Ruthenium Oxide Nanosheets via Ultrasonic Exfoliation

Ruthenium oxide monolayer nanosheets can efficiently produced using probe-type ultrasonication. Major advantages of ultrasonic nanosheet exfoliation are process efficiency, high yields, short treatment and facile, safe operation. Due to its high efficiency and superior quality of produced nanosheets, ultrasonication is used for the industrial production of numerous nanosheets including graphene and borophene.

Ultrasonic Exfoliation of Ruthenium Oxide Nanosheets

Ruthenium oxide (RuO2, also known as ruthenate) nanosheets offer unique properties such as high conductivity, low resistivity, high stability, high work function and good susceptibility to dry etching. This makes ruthenium oxide an good material for electrodes in memory devices and transistors.

SEM images of exfoliated RuO2 nanosheets using a) 1 minute and b) 7 minutes of ultrasonication.
(study and pictures: ©Kim et al., 2021)

Case Study: Highly Efficient RuO2 Exfoliation using a Probe-Type Ultrasonicator

Kim et al. (2021) showed in their study the significant improvement in exfoliation of ruthenium oxide monolayer nanosheets. The researcher created high yields of thin RuO2 metal oxide sheets using ultrasonication. The conventional intercalation process through ion exchange reactions is slow and produces only limited amounts of two-dimensional (2D) nanosheets due to the size of molecules and chemical energy required for the reaction. In order to make the process faster and increase the amount of ruthenium oxide nano-sheets produced, they intensified the exfoliation process by applying ultrasound energy to the solution of RuO2 oxide. They found that after just 15 minutes of ultrasonication, the amount of sheets increased by over 50%, simultaneously the lateral size of the sheets decreased. Density functional theory calculations demonstrated that the activation energy of exfoliation is significantly reduced by splitting the RuO2 layers into a small lateral size. Thissize reduction happens because the sonication helped to break apart the layers of metal oxide more easily. This research underlines that using ultrasound is a good and easy way to make ruthenium oxide monolayer nanosheets. This shows that an ultrasonic-supported ion exchange process offers a facile and efficient approach for fabricating 2D metal oxide nanosheets. The befits of ultarsonic exfoliation explain why ultrasonic exfoliation and delamination is widely used as production technique for 2D nanomaterials, also known as xenes, including graphene and borophene.

Ultrasonic exfoliation promotes the highly efficient and accelerated production of ruthenium oxide 2D nanosheets at large scale
(study and pictures: ©Kim et al., 2021).

Protocol for Ultrasonically-Assisted Ruthenium Oxide Exfoliation

The following protocol is a step-by-step instruction for synthesizing RuO2 nanosheets using ultrasonically supported ion exchange reaction process as describes by Kim et al. (2021).
 

1. Prepare a solution of RuO2 and an intercalant by dissolving them in solvent (2-propanol) and stirring for up to 3 days.
2. Apply ultrasound energy using a probe-type ultrasonicator (e.g., probe-type ultrasonicator UP1000hdT (1000W, 20kHz) with sonotrode BS4d22) to the solution for 15 minutes in order to increase the yield of RuO2 nanosheets by over 50% and to split the RuO2 layers into a uniformly small lateral size.
3. Use density functional theory calculations to confirm the activation energy of exfoliation is significantly reduced.
4. Collect the resulting RuO2 nanosheets, which can be used for various applications.

 
The simplicity of this protocol for ultrasonic exfoliation of RuO2 nanosheets underlines the benefits of ultrasonic nanosheet production. Sonication is a highly efficient technique to produce high-quality monolayer RuO2 nanosheets with a thickness of approximately 1 nm. The protocol was also found to be scalable and reproducible, making it suitable for large-scale production of RuO2 nanosheets for various applications in electronics, catalysis, and energy storage.

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 3-mm sonotrode. Arrows show the place of splitting (exfoliation) with cavitation bubbles penetrating the split.
(study and pictures: © Tyurnina et al. 2020

High Performance Ultrasonicators for RuO2 Exfoliation

For the production of high-quality ruthenium oxide nano-sheets and other xenes, reliable high-performance ultrasonic equipment is required. Amplitude, pressure and temperature essential parameters, which are crucial for reproducibility and consistent product. Hielscher Ultrasonics processors are powerful and precisely controllable systems, which allow for the exact setting of process parameters and continuous high-power ultrasound output. Hielscher industrial ultrasonicators 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. The robustness of Hielscher ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
Our customers are satisfied by the outstanding robustness and reliability of Hielscher Ultrasonics systems. The installation in fields of heavy-duty application (e.g., large scale nanomaterial processing), demanding environments and 24/7 operation ensure efficient and economical processing. Ultrasonic process intensification reduces processing time and achieves better results, i.e. higher quality, higher yields, innovative products.

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: