Highly-Selective Harvesting of (6,4) SWCNTs Using the Aqueous Two-Phase Extraction Method and Nonionic Surfactants.

Monochiral single-walled carbon nanotubes (SWCNTs) are indispensable for advancing the technology readiness level of nanocarbon-based concepts. In recent times, many separation techniques have been developed to obtain specific SWCNTs from raw unsorted materials to catalyze the development in this area. This work presents how the aqueous two-phase extraction (ATPE) method can be enhanced for the straightforward isolation of (6,4) SWCNTs in one step. Introducing nonionic surfactant into the typically employed mixture of anionic surfactants, which drive the partitioning, is essential to increasing the ATPE system's resolution. A thorough analysis of the parameter space by experiments and modeling reveals the underlying interactions between SWCNTs, surfactants, and phase-forming agents, which drive the partitioning. Based on new insight gained on this front, a separation mechanism is proposed. Notably, the developed method is highly robust, which is proven by isolating (6,4) SWCNTs from several raw SWCNT materials, including SWCNT waste generated over the years in the laboratory.

Understanding the partitioning behavior of single-walled carbon nanotubes using an aqueous two-phase extraction system composed of non-ionic surfactants and polymers.

In this work, a Pluronic/Dextran system was developed to discover the mechanism of the aqueous two-phase extraction (ATPE) technique, which is widely employed for the sorting of single-walled carbon nanotubes (SWCNTs) and other types of nanomaterials. The role of the phase-forming components and partitioning modulators was comprehensively investigated to gain greater insights into the differentiation process. The obtained results revealed that sodium dodecyl sulfate and sodium dodecylbenzene sulfonate operated as excellent partitioning modulators, enabling the diameter-based sorting of SWCNTs. Additionally, the data strongly suggested that different densities of various SWCNT species drove the movement of SWCNTs in the ATPE system. Consequently, the largest diameter SWCNTs were first influenced by surfactants and, thus, the nanotubes migrated towards a lower density top phase in the following order (7,5) > (8,3) > (6,5) > (6,4). Based on the in-depth analysis of the partitioning system, a mechanism was proposed that described the method in which the popular ATPE separation technique operates.

En route to single-step, two-phase purification of carbon nanotubes facilitated by high-throughput spectroscopy.

Chirality purification of single-walled carbon nanotubes (SWCNTs) is desirable for applications in many fields, but general utility is currently hampered by low throughput. We discovered a method to obtain single-chirality SWCNT enrichment by the aqueous two-phase extraction (ATPE) method in a single step. To achieve appropriate resolution, a biphasic system of non-ionic tri-block copolymer surfactant is varied with an ionic surfactant. A nearly-monochiral fraction of SWCNTs can then be harvested from the top phase. We also found, via high-throughput, near-infrared excitation-emission photoluminescence spectroscopy, that the parameter space of ATPE can be mapped to probe the mechanics of the separation process. Finally, we found that optimized conditions can be used for sorting of SWCNTs wrapped with ssDNA as well. Elimination of the need for surfactant exchange and simplicity of the separation process make the approach promising for high-yield generation of purified single-chirality SWCNT preparations.

Thermoelectric Properties of Thin Films from Sorted Single-Walled Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) remain one of the most promising materials of our times. One of the goals is to implement semiconducting and metallic SWCNTs in photonics and microelectronics, respectively. In this work, we demonstrated how such materials could be obtained from the parent material by using the aqueous two-phase extraction method (ATPE) at a large scale. We also developed a dedicated process on how to harvest the SWCNTs from the polymer matrices used to form the biphasic system. The technique is beneficial as it isolates SWCNTs with high purity while simultaneously maintaining their surface intact. To validate the utility of the metallic and semiconducting SWCNTs obtained this way, we transformed them into thin free-standing films and characterized their thermoelectric properties.

One-step sorting of single-walled carbon nanotubes using aqueous two-phase extraction in the presence of basic salts.

We demonstrate a simple one-step approach to separate (6,5) CNTs from raw material by using the aqueous two-phase extraction method. To reach this goal, stable and inexpensive K2CO3, Na2CO3, Li2CO3, and K3PO4 basic salts are used as modulators of the differentiation process. Under the appropriate parameters, near monochiral fractions become available for straightforward harvesting. In parallel, we show that the isolation process is strongly affected not only by pH but by the inherent nature of the introduced chemical species as well. The results of our study also reveal that the commonly used ingredients of the biphasic system make a strong contribution to the course of the separation by having far from neutral pH values themselves.