Progress on frontier application of graphene

Graphene is made of carbon atoms in the form of sp ² Two-dimensional carbon nanomaterials with hexagonal honeycomb lattice composed of hybrid orbitals are the most powerful materials known by human beings. Since it was first prepared by 2 scientists (Andre Geim and Konstantin Novoselov) from the University of Manchester in the UK in 2004, graphene has attracted wide attention in the scientific community and is considered to be a revolutionary material affecting the future. The application of graphene in various fields is related to its electrical and mechanical properties. Graphene is widely used and can be combined with other substances to achieve better performance. This paper introduces the research progress of graphene from the perspectives of new energy battery, biomedical field, seawater desalination, and photochemistry.

1.1 Conductive additives and electrode Composites

Graphene material has good conductivity and is easy to be processed into a thin film. Adding graphene as a conductive additive to the cathode of a lithium-ion battery can greatly improve the conductivity of the battery and then improve the electrochemical performance. As a negative electrode material, it can provide reversible storage space for lithium ions, improve capacity and rapid charge and discharge. For example, coating graphene material on the surface of tin dioxide (a cathode material for lithium-ion batteries) can effectively alleviate the problem of volume expansion during battery charge and discharge and improve the stability of capacity and cycle. The composite of silicon nanomaterials and graphene materials has better performance than the general conductive agent, reduces the loss of multiple cycles, reduces the cost, and greatly improves its cycle reversible specific capacity. The team of Cheng Qian, a Japanese electrical appliance company, developed a honeycomb porous graphene sponge. When it is used as a conductive additive for lithium-ion positive and negative electrodes, it can effectively improve the electronic conductivity of battery electrodes, reduce the charge transfer resistance of active substances, and improve the battery rate performance and cycle. Graphene is an important research direction of conductive additive materials.

The composite conductive agent composed of graphene conductive agent and carbon material with higher conductivity can make the conductive agent more fully in contact with active substances, build a cooperative conductive network from different dimensions, and better improve the performance of the positive electrodes. Jiang Rongyan of Shandong University and others significantly improved the performance of manganese dioxide (MnO2) based electrode materials by adding 5% and 10% carbon black and graphene. The research team of Tsinghua University used 1% super-p (SP) and 0.2% graphene nanosheet (GN) as the binary conductive agents to build an effective conductive network in LiCoO2 (lithium cobalt oxide) electrode, improve the battery magnification performance and cycle, which is better than the battery containing 3% SP in the market, and further demonstrated the commercial potential of GN additive for high-performance lithium-ion battery.

1.2 Fluid collector

The collector is an important part of a battery cell. A good collector needs the advantages of macro size, independent self-support, good stability, good conductivity, and low cost. Graphene is very suitable for flexible energy storage devices because of its high conductivity and high flexibility. As early as 2012, the Institute of metals of the Chinese Academy of Sciences replaced the metal collector with a three-dimensional connected graphene network as the collector in the battery [7]. The Ruoff research group uses foam graphene as a collector and is used in lithium-ion batteries. After that, foam graphene is used as the collector of all kinds of lithium-ion batteries. A graphene sponge is also a kind of three-dimensional carbon material that can be used as a battery collector, with good mechanical properties and conductivity.

2.1 Biomedical sensors

In the biomedical field, graphene research mainly focuses on ① the research and development of graphene oxide biological detector equipment for biomolecular detection; ② The antibacterial effect of graphene oxide, the biosafety of graphene and the mechanism of toxicity were studied; ③ Research on graphene in biological photothermal therapy and optical storage [9]. A biomedical sensor is an instrument that is sensitive to biological substances and converts their concentration into electrical signals for detection. A thermoelectric sensing device based on graphene has been designed by the research team of the University of Melbourne. The device first constructs a zigzag graphene nanobelt with hydrogen passivation at the edge and then makes the surface of graphene nanobelt close to a single biological molecule, so as to accurately detect a single molecule. Bhatnagar, a CSIR company in India, designed a graphene quantum dot and polyamide amine (PAMAM) nanocomposite modified gold electrode hypersensitive cardiac troponin I antibody for rapid detection of human myocardial infarction.

Graphene is a promising nano DNA sequencing material. Graphene-based sensors can be used for DNA sequencing, but the market scale is small. The principle is that nanopores are combined with graphene-based sensors to allow a single DNA molecule to pass through the sensor, so as to realize single DNA molecule sequencing [12]. Liang Lijun of Zhejiang University studied the perforation behavior of DNA molecules in multilayer graphene nanopores and found that multilayer graphene was better than monolayer graphene in the accuracy of DNA sequencing.

2.2 Antibacterial effect and biosafety of graphene oxide

Because the abuse of traditional antibiotics will cause the problem of drug resistance and weaken the antibacterial performance, and nanomaterials have unique structural characteristics and can be used to make efficient and safe antibacterial agents, nano antibacterial materials have attracted people’s attention. Graphene derivatives such as graphene oxide have great application potential in the field of antibacterial. Liu Shaobin of Nanyang University of technology in Singapore and others found the destructive effect of graphene oxide (go) on Escherichia coli using an atomic force microscope. Go blocks the interaction between the cells and the surrounding environment by wrapping the cells of this bacterium, and prevents the continuous appreciation of cells, resulting in the loss of activity of this kind of cells. However, the size of the graphene oxide sheet is small, which can not effectively isolate the cells from the environment. Kulshrestha, Muslim University of Aligarh, India, and others combined graphene oxide with zinc ions to form graphene/zinc oxide nanocomposites (gznc). They explored the potential impact of gznc on the cariogenic properties of Streptococcus mutants and found that it had a very significant antibacterial effect on Streptococcus mutants. Gznc had the ability to effectively inhibit the formation of Streptococcus mutans biofilm. The antibacterial mechanism of graphene oxide mainly includes oxidative stress and direct damage to the bacterial cell walls and cell membranes. At present, many people in academic circles doubt the antibacterial performance of go, and further research is needed.

2.3 Gene vector

At present, the construction of a safe and effective gene vector is the key and difficult point of gene therapy. Graphene and its derivatives can be used as gene carriers mainly because of their following properties: ① easy chemical modification; ② Can bind nucleotides; ③ It can protect nucleotides from enzymatic decomposition; ④ Easy to be absorbed by cells; ⑤ Low toxicity. Dong Haifeng of Nanjing University constructed a pei-gnr gene vector by using the electrostatic interaction between graphene nanoribbons (GNR) and polyethyleneimine (PEI). Feng Liangzhu of Suzhou University effectively wrapped positively charged polyethyleneimine molecules on the surface of nanographene by electrostatic adsorption method. A series of gene vectors were constructed based on graphene. The constructed alkaline graphene oxide (NGO) – Pei complex was proved to have gene loading capacity on the cell level [19]. Imani Rana and his team at McGill University in Canada used phospholipid polymer (PL-PEG) and cell-penetrating peptide (CPP) to improve the stability and siRNA transfection ability of go-based nanocarriers [20]. Because different graphene materials have different effects on the performance of gene vectors, more systematic comparative research is needed to further optimize the design of graphene gene vectors.

3.1 Desalination

Seawater desalination is one of the important ways to solve the water resources crisis. With the development of water treatment technology, especially seawater desalination devices, graphene is considered as a potential electrode material for capacitive desalination in seawater desalination because of its excellent conductivity, controllable surface morphology, and good chemical properties. There are many kinds of graphene materials, among which graphene oxide is suitable for water treatment. There are many ways of seawater desalination, among which the method that can use graphene is capacitive deionization (CDI). El deen of Korea’s Quanbei National University and others compounded granular nano manganese dioxide (MnO2) and rod-shaped nano MnO2 with graphene respectively and compared the characteristics of different forms of nanographene / MnO2 composites. It was found that rod-shaped nano MnO2 as an electrode had a better capacitive deionization effect, with a single cycle desalination amount of 5.01mg/g and a desalination rate of 93%, And has excellent recycling capacity. Han Dengcheng of Shandong University and others introduced a one-dimensional MnO2 nanostructure in the middle of graphene lamella, which effectively improved the material capacitance, increased the effective contact area between the material and ions in the solution, and improved the desalination performance. Rohit Karnik, Department of mechanical engineering, Massachusetts Institute of Technology, found in the experiment that desalting requires the design of a tough graphene-based membrane to ensure that the filter membrane can withstand high-pressure flow, so as to eliminate salt ions in seawater.

3.2 Graphene can be used as adsorbent

Graphene is very suitable as an adsorbent to adsorb organic substances (especially macromolecular organic pollutants) and inorganic anions, and graphene oxide has a good adsorption effect on inorganic pollutants. Chi Caixia and others at Suihua University, who used ascorbic acid as the reducing agent, prepared graphene aerogels by reduction induced self-assembly method and used this material to adsorb toluene. The material showed good adsorption and recycling performance. The Yang Caixia composite hydrogel material was prepared by sol-gel method using the biocompatible polyvinyl alcohol (PVA) in Qingdao University, and the adsorption capacity of methylene blue on the material was studied. The adsorption capacity of PVA/GO was as high as 476mg/g. Graphene hydrogel materials greatly improve the adsorption performance and effectively avoid the two pollution problems caused by two-dimensional graphene materials directly used in water treatment. Zhao Jinping, Institute of materials science, Shenyang National Laboratory, Chinese Academy of Sciences, and others prepared graphene material with ultra-low density (2.1mg / cm3) nitrogen-doped porous shape by hydrothermal method. The material can adsorb crude oil and organic solvents equivalent to 200 ~ 600 times its own mass.

3.3 Graphene is used as filtration and separation material

Wu Hengan, a professor in the Department of modern mechanics at the University of Science and Technology of China, and the University of Manchester in the United Kingdom found that graphene oxide films have the properties of rapid and accurate screening of ions. Wu Hengen’s research group used the molecular simulation method to study the ion filtration mechanism of graphene nanochannel. It is found that the graphene oxide film in water interacts with water to form a capillary channel with a width of about 0.9 nm, and the ions with a diameter of more than 0.9 nm will be completely blocked. The interaction between graphene and ions makes ions gather in the nanochannels, which promotes the rapid diffusion of ions, also known as the “ion sponge effect”. This research means that the manufacture of filtration devices that turn seawater into drinking water is expected to become a reality.

Researchers at the University of Manchester in the UK have developed a new type of graphene oxide film. They use epoxy resin coating to form a “blocking wall” on both sides of the film to effectively control the expansion of the film in water. When the membrane expands, this method can control the size of microvoids on the membrane, so as to achieve the goal of more accurate filtration of fine and small salt ions. It is expected to realize the large-scale market-oriented application of this technology in the future [28]. Shanghai Institute of Applied Physics, Shanghai University, and Zhejiang Agriculture and Forestry University have jointly developed and designed a laminated graphene oxide film. The film can precisely control the layer spacing through hydrated ions, and can interceptions including potassium ions in a salt solution, so as to make water pass quickly and achieve the effect of accurately screening water molecules and different ions.

Graphene has attracted the keen attention of scientific and industrial circles because of its unique physical and chemical properties and great advantages. In addition to the fields mentioned above, scientists in many fields have great enthusiasm for graphene. In recent years, graphene has made a lot of research results in the field of application and preparation, but the latest applied research results of graphene still have a long way to go from the large-scale market application. Graphene is difficult to be used to produce a product alone, but it is combined with different materials according to its different characteristics to achieve the corresponding purpose. Therefore, the research on graphene composites should be strengthened.

China has developed rapidly in the field of graphene composites, which is not much different from the international advanced level. Foreign countries pay more attention to the middle-end application of graphene composites, such as energy storage; China pays more attention to the field of new functional materials, such as wearable devices. China should learn from international research methods, learn from each other, strengthen institutional cooperation, optimize the industrial layout and fully realize the utilization of graphene.