Extraction of Linear Carbon Chains Unravels the Role of the Carbon Nanotube Host

Abstract

Linear carbon chains (LCCs) have been shown to grow inside double-walled carbon nanotubes (DWCNTs), but isolating them from this hosting material represents one of the most challenging tasks toward applications. Herein we report the extraction and separation of LCCs inside single-walled carbon nanotubes (LCCs@SWCNTs) extracted from a double-walled host LCCs@DWCNTs by applying a combined tip-ultrasonic and density gradient ultracentrifugation (DGU) process. High-resolution transmission electron microscopy, optical absorption, and Raman spectroscopy show that not only short LCCs but clearly long LCCs (LLCCs) can be extracted and separated from the host. Moreover, the LLCCs can even be condensed by DGU. The Raman spectral frequency of LCCs remains almost unchanged regardless of the presence of the outer tube of the DWCNTs. This suggests that the major importance of the outer tubes is making the whole synthesis viable. We have also been able to observe the interaction between the LCCs and the inner tubes of DWCNTs, playing a major role in modifying the optical properties of LCCs. Our extraction method suggests the possibility toward the complete isolation of LCCs from CNTs.

Nanotube‐Based 1D Heterostructures Coupled by van der Waals Forces

“…While inner nanotubes are typically extracted by sonication, [103,106,213] the sonication is known to cut the tubes into short pieces and create a lot of defects. When applying this technique to LCC encapsulated inside DWCNTs (LCC@DWCNTs), intending to obtain LCC@SWCNT samples, the Raman signal of the LCCs was greatly reduced, indicative of the destruction of most of the encapsulated LCCs, [214] in particular when taking into account its giant Raman cross-section. [118] A different strategy that does not destroy the newly synthesized structures is thus highly required.…”

A review of functional linear carbon chains (oligoynes, polyynes, cumulenes) and their applications as molecular wires in molecular electronics and optoelectronics

“…73 These polyynes can be extracted together with the inner tubes from the hosting outer tube of the DWCNTs. 74 The CNTs act as a cage to protect the polyyne chains.…”

Structure of inorganic nanocrystals confined within carbon nanotubes

“…Encapsulation of inorganic crystals within CNTs is an attractive route for the template-assisted synthesis of new functional materials. CNTs not only act as moulds to control the dimensions of the new nanostructures, but also play a protective role, allowing the formation of nanostructures with a high interest due to their optical, chemical and electronic properties, but which stability at ambient conditions is extremely low [77,78]. CNTs provide by themselves interesting characteristics to the new synthesized hybrids.…”