Exfoliation

Researchers at Queen’s University in Kingston, Canada have developed a simple yet effective exfoliation process for producing few-layer graphene nanoplatelets (FL-GNPs). Utilizing this one-step, chemical and solvent-free process the researchers were able to convert graphite flakes (+100 mesh, purity >97%) into FL-GNPs at a high yield (90%) and to subsequently form thermoplastic/FL-GNPs composites with improved electrical and mechanical properties.

TEM image of isolated FL-GNP

The exfoliated graphene nanoplatelets had a high specific surface area (325 m²/g), an aspect ratio above 500 (approximate lateral dimensions of 2µm and thickness of 3.5 nm), and a Raman D/G ratio of 0.3; indicating a structure with few defects. The flexural modulus of polyamide/FL-GNP composites containing 15 volume % FL-GNPs improved from 1850 MPa to 5,080 MPa while the electrical conductivity rose from 5x10-14 S/m to 21 S/m. Surface-coating the FL-GNPs through the addition of a coating agent during the last stages of the exfoliation process rendered the FL-GNPs more hydrophilic, thus, forming stable dispersions in water.

In December 2011 the EU launched a graphene project called NanoMaster with an aim to develop up-scale processing methods for production of graphene and expanded graphite reinforced thermoplastic masterbatches and compounds. Today the project partners announced that the project is entering its final phase, and is reporting exciting results.

Recently, the project team focused on optimizing and up-scaling the processes for graphene and expanded graphite production, and their subsequent compounding with a range of thermoplastics. They have now achieved a graphene production capacity increase from 50 grams to 2.5 Kg.

Researchers at from Korea's KAIST institute developed a new method to fabricate defect-free graphene. Using this graphene, they developed a promising high-performance anode for Li-Ion batteries.

The method starts with a Pyrex tube and fill it with graphite powder. The open-ended tube is placed in another, larger tube and potassium is added to the gap between the tubes. The tubes are sealed and heated - which causes the potassium to move inside the micropores in the graphite powder - creating a potassium-graphite compound. This is placed in a pyridine solution, which expands the layer and separates them to form graphene nanosheets - which are then exfoliated to create a single graphene sheet.

The recent years interest in graphene started when Andre Geim and Konstantin Novoselov first managed to isolate the material by using the 'scotch-tape' method. This simply and "primitive" method eventually led to their Nobel-Prize in 2010, and the graphene boom started.

But atomic processes behind the micromechanical cleavage in this method have never been really understood - until now. A research team from Russia, the USA and Finland researched the physics, kinetics and energetics behind the regarded this method, using molybdenum disulphide (MoS₂) as the model material.

Researchers from Penn State University and Japan's Shinshu University developed a simple and scalable process to make strong, stretchable graphene oxide fibers. Those fibers can easily be scrolled into yarns that have strengths approaching that of Kevlar.

The new GO fiber is the strongest carbon fiber ever. The researchers believe that pockets of air inside the fiber keep it from being brittle. But those fibers can also be altered to make other useful materials. For example, removing the oxygen results in a fiber with high electrical conductivity, while adding silver nanorods increases the conductivity (to the same level as copper, while being much lighter than copper).

Researchers from the University of Osnabrück and the University of Duisburg-Essen have studied the hydration layers trapped between graphene and a hydrophilic substrate - when graphene is produced using exfoliation on a hydrophilic substrate. While it is possible to reduce that hydration layer (by heating it), the researchers demonstrated that it is principally impossible to completely drive this hydration layer out of the confined space.

This layer will always influence the properties of the graphene on top of it. The researchers further demonstrated that it is possible to accelerate and to control the reorganization of the water (by 2D Ostwald ripening) that is present within the first hydration layer. Using this method, one can create "nanoblisters" filled with condensed fluid water. These nanoblisters could actually be a very suitable candidates for both storage and release of chemicals in aqueous environment.

Researchers from Italy's Institute of Organic Synthesis and Photoreactivity (ISOF) developed a new way to analyze the production process of 2D materials (such as BN or graphene). The new suggested process can be used for process control of 2D and composite materials produced via exfoliation.

The researchers explain that today there are many different methods and production processes used to produce graphene. But it is difficult today to compare the quality of these materials. The new suggested method may help to better understand these different materials and standardize their quality.

Researchers from England and Ireland's Trinity College developed a method to produce graphene flakes using very simple equipment. The idea is to simply mix powdered graphite with N-methyl-pyrrolidone and then mix it in a blender at high speed. This results in graphene flakes which are about a nanometer thick and 100 nanometer long. This method actually work with a regular kitchen blender!

The researchers say that the blender blades separate the graphite into graphene sheets without damaging the 2D structure. During their experiments, they made several grams of the graphene material, but they say it can be scaled up to produce in ton quantities.

Researchers from the University of Texas and the University of Science and Technology of China developed a new graphene-like material (called VOPO₄) that can be useful as a working electrode of flexible supercapacitors together with graphene.

VOPO₄, which is less than 6 atoms, was developed by using a 2-2-propanol-assisted ultrasonic method to exfoliate bulk VOPO₄·2H₂O into VOPO₄ nanosheets. The researchers created a hybrid graphene-VOPO₄ sheet that achieves both high planar conductivity and better electrochemical performance compared to pure graphene.

Graphene Laboratories announced that they have successfully managed to convert Lomiko Metal's Quatre Milles property graphite to graphene. They have actually produced graphene oxide (GO) and reduced graphene oxide (RGO) samples. The companies hope that they will be able to create graphene materials on a larger scale and at a reduced price.

In the first step of the conversion process the natural graphite flakes were oxidized and turned into GO by modified Hummer's method. This resulted in a stable aqueous dispersion with concentration of 40 g/L. The GO was then converted into RGO, with a surface area of 500 m² /g and an electrical conductivity 4 S/cm.