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Alberta oilsands asphaltenes (AOAs) are carbon-rich hydrocarbons obtained from the heaviest fraction in Alberta oilsands bitumen. They have little value in the current market. Asphaltenes are considered a problematic stream for bitumen transportation and processing, and they may be a potential feedstock for carbon fiber (CF) production. Effort has been devoted by researchers and the oil industry for developing asphaltenes into value-added products, in particular CFs. Major barriers have been identified for the conversion of asphaltenes to CFs. One of them is purification and priming of the AOA feedstock as the raw material varied significantly from extraction and applied isolation technologies. Here, we report the purification of raw AOAs for the purpose of forming AOA-green fibers through electrospinning, the comparison with the non-purified AOA raw materials, and the validation of the potential of conversion of asphaltenes toward CFs. Thermogravimetric analysis, elemental analysis, and scanning electron microscopy were carried out. AOA-green fibers were obtained with the as-received AOAs and the maltene-free AOAs by three optimized electrospinning protocols. These green fibers can be spun to a large size mat with a high degree of alignment through adjusting the collector rotation velocity. The diameters of the obtained AOA-green fibers are mostly in the range of 4–15 μm. The green fibers from the as-received AOAs could sustain up to 200 °C in air but fused with further increase of temperature, while the green fibers from the purified AOAs showed improved mechanical strength and were able to withstand temperatures up to 300 °C in air without fusing. This work will be of interest to the CF industry as a potential alternative approach for low-cost precursors.

Current processes to manufacture nanotubes at commercial scales are unfortunately imperfect and commonly generate undesirable byproducts. After manufacturing, purification is necessary and is a rate and cost determining step in advancing the development of commercial products based on nanotubes. Boron nitride nanotubes (BNNTs) produced without metal catalysts from high-temperature processes are known to contain a significant amount (e.g., 50 wt %) of various boron derivatives. Herein we report a simple yet efficient and scalable process to purify these types of BNNT materials at commercial scales, from a few grams to hundreds of grams, at purity over 85 wt % in a single step. The process relies on a vertically mounted flow tube reactor and scrubber system that can be operated under pure or diluted chlorine gas flow at temperatures up to 1100 °C. The main chemical reactions driving the purification are the conversion of boron and BN derivatives into BCl3and HCl, which are removed as gaseous species, while pristine BNNTs are left behind. The preferential etching of impurities over pristine BNNTs shows the extreme chemical resistance of BNNTs in this harsh environment and opens up new applications for this nanomaterial. The process has been examined at various temperatures, up to 1050 °C, and the resulting materials display improved BNNT purity and quality across a range of imaging and spectroscopic assessments. The recommended temperature to optimize quality with yield is 950 °C, although higher quality material is obtained at a higher temperature.

We recently demonstrated scalable manufacturing of boron nitride nanotubes (BNNTs) directly from hexagonal BN (hBN) powder by using induction thermal plasma, with a high-yield rate approaching 20 g/h. The main finding was that the presence of hydrogen is crucial for the high-yield growth of BNNTs. Here we investigate the detailed role of hydrogen by numerical modeling and in situoptical emission spectroscopy (OES) and reveal that both the thermofluidic fields and chemical pathways are significantly altered by hydrogen in favor of rapid growth of BNNTs. The numerical simulation indicated improved particle heating and quenching rates (∼105K/s) due to the high thermal conductivity of hydrogen over the temperature range of 3500–4000 K. These are crucial for the complete vaporization of the hBN feedstock and rapid formation of nanosized B droplets for the subsequent BNNT growth. Hydrogen is also found to extend the active BNNT growth zone toward the reactor downstream, maintaining the gas temperature above the B solidification limit (∼2300 K) by releasing the recombination heat of H atoms, which starts at 3800 K. The OES study revealed that H radicals also stabilize B or N radicals from dissociation of the feedstock as BH and NH radicals while suppressing the formation of N2or N2+species. Our density functional theory calculations showed that such radicals can provide faster chemical pathways for the formation of BN compared with relatively inert N2.

Boron nitride nanotubes (BNNTs) exhibit a range of properties that hold great potential for many fields of science and technology; however, they have inherently low chemical reactivity, making functionalization for specific applications difficult. Here we propose that covalent functionalization of BNNTs viareduction chemistry could be a highly promising and viable strategy. Through density functional theory calculations of the electron affinity of BNNTs and their binding energies with various radicals, we reveal that their chemical reactivity can be significantly enhanced viareducing the nanotubes (i.e., negatively charging). For example, a 5.5-fold enhancement in reactivity of reduced BNNTs toward NH2radicals was predicted relative to their neutral counterparts. The localization characteristics of the BNNT π electron system lead the excess electrons to fill the empty p orbitals of boron sites, which promote covalent bond formation with an unpaired electron from a radical molecule. In support of our theoretical findings, we also experimentally investigated the covalent alkylation of BNNTs viareduction chemistry using 1-bromohexane. The thermogravimetric measurements showed a considerable weight loss (12–14%) only for samples alkylated using reduced BNNTs, suggesting their significantly improved reactivity over neutral BNNTs. This finding will provide an insight in developing an effective route to chemical functionalization of BNNTs.

The purity of single-wall carbon nanotube (SWCNT) ensembles is critical, but assessing the purity in terms of metal vs semiconductor content is challenging at high purities. We describe possible bulk Raman spectroscopy based procedures to assess this metallicity and compare it to absorption procedures. A simple metric for metallicity is the G+band peak intensity ratio at two appropriate wavelengths. Related metallic G–band area derived metrics extend to higher purities. The G band signal scales linearly over orders of magnitude in concentration. However, the ratio-derived metrics may still be nonlinear because of resonance. Therefore, they break down if the tube diameter distributions differ greatly between samples, and other complications are possible. Additionally, the absolute Raman cross sections for each type of SWCNT can be estimated, and the abundance of semiconductors and metals can be tracked independently. Raman-derived metallicity figures of merit can meaningfully evaluate samples of purities which are not otherwise easily accessible, but there are important limitations to this simple approach to metallicity assessment.

Boron nitride nanotubes (BNNTs) exhibit a range of properties that are as compelling as those of carbon nanotubes (CNTs); however, very low production volumes have prevented the science and technology of BNNTs from evolving at even a fraction of the pace of CNTs. Here we report the high-yield production of small-diameter BNNTs from pure hexagonal boron nitride powder in an induction thermal plasma process. Few-walled, highly crystalline small-diameter BNNTs (∼5 nm) are produced exclusively and at an unprecedentedly high rate approaching 20 g/h, without the need for metal catalysts. An exceptionally high cooling rate (∼105K/s) in the induction plasma provides a strong driving force for the abundant nucleation of small-sized B droplets, which are known as effective precursors for small-diameter BNNTs. It is also found that the addition of hydrogen to the reactant gases is crucial for achieving such high-quality, high-yield growth of BNNTs. In the plasma process, hydrogen inhibits the formation of N2from N radicals and promotes the creation of B–N–H intermediate species, which provide faster chemical pathways to the re-formation of a h-BN-like phase in comparison to nitridation from N2. We also demonstrate the fabrication of macroscopic BNNT assemblies such as yarns, sheets, buckypapers, and transparent thin films at large scales. These findings represent a seminal milestone toward the exploitation of BNNTs in real-world applications.

Single-walled carbon nanotubes (SWCNT) exhibit amongst the best mechanical, thermal and electrical properties of any known material. With their very high aspect ratios, SWCNT are well-suited to making ultra-light multifunctional structural composites. In this work, covalent chemistry is used to integrate SWCNT into a single component epoxy resin (aerospace grade MY0510) as well as an industrialized epoxy resin system for sporting goods. In particular, reduced SWCNT react directly with epoxide groups to create direct connections to the resin backbone. As the reduction process naturally exfoliates the SWCNT bundles, excellent dispersion is readily obtained. Substantial mechanical property improvements of the modified resin and carbon fibre composites have been observed through well-controlled processing. Their mechanical properties, specifically impact resistance, compression after impact strength and fracture toughness of the modified resin and fibre composites are discussed.