Environmentally Conscious Highly Effective Sorting of Single-Walled Carbon Nanotubes Using Recurrent Conjugated Polymer Extraction

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising materials for electronics and photonics due to their unique properties. To achieve high performance, the sorting of as-synthesized SWCNT mixtures is necessary, generating material with defined properties tailored for a specific application. Currently, it is possible to obtain such materials by using several SWCNT partitioning methods. However, such procedures require further improvements to unlock the industrial-scale production of SWCNTs of properties tailored for a specific application. The overall low efficiency of the SWCNT purification process and its nonsustainable nature are among the numerous obstacles that hinder their potential applications. Herein, we employed multiple rounds of conjugated polymer extraction (CPE) with a novel conjugated polymer (CP) addition scheme to considerably increase the amounts of isolated (6,5) and (7,5) SWCNTs, reaching up to 25% and 10%, respectively. While maintaining high chiral purity, the consumption of SWCNT raw material and CP was substantially reduced. This translated to a reduction of costs for the isolation of 1 mg of monochiral SWCNTs by nearly half compared with the most efficient chromatographic methods to date. Besides that, the proposed strategy, which relied on the deliberate addition of 4 times weight excess of the polymer with respect to SWCNTs at the initial extraction step, facilitated very short processing (sonication and centrifugation), shortening the purification time by ca. 76%, compared to the high volume shear-mixing technique, while simultaneously reducing electricity consumption. A series of consecutive isolations required only a modest addition of polymer to reach the desired SWCNT separation yield. Such a stepwise approach displayed considerable benefits compared to a typically engaged single-stage CPE process, achieving an unprecedented extraction performance. Most importantly, we show that the proposed approach fulfills the principles of green chemistry. First, the raw material consumption is reduced through repeated use or recycling, further enhancing the sustainability and cost-effectiveness of recurrent chirality-selective isolation of SWCNTs. Second, we discovered that the process may be conducted in naturally occurring green solvents such as p-cymene, thus avoiding the typically employed hazardous organic liquid media.