Cleanly Removable Surfactant for Carbon Nanotubes

Abstract

Surfactants, molecular surface-active agents, are widely used to stabilize single-walled carbon nanotubes (SWCNTs) and many other nanomaterials in water to facilitate solution processing and device integration. However, it is notoriously difficult to cleanly remove surfactants when they are no longer needed. Even high-temperature thermal annealing leaves residues that can degrade the otherwise remarkable electrical and optical properties of SWCNTs. Moreover, thermal annealing damages smaller-diameter nanotubes (<1 nm) due to aggressive oxidation at elevated temperatures. To address this challenge, we report the synthesis of ammonium deoxycholate (ADC) that can be cleanly removed at a relatively low temperature that preserves the SWCNT structure. We find that ADC is as efficient as sodium deoxycholate (a commonly used surfactant featuring the same anion) at individually dispersing SWCNTs in water. However, replacing the metal cation (Na+) of sodium deoxycholate with ammonium (NH4 +) to form ADC reduces the peak thermal decomposition temperature by nearly 70 °C. Furthermore, unlike sodium deoxycholate, thermal annealing of ADC in Ar leaves behind only a small amount of carbonized residue that can be cleanly decomposed in the presence of 5% O2 at 400 °C, a condition that preserves SWCNTs even with a small diameter of just 0.76 nm. This work uncovers the chemical origin of residues from the thermal annealing of surfactant-processed carbon nanomaterials and provides an unexpectedly simple solution to this persistent challenge.

Gel Chromatography for Separation of Single-Walled Carbon Nanotubes

“…To compensate for this, Zhang et al reported in a recent study that the use of ammonium deoxycholate as a surfactant enabled clean removal from SWNT through heat treatment. In contrast to DOC, about 20% remained; even at high temperatures above 500 °C, ADC was removed to 5% or less at 400 °C or higher [ 117 ]. Nevertheless, there is still an issue that high temperatures can cause damage to SWNTs, which is the same for acid treatment.…”

Recent Advances in Structure Separation of Single‐Wall Carbon Nanotubes and Their Application in Optics, Electronics, and Optoelectronics

“…[441] Similar problem is also unavoidable for surfactants and other dispersant molecules, as demonstrated by thermogravimetric analysis. [436,[442][443][444][445] Therefore, the complete removal of dispersant molecules still remains a challenge.…”

“…Carbon is an amazing element that has many different stable forms including three‐dimensional diamond, 2D graphene, 1D nanotubes, and 0D fullerene. Research on carbon materials has attracted much attention in the fields of science and industrial technology since the discoveries of fullerene in 1985, [ 1 ] nanotubes in 1991, [ 2 ] and graphene in 2004. [ 3 ] Single‐wall carbon nanotubes (SWCNTs) are some of the most studied carbon materials and were produced for the first time by Iijima, Bethume et al.…”

Polymethyl(1–Butyric acidyl)silane–Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single–Walled Carbon Nanotubes

“…For non-covalent chemical modifications, the choice of dispersing agents is crucial to the effective individualization and efficient sorting of metallic or semiconducting SWNTs. Typical dispersing agents are limited to classic surfactants [22][23][24], ionic liquids [25], and biological substances [12,26,27] applicable in water media as well as varying polymers [28][29][30] applicable in water or non-water media. In the case of polymers, both the water-soluble nonaromatic species [31][32][33] and the non-water-soluble π-conjugated ones are selective for sc-SWNTs [34][35][36][37].…”