Extraction of (9,8) single-walled carbon nanotubes by fluorene-based polymers

High-yield and chirality-selective isolation of single-walled carbon nanotubes using conjugated polymers and small molecular chaperones

Single-walled carbon nanotubes (SWCNTs) have potential for a wide range of applications in diverse fields, but the heterogeneous properties of the synthesized mixtures of SWCNT types hinder the realization of these aspirations. Recent developments in extractive purification methods of polychiral SWCNT mixtures have somewhat gradually alleviated this problem, but either the yield or purity of the obtained fractions remains unsatisfactory. In this work, we showed the possibility of simultaneously achieving both the aforementioned goals, commonly considered mutually exclusive, via the enhancement of the capabilities of the conjugated polymer extraction (CPE) technique. We found that combining small molecular species, which alone are unwanted in the system, with a selective poly(9,9'-dioctylfluorenyl-2,7-diyl-alt-6,6'-(2,2'-bipyridine)) polymer increased the concentration of the harvested SWCNTs by an order of magnitude while maintaining near-monochiral purity of the materials. The conducted modeling revealed that the presence of these additives facilitated the folding of conjugated polymers around (6,5) SWCNTs, leading to a substantial increase in the concentration and quality of the SWCNT suspension. The obtained results lay the foundation for the widescale implementation of the CPE of usually scarcely available chirality-defined SWCNTs owing to the molecular chaperones expediting the folding of the conjugated polymers.

Mixed-Solvent Engineering as a Way around the Trade-Off between Yield and Purity of (7,3) Single-Walled Carbon Nanotubes Obtained Using Conjugated Polymer Extraction

The inability to purify nanomaterials such as single-walled carbon nanotubes (SWCNTs) to the desired extent hampers the progress in nanoscience. Various SWCNT types can be purified by extraction, but it is challenging to establish conditions giving rise to the isolation of high-purity fractions. The problem stems from the fact that common organic solvents or water cannot provide an optimal environment for purification. Consequently, one must often decide between the separation yield and purity of the product. This article reports how through the self-synthesis of poly(9,9-dioctylfluorene-alt-benzothiadiazole) with tailored characteristics, in-depth elucidation of the extraction process, and mixed-solvent engineering, a high-yield isolation of monochiral (7,3) SWCNTs is developed. The combination of toluene and tetralin affords a separation medium of unique properties, wherein both high yield and exceptional purity can be attained simultaneously. The reported results pave the way for further research on this rare chirality, which, as illustrated herein, is much more reactive than any of the previously separated SWCNTs.

Polyoxometalate steric hindrance driven chirality-selective separation of subnanometer carbon nanotubes

Subnanometer single-chirality single-walled carbon nanotubes (SWCNTs) are of particular interest in multiple applications. Inspired by the interdisciplinary combination of redox active polyoxometalates and SWCNTs, here we report a cluster steric hindrance strategy by assembling polyoxometalates on the outer surface of subnanometer SWCNTs via electron transfer and demonstrate the selective separation of monochiral (6,5) SWCNTs with a diameter of 0.75 nm by a commercially available conjugated polymer. The combined use of DFT calculations, TEM, and XPS unveils the mechanism that selective separation is associated with tube diameter-dependent interactions between the tube and clusters. Sonication drives the preferential detachment of polyoxometalate clusters from small-diameter (6,5) SWCNTs, attributable to weak tube-cluster interactions, which enables the polymer wrapping and separation of the released SWCNTs, while strong binding clusters with large-diameter SWCNTs provide steric hindrance and block the polymer wrapping. The polyoxometalate-assisted modulation, which can be rationally customized, provides a universal and robust pathway for the separation of SWCNTs.

Enrichment of high-purity large-diameter semiconducting single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes SWCNTs (s-SWCNTs) are considered one of the most promising alternatives to traditional silicon-based semiconductors. In particular, large-diameter s-SWCNTs (>1.2 nm) exhibit more advantages over small-diameter ones in high-performance electronic applications because of their higher charge carrier mobility and reduced Schottky barrier height. Great efforts have been made to enriching large-diameter s-SWCNTs from mass-produced raw CNTs that contain both metallic SWCNTs and s-SWCNTs. Among separation technologies, the effective and scalable ones are conjugated polymer wrapping (CPW), gel permeation chromatography (GC), aqueous two-phase extraction (ATPE), and density gradient ultracentrifugation (DGU). In this review, we survey recent progress on enriching large-diameter s-SWCNTs using those methods and outline the strategies and challenges in the separation according to the electronic type and chirality of SWCNTs. Finally, we highlight some applications of the enriched large-diameter s-SWCNTs and outlook for the future of SWCNT-based electronic devices.

Versatile Types of Inorganic/Organic NIR-IIa/IIb Fluorophores: From Strategic Design toward Molecular Imaging and Theranostics

In vivo imaging in the second near-infrared window (NIR-II, 1000-1700 nm), which enables us to look deeply into living subjects, is producing marvelous opportunities for biomedical research and clinical applications. Very recently, there has been an upsurge of interdisciplinary studies focusing on developing versatile types of inorganic/organic fluorophores that can be used for noninvasive NIR-IIa/IIb imaging (NIR-IIa, 1300-1400 nm; NIR-IIb, 1500-1700 nm) with near-zero tissue autofluorescence and deeper tissue penetration. This review provides an overview of the reports published to date on the design, properties, molecular imaging, and theranostics of inorganic/organic NIR-IIa/IIb fluorophores. First, we summarize the design concepts of the up-to-date functional NIR-IIa/IIb biomaterials, in the order of single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth-doped nanoparticles (RENPs), and organic fluorophores (OFs). Then, these novel imaging modalities and versatile biomedical applications brought by these superior fluorescent properties are reviewed. Finally, challenges and perspectives for future clinical translation, aiming at boosting the clinical application progress of NIR-IIa and NIR-IIb imaging technology are highlighted.

Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced SWNTs have poor solubility, and they are mixtures of metallic SWNTs (m-SWNTs) and s-SWNTs, which limits their practical applications. Conjugated polymer wrapping is a promising method to disperse and separate s-SWNTs, due to its high selectivity, high separation yield and simplicity of operation. In this review, we summarize the recent progress of the conjugated polymer wrapping method, and discuss possible separation mechanisms for s-SWNTs. We also discuss various parameters that may affect the selectivity and sorting yield. Finally, some electronic applications of polymer-sorted s-SWNTs are introduced. The aim of this review is to provide polymer chemist a basic concept of polymer based SWNT separation, as well as some polymer design strategies, influential factors and potential applications.

A Mixed-Extractor Strategy for Efficient Sorting of Semiconducting Single-Walled Carbon Nanotubes

A general strategy for sorting semiconducting single-walled carbon nanotubes (s-SWNTs) with high efficiency using a mixed-extractor is reported. When the two extractors have a sufficient difference in binding energy with s-SWNTs, and skeleton flexibility, the mixture shows enhanced yield for sorting s-SWNTs. The strategy could be effective when applied to increase the sorting yield of other selective dispersion systems.

"Smart poisoning" of Co/SiO2 catalysts by sulfidation for chirality-selective synthesis of (9,8) single-walled carbon nanotubes

The chirality-selective synthesis of relatively large (diameter > 1 nm) single-walled carbon nanotubes (SWCNTs) is of great interest for a variety of practical applications, but only a few catalysts are available so far. Previous studies suggested that S (compounds) can enhance the chirality-selectivity of Co catalysts in SWCNT synthesis, however, the mechanism behind is not fully understood, and no tailorable methodology has yet been developed. Here, we demonstrate a facile approach to achieve the chirality-selective synthesis of SWCNTs by the sulfidation-based poisoning of silica-supported Co catalysts using a mixture of H₂S and H₂. The UV-vis-NIR, photoluminescence, and Raman spectroscopy results together show that the resulting SWCNTs have a narrow diameter distribution of around 1.2 nm, and (9,8) nanotubes have an abundance of ∼38% among the semiconducting species. More importantly, the carbon yield achieved by the sulfided catalyst (2.5 wt%) is similar to that of the nonsulfided one (2.7 wt%). The characterization of the catalysts by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence, and H₂ temperature-programmed reduction shows that the sulfidation leads to the formation of Co₉S₈ nanoparticles. However, Co₉S₈ nanoparticles are reduced back to regenerate metallic Co nanoparticles during the synthesis of SWCNTs, which maintain a high carbon yield. In this process, Co₉S₈ nanoparticles seemingly intermediate the production of Co nanoparticles with narrow size distribution. Due to the fact that the poisoning step improves the quality of the end-product rather than hampering the growth process, we have coined the process developed as "smart poisoning". This study not only reveals the mechanism behind the beneficial role of S in the selective synthesis of relatively large SWCNTs but also presents a promising method to create chirality-selective catalysts with high activity for scalable synthesis.

Bolometric-Effect-Based Wavelength-Selective Photodetectors Using Sorted Single Chirality Carbon Nanotubes

This paper exploits the chirality-dependent optical properties of single-wall carbon nanotubes for applications in wavelength-selective photodetectors. We demonstrate that thin-film transistors made with networks of carbon nanotubes work effectively as light sensors under laser illumination. Such photoresponse was attributed to photothermal effect instead of photogenerated carriers and the conclusion is further supported by temperature measurements. Additionally, by using different types of carbon nanotubes, including a single chirality (9,8) nanotube, the devices exhibit wavelength-selective response, which coincides well with the absorption spectra of the corresponding carbon nanotubes. This is one of the first reports of controllable and wavelength-selective bolometric photoresponse in macroscale assemblies of chirality-sorted carbon nanotubes. The results presented here provide a viable route for achieving bolometric-effect-based photodetectors with programmable response spanning from visible to near-infrared by using carbon nanotubes with pre-selected chiralities.

Effect of side-chain halogenation on the interactions of conjugated polymers with SWNTs

Halogenation of polyfluorene side-chain ends with bromine or iodine causes significant differences in the nanotube species that are dispersed in solvent, indicating that subtle changes in polymer structure can affect polymer-nanotube interactions.