High-performance, recyclable ultrafiltration membranes from P4VP-assisted dispersion of flame-resistive boron nitride nanotubes

Lyotropic Boron Nitride Nanotube Liquid Crystals: Preparation, Characterization, and Wet-Spinning for Fabrication of Composite Fiber

Microfiber fabrication via wet-spinning of lyotropic liquid crystals (LCs) with anisotropic nanomaterials has gained increased attention due to the microfibers' excellent physical/chemical properties originating from the unidirectional alignment of anisotropic nanomaterials along the fiber axis with high packing density. For wet-spinning of the microfibers, however, preparing lyotropic LCs by achieving high colloidal stability of anisotropic nanomaterials, even at high concentrations, has been a critically unmet prerequisite, especially for recently emerging nanomaterials. Here, we propose a cationically charged polymeric stabilizer that can efficiently be adsorbed on the surface of boron nitride nanotubes (BNNTs), which provide steric hindrance in combination with Coulombic repulsion leading to high colloidal stability of BNNTs up to 22 wt %. The BNNT LCs prepared from the dispersions with various stabilizers were systematically compared using optical and rheological analysis to optimize the phase behavior and rheological properties for wet-spinning of the BNNT LCs. Systematic optical and mechanical characterizations of the BNNT microfibers with aligned BNNTs along the fiber axis revealed that properties of the microfibers, such as their tensile strength, packing density, and degree of BNNT alignment, were highly dependent on the quality of BNNT LCs directly related to the types of stabilizers.

Scalable, Highly Pure, and Diameter-Sorted Boron Nitride Nanotube by Aqueous Polymer Two-Phase Extraction

Boron nitride nanotube (BNNT) has attracted recent attention owing to its exceptional material properties; yet, practical implementation in real-life applications has been elusive, mainly due to the purity issues associated with its large-scale synthesis. Although different purification methods have been discussed so far, there lacks a scalable solution method in the community. In this work, a simple, high-throughput, and scalable purification of BNNT is reported via modification of an established sorting technique, aqueous polymer two-phase extraction. A complete partition mapping of the boron nitride species is established, which enables the segregation of the highly pure BNNT with a major impurity removal efficiency of > 98%. A successful scaling up of the process is illustrated and provides solid evidence of its diameter sorting behavior. Last, towards its macroscopic assemblies, a liquid crystal of the purified BNNT is demonstrated. The effort toward large-scale solution purification of BNNT is believed to contribute significantly to the macroscopic realization of its exceptional properties in the near future.

Properties and applications of boron nitride nanotubes

Nanomaterials have received increasing attention due to their controllable physical and chemical properties and their improved performance over their bulk structures during the last years. Carbon nanostructures are one of the most widely searched materials for use in different applications ranging from electronic to biomedical because of their exceptional physical and chemical properties. However, BN nanostructures surpassed the attention of the carbon-based nanostructure because of their enhanced thermal and chemical stabilities in addition to structural similarity with the carbon nanomaterials. Among these nanostructures, one dimensional-BN nanostructures are on the verge of development as new materials to fulfill some necessities for different application areas based on their excellent and unique properties including their tunable surface and bandgap, electronic, optical, mechanical, thermal, and chemical stability. Synthesis of high-quality boron nitride nanotubes (BNNTs) in large quantities with novel techniques provided greater access, and increased their potential use in nanocomposites, biomedical fields, and nanodevices as well as hydrogen uptake applications. In this review, properties and applications of one-dimensional BN (1D) nanotubes, nanofibers, and nanorods in hydrogen uptake, biomedical field, and nanodevices are discussed in depth. Additionally, research on native and modified forms of BNNTs and also their composites with different materials to further improve electronic, optical, structural, mechanical, chemical, and biological properties are also reviewed. BNNTs find many applications in different areas, however, they still need to be further studied for improving the synthesis methods and finding new possible future applications.

Boron Nitride Nanotube-Based Separator for High-Performance Lithium-Sulfur Batteries

To prevent global warming, ESS development is in progress along with the development of electric vehicles and renewable energy. However, the state-of-the-art technology, i.e., lithium-ion batteries, has reached its limitation, and thus the need for high-performance batteries with improved energy and power density is increasing. Lithium-sulfur batteries (LSBs) are attracting enormous attention because of their high theoretical energy density. However, there are technical barriers to its commercialization such as the formation of dendrites on the anode and the shuttle effect of the cathode. To resolve these issues, a boron nitride nanotube (BNNT)-based separator is developed. The BNNT is physically purified so that the purified BNNT (p−BNNT) has a homogeneous pore structure because of random stacking and partial charge on the surface due to the difference of electronegativity between B and N. Compared to the conventional polypropylene (PP) separator, the p−BNNT loaded PP separator prevents the dendrite formation on the Li metal anode, facilitates the ion transfer through the separator, and alleviates the shuttle effect at the cathode. With these effects, the p−BNNT loaded PP separators enable the LSB cells to achieve a specific capacity of 1429 mAh/g, and long-term stability over 200 cycles.

Highly Aligned Array of Heterostructured Polyflourene-Isolated Boron Nitride and Carbon Nanotubes

Boron nitride nanotubes (BNNTs) have attracted increasing attention for their exceptional thermal, electronic, and optical properties. However, the progress in BNNTs applications has largely been limited by the low purity of as-synthesized BNNTs and inefficient solution-processing protocols due mainly to the instability of BNNTs in most of the solvents. Therefore, fabrication of highly pure, stable, and fully individualized BNNTs in a rational manner is required. Here, we report a significant improvement in the preparation of well-dispersed BNNTs, utilizing conjugated polymers that interact with BNNTs, allowing selective sorting and individualization of the nanotubes. Evidence of strong interactions between the polymers and BNNTs was observed by optical absorption and photoluminescence spectroscopies, while effective individualization was observed by electron microscopy. The sorted BNNTs were successfully used in a solution-processing protocol called dose-controlled, floating evaporative self-assembly (DFES) previously established for single-walled carbon nanotubes (SWCNT) array fabrication. A device fabricated via DFES from the sorted BNNTs mixed with polymer-wrapped, semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibited an on-state conductance of 253 ± 6 μS μm^-1 and an on/off ratio of 10^6.6±0.4 for a gate voltage of -0.1 V. This breakthrough in BNNT dispersion and isolation is a significant advancement toward the exploitation of BNNTs in future applications.

Boron Nitride Nanotube (BNNT) Membranes for Energy and Environmental Applications

Owing to their extraordinary thermal, mechanical, optical, and electrical properties, boron nitride nanotubes (BNNTs) have been attracting considerable attention in various scientific fields, making it more promising as a nanomaterial compared to other nanotubes. Recent studies reported that BNNTs exhibit better properties than carbon nanotubes, which have been extensively investigated for most environment-energy applications. Irrespective of its chirality, BNNT is a constant wide-bandgap insulator, exhibiting thermal oxidation resistance, piezoelectric properties, high hydrogen adsorption, ultraviolet luminescence, cytocompatibility, and stability. These unique properties of BNNT render it an exceptional material for separation applications, e.g., membranes. Recent studies reported that water filtration, gas separation, sensing, and battery separator membranes can considerably benefit from these properties. That is, flux, rejection, anti-fouling, sensing, structural, thermal, electrical, and optical properties of membranes can be enhanced by the contribution of BNNTs. Thus far, a majority of studies have focused on molecular simulation. Hence, the requirement of an extensive review has emerged. In this perspective article, advanced properties of BNNTs are analyzed, followed by a discussion on the advantages of these properties for membrane science with an overview of the current literature. We hope to provide insights into BNNT materials and accelerate research for environment-energy applications.

Effect of Polymeric In Situ Stabilizers on Dispersion Homogeneity of Nanofillers and Thermal Conductivity Enhancement of Composites

Boron nitride (BN) nanofiller-based polymer composites have been considered promising candidates for efficient heat-dissipating packaging materials because of their superior thermal conductivity, mechanical strength, and chemical resistance. However, strong aggregation of the BN nanofillers in the composite matrix as well as the difficulty in the modification of the chemically inert surface prevents their effective use in polymer composites. Herein, we report an effective method by using in situ stabilizers to achieve homogeneous dispersion of boron nitride (BN) nanofillers in an epoxy-based polymeric matrix and demonstrate their use as efficient heat-dissipating materials. Poly(4-vinylpyridine) (P4VP) is designed and added into the epoxy resin to produce in situ stabilizers during preparation of hexagonal BNs (h-BNs) and BN nanotubes (BNNTs) dispersion. In-depth experimental and theoretical studies indicated that the homogeneous distribution of BN nanofillers in epoxy composites achieved by using the in situ stabilizer enhanced the thermal conductivity of the composite by ∼27% at the same concentration of the BN nanofillers. In addition, the thermal conductivity of the h-BN/epoxy composite (∼3.3 W/mK) was dramatically improved by ∼48% (4.9 W/mK) when the homogeneously dispersed BNNTs (∼1.8 vol %) were added. The concept of the proposed in situ stabilizer can be further utilized to prepare the epoxy composites with the homogeneous distribution of BN nanofillers, which is critical for reproducible and position-independent composite properties.

Facile and Novel Eco-Friendly Poly(Vinyl Alcohol) Nanofilters Using the Photocatalytic Property of Titanium Dioxide

This study aimed to develop a highly efficient nanofilter for capturing fine particles using electrostatic forces. Poly(vinyl alcohol) (PVA), a water-soluble synthetic polymer, was selected as the main component of the filter because it can be easily fabricated by electrospinning. Titanium dioxide (TiO₂) nanopowder with an anatase structure was applied to the nanofilters as it has the highest photocatalytic activity among the existing photocatalysts. PVA nanofilters fabricated by electrospinning could still be dissolved in water by hydrolysis. Therefore, heat treatment was performed to make the nanofilters stable, thereby forming C=O bonds by keto-enol tautomerization. Structural changes in the PVA nanofilter before and after heat treatment were investigated by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis. As the TiO₂ concentration increased, the fiber diameter of the PVA nanofilter decreased and a homogeneous fiber was obtained. The filtration efficiency and pressure drop also improved significantly, compared to those of the PVA-only nanofilter. Moreover, we observed eco-friendly decomposition of the PVA/TiO₂ nanofilter into water and carbon dioxide by a photocatalytic reaction under UV irradiation.

Boron nitride nanotubes: synthesis and applications

Boron nitride nanotube (BNNT) has similar tubular nanostructure as carbon nanotube (CNT) in which boron and nitrogen atoms arranged in a hexagonal network. Owing to the unique atomic structure, BNNT has numerous excellent intrinsic properties such as superior mechanical strength , high thermal conductivity, electrically insulating behavior, piezoelectric property, neutron shielding capability, and oxidation resistance. Since BNNT was first synthesized in 1995, developing efficient BNNT production route has been a significant issue due to low yield and poor quality in comparison with CNT, thus limiting its practical uses. However, many great successes in BNNT synthesis have been achieved in recent years, enabling access to this material and paving the way for the development of promising applications. In this article, we discussed current progress in the production of boron nitride nanotube, focusing on the most common and effective methods that have been well established so far. In addition, we presented various applications of BNNT including polymer composite reinforcement, thermal management packages, piezo actuators, and neutron shielding nanomaterial.