Ultrasonik grafen ishlab chiqarish

Ultrasonic synthesis of graphene via graphite exfoliation is the most reliable and advantageous method to produce high-quality graphene sheets on industrial scale. Hielscher high-performance ultrasonic processors are precisely controllable and can generate very high amplitudes in 24/7 operation. This allows to prepare high volumes of pristine graphene in a facile and size-controllable way.

Ultrasonic Preparation of Graphene

Since the extraordinary characteristics of graphite are known, several methods for its preparation have been developed. Beside to chemical production of graphenes from graphene oxide in multi-step processes, for which very strong oxidizing and reducing agents are needed. Additionally, the graphene prepared under these harsh chemical conditions often contain a large amount of defects even after reduction compared to graphenes obtained from other methods. However, ultrasound is a proven alternative to produce high quality graphene, also in large quantities. Researchers have developed slightly different ways using ultrasound, but in general the graphene production is a simple one-step process.

Suvdagi grafit parchasining sono-mexanik eksfoliatsiyasini aks ettiruvchi yuqori tezlikdagi (a dan f gacha) kadrlar ketma-ketligi UP200S yordamida, 3 mm sonotrodli 200 Vt ultrasonikator. O'qlar bo'linish joyini (eksfoliatsiyani) ko'rsatadi, ular bo'linishga kirib boradigan kavitatsiya pufakchalari.
(o'rganish va rasmlar: © Tyurnina va boshqalar. 2020

Advantages of Ultrasonic Graphene Exfoliation

Hielscher probe-type ultrasonicators and reactors turn graphene exfoliation into a highly efficient process used to produce graphene from graphite through the application of powerful ultrasound waves. This technique offers several advantages over other methods of graphene production. Major benefits of ultrasonic graphene exfoliation are the following:

• High efficiency: Graphene exfoliation via probe-type ultrasonication is a very efficient method of graphene production. It can produce large amounts of high-quality graphene in a short period of time.
• Low cost: The equipment required for ultrasonic exfoliation in industrial graphene production is relatively inexpensive compared to other methods of graphene production, such as chemical vapor deposition (CVD) and mechanical exfoliation.
• Masshtablilik: Exfoliating graphene via ultrasonicator can be easily scaled up for large-scale production of graphene. Ultrasonic exfoliation and dispersion of graphene can be run in batch as well as in continuous inline process. This makes it a viable option for industrial-scale applications.
• Control over graphene properties: Graphene exfoliation and delamination using probe-type ultrasonication allows for precise control over the properties of the graphene produced. This includes its size, thickness, and number of layers.
• Minimal environmental impact: Graphene exfoliation using an ultrasonic proven is a green method of graphene production, as it can be used with non-toxic, environmentally benign solvents such as water or ethanol. This means that ultrasonic graphene delamination allows to avoid or reduce the use of harsh chemicals or high temperatures. This makes it an environmentally friendly alternative to other graphene production methods.

Overall, graphene exfoliation using Hielscher probe-type ultrasonicators and reactors offers a cost-effective, scalable, and environmentally friendly method of graphene production with precise control over the properties of the resulting material.

Example for the Simple Production of Graphene using Sonication

Graphite is added in a mixture of dilute organic acid, alcohol, and water, and then the mixture is exposed to ultrasonic irradiation. The acid works as a “molecular wedge” which separates sheets of graphene from the parent graphite. By this simple process, a large quantity of undamaged, high-quality graphene dispersed in water is created. (An et al. 2010)
 

Graphene Direct Exfoliation

Ultrasound allows for the preparation of graphenes in organic solvents, surfactants/water solutions, or ionic liquids. This means that the use of strong oxidizing or reducing agents can be avoided. Stankovich et al. (2007) produced graphene by exfoliation under ultrasonication.
The AFM images of graphene oxide exfoliated by the ultrasonic treatment at concentrations of 1 mg/mL in water always revealed the presence of sheets with uniform thickness (~1 nm; example is shown in the picture below). These well-exfoliated samples of graphene oxide contained no sheets either thicker or thinner than 1nm, leading to a conclusion that complete exfoliation of graphene oxide down to individual graphene oxide sheets was indeed achieved under these conditions. (Stankovich et al. 2007)

AFM image of exfoliated GO sheets with three height profiles acquired in different locations
(picture and study: ©Stankovich et al., 2007)

Preparation of Graphene Sheets

Stengl et al. have shown the successful preparation of pure graphene sheets in large quantities during the production of nonstoichiometric TiO2 graphene nanocomposit by thermal hydrolysis of suspension with graphene nanosheets and titania peroxo complex. The pure graphene nanosheets were produced from natural graphite using a high intensity cavitation field generated by Hielscher ultrasonic processor UIP1000hd in a pressurized ultrasonic reactor at 5 bar. The graphene sheets obtained, with high specific surface area and unique electronic properties, can be used as a good support for TiO2 to enhance the photocatalytic activity. The research group claims that the quality of the ultrasonically prepared graphene is much higher than graphene obtained by Hummer’s method, where graphite is exfoliated and oxidized. As the physical conditions in the ultrasonic reactor can be precisely controlled and by the assumption that the concentration of graphene as a dopant will vary in the range of 1 – 0.001%, the production of graphene in a continuous system on commercial scale is easily installed. Industrial ultrasonicators and inline reactors for efficient exfoliation of high-quality graphene are readily available.

Preparation by Ultrasonic Treatment of Graphene Oxide

Oh et al. (2010) have shown a preparation route using ultrasonic irradiation to produce graphene oxide (GO) layers. Therefore, they suspended twenty-five milligrams of graphene oxide powder in 200 ml of de-ionized water. By stirring they obtained an inhomogeneous brown suspension. The resulting suspensions were sonicated (30 min, 1.3 × 105J), and after drying (at 373 K) the ultrasonically treated graphene oxide was produced. A FTIR spectroscopy showed that the ultrasonic treatment did not change the functional groups of graphene oxide.

SEM image of graphene pristine nanosheets obtained by ultrasonication (Oh et al., 2010)

Functionalization of Graphene Sheets

Xu and Suslick (2011) describe a convenient one-step method for the preparation of polystyrene functionalized graphite. In their study, they used graphite flakes and styrene as basic raw material. By sonicating the graphite flakes in styrene (a reactive monomer), the ultrasound irradiation resulted in the mechanochemical exfoliation of graphite flakes into single-layer and few-layer graphene sheets. Simultaneously, the functionalization of the graphene sheets with the polystyrene chains has been achieved.
The same process of functionalization can be carried out with other vinyl monomers for composites based on graphene.

Graphene Dispersions

The dispersion grade of graphene and graphene oxide is extremely important to use the full potential of graphene with its specific characteristics. If graphene is not dispersed under controlled conditions, the polydispersity of graphene dispersion can lead to unpredictable or nonideal behavior once it is incorporated into devices since the properties of graphene vary as a function of its structural parameters. Sonication is a proven treatment to weaken the interlayer forces and allows for an accurate control of the important processing parameters.
“For graphene oxide (GO), which is typically exfoliated as single-layer sheets, one of the main polydispersity challenges arises from variations in the lateral area of the flakes. It has been shown that the mean lateral size of GO can be shifted from 400 nm to 20 μm by changing the graphite starting material and the sonication conditions.” (Green et al. 2010)
The ultrasonic dispersing of graphene resulting in fine and even colloidal slurries has been demonstrated in various other studies. (Liu et al. 2011/ Baby et al. 2011/ Choi et al. 2010)
Zhang et al. (2010) have shown that by the usage of ultrasonication a stable graphene dispersion with a high concentration of 1 mg·mL−1 and relatively pure graphene sheets are achieved, and the as-prepared graphene sheets exhibit a high electric conductivity of 712 S·m⁻¹. The results of Fourier transformed infrared spectra and Raman spectra examination indicated that the ultrasonic preparation method has less damage to the chemical and crystal structures of graphene.

High Performance Ultrasonicators for Graphene Exfoliation

For the production of high-quality graphene nano-sheets, reliable high-performance ultrasonic equipment is required. Amplitude, pressure and temperature an essential parameters, which are crucial for reproducibility and consistent product quality. Hielscher Ultrasonics’ ultrasonic processors are powerful and precisely controllable systems, which allow for the exact setting of process parameters and continuous high-power ultrasound output. 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. The robustness of Hielscher’s 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, 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.
Quyidagi jadvalda ultrasonikatorlarimizning taxminiy qayta ishlash quvvati ko'rsatilgan:

Preparation of Carbon Nanoscrolls

Carbon Nanoscrolls are similar to multi-walled carbon nanotubes. The difference to MWCNTs is the open tips and the full accessibility of the inner surfaces to other molecules. They can be synthesized wet-chemically by intercalating graphite with potassium, exfoliating in water and sonicating the colloidal suspension. (cf. Viculis et al. 2003) The ultrasonication assists the scrolling up of the graphene monolayers into carbon nanoscrolls (see graphic below). A high conversion efficiency of 80% has been achieved, that makes the production of nanoscrolls interesting for commercial applications.

Ultrasonic synthesis of Carbon Nanoscrolls (Viculis et al. 2003)

Preparation of Nanoribbons

The research group of Hongjie Dai and his colleagues from Stanford University found a technique to prepare nanoribbons. Graphene ribbons are thin strips of graphene that may have even more useful characteristics than graphene sheets. At widths of about 10 nm or smaller, the graphene ribbons behavior is similar to a semiconductor as electrons are forced to move lengthwise. Thereby, it could be interesting to use nanoribbons with semiconductor-like functions in electronics (e.g. for smaller, faster computer chips).
Dai et al. preparation of graphene nanoribbons bases on two steps: firstly, they loosened the layers of graphene from graphite by a heat treatment of 1000ºC for one minute in 3% hydrogen in argon gas. Then, the graphene was broken up into strips using ultrasonication. The nanoribbons obtained by this technique are characterized by much ‘smoother’ edges than those made by conventional lithographic means. (Jiao et al. 2009)