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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ORDERin1D (Order in one dimension: Functional hybrids of chirality-sorted carbon nanotubes)

Teaser

Summary

The aim of this ERC grant is to develop novel nanohybrids by encapsulating various molecules inside the hollow core of Carbon Nanotubes (CNTs).

CNTs can be visualized as a one atom thick layer of carbon atoms (i.e. a sheet of graphene) rolled up in a hollow cylindrical structure with a diameter of only 0.5 to 2 nanometers. These nanoscale structures possess remarkable electronic and optical properties, strongly dependent on the way the graphene sheet is rolled up into a cylinder determining the exact chiral structure of the CNTs. Each CNT structure will absorb and emit light at different wavelengths, thereby allowing the identification of the different CNT structures present in a specific sample by optical spectroscopy.

The hollow core of CNTs is just large enough to fit a single row of molecules inside, and after encapsulation, this single row of molecules can behave very differently in comparison to the same molecules embedded in a macroscopic material. Not only the properties of the molecules themselves, but also the properties of the CNTs change drastically due to the close interaction with the encapsulated molecules. In this project, filling of CNTs with various functional molecules is being investigated to promote new functionalities of both the individual building blocks (CNTs and encapsulated molecules) and the novel nanohybrid materials that are formed through the one-dimensional confinement of the molecules inside the CNTs.

There exist more than 160 different CNT structures within a diameter range of 0.5-2nm, each having a slightly different chiral structure. Although this provides a very large platform where for each molecule an ideal CNT structure that nicely fits around it can be found, unfortunately, synthesis techniques always produce a mixture of different chiral structures and diameters, each with different electronic and optical properties. Therefore, sorting of the CNTs based on their specific chiral structure is extremely important and one of the overall objectives of this project is to develop new sorting protocols for specific CNT chiral structures.

Such novel nanhybrid materials, with well-defined structure, can have a direct impact on the societal challenges of the future: including energy harvesting, water purification, ultrafast electro-optical modulators for optical data communication, ultrasensitive sensors, drug delivery and nanoprobes for bio-imaging applications.

Work performed

In view of the research program that has been granted by the ERC, the ORDERin1D ERC starting grant research team has initialized and expanded several research directions outlined in the proposal, which resulted in several high impact research results.

By performing temperature-dependent investigations of the emission spectra of empty and water-filled (6,5) CNTs, the ERC team was able to observe for the first time a peculiar quasi phase transition occurring in a chain of water molecules inside CNTs. We found that at low temperature (below 150K) the water dipoles all align in a ferroelectric manner with all dipoles pointing in the same direction. With temperature increasing, other ordered structures can be formed until a random orientation of water dipoles is obtained at high temperature.

Well-defined organic dye molecules were encapsulated inside CNTs with different diameters. After optical excitation of the dye molecules, they transfer their excitation energy to the CNTs, thereby photosensitizing the CNTs. Interestingly, we found that depending on the CNT diameter, the dyes adopt specific molecular arrangements (e.g. single file to double file arrangements in smaller and larger diameter CNTs) which strongly influences the excitation energy needed to excite the dye molecules. As such, one is able to tune the excitation energy of the dye, by selecting a specific CNT diameter.

By encapsulating more than 30 different compounds with different static dielectric constant inside the CNTs, we were able to understand the origin of electronic shifts of the optical transitions of CNTs induced by the dielectric constant of the fillers.

In view of the previous results, we developed new sorting protocols for larger diameter CNTs that are sufficiently large to encapsulate the above mentioned dye molecules. By systematic investigations of the parameter variations in aqueous two-phase separations, we were able to understand the mechanism behind the sorting methodology and as such introduce predictive sorting of different CNT structures.

These research findings resulted in several high impact publications and have been the topic of various invited and contributed presentations at the most important scientific meetings in the field.

Final results

In summary, this project has developed new methods for sorting carbon nanotubes and modifying their interior hollow space. We also addressed more fundamental scientific questions such as the observation of a quasi-phase transition in a one-dimensionally confined chain of water molecules, which was unexpected as theory did not predict such phase transitions to exist. Further we also focused on developing new methodologies to characterize the filling of CNTs as well as to investigate the mechanism behind the sorting techniques of different CNT structures.

Further work will explore the specific alignment of dipolar dyes inside CNTs, phase transitions in other CNT diameters as well as investigation of the transport of molecules inside the CNTs. The ERC-funded research team consisting of both PhD students and postdocs is looking forward to more exciting results.