Boron Nitride Nanotubes – Exfoliated and Dispersed using Sonication
Ultrasonication is successfully applied to the processing and dispersion of boron nitride nanotubes (BNNTs). High-intensity sonication provides homogeneous detangling and distribution in various solutions and is thereby a crucial processing technique to incorporate BNNTs into solutions and matrices.
Ultrasonic Processing of Boron Nitride Nanotubes
In order to incorporate boron nitride nanotubes (BNNTs) or boron nitride nanostructures (BNNs) such as nanosheets and nanoribbons into liquid solutions or polymeric matrices, an efficient and reliable dispersion technique is required. Ultrasonic dispersion provides the required energy to exfoliate, detangle, disperse, and functionalize boron nitride nanotubes and boron nitride nanostructures with high efficiency. The precisely controllable processing parameters of high-intensity ultrasound (i.e. energy, amplitude, time, temperature, and pressure) allow to individually adjust the processing conditions to the targeted process goal. This means ultrasonic intensity can be adjusted in regards to the specific formulation (quality of BNNTs, solvent, solid-liquid concentration etc.), thereby obtaining optimum results.
The applications of ultrasonic BNNT and BNN processing cover the full range from the homogeneous dispersion of two-dimensional boron nitride nanostructures (2D-BNNs), to their functionalization and chemical exfoliation of mono-layer hexagonal boron nitride. Below, we present to the details on ultrasonic dispersion, exfoliation, and functionalization of BNNTs and BNNs.
Ultrasonic Dispersion of Boron Nitride Nanotubes
When boron nitride nanotubes (BNNTs) are used to reinforce polymers or to synthesize new materials, a uniform and reliable dispersion into the matrix is required. Ultrasonic dispersers are widely used to disperse nano materials such as CNTs, metallic nanoparticles, core-shell particles and other types of nano particles into a second phase.
Ultrasonic dispersion has been successfully applied to detangle and distribute BNNTs uniformly in aqueous and non-aqueous solutions including ethanol, PVP ethanol, TX100 ethanol as well as various polymers (e.g. polyurethane).
A common used surfactant to stabilize an ultrasonically prepared BNNT dispersion is a 1%wt sodium dodecyl sulfate (SDS) solution. For instance, 5 mg BNNTs are ultrasonically dispersed in a vial with 5 mL of 1%wt. SDS solution using an ultrasonic probe-type disperser such as the UP200St (26kHz, 200W).
Aqueous Dispersion of BNNTs using Ultrasound
Due to their strong van der Waals interactions and hydrophobic surface, boron nitride nanotubes are poorly dispersible in water-based solutions. To solve these problems, Jeon et al. (2019) used Pluronic P85 and F127, which have both hydrophilic groups and hydrophobic groups to functionalize BNNT under sonication.
Surfactant-Free Exfoliation of Boron Nitride Nanosheets using Sonication
Lin et al. (2011) present a clean method of exfoliation and dispersion of hexagonal boron nitride (h-BN). Hexagonal boron nitride is traditionally considered to be insoluble in water. However, they were able to demonstrate that water is effective to exfoliate the layered h-BN structures using ultrasonication, forming “clean” aqueous dispersions of h-BN nanosheets without the use of surfactants or organic functionalization. This ultrasonic exfoliation process produced few-layered h-BN nanosheets as well as monolayered nanosheet and nanoribbon species. Most nanosheets were of reduced lateral sizes, which was attributed to the cutting of parent h-BN sheets induced by the sonication-assisted hydrolysis (corroborated by the ammonia test and spectroscopy results). The ultrasonically induced hydrolysis also promoted the exfoliation of h-BN nanosheets in assistance to the polarity effect of the solvent. The h-BN nanosheets in these “clean” aqueous dispersions exhibited good processability via solution methods retaining their physical characteristics. The dispersed h-BN nanosheets in water also exhibited strong affinity toward proteins such as ferritin, suggesting that the nanosheet surfaces were available for further bio-conjugations.
Ultrasonic Size Reduction and Cutting of Boron Nitride Nanotubes
The length of boron nitride nanotubes plays a crucial role when it comes to the subsequent processing of BNNTs into polymers and other functionalized materials. Therefore it is an important fact that sonication of the BNNTs in solvent could not only separate BNNTs individually, but also shorten the bamboo structured BNNTs under controlled conditions. The shortened BNNTs have a much lower chance of bundling during composite preparation.Lee at al. (2012) demonstrated that the lengths of functionalized BNNTs can be efficiently shortened from >10µm to ∼500nm by ultrasonication. Their experiments suggest that effective ultrasonic dispersion of BNNT in solution is necessary for such cutting of BNNT size reduction and cutting.
High-Performance Ultrasonicators for BNNT Processing
The smart features of Hielscher ultrasonicators are designed to guarantee reliable operation, reproducible outcomes and user-friendliness. Operational settings can be easily accessed and dialled via intuitive menu, which can be accessed via digital colour touch-display and browser remote control. Therefore, all processing conditions such as net energy, total energy, amplitude, time, pressure and temperature are automatically recorded on a built-in SD-card. This allows you to revise and compare previous sonication runs and to optimize the exfoliation and dispersion process of boron nitride nanotubes and nanomaterials to highest efficiency.
Hielscher Ultrasonics systems are used worldwide for the manufacturing of high-quality BNNTs. Hielscher industrial ultrasonicators can easily run high amplitudes in continuous operation (24/7/365). Amplitudes of up to 200µm can be easily continuously generated with standard sonotrodes (ultrasonic probes / horns). For even higher amplitudes, customized ultrasonic sonotrodes are available. Due to their robustness and low maintenance, our ultrasonic exfoliation and dispersion systems are commonly installed for heavy duty applications and in demanding environments.
Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.
Hielscher ultrasonic processors for the dispersion and exfoliation of boron nitride nanotubes as well as CNTs and graphene are already installed worldwide on commercial scale. Contact us now to discuss your BNNT manufacturing process! Our well-experienced staff will be glad to share more information on the exfoliation process, ultrasonic systems and pricing!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices|
|1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Sang-Woo Jeon, Shin-Hyun Kang, Jung Chul Choi, Tae-Hwan Kim (2019): Dispersion of Boron Nitride Nanotubes by Pluronic Triblock Copolymer in Aqueous Solution. Polymers 11, 2019.
- Chee Huei Lee, Dongyan Zhang, Yoke Khin Yap (2012): Functionalization, Dispersion, and Cutting of Boron Nitride Nanotubes in Water. Jouranl of Physical Chemistry C 116, 2012. 1798–1804.
- Lin, Yi; Williams, Tiffany; Xu, Tian-Bing; Cao, Wei; Elsayed-Ali, Hani; Connell, John (2011): Aqueous Dispersions of Few-Layered and Monolayered Hexagonal Boron Nitride Nanosheets from Sonication-Assisted Hydrolysis: Critical Role of Water. The Journal of Physical Chemistry C 2011.
- Yuanlie Yu, Hua Chen, Yun Liu, Tim White, Ying Chen (2012): Preparation and potential application of boron nitride nanocups. Materials Letters, Vol. 80, 2012. 148-151.
- Luhua Li, Ying Chen, Zbigniew H. Stachurski (2013): Boron nitride nanotube reinforced polyurethane composites. Progress in Natural Science: Materials International Vol. 23, Issue 2, 2013. 70-173.
- Yanhu Zhan, Emanuele Lago, Chiara Santillo, Antonio Esaú Del Río Castillo, Shuai Hao, Giovanna G. Buonocore, Zhenming Chen, Hesheng Xia, Marino Lavorgna, Francesco Bonaccorso (2020): An anisotropic layer-by-layer carbon nanotube/boron nitride/rubber composite and its application in electromagnetic shielding. Nanoscale 12, 2020. 7782-7791.
- Kalay, Şaban; Çobandede, Zehra; Sen, Ozlem; Emanet, Melis; Kazanc, Emine; Culha, Mustafa (2015): Synthesis of boron nitride nanotubes and their applications. Beilstein Journal of Nanotechnology Vol 6, 2015. 84-102.
Facts Worth Knowing
Boron Nitride Nanotubes and Nanomaterials
Boron nitride nanotubes offer a unique atomic structure assembled of boron and nitrogen atoms arranged in a hexagonal network. This structure gives BNNT numerous excellent intrinsic properties such as superior mechanical strength, high thermal conductivity, electrically insulating behavior, piezoelectric property, neutron shielding capability, and oxidation resistance. The 5 eV band gap can also be tuned using transverse electric fields, which make BNNTs interesting for electronic devices. Additionally, BNNTs have high oxidation resistance up to 800°C, show excellent piezoelectricity, and could be a good room-temperature hydrogen storage material.
BNNTs vs Graphene: BNNTs are the structural analogs of graphene. The main difference between boron nitride-based nanomaterials and their carbon-based counterparts is the nature of the bonds between the atoms. The bond C-C in carbon nanomaterials has a pure covalent character, while B-N bonds present a partially ionic character due to the e−pairs in sp2 hybridized B-N. (cf. Emanet et al. 2019)
BNNTs vs. Carbon Nanotubes: Boron nitride nanotubes (BNNTs) exhibit a similar tubular nanostructure to carbon nanotubes (CNTs) in which boron and nitrogen atoms arranged in a hexagonal network.