GRAPHENE AND ITS APPLICATIONS

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Graphene is a one-atom-thick sheet of carbon atoms arranged in a honeycomb-like pattern. It is an  is an allotrope of carbon. Graphene is considered to be the world's thinnest, strongest and most conductive material - of both electricity and heat. All of these properties are exciting researchers and businesses around the world - as graphene has the potential to revolutionize entire industries - in the fields of electricity, conductivity, energy generation, batteries, sensors and more.

Like graphite, graphene is entirely composed of carbon atoms and 1mm of graphite contains some 3 million layers of graphene. Whereas graphite is a three-dimensional crystalline arrangement, graphene is a two-dimensional crystal only an atom thick. The carbons are perfectly distributed in a hexagonal honeycomb formation only 0.3 nanometres thick, with just 0.1 nanometres between each atom.

This 100% pure carbon simplicity confers some remarkable properties on graphene.

Graphene conducts electricity better than copper. It is 200 times stronger than steel but six times lighter. It is almost perfectly transparent since it only absorbs 2% of light. It impermeable to gases, even those as light as hydrogen or helium, and, if that were not enough, chemical components can be added to its surface to alter its properties.

Another advantage of graphene is that is opens up paths to other two-dimensional materials as small as atoms. Boron nitride, molybdenum sulphate and tungsten or even 100% silicon sillicene are some of the peculiar-sounding names that could become more common. Some isolate, others conduct. Piling up these molecules layer-by-layer would create new materials with new properties.

Synthesis of graphene

Graphene synthesis means any process of fabricating or extracting graphene from graphite. The method to be chosen is governed by the desired size, quantity, and purity. Synthesis technique contributes to the structure and properties of graphene produced. There are variations of graphene layers from different techniques such as a single layer, double layer, or multiple layers, and they have different applications in various fields of science and technology like energy storage devices, biotechnology, memory, electronics, sensors, etc. Researchers employ different techniques especially when a large quantity is required. Subsequently, we will discuss various synthesis techniques, applications, its status now, progress so far, and future prospects.

In the synthesis of graphene-based materials, ball milling and hydrothermal methods show to be cheaper, the electrospinning method exhibits the benefits in the nanowire composite assembly, and the microwave-assisted method is easier and superfast in fabrication. We also explained methods of graphene synthesis while its derivatives are discussed in the second chapter of this book. The third chapter explained the new technique such as liquid phase exfoliation method for the synthesis and concentration enhancement of graphene which is suitable for the fabrication of the highly efficient modern electronic devices.

Applications of graphene/GO/rGO

Graphite and its derivate recently gained science and engineering awareness due to its numerous applications. The discovery of graphene is rightly regarded as a milestone in the world of material science; as can be seen in the worldwide attention, the material has received in the fields of electronics, photonics, capacitors/supercapacitors, biosensing, etc. They are used in numerous applications as illustrated below. In this book, applications of graphene and its derivatives are discussed in detail. These applications include photocatalysis, electronics, gas sensing, graphene-based heterogeneous electrodes for energy storage devices, etc. In addition, sound devices based on graphene is also explained in this book.

Mechanical strength

Graphene is the world's strongest material, and can be used to enhance the strength of other materials. Dozens of researchers have demonstrated that adding even a trace amount of graphene to plastics, metals or other materials can make these materials much stronger - or lighter (as you can use a smaller amount of material to achieve the same strength).

 

Thermal applications

Graphene is the most heat conductive found to date. As graphene is also strong and light, it means that it is a great material for making heat-spreading solutions, such as heat sinks or heat dissipation films. This could be useful in both microelectronics (for example to make LED lighting more efficient and longer lasting) and also in larger applications - for example thermal foils for mobile devices. Huawei's latest smartphones, for example, have adopted graphene-based thermal films.

 

Energy storage

Since graphene is the world's thinnest material, it also extremely high surface-area to volume ratio. This makes graphene a very promising material for use in batteries and supercapacitors. Graphene may enable batteries and supercapacitors (and even fuel-cells) that can store more energy - and charge faster, too.

 

Coatings ,sensors, electronics and more

Graphene has a lot of promise for additional applications: anti-corrosion coatings and paints, efficient and precise sensors, faster and efficient electronics, flexible displays, efficient solar panels, faster DNA sequencing, drug delivery, and more.

Graphene is such a great and basic building block that it seems that any industry can benefit from this new material. Time will tell where graphene will indeed make an impact - or whether other new materials will be more suitable.

 

Electronics

GO are used in electronic fabrications as initial materials. Electronic devices such as graphene effect transistors (GFETs) and field effect transistors (FETs) are graphene-based. Reduced graphene oxides (rGO) are used as chemical sensors. Functionalized graphene oxide in conjunction with glucose oxidase deposited on electrode material is used as an electrochemical glucose sensor. They are widely used in the manufacturing of electronic devices like light-emitting diodes (LEDs) and solar cells. Reduced graphene oxide dispersed in a solvent can be used in the production of the transparent electrode, which is an alternative transparent electrode like FTO and ITO.

 

Water purification

As far, back as the 1960s, scientists have started studying graphite oxide usage in desalination of water. In 2011, some group of researchers employed the principle of reverse osmosis using GO to achieve the same goal. It was discovered that graphite allows water to pass through but retain some larger ions. Its narrow mono- or bilayer capillaries allow water but restrain heavy ions.

Moreover, in the year 2015, a group of scientists also purified water using graphene tea by removing 95% of heavy metal ions in water solution.

It was reported that in 2006, engineers fabricated graphene-based thin film powered by solar energy that possesses the quality of filtering dirty and salty water. These films are non-heavy and can be easily produced on a large scale.

 

Biosensors

Graphene oxide and reduced graphene oxide have been incorporated into many gadgets. These GO-/rGO-based gadgets are fabricated with the quality to identify biologically significant molecules. GO/rGO uses fluorescence resonance energy transfer (FRET) characteristics to work effectively as a biosensor.

 

Elemental storage

All elements that form part of GO or rGO functional groups can be effectively stored in their sheets and extracted later for use and are also being explored for their applications in hydrogen storage.

 

Plasmonics

Recently, the science of plasmonics discovered that near field infrared optical microscopy and infrared spectroscopy of graphene provide accommodations for plasmonic surface mode.

 

Radio wave absorption

A heavenly crammed graphene layer deposited on glass substrates absorbs radio waves of the wavelength range of 125–165 GHz bandwidth by 90%. In our modern houses, graphene serves as roof, door, and window coatings to safeguard houses from radio wave interference.

 

Nanoantennas

A nanoantenna called graphene-based plasmonic nanoantenna (GPN) operates on a wavelength of millimeter within the radio wavelength range. This nanoantenna is better than our conventional antennas because its operational surface plasmon polaritons wavelength is much smaller compared to the wavelength of electromagnetic waves propagating at the same frequency. Our conventional antenna operational frequencies range from 100 to 1000, which is very huge compared to GPNs.

 

Sound transducers

Graphene has been predicted as a good candidate for the manufacturing of electrostatic audio microphones and speakers due to their lightweight, which provides moderately good frequency response. In 2015 an A model audio ultrasonic microphone and the speaker was fabricated; it operates at a frequency range of 20–500 kHz. Its performance operation was up to 99% efficiency, good and uniform frequency output throughout the audible range.

Graphene in Fuel Cells

Even hydrogen atoms, known as the smallest atom, cannot pass through Graphene. In another 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.

 

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 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 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

Unlike X-rays, T-waves which can be used for body scanning are harmless to human body. However, there is a catch. T-waves, or THZ radiation, is hard to both detect and generate. The good news is, with the help of some modifications and other materials, CVD graphene can detect THZ radiation successfully. This will not only lead to safer body scans, but also incredibly faster internet in the future.

 

Graphene as a Superconductor

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.

 

Graphene Security Sensors

One of the first practical and real applications of graphene was security labels. Instead of the bulky sensors that many stores use, the sensors made with graphene are smaller, more aesthetic, able to bend without creating a damage on the circuit, and cost only a couple cents per tag.

 

Graphene in Food Packaging

Graphene can also be used as a coating material because it prevents the transfer of water and oxygen. Graphene membranes 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 in Crop Protection

Graphene is a great material for sensors. Micro-sized sensors can be produced thanks to graphene’s unique structure. It can detect whether a molecule is dangerous or not for the environment. These sensors can be used in food industry, especially in crop protection. Farmers can track and detect dangerous and harmful gasses to crop and they can determine the ideal areas for the growth of the crop depending on the atmospheric conditions, and even the moisture level and “thirst” of the plants with the help of graphene sensors.

 

Graphene in Insulation

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.

 

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 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 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.