Graphene is a fascinating allotrope of carbon that manifests as an extraordinary two-dimensional planar sheet with remarkable properties.
One way to think of graphene is as a single atomic graphite layer. Graphene is technically a non-metal but is often referred to as a quasi-metal due to its properties being like that of a semi-conducting metal.
Introduction:
Graphene possesses numerous distinctive properties that set it apart from other non-metallic materials. It is composed of an isolated single layer of carbon hexagons with sp2 hybridized C-C bonding and π-electron clouds. From an engineering perspective, the presence of thin carbon flakes, including mono-layer graphene, holds significant importance due to their intriguing structural and physical characteristics. Moreover, they demonstrate promising potential for applications in various technological fields.
Characteristics of Graphene
Graphene has garnered immense interest among scientists since its discovery due to its exceptional properties. In 2004, researchers Andre Geim and Kostya Novoselov at the University of Manchester successfully isolated graphene, earning them the Nobel Prize in Physics in 2010 for their groundbreaking work. Graphene is a one-atom-thick layer of sp2-hybridized carbon atoms arranged tightly in a 2D honeycomb lattice, as depicted in Figure 1.
Carbon, one of the most abundant elements in the human body and the universe by mass, forms the chemical basis of all living materials. Therefore, graphene holds promise as an ecologically friendly material for numerous applications. Its band structure is unique, with the valence and conduction bands touching each other at six Dirac points, exhibiting zero band gap semiconductor behavior. Graphene possesses exceptional properties including high fracture strength, excellent electrical and thermal conductivity, fast mobility of charge carriers (2 × 105 cm2/Vs, 200 times higher than silicon), a large specific surface area (2600 m2.g-1), and biocompatibility, surpassing those of other materials.
Carbon’s ability to form a chemically stable, two-dimensional, one-atom-thick sheet gives rise to graphene, which is approximately 300 times stronger than steel. It is also the lightest material known, with a weight of about 0.77 mg per square meter. Graphene exhibits electron mobility exceeding 15,000 cm2 V-1 s-1 and tensile stiffness on the order of 150,000,000 psi. Additionally, it is an excellent conductor of heat at room temperature, with a reported thermal conductivity of approximately 5300 Wm-1 K-1. Graphene also displays low coefficient of thermal expansion and high optical transmittance. These exceptional chemical and physical properties have attracted attention across a wide range of application areas.
Given its remarkable electronic properties, particularly its high charge transport mobility, graphene plays a pivotal role in the production of sensitive nanodevices, nanoelectronics, and nanosensors. Furthermore, graphene serves as a promising building block for high-performance electronics, sensors, and energy storage devices. Its integration into various electronic and optoelectronic applications, such as gas sensors, transistors, solar cells, and liquid crystal elements, benefits from its low electrical noise and ballistic transport properties. Figure 2 illustrates some of the existing and potential application areas of graphene.
Applications of Graphene Sheet
Graphene Batteries
Graphene-enhanced Li-ion batteries exhibit remarkable characteristics, including an extended lifespan, increased capacity, faster charging time, as well as flexibility and lightweight properties. These attributes make them suitable for applications in wearable electronics.
Thermoelectric Devices
Seebeck effect is defined as a thermoelectric effect occurring when heat is applied to one of the two dissimilar electric conductors (or semiconductors) to move the electrons from the hot part to the cooler part and produce electricity. However, the energy generated by this method is really small, usually quantified by microvolts. Still, it is believed that it can be used to benefit from the heat generated by the engines, which is practically wasted. Graphene can be used to increase the Seebeck effect created by Strontium Titanate, almost up to 5 times.
Graphene Sheet in Nuclear Plants
Heavy water, utilized in nuclear power plants to facilitate reactor cooling, presents challenges due to its high production costs and significant CO2 emissions amounting to approximately a million tons. However, pioneering research conducted at the University of Manchester has unveiled a promising solution. Scientists have identified graphene membranes as a greener and cost-effective alternative for heavy water production.
Graphene Sheet in Fuel Cells
It is known fact that even hydrogen atoms, known as the smallest atom, cannot pass through graphene. In a research, Sir Andre Geim and his team have tested if protons would be blocked by graphene or not. Suprisingly, protons could pass through graphene. This property would improve fuel cells performance by lowering the fuel crossover which is a major problem with fuel cells that decreases durability and efficiency.
Drug Delivery & Cancer Treatment
Recently graphene has showed promise similar to carbon nanotubes in various biomedical applications such as drug delivery and cancer therapy. Graphene can provide a larger specific surface area than other commonly used carbon nanomaterials and forms strong pi bonds with the drug molecules which can therefore act as a good candidate for drug loading.
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.
Touchscreens
Indium tin oxide (ITO) is the commercial product used as transparent conductor of the smartphones, tablets, and computers. Researchers from the Rice University have developed a graphene-based thin film to be used in touchscreens. It is found that graphene-based thin film beats ITO and any other materials in terms of performance because it has lower resistance and higher transparency. Thus, graphene is the new candidate material for the replacement of ITO.
Hard Drives and Memories
Usually, graphene is not considered magnetic, at least not in a controllable or useful way. In 2015, researchers from U.S. Naval Research Laboratory have found a way to turn graphene into a reliable and controllable electromagnetic material. If this innovation is used in hard drives, it is expected to have a capacity almost a million times greater than what we use today.
Superconductors
Scientists have discovered that graphene can also be used as a superconductive material. Two layers of Graphene can conduct the electron without any resistance. This can be accomplished by twisting these two layers of graphene at a ‘magic angle’ which is 1.1°. Most of the superconductive materials show their properties at temperatures close to absolute zero. Even High temperature superconductive materials relative to usual ones can work at around -140°C. In other words, these superconductive materials require a huge energy for cooling. If graphene can be used as a superconductive material at temperatures close to room temperature, there will be a huge revolution for many application areas.
Optoelectronics
A research conducted by the collaboration of different universities has shown that integrating graphene with silicon can beat current silicon photonic technology because devices made by graphene are cheaper, simpler and work at high-scale wavelengths. Apparently, graphene will present a low-energy optical telecommunication and many other convenient optical systems.
Food Packaging
Graphene can also be used as a coating material because it prevents the transfer of water and oxygen. Graphene sheets can be used in food or pharmaceutical packaging by keeping food and medicines fresh for longer time. It may seem a simple application, but it can dramatically reduce the amount of food waste people throw away every day.
Graphene Sheet in Water Purification
Normally, water purification is not a simple process and feasibility of the process depends on how heavily the water is contaminated. An Australian scientist has found a low-cost technique to purify water at one step. Soybean-based graphene sheet, which is also called ‘GrapHair’, is used as a filter. This filter can make dirty water drinkable. it is more efficient, cheaper and environmentally friendly compared to other methods.
Helmets
An ideal helmet would be strong, resistant to impact, durable, comfortable, and light. Graphene is incredibly strong, light, and flexible. It’s even used in bulletproof vests, so it can resist impacts. With these properties, graphene is commercially used in motorbike helmets.
Insulation Material
Graphene can be used as a superconductor or insulator material when two sheets of graphene are arranged at a magic angle. Most of the metal parts of the cars, ships or planes suffer from rusting. When graphene is combined with paint, it can be a great insulation material for creating rust-free surfaces. Another application can be coating of bricks and stones. In this way, water-proof houses can be constructed.
Automotive
The extraordinary strength and hardness of graphene, coupled with its flexibility, is perfect to start creating cars that are immune to shocks. Moreover, accident-proof vehicles could also be created. This would result in a direct decline in road mortality. Graphene cars, which we may see in the showrooms within a decade, are also expected to be cheaper and lighter.
Radiation Shielding
Scientists have been trying to keep the radiation at minimum since it is very dangerous for human health. For this purpose, a variety of materials can be used as a shielding material to radiation but there are many parameters that affects the efficiency of shielding. Graphene is known as a weak radiation absorber, but scientists have found that it can be a great shielding material when it is used in multi-layered form which are graphene slabs. Graphene is an outstanding material for this purpose thanks to its low manufacturing cost, light weight and high efficiency compared to any other shielding materials.
Thermal and Infrared Vision
A great advance that we could see is the development of graphene lenses that allows thermal and infrared vision. The graphene allows manufacturing such ultrathin devices with a built-in camera that gives the user an infrared and thermal vision. Something that until now we have only seen in science fiction movies.
Conclusion:
Graphene, owing to its extraordinary chemical and physical properties, has garnered significant interest across diverse application areas. Its exceptional electronic properties, including high charge transport mobility, make it a crucial material in the production of sensitive nanodevices, nanoelectronics, and nanosensors. Moreover, graphene serves as a promising foundation for high-performance electronics, sensors, and energy storage devices.
Additionally, the unique characteristics of graphene, such as its high fracture strength, excellent thermal and electrical conductivity, and large specific surface area, have propelled its exploration in fields such as flexible electronics, biomedical devices, and energy conversion systems. The versatility of graphene has inspired advancements in areas such as transparent conductive coatings, water filtration membranes, and catalysis.
With its diverse range of applications and potential for innovation, graphene continues to be a focal point of research and development, driving breakthroughs in multiple scientific and technological domains.
