Graphene, called the miracle material, has taken its place among the global rush industry. Today, there has been a great enhancement in graphene rush globally. Graphene is a material composed of pure carbon, similar to graphite but with characteristics that make it extraordinarily light and strong. A sheet of one square meter of graphene weighs 0.77 milligrams. Its strength is 200 times greater than that of steel and its density is similar to that of carbon fiber.
Its applications are virtually unlimited and promise to revolutionize many fields: from electronics and computing to construction or even health. You can find nearly all applications of graphene in this list – some already commercialized, some need years to materialize.
Graphene synthesis
Graphene Synthesis by Liquid-phase exfoliation (LPE)
Layered materials such as graphite consist of two-dimensional platelets weakly stacked to form three-dimensional structures. In graphite, these layers form strong chemical bonds in-plane but display weak out-of-plane bonding. This facilitates the exfoliation process to form so-called nanosheets (about micrometers wide but less than a nanometer thick).
Such exfoliation leads to an increase in the material’s surface area, over 1000 (m2/g), and enhanced surface activity. The increase in the surface area of material can enhance their chemical and physical reactivity. This is very vital in many applications where the surface activity is important such as catalytic materials, ion exchange, fillers materials in composites, intumescent (or thermally expanded) material.
Liquid-phase exfoliation of natural graphite
The liquid phase exfoliation method and exfoliation of GO of graphite are technically similar, but the first does not involve the oxidation step. Graphene flakes can be produced by exfoliation of graphite using chemical wet dispersion followed by ultrasonication in water and organic solvents.
This method’s principal attraction is a simple and scalable process where pristine graphite or expandable graphite is subjected to a solvent treatment to weaken the van der Waals attractive forces between graphene interlayers. External driving forces such as ultrasonication, shearing, or electric field can be applied to help exfoliation into graphene. Graphene’s exfoliation occurs because of the strong interactions between the solvent molecules and the graphitic basal planes, overcoming the energetic penalty for exfoliation and subsequent dispersion. For successful exfoliation, overcoming the van der Waals attractions between the adjacent layers of graphite is necessary.
Liquid-phase exfoliation by ionic liquids
Utilizing ionic liquids (ILs) in graphite exfoliation is considered green chemistry due to it is nontoxic, stable chemically, no need for vapor pressure, recyclable by distillation or ion change. Exfoliation by ionic liquids is also considered a one-step procedure (direct exfoliation). Ionic liquids give graphene unique properties, unlike chemical modification that destroys the graphene electronic structure. Ion liquids are completely organic or partially inorganic salts with a melting point below (100 °C). The most significant factor in this technique is the surface tension of ILs, which has to be very close to that of graphene.
Fukushima et al. were the first to use ILs to untangle carbon nanotubes using imidazolium-based ILs as solvents assuming interactions between the positive charge of the imidazolium rings and p electrons of the nanotube. Liu et al. prepared graphene nanosheets using imidazolium ILs assisted electrochemical synthesis. Zhou et al. incorporated polymerized ionic liquid with 1-butyl-3-methylimidazolium hexafluorophosphate to disperse graphene. Nonoxidized few-layer graphene highly concentrated and stable colloidal (0.95 mg/mL) was prepared by ultrasonication of natural graphite flakes in this ionic liquid. Nuvoli et al. prepared high concentration few-layer graphene sheets using LPE by grounding and then sonication of graphite in 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIH) as an ionic liquid. The graphene concentration (up to 5.33 mg/ mL) is obtained. Ionic liquids can be useful when green chemistry and/ or a nonvolatile, stable solvent medium is required.
In 2014, Shang et al. prepared large quantities of solvent-free graphene nanosheets and nanodots with low oxygen content have by mechanical grinding exfoliation of natural graphite in a small quantity of ionic liquids (1-Butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6). Electrochemical exfoliation of graphite rods was used to synthesis carbon dots (CDs) by dissolved cheap salts (NaCl and KCl) in distilled water as an electrolyte. Generally, exfoliation using ionic liquids has been associated with other techniques as electrochemical exfoliation, mechanical grinding, or sonication to be more producible.
Medicinal Application of Graphene
- Graphene in Drug Delivery
Functionalized graphene can be used to carry chemotherapy drugs to tumors for cancer patients. Graphene based carriers targeted cancer cells better and reduced and decreased toxicity of the effected healthy cells. Drug delivery is not limited to cancer treatment, anti-inflammatory drugs have also been carried by graphene & chitosan combinations and yielded promising results.
- Graphene in Cancer Treatment
Graphene can also detect cancer cells in the early stages of the disease. Moreover, it can stop them from growing any further in many types of cancer by intervening the correct formation of the tumor or causing autophagy which leads to the death of cancer cells.
- Graphene in Gene Delivery
Gene delivery is a method used to cure some genetic diseases by bringing foreign DNA into cells. Graphene Oxide modified by Polyethyleneimine can be used for these purposes is expected to show low cytotoxicity, as it did in the drug delivery case.
- Graphene in Photothermal Therapy
Photothermal therapy (PTT) is a approach used to eliminate abnormal cells in the targeted area of the body by irradiating a special agent which creates heat capable of destructing those cells. Graphene oxide increases effectiveness of PTT by a number of ways. First, it can be used to carry chemotherapeutic drugs to the tumor cells while they are being exposed to PTT simultaneously. Combining chemo and PTT like this is more effective than using one of these approaches alone. A nanocomposite of reduced graphene oxide (QD-CRGO) can be used during PTT for bioimaging of the cancer cells. Moreover, in their research, a group of scientists from Texas Tech and Texas A&M University have shown that using graphene oxide functionalized with biocompatible porphyrin as a platform for PTT for brain cancer have killed more cancer cells than PTT alone, while giving no harm to the healthy cells.
- Graphene in Diabetes Monitoring
Scientists from the University of Bath have developed a blood glucose monitoring test which does not pierce the skin, unlike currently used finger prick tests. This patch, including a graphene sensor, is able to work on a small area containing at least one hair follicle. It detects the glucose by pulling it from the fluid present between the cells. This does not only end the painful methods of blood sugar monitoring, but is also expected to increase the accuracy of the results.
- Graphene in Dialysis
Graphene membranes are not only useful for the energy, nuclear and food industries. A group of researchers from MIT showed that graphene can be used to filter the blood from wastes, drugs and chemicals as well. Graphene’s superiority in this case is that it is 20 times thinner than traditional membranes which leads to significant decrease in the time spent in the dialysis for the patients.
- Graphene in Bone and Teeth Implantation
Hydroxyapatite, a form of calcium apatite, is a material used as a synthetic bone substitute for regenerated bone and dental tissues. Graphene, combined with Hydroxyapatite and Chitosan, have shown increase in the strength, corrosion resistance, flexibility and mechanical & osteogenic properties of the substitute when compared to HAp alone.
- Graphene in Tissue Engineering and Cell Therapy
Bones are not the only tissue graphene can cure. Certain forms of graphene were shown to be compatible with human osteoblasts and human mesenchymal cells, showing similar properties with the cells’ physiological microenvironment. Cells grown with this method demonstrated better growth, proliferation, and differentiation while being ineffective on the cells’ viability. Stem cells are especially important in tissue reengineering to improve the lives of people with neuronal disorders or neurodegenerative diseases.
- Graphene UV Sensors
UV sensors are used for detecting dangerous levels of ultra-violet radiation which can lead to skin problems or even cancer. However, it is not the only use of UV sensors, they are used in the military, optical communication, and environmental monitoring as well. On its own, graphene may not present a high photoresponsivity but when it is combined with other materials, they create flexible, transparent, environmentally-friendly and low-cost UV sensors which will lead to technologies such as wearable electronics in the close future.
- Graphene for the Brain
Mysteries about the brain haven’t been revealed completely yet. A graphene-based technology may allow scientists to uncover many of the unknowns by recording brains electrical activity. This new device is able to hear the frequencies below older technologies’ limits, and it doesn’t interfere with the functioning of the brain. Besides research on how the brain works, the technology can help the scientists to understand the reasons behind epilepsy seizures and develop treatments for the patients. Moreover, discovering more about the brain could lead to developing new Brain-Computer interfaces which are used in many areas including control of prosthetic limbs.
- Graphene in HIV Diagnosis
Despite all the improvements, there are many drawbacks on current HIV diagnosis methods. They can either detect the antibodies in the body nearly a month later the patient was infected, or they can detect the virus itself however these methods take some time to process themselves and more expensive when compared to the antibody method. A biosensor made of silicon or graphene, containing Gold Nanoparticles was developed by Spanish National Research Council, which targets p24, an antigen found on HIV. The new method can detect the virus only a week after being infected and at levels 100,000 times lower than what the current tests can notice. Moreover, results of the test are ready within 5 hours of being tested.
- Graphene Biosensors
One of the advantages of graphene is its ability to detect minimal amounts of substances. Even a single molecule in a large volume can be detected with it. Biosensors made of graphene, graphene oxide or reduced graphene oxide show ultrasensitive properties when detecting DNA, ATP, dopamine, oligonucleotides, thrombin, and different atoms. There are several medical companies that already sell medical sensors made with graphene.
- Graphene Bactericide
Graphene is a magnificent bactericidal material as it avoids the generation of microorganisms, such as bacteria, viruses, and fungi, by damaging their cell membranes between its outer layers. When compared to different derivatives of Graphene, Graphene Oxide and reduced Graphene Oxide shows the best antibacterial effects. GO can also be used as a compound with silver nanoparticles to increase antibacterial properties even further.
- Graphene in Birth Control
Graphene has all the properties that is desired in a condom: it is flexible, extra strong and extremely thin. Researchers from Manchester University have worked on developing a “supercondom” made of graphene and latex combined. The research has received many funding, including one from Bill and Melinda Gates Foundation.
- Graphene in Deaf-Mute Communication
A group of Chinese scientists have developed a wearable, bio-integrated device that can translate sign language into text and spoken language. The device uses graphene’s incredible conductivity and flexibility properties.
- Graphene in Body Scans
A group of Chinese scientists have developed a wearable, bio-integrated device that can translate sign language into text and spoken language. The device uses graphene’s incredible conductivity and flexibility properties.