Carbon nanotube fibers (CNTFs), composed of numerous aligned CNTs, show promise for a range of industries and applications based on the extraordinary thermal and electrical conductivities of individual CNTs. However, poor interfacial junctions between adjacent CNTs hinder phonon and electron transport, resulting in CNTFs with significantly lower conductivities than individual CNTs. Coalescing smaller-diameter CNTs into larger-diameter CNTs may create a more integrated network with reduced junction resistances, thereby improving interfacial junctions and, thus, transport properties. In this work, we employ ultraviolet pulsed laser annealing (UV-PLA) for targeted heating of CNTFs to induce coalescence. Raman spectroscopy is used to quantify CNT coalescence by analyzing radial breathing modes (RBMs), and the G- (graphitic) and D- (disordered) peaks. Our findings indicate that CNT coalescence can be induced within microseconds using UV-PLA. UV-PLA-coalesced CNTFs were shown to have exceptional thermal conductivities of up to 777 W/mK and electrical conductivities of up to 13.4 MS/m, after redoping.

Carbon nanotube (CNT) wires approach copper's specific conductivity and surpass carbon fiber's strength, with further improvement anticipated with greater aspect ratios and incorporation of dopants with long-range structural order. Fullerenes assemble into multitudes of process-dependent supramolecular crystals and, while initially insulating, they become marginally conductive (up to 0.05 MSm^-1) and superconductive (T_c=18^∘K with K and 28^∘K with Rb) after doping. These were small (100's μm long), soft (hardness comparable to indium), and typically unaligned, which hindered development of fullerene based wires. Individual fullerenes were previously incorporated into CNT fibers, although randomly without self-assembly into supramolecules. Here, a simple variation in established CNT acid extrusion creates a fiber composed of uniaxial chains of aligned fullerene supramolecules, self-assembled between aligned few-walled CNT bundles. This will provide a testbed for novel fullerene wire transport and prospects in CNT wire advancement.

The conductivity and strength of carbon nanotube (CNT)wires currentlyrival those of existing engineering materials; fullerene-based materialshave not progressed similarly, despite their exciting transport propertiessuch as superconductivity. This communication reveals a new mechanicallyrobust wire of mutually aligned fullerene supramolecules self-assembledbetween CNT bundles, where the fullerene supramolecular internal crystalstructure and outer surface are aligned and dispersed with the CNTbundles. The crystallinity, crystal dimensions, and other structuralfeatures of the fullerene supramolecular network are impacted by anumber of important production processes such as fullerene concentrationand postprocess annealing. The crystal spacing of the CNTs and fullerenesis not altered, suggesting that they are not exerting significantinternal pressure on each other. In low concentrations, the additionof networked fullerenes makes the CNT wire mechanically stronger.More importantly, novel mutually aligned and networked fullerene supramoleculesare now in a bulk self-supporting architecture.

Macroscopic assemblies of aligned carbon nanotubes (CNTs) have been doubling in conductivity every three years and have now surpassed 10 MS/m [1]. They are promising for replacing copper- or aluminum-based electrical cables in applications where flexibility or weight savings are critical considerations. Understanding of transport processes in these ordered CNT assemblies is critical towards further conductivity improvement; yet, fiber-level transport is still poorly understood. Here, we studied thermoelectric and electrical properties of aligned CNT fibers and bundles produced by solution spinning. We first measured thermoelectric properties while tuning the Fermi energy and demonstrated a giant thermoelectric power factor [2]. We then performed temperature- and magnetic field-dependent conductivity measurements. In contrast to the majority of transport studies of CNT networks [3,4], our aligned CNT fibers exhibited a metallic behavior in a wide temperature range (30-300 K), i.e., conductivity monotonically increasing with decreasing temperature, which we attribute to the excellent sample morphology. At temperatures below 30 K, we observed a gradual decrease of conductivity with decreasing temperature, together with negative magnetoresistance, consistent with the weak localization theory for disordered metals. We determined the dimensionality and coherence lengths of carriers via analysis of the weak localization behavior. In addition to macroscopic CNT fibers with diameters of ~10 μm, we also conducted conductivity measurements on individual crystalline CNT bundles (with diameters ~ 50 nm and lengths ~ 30 μm) that constitute the fibers. References [1] L. W. Taylor, O. S. Dewey, R. J. Headrick, N. Komatsu, N. M. Peraca, G. Wehmeyer, J. Kono, and M. Pasquali, Carbon N. Y. 171 , 689 (2021). [2] N. Komatsu, Y. Ichinose, O. S. Dewey, L. W. Taylor, M. A. Trafford, Y. Yomogida, G. Wehmeyer, M. Pasquali, K. Yanagi, and J. Kono, Nat. Commun. 12 , 4931 (2021). [3] W. Zhou, J. Vavro, C. Guthy, K. I. Winey, J. E. Fischer, L. M. Ericson, S. Ramesh, R. Saini, V. A. Davis, C. Kittrell, M. Pasquali, R. H. Hauge, and R. E. Smalley, J. Appl. Phys. 95 , 649 (2004). [4] N. F. Zorn and J. Zaumseil, Appl. Phys. Rev. 8 , 41318 (2021).

Low-dimensional materials have recently attracted much interest as thermoelectric materials because of their charge carrier confinement leading to thermoelectric performance enhancement. Carbon nanotubes are promising candidates because of their one-dimensionality in addition to their unique advantages such as flexibility and light weight. However, preserving the large power factor of individual carbon nanotubes in macroscopic assemblies has been challenging, primarily due to poor sample morphology and a lack of proper Fermi energy tuning. Here, we report an ultrahigh value of power factor (14 ± 5 mW m −1 K −2 ) for macroscopic weavable fibers of aligned carbon nanotubes with ultrahigh electrical and thermal conductivity. The observed giant power factor originates from the ultrahigh electrical conductivity achieved through excellent sample morphology, combined with an enhanced Seebeck coefficient through Fermi energy tuning. We fabricate a textile thermoelectric generator based on these carbon nanotube fibers, which demonstrates high thermoelectric performance, weavability, and scalability. The giant power factor we observe make these fibers strong candidates for the emerging field of thermoelectric active cooling, which requires a large thermoelectric power factor and a large thermal conductivity at the same time.

Boron nitride nanotubes (BNNT) are poised to fill an electrically insulating, high-temperature, high strength niche. Despite significant progress over the past two decades, BNNTs are not yet synthesized in high enough quantity and quality to permit their use in engineering applications. The next necessary step to make BNNTs accessible for research and applications is to improve the availability of high-quality BNNTs. Here, we present a scalable bulk purification technique that yields high-purity BNNTs. Bulk synthesized material is introduced to a wet oxygen environment at elevated temperatures to remove elemental boron and hexagonal boron nitride impurities with a final yield of purified BNNTs near 10 wt %. This process shows full removal of impurities, as observed by scanning electron microscopy (SEM), cryogenic transmission electron microscopy (TEM), and high-resolution TEM. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy show minimal BNNT functionalization, while high-resolution TEM shows damage to large-diameter BNNTs.

Lightweight materials for next-generation electrical and mechanical applications are expected to have significant impacts on aerospace and ground transportation by reducing fuel consumption. Assessing the potential of novel wiring or fibers requires accurate measurement of linear density. The linear densities of fibers are measured by determining the fiber's resonant frequency vibroscopically, which requires complex mechanical equipment for vibrating the fiber. Here, we leverage the electrical conductivity of carbon nanotube (CNT) fibers to induce vibrations by applying an alternating current (AC) to a fiber under a known tension in the presence of a permanent magnetic field, eliminating the need for mechanical actuation. The fiber vibrates at maximum amplitude when the AC frequency matches the fiber's fundamental resonant frequency, creating an audible sound and inducing measurable changes in the fiber electrical properties. Linear density can be calculated accurately from the resonant frequency or the changes in electrical properties in this simplified apparatus during a tensile test.

The Suzuki-Miyaura cross-coupling reaction is a foundation stone of modern organic synthesis, as evidenced by its widespread use in the preparation of pharmaceuticals, agrochemicals, polymers, and other functional materials. With the prevalence of this venerable reaction in industrial synthesis, it is prudent to ensure its application adheres to the tenets of green chemistry. The introduction of cross-coupling catalysts that are active in sustainable solvents is therefore an important endeavor. In this report, a melamine-palladium complex is introduced as a versatile catalyst for the Suzuki-Miyaura cross-coupling reaction. This catalyst is soluble and active in both water and the renewable organic solvent ethyl lactate. The melamine-palladium catalyst can also be cross-linked by reaction with formaldehyde to generate an insoluble polymeric catalyst that can be recovered after the cross-coupling. The melamine-palladium system is inexpensive, easy to handle, bench-stable, and effective in catalysis in the presence of a variety of impurities (high cross-coupling yields were obtained in reactions run in unfiltered river water to illustrate this final point). Additionally, investigations reported herein revealed an intriguing relationship between catalytic efficiency and the base employed in the cross-coupling reaction. Implications for the mechanism of transmetalation in aqueous Suzuki-Miyaura cross-coupling reaction are discussed.

The melamine/Pd(OAc) 2 is soluble and active in both water and the renewable nontoxic organic solvent ethyl lactate (ELA).