Ultrasonic Borophene Synthesis on Industrial Scale

Borophene, a two-dimensional nanostructured derivative of boron, can be efficiently synthesized via a facile and low-cost ultrasonic exfoliation. Ultrasonic liquid-phase exfoliation can be used to produce large quantities of high-quality borophene nanosheets. The ultrasonic exfoliation technique is widely used to produce 2D nanomaterials (e.g., graphene) and is well known for its advantages of high quality nanosheets, high yields, rapid and facile operation, as well as overall efficiency.

Ultrasonic Exfoliation Method for Borophene Preparation

Probe-type ultrasonicators are the preferred method for efficient borophene exfoliation.Ultrasonically driven liquid-phase exfoliation is widely used to prepare 2D nanosheets from various bulk precursors including graphite (graphene), boron (borophene) amongst others. Compared with the chemical exfoliation technique, the ultrasonically-assisted liquid-phase exfoliation is considered as the more promising strategy to prepare 0D and 2D nanostructures such as boron quantum dots (BQDs) and borophene. (cf. Wang et al., 2021)
The scheme left shows the ultrasonic low temperature liquid exfoliation process of 2D few-layer borophene sheets.(Study and picture: ©Lin et al., 2021.)

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Ultrasonic reactor for large scale borophene exfoliation. The stainless steel reactor is equipped with a powerful industrial 2000 watts ultrasonicator (20kHz).

Sonochemical reactor equipped with a 2000 watts industrial ultrasonic processor UIP2000hdT for large scale borophene exfoliation.

Case Studies of Ultrasonic Borophene Exfoliation

The exfoliation and delamination using power ultrasound in a liquid-phase process has been widely studied and successfully applied to borophene and other boron derivatives such as boron quantum dots, boron nitride or magnesium diboride.

α-Borophene

In the study performed by Göktuna and Taşaltın (2021), α borophene was prepared via a facile and low-cost ultrasonic exfoliation. The ultrasonically synthesized borophene nanosheets exhibit a α borophene crystalline structure.
Protocol: 100 mg boron microparticles were sonicated in 100 ml DMF at 200 W (e.g., using the UP200St with S26d14) for 4h in a nitrogen (N2) flow controlled cabin to prevent oxidization during the ultrasonic liquid-phase exfoliation process. The solution of exfoliated boron particles was centrifugated with 5000 rpm and 12,000 rpm for 15 min respectively, then borophene carefully collected and dried in a vacuum ambient for 4h at 50ºC. (cf. Göktuna and Taşaltın, 2021)

Process steps of borophene exfoliation using the ultrasonic delamination technique

Schematic illustration of borophene with few layers exfoliated by the probe ultrasonic assisted solvothermal treatment process.
Study and picture: ©Zhang et al., 2020

Few-Layer Borophene

Zhang et al. (2020) report an acetone solvothermal liquid phase exfoliation technique, which allows for the production of high quality borophene with large horizontal size. Using the swelling effect of the acetone, the boron powder precursor was first wetted in acetone. Then, the wetted boron precursor was further solvothermally treated in acetone at 200ºC, followed by sonication with a probe-type sonicator at 225 W for 4h. Borophene with a few layers of boron and a horizontal size up to 5.05 mm was finally obtained. The acetone solvothermal-assisted liquid phase exfoliation technique can be used to prepare boron nanosheets with large horizontal sizes and of high quality. (cf. Zhang et al., 2020)
When XRD pattern of the ultrasonically exfoliated borophene is compared with the bulk boron precursor, a similar XRD pattern can be observed. Most of the major diffraction peaks can be indexed to the b-rhombohedral boron, suggesting that the crystalline structure is nearly conserved before and after the exfoliation treatment.

Ultrasonically exfoliated borophene

SEM images with low resolution (a) and high resolution (b) of borophene with few layers obtained by ultrasonically-assisted solvothermal exfoliation in acetone
Study and picture: ©Zhang et al., 2020

The ultrasonic exfoliation process of borophene preserves its crystalline structure.

XRD patterns (a) and Raman spectra (b) of untreated bulk boron and borophene with few layers obtained by probe ultrasonic assisted solvothermal exfoliation.
Study and picture: ©Zhang et al., 2020

Sonochemical Synthesis of Boron Quantum Dots

Hao et al. (2020) successfully prepared large-scale and uniform crystalline semiconductor boron quantum dots (BQDs) from expanded boron powder in acetonitrile, a highly polar organic solvent, using a powerful probe-type ultrasonicator (e.g., UP400St, UIP500hdT or UIP1000hdT). The synthesized boron quantum dots with 2.46 ±0.4 nm in lateral size and 2.81 ±0.5 nm in thickness.
Protocol: In a typical preparation of boron quantum dots, 30 mg of the boron powder was first added into a three-necked flask and then 15 mL of acetonitrile was added into the bottle before the ultrasonication process. The exfoliation was performed at an output power of 400 W (e.g., using the UIP500hdT), 20kHz frequency and ultrasonic time of 60 min. To avoid overheating of the solution during ultrasonication, cooling using an ice bath or lab chiller was applied for a constant temperature. The resultant solution was centrifuged at 1500 rpm for 60 min. The supernatant contained boron quantum dots was extracted gently. All the experiments were conducted at room temperature. (cf. Hao et al., 2020)
In the study of Wang et al. (2021), the researcher prepare boron quantum dots using the ultrasonic liquid phase exfoliation technique, too. They obtained monodispersed boron quantum dot with a narrow size distribution, excellent dispersibility, high stability in IPA solution, and two-photo fluorescence.

Ultrasonically synthesized boron quantum dots.

TEM images and the corresponding diameter distribution of the BQDs prepared under differently ultrasonic conditions. (a) TEM image of BQDs-2 synthesized at 400 W for 2 h. (b) TEM image of BQDs-3 synthesized at 550 W for 1 h. (c) TEM image of BQDs-3 synthesized at 400 W for 4 h. (d) Diameter distribution of the quantum dots acquired from (a). (e) Diameter distribution of the quantum dots acquired from (b). (f) Diameter distribution of the quantum dots acquire from (c).
Study and picture: ©Hao et al., 2020

Ultrasonic Exfoliation of Magnesium Diboride Nanosheets

The process of exfoliation was carried out by suspending 450mg of magnesium diboride
(MgB2) powder (approx. 100 mesh size / 149 microns) in 150 ml of water and exposing it to ultrasonication for 30 minutes. The ultrasonic exfoliation can be carried out with a probe-type ultrasonicator such as the UP200Ht or UP400St with an amplitude of 30% and cycle mode of 10sec on/off pulses. The ultrasonic exfoliation results in a dark black suspension. The black color can being attributed to the color of pristine MgB2 powder.

Ultrasonicator UP200St (200W) exfoliating borophene in acetonitril

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Ultrasonic graphene exfoliation in water

A high-speed sequence (from a to f) of frames illustrating sono-mechanical exfoliation of a graphite flake in water using the UP200S, a 200W ultrasonicator with 3mm sonotrode. Arrows show the place of splitting (exfoliation) with cavitation bubbles penetrating the split.
© Tyurnina et al. 2020

Powerful Ultrasonicators for Borophene Exfoliation at Any Scale

Hielscher ultrasonicators can be remotely controlled via browser control. Sonication parameters can be monitored and adjusted precisely to the process requirements.Hielscher Ultrasonics designs, manufactures, and distributes robust and reliable ultrasonicators at any size. From compact lab ultrasonic devices to industrial ultrasonic probes and reactors, Hielscher has the ideal ultrasonic system for your process. With long-time experience in applications such as nanomaterial synthesis and dispersion, our well-trained staff will recommend you the most suitable setup for ypour requirements. Hielscher industrial ultrasonic processors are known as reliable work horses in industrial facilities. Capable to deliver very high amplitudes, Hielscher ultrasonicators are ideal for high-performance applications such as borophene or graphene exfoliation as well as nanomaterial dispersions. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available.
All equipment is designed and manufactured in our headquarter in Germany. Before delivery to the customer, every ultrasonic device is carefully tested under full load. We strive for customer satisfaction and our production is structured to fulfil highest quality assurance (e.g., ISO certification).

Why Hielscher Ultrasonics?

  • high efficiency
  • state-of-the-art technology
  • reliability & robustness
  • batch & inline
  • for any volume
  • intelligent software
  • smart features (e.g., data protocolling)
  • CIP (clean-in-place)

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

Facts Worth Knowing

Borophene

Borophene is a crystalline atomic monolayer of boron, i.e., it is a two-dimensional allotrope of boron (also called boron nanosheet). Its unique physical and chemical characteristics turn borophene into a valuable material for numerous industrial applications.
Borophene’s exceptional physical and chemical properties include unique mechanical, thermal, electronic, optical and superconducting facets.
This opens possibilities to use borophene for applications in alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, oxygen reduction and evolution, as well as CO2 electroreduction reaction. Especially high interest goes into borophene as an anode material for batteries and as hydrogen storage material. Due to high theoretical specific capacities, electronic conductivity and ion transport properties, borophene qualifies as great anode material for batteries. Due to the high adsorbtion capacity of hydrogen to borophene, it offers great potential for hydrogen storage – with a stroage capacity over 15% of its weight.

Borophene for Hydrogen Storage

Two-dimensional (2D) boron-based materials are receiving much attention as H2 storage media due to the low atomic mass of boron and the stability of decorating alkali metals on the surface, which enhance interactions with H2. Two-dimensional borophene nanosheets, which can be easily synthesized using ultrasonic liquid-phase exfoliation as describes above, have shown a good affinity for different metal-decorating atoms, in which clustering of metal atoms can occur. Using a variety of metal decorations, such as Li, Na, Ca, and Ti on different borophene polymorphs, impressive H2 gravimetric densities have been obtained ranging from 6 to 15 wt %, exceeding the US department of energy (DOE) requirement for onboard storage of6.5wt% H2. (cf. Habibi et al., 2021)


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