potassium and cesium ions. Finally, based on the liquid chromatography analyzes, the sorption of cesium with the functionalized carbon supports is studied. The main results of this work are the demonstration of both a good selectivity of cesium trapping and a high sorption capacity by hybrid single-walled carbon nanotubes.