Additive-Free Assemblies of Ramified Single-Walled Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) are difficult to process, and their assembly in macroscopic materials that allow us to benefit from the exceptional properties of the nanotubes is of crucial interest for applications. The developed CNT processing procedures usually involve additives that remain in the final product and are known to diminish the properties of the CNT-based material. Here, we propose a multistep approach to process single-walled carbon nanotubes (SWNTs) and obtain macroscopic additive-free SWNT materials. High-quality dispersion of purified SWNTs is first induced in polar solvent due to their preceding reduction reaction with an alkali metal. The partial debundling process occurring at this stage leads to ramified SWNTs. They can then be self-assembled by attractive intermolecular forces through a controlled destabilization of the dispersions by a simple oxidation. Swollen gels of SWNTs are formed at an air/solvent interface. After freeze-drying, the additive-free SWNT material shows a hierarchical structure with highly interconnected SWNTs. Thanks to the obtained ramification of the SWNTs, these latter are able to well entangle what guarantees the robustness of the obtained additive-free SWNT material. Moreover, this integrated process offers an increase of the accessible surface compared to that of the raw bundled SWNTs. The obtained assembled SWNTs show an improved adsorption capacity.