Graphene has excellent optical, electrical and mechanical properties, and has important application prospects in the fields of material science, micro-nano processing, energy, biomedicine and drug delivery, and is considered as a revolutionary material in the future. Physicists Andrei Grimm and Konstantin Novoselov of the University of Manchester in England successfully separated graphene from graphite by micromachining, so * * * won the 20 10 Nobel Prize in Physics. The common methods of graphene powder production are mechanical stripping, redox and SiC epitaxial growth, and the method of thin film production is chemical vapor deposition (CVD).
2065438+On March 3, 20081,the first automatic production line of graphene organic solar photovoltaic devices in China was started in Heze, Shandong.
Basic introduction Chinese name: Graphene English name: Graphene Application fields: physics, materials, electronic information, computers, etc. Carrier mobility:15000 cm2/(v s) (room temperature) Thermal conductivity: 5300W/mK (single layer) Theoretical Young's modulus: 1.0TPa Research history, physical and chemical properties, chemical properties, preparation methods, main classification, single-layer graphene, double-layer graphene and few-layer graphene. In fact, graphene originally exists in nature, but the single-layer structure is difficult to peel off. Graphene is stacked layer by layer to form graphite, and the graphite with a thickness of 1 mm contains about 3 million layers of graphene. Pencil gently across the paper, leaving traces may be several layers or even just a layer of graphene. In 2004, Andre Geim and Konstantin Novoselov, two scientists from Manchester University, discovered that they could make graphite flakes thinner and thinner in a very simple way. They stripped the graphite sheet from the highly oriented pyrolytic graphite, then stuck both sides of the sheet on a special tape, and tore the tape to split the graphite sheet in two. Keep going like this, the sheets are getting thinner and thinner. Finally, they got a thin sheet consisting of only one layer of carbon atoms, which is graphene. Since then, new methods for preparing graphene have emerged one after another. In 2009, Andre Geim and Konstantin Novoselov discovered integer quantum Hall effect and room temperature quantum Hall effect in single-layer and double-layer graphene systems respectively, and they won the 20 10 Nobel Prize in physics. Before the discovery of graphene, most physicists thought that thermodynamic fluctuations did not allow any two-dimensional crystal to exist at a finite temperature. Therefore, its discovery immediately shocked the condensed matter physics community. Although both theoretical and experimental circles believe that a perfect two-dimensional structure cannot exist stably at non-absolute zero, a single-layer graphene can be prepared in the experiment. On March 3rd, 2065438, the first automatic production line of graphene organic solar photovoltaic devices in China was started in Heze, Shandong. This project mainly produces graphene organic solar cells (hereinafter referred to as graphene OPV) which can generate electricity in low light, and solves three major solar power generation problems: limited application, sensitive angle and difficult modeling. 2065438+On June 27th, 2008, China Graphene Industry Technology Innovation Strategic Alliance issued the newly formulated group standard "Guide to Naming Graphene Materials". This standard specifies the naming method of new products related to graphene materials. Physical and chemical properties Physical properties The arrangement of carbon atoms in graphene with internal structure is the same as that of graphite monoatomic layer, which has the following characteristics: carbon atoms have four valence electrons, three of which generate sp 2 bonds, that is, each carbon atom contributes an unbound electron on the pz orbit, and the pz orbit of adjacent atoms is perpendicular to the plane to form π bonds, and the newly formed π bonds are in a semi-filled state. It is confirmed that the coordination number of carbon atoms in graphene is 3, the bond length between every two adjacent carbon atoms is1.42×10-10 m, and the included angle between bonds is 120. In addition to the honeycomb layered structure in which σ bonds are connected with other carbon atoms to form hexagonal rings, the pz orbital of each carbon atom perpendicular to the layer plane can form a large π bond of polyatomic atoms (similar to benzene rings) throughout the whole layer, so it has excellent electrical conductivity and optical properties. Graphene structure diagram Mechanical properties of single-layer graphene structure diagram Graphene is one of the materials with the highest known strength, and it also has good toughness and can be bent. The theoretical Young's modulus of graphene is 1.0 kpa, and the intrinsic tensile strength is 130GPa. The reduced graphene modified by hydrogen plasma also has very good strength, and the average modulus can reach 0.25TPa. The graphite paper composed of graphene sheets has many holes, so it is very brittle. Functionalized graphene is obtained by oxidation, and then graphite paper made of functionalized graphene will be exceptionally strong and tough. The carrier mobility of electronic effect graphene at room temperature is about15000 cm2/(v s), which is more than 10 times that of silicon material and more than twice that of indium antimonide (InSb) with the highest carrier mobility. Under certain conditions, such as low temperature, the carrier mobility of graphene can even be as high as 250,000 cm2/(v s). Unlike many materials, the electron mobility of graphene is less affected by temperature changes. At any temperature between 50 and 500 K, the electron mobility of single-layer graphene is about15000 cm2/(v s). Graphene is composed of fullerenes, carbon nanotubes and graphite. In addition, the semi-integer quantum Hall effect of electron carriers and hole carriers in graphene can be observed by changing the chemical potential under the action of electric field. Scientists have observed this quantum Hall effect of graphene at room temperature. The carriers in graphene follow a special quantum tunneling effect and do not backscatter when encountering impurities, which is why graphene has local superconductivity and high carrier mobility. Electrons and photons in graphene have no rest mass, and their velocity is a constant independent of kinetic energy. Graphene is a zero-distance semiconductor because its conduction band and valence band intersect at Dirac point. At six positions of Dirac point, Brillouin zone on the edge of momentum space is divided into two equivalent triplets. In contrast, the principal point of traditional semiconductors is usually γ, and the momentum is zero. Thermal Performance Graphene has very good thermal conductivity. The thermal conductivity of pure defect-free monolayer graphene is as high as 5300W/mK, which is the highest thermal conductivity of carbon materials so far, higher than that of single-walled carbon nanotubes (3500W/mK) and multi-walled carbon nanotubes (3000W/mK). When used as a carrier, the thermal conductivity can also reach 600 W/MK, and the ballistic thermal conductivity of graphene can reduce the lower limit of ballistic thermal conductivity per unit circumference and length of carbon nanotubes. Experimental value of thermal conductivity Optical properties of resistance and temperature coefficient Graphene has very good optical properties, and its absorption rate is about 2.3% in a wide wavelength range, and it looks almost transparent. Within the range of several layers of graphene thickness, the absorption rate increases by 2.3% as the thickness of each layer increases. Large-area graphene films also have excellent optical properties, and their optical properties change with the change of graphene thickness. This is an unusual low-energy electronic structure of single-layer graphene. At room temperature, the band gap of graphene can be adjusted from 0 to 0~0.25eV by applying voltage to the double-gate double-layer graphene field effect transistor. When a magnetic field is applied, the optical echo of graphene nanoribbons can be tuned to the terahertz range. When the incident light intensity exceeds a certain critical value, the absorption of graphene will reach saturation. These characteristics enable graphene to be used as a passive mode-locked laser. When the input light intensity exceeds the threshold, this unique absorption may become saturated, which is called saturation effect. Graphene can be saturated and easily excited in the near infrared region due to global light absorption and zero band gap. Because of this special property, graphene is widely used in ultrafast photonics. The optical reflection of graphene/graphene oxide layer can tune electricity. Under stronger laser irradiation, graphene may have nonlinear optical Kerr effect with nonlinear phase shift. Solubility: it shows good solubility in nonpolar solvents, and has super hydrophobicity and super lipophilicity. Melting point: in the study of 20 15, scientists said it was about 4 125K, and other studies indicated that the melting point might be around 5000K. Other characteristics: it can adsorb and desorb various atoms and molecules. Chemical Properties Graphene is similar to graphite in chemical properties, and can adsorb and desorb various atoms and molecules. When these atoms or molecules are used as donors or acceptors, the concentration of graphene carriers can be changed, and graphene itself can maintain good conductivity. When other substances such as H+ and OH- are adsorbed, some derivatives will be produced, which will make the conductivity of graphene worse, but no new compounds will be produced. Therefore, graphite can be used to infer the properties of graphene. For example, the formation of graphitic alkanes is based on two-dimensional graphene, and each carbon atom adds one more hydrogen atom, so that the sp 2 carbon atom in graphene becomes sp 3 hybridization. Soluble fragments of graphene can be prepared by chemically modifying graphite in the laboratory. Composite Graphene Oxide (GO): A layered material made of graphite oxide. After the massive graphite was treated with fuming concentrated acid solution, the graphene layer was oxidized into hydrophilic graphene oxide, and the spacing between graphite layers was 3.35 before oxidation. Increase to 7~ 10? After heating in water or ultrasonic stripping, it is easy to form a separated graphene oxide lamellar structure. XPS, infrared spectrum (IR), solid-state nuclear magnetic resonance (NMR) and other characterization results show that graphene oxide contains a large number of oxygen-containing functional groups, including hydroxyl groups, epoxy functional groups, carbonyl groups, carboxyl groups and so on. Hydroxyl and epoxy functional groups are mainly located on the surface of graphite substrate, while carbonyl and carboxyl groups are located on the edge of graphene. Graphane: It can be obtained by reacting graphene with hydrogen. It is a saturated hydrocarbon with the molecular formula of (CH) n, in which all carbon is sp 3 hybrid, forming a hexagonal network structure, and hydrogen atoms are bonded to carbon from both ends of the graphene plane in an alternating form. Graphane shows semiconductor characteristics and has a direct band gap. Nitrogen-doped graphene or carbonitride: nitrogen atoms are introduced into the crystal lattice of graphene to become nitrogen-doped graphene, and the generated nitrogen-doped graphene shows better performance than pure graphene, showing a disordered, transparent and wrinkled gauze shape, and some sheets are stacked together to form a multi-layer structure, showing higher specific capacitance and good cycle life. Biocompatibility: the implantation of carboxyl ions can make the surface of graphene material have active functional groups, thus greatly improving the cellular and biological reaction activity of the material. Compared with tubular carbon nanotubes, graphene is more suitable for the study of biomaterials. Moreover, compared with carbon nanotubes, graphene has longer edges, is easier to be doped and chemically modified, and is easier to accept functional groups. Oxidation: can react with active metals. Reducibility: It can be oxidized in air or with acid. Graphene can be cut into small pieces by this method. Graphene oxide is a layered material obtained by graphite oxidation. It is easy to form a separated graphene oxide lamellar structure by heating in water or ultrasonic stripping. Addition reaction: Using the double bond on graphene, the required groups can be added through addition reaction. Stability: The structure of graphene is very stable, and the carbon-carbon bond is only 1.42. The connection between carbon atoms in graphene is very flexible. When an external force is applied to graphene, the surface of carbon atoms will bend and deform, so that carbon atoms do not need to be rearranged to adapt to the external force, thus maintaining structural stability. This stable lattice structure makes graphene have excellent thermal conductivity. In addition, when electrons in graphene move in orbit, they will not be scattered due to lattice defects or the introduction of foreign atoms. Because of the strong interatomic force, at room temperature, even if the surrounding carbon atoms collide, the interference of electrons in graphene is very small. At the same time, graphene is aromatic and has the property of aromatic hydrocarbon. Preparation method Mechanical stripping method Mechanical stripping method is a method to obtain graphene thin-layer materials by using friction and relative motion between objects and graphene. This method is simple to operate, and the obtained graphene usually maintains a complete crystal structure. In 2004, two British scientists peeled off natural graphite layer by layer with transparent tape to obtain graphene, which was also classified as mechanical peeling. This method was once considered inefficient and unable to be industrialized for large-scale production. Although this method can prepare micron-sized graphene, it is difficult to realize large-scale synthesis because of its low controllability. Redox method Redox method is to use chemical reagents such as sulfuric acid and nitric acid and oxidants such as potassium permanganate and hydrogen peroxide to oxidize natural graphite, increase the spacing between graphite layers, and insert oxides between graphite layers to prepare graphite oxide. Then, the reactant was washed with water, and the washed solid was dried at a low temperature to prepare graphite oxide powder. Graphene oxide was prepared by stripping graphite oxide powder by physical stripping and high temperature expansion. Finally, graphene oxide was reduced by chemical method to obtain graphene (RGO). The method is simple in operation and high in yield, but the product quality is low. The oxidation-reduction method uses strong acids such as sulfuric acid and nitric acid, which is dangerous and requires a lot of water for cleaning, which brings great environmental pollution. Graphene prepared by redox method is rich in oxygen-containing functional groups and easy to modify. However, when reducing graphene oxide, it is difficult to control the oxygen content of the reduced graphene. Under the influence of all external factors, such as sunlight and high temperature in the carriage during transportation, graphene oxide will be continuously reduced. Therefore, the quality of graphene products produced by redox method is often inconsistent and difficult to control. Directional epiphysis method is to "seed" graphene by using the atomic structure of the growth substrate. Carbon atoms were infiltrated into ruthenium at 1 150℃ and then cooled to 850℃. After cooling, a large number of carbon atoms adsorbed before will float to the surface of ruthenium, and finally the carbon atoms in the lenticular monolayer will grow into a complete graphene layer. After the first layer was covered, the second layer began to grow. Graphene at the bottom will have a strong interaction with ruthenium, and after the second layer, it will be almost completely separated from ruthenium, leaving only a weak coupling. However, the thickness of graphene sheets produced by this method is often uneven, and the adhesion between graphene and matrix will affect the characteristics of carbon layers. Silicon carbide epitaxial method SiC epitaxial method is to sublimate silicon atoms out of the material under the high temperature environment of ultra-high vacuum, and reconstruct the remaining C atoms through self-assembly, thus obtaining graphene based on SiC substrate. This method can obtain high-quality graphene, but this method requires high equipment. Hemmer method graphite oxide was prepared by Hummer method; Putting graphite oxide into water for ultrasonic dispersion to form a uniformly dispersed graphene oxide solution with a mass concentration of 0.25 g/L- 1 g/L, and then dropping 28% ammonia water into the graphene oxide solution; Dissolving a reducing agent in water to form an aqueous solution with a mass concentration of 0.25g/L to 2g/L; Uniformly mixing the prepared graphene oxide solution and the reducing agent aqueous solution, stirring the obtained mixed solution under the condition of oil bath, filtering, washing and drying after the reaction to obtain graphene. Chemical Vapor Deposition Chemical Vapor Deposition (CVD) is a method for preparing graphene thin films by vapor deposition from carbon-containing organic gases. This is the most effective method to produce graphene thin films at present. Graphene prepared by this method has the characteristics of large area and high quality, but the cost is high at this stage, and the process conditions need to be further improved. Due to the thin thickness of graphene film, large-area graphene film cannot be used alone, and it must be attached to macro devices, such as touch screens and heating devices. Some scholars use low-pressure vapor deposition method to generate single-layer graphene on infrared surface. Through further research, we can know that this graphene structure can cross the metal steps and gradually form a continuous, micron-sized single-layer carbon structure on the Ir surface. Millimeter-scale single crystal graphene was obtained by surface segregation. The epitaxial growth of graphene and graphene on polycrystalline Ni films in centimeter scale has been discovered by some scholars. After the surface of Ni film with a thickness of 300 nm is heated at 1000℃ and exposed to CH 4 atmosphere, after a period of reaction, a small amount of graphene film with a large area will be formed on the metal surface. Single-layer graphene refers to a two-dimensional carbon material (hexagonal honeycomb structure) composed of a layer of carbon atoms with benzene ring structure. Double-layer or double-layer graphene: refers to a two-dimensional carbon material composed of two layers of carbon atoms which are periodically and closely stacked in different stacking ways (including AB stacking and AA stacking) into a benzene ring structure (that is, a hexagonal honeycomb structure). A few layers refers to a two-dimensional carbon material composed of 3- 10 layers of carbon atoms which are periodically and closely packed in a benzene ring structure (i.e. hexagonal honeycomb structure) in different stacking modes (including ABC stacking and ABA stacking). Multilayer Graphene Multilayer Graphene is also called multilayer graphene: it refers to a two-dimensional carbon material with a thickness of more than 10 and less than 10nm, in which carbon atoms with benzene ring structure (i.e. hexagonal honeycomb structure) are periodically and closely stacked in different stacking ways (including ABC stacking and ABA stacking). Main applications With the gradual breakthrough of mass production and large-size problems, the pace of industrial application of graphene is accelerating. Based on the existing research results, the first commercial applications may be mobile devices, aerospace and new energy batteries. The basic research of graphene is of special significance to the basic research of physics, which makes some quantum effects that can only be demonstrated in theory before can be verified by experiments. In two-dimensional graphene, the mass of electrons seems to be nonexistent. This property makes graphene a rare condensed matter and can be used to study relativistic quantum mechanics. Because massless particles must move at the speed of light, they must be described by relativistic quantum mechanics, which provides a new research direction for theoretical physicists: some experiments that originally needed to be carried out in giant particle accelerators can be carried out in small laboratories with graphene. The semiconductor with zero energy gap is mainly single-layer graphene, and this electronic structure will seriously affect the role of gas molecules on its surface. The results of hydrogenation and oxidation of graphene show that single-layer graphene has the function of enhancing the surface reactivity compared with bulk graphite, indicating that the electronic structure of graphene can regulate its surface reactivity. In addition, the electronic structure of graphene can be changed by the induction of gas molecular adsorption, not only the concentration of carriers can be changed, but also different graphene can be doped. Sensor Graphene can be made into a chemical sensor, which mainly depends on the surface adsorption performance of graphene. According to the research of some scholars, the sensitivity of graphene chemical detector can be comparable to the limit of single molecule detection. Graphene's unique two-dimensional structure makes it very sensitive to the surrounding environment. Graphene is an ideal material for electrochemical biosensor, and the sensor made of graphene has good sensitivity in detecting dopamine and glucose in medicine. Schematic diagram of transistor of graphene sensor excited by infrared beam; Graphene can be used as transistor. Because of the high stability of graphene structure, this transistor can still work stably on the scale close to a single atom. In contrast, the transistor made of silicon at present will lose its stability on the scale of 10 nanometer; The ultra-fast reaction speed of electrons in graphene to the external field makes the transistor made of graphene reach a very high working frequency. For example, in February of 20 10, IBM announced that it would increase the working frequency of graphene transistors to 100GHz, which was higher than that of silicon transistors of the same scale. Flexible display flexible display has attracted much attention at the Consumer Electronics Show and has become the development trend of mobile device display in the future. Flexible display has a broad market in the future, and the prospect of graphene as a basic material is also optimistic. For the first time, Korean researchers made a flexible transparent liquid crystal display composed of multilayer graphene and fiberglass polyester sheets. Researchers from South Korea's Samsung Company and Sungkyunkwan University made a piece of pure graphene the size of a TV set on a 63 cm wide flexible transparent fiberglass polyester board. They said that this is by far the largest graphene block. Subsequently, they used graphene blocks to make flexible touch screens. Researchers say that in theory, people can roll up their smartphones and stick them behind their ears like pencils. New energy battery New energy battery is also an important field of graphene's earliest commercialization. Massachusetts Institute of Technology has successfully developed a flexible photovoltaic panel coated with graphene nano-coating, which can greatly reduce the cost of manufacturing transparent deformable solar cells and may be applied to small digital devices such as night vision goggles and cameras. In addition, the successful research and development of graphene super battery has also solved the problems of insufficient battery capacity and long charging time of new energy vehicles, greatly accelerating the development of new energy battery industry. This series of research results paved the way for the application of graphene in the new energy battery industry. Graphene-based supercapacitor structure and theoretical energy density of graphene under different voltages Graphene filters used for seawater desalination are more used than other seawater desalination technologies. After the graphene oxide film in water environment is in close contact with water, a channel with a width of about 0.9 nm can be formed, and ions or molecules smaller than this size can quickly pass through. By further compressing the capillary channel size and controlling the pore size in graphene film by mechanical means, the salt in seawater can be filtered efficiently. Graphene, a hydrogen storage material, has the advantages of light weight, high chemical stability and high specific surface area, and is the best candidate for hydrogen storage materials. Aerospace Because of its high conductivity, high strength and ultra-thinness, the application advantages of graphene in aerospace military industry are also extremely prominent. In 20 14, NASA developed a set of graphene sensors used in aerospace field, which can well detect trace elements in the upper atmosphere of the earth and structural defects on spacecraft. Graphene will also play a more important role in the potential application of ultra-light aircraft materials. The new photosensitive element with graphene as the photosensitive element material is expected to improve the photosensitive ability by thousands of times compared with the existing CMOS or CCD through a special structure, and the energy consumption is only 10%. It can be used in the fields of monitors, satellite imaging, cameras, smart phones, etc. Composite material Graphene-based composite material is an important research direction in the application field of graphene, which shows excellent performance in the fields of energy storage, liquid crystal devices, electronic devices, biomaterials, sensing materials and catalyst carriers, and has broad application prospects. At present, the research of graphene composites mainly focuses on graphene polymer composites and graphene-based inorganic nanocomposites. With the development of graphene research, the application of graphene reinforcement in bulk metal matrix composites has attracted more and more attention. Multifunctional polymer composites and high-strength porous ceramic materials made of graphene enhance many special properties of the composites. Composite bio-graphene is used to accelerate the osteogenic differentiation of human bone marrow mesenchymal stem cells, and also used to manufacture biosensor of epitaxial graphene on silicon carbide. Meanwhile, graphene can be used as a neural interface electrode without changing or destroying characteristics, such as signal intensity or scar tissue formation. Because of its flexibility, biocompatibility and conductivity, graphene electrode is much more stable than tungsten or silicon electrode in vivo. Graphene oxide is very effective in inhibiting the growth of Escherichia coli and will not harm human cells. Development Prospect The research and application development of graphene continues to heat up. Materials related to graphite and graphene are widely used in battery electrode materials, semiconductor devices, transparent liquid crystal displays, sensors, capacitors, transistors and so on. In view of the excellent performance and potential application value of graphene materials, a series of important progress has been made in chemistry, materials, physics, biology, environment, energy and other disciplines. Researchers are committed to trying different methods in different fields to prepare high-quality and large-area graphene materials. Through the continuous optimization and improvement of graphene preparation process, the preparation cost of graphene is reduced, and its excellent material properties are widely used and gradually industrialized. China also has unique advantages in graphene research. From the production point of view, graphite, as a raw material for graphene production, is rich in energy storage and low in price in China. It is precisely because of the application prospect of graphene that many countries have established graphene-related technology research and development centers, trying to commercialize graphene, and then obtain potential application patents in industrial, technical and electronic related fields. For example, the European Commission regards graphene as a "flagship technology project in the future" and has set up a special R&D plan, allocating 65.438+0 billion euros in the next 65.438+00 years. Britain * * * also invested in the establishment of the National Graphene Research Institute (NGI), trying to make this material enter the production line and market from the laboratory in the next few decades. Graphene is expected to become a new generation of devices in many applications. In order to explore the wider application fields of graphene, it is necessary to continue to seek more excellent graphene preparation technology to make it better applied. Although graphene has been synthesized and proved to exist for more than ten years, it has become a hot topic for scholars this year. Its excellent optical, electrical, mechanical and thermal properties urge researchers to study it deeply. With the continuous development of graphene preparation methods, graphene will be more widely used in various fields in the near future. The industrialization of graphene is still in its infancy, and some applications are not enough to reflect various "ideal" properties of graphene. However, many researchers in the world are exploring "killer" applications, and there are too many challenges to be faced in testing and certification in the future, which requires constant innovation in means and methods.