The method of getting graphene products

Graphite intercalation

In this method, natural flake graphite was used as raw material and alkali metal elements were used as intercalation agent. Graphite interlaminar compounds accelerate the graphite stripping process from two aspects. Firstly, the intercalation agent increases the distance between graphite layers and weakens the van der Waals force between graphite layers. Secondly, after lithium, potassium, cesium and other alkali metals are inserted, an electron is input into the graphite lattice, so that the crystal surface is negatively charged, generating electrostatic repulsion, making the graphite crystal prone to peel apart. Finally, graphene sheets were obtained by ultrasound and centrifugation.

However, the graphene sheets prepared by this method are multilayer (>, 10 layers), with a thickness of more than dozens of nanometers, and the addition of intercalated materials will destroy the sp2 hybrid structure of graphene, thus affecting the physical and chemical properties of graphene.

Solution stripping

Solvent stripping method is to disperse the graphite in the solvent to form a low-concentration dispersion solution, use ultrasound or high-speed shear effect to weaken the van der Waals force between the graphite layers, insert the solvent between the graphite layers, peel layer by layer, and prepare graphene. In 2014, Paton et al. first dispersed graphite in a solvent of n-methylpyrrolidone (NMP), and used simple high-speed shear to realize rapid and efficient stripping of graphite to obtain a few layers of graphene stable dispersion solution, and proposed an effective way to realize large-scale production of graphene.

High quality graphene can be prepared by liquid-phase stripping method. No chemical reaction is introduced in the whole liquid-phase stripping process, avoiding the introduction of structural defects on the surface of graphene, which provides high-quality graphene for the application of high-performance electronic devices. The main disadvantage is that the yield is very low and is not suitable for mass production and commercial applications.

Chemical vapor deposition (CVD) method

This method is the main method to prepare semiconductor film materials in large scale in industry by means of chemical reaction of reaction materials in gaseous state at high temperature and solid material deposition on metal matrix surface after annealing. The preparation of graphene by CVD method is to decompose the gas into carbon atoms and hydrogen atoms by high temperature heating, and then carbon atoms are deposited on the surface of the substrate by annealing to form graphene. Finally, the metal substrate is removed by chemical etching. In 2009, Hong et al. deposited graphene with 6 ~ 10 atomic layer thickness on nickel layer for the first time by CVD method. In 2013, Bharathi et al. prepared monocrystalline graphene with a diameter of about 1cm by CVD method.

CVD method is considered as the most promising method to produce high-quality and large-area graphene, and the most promising industrial method to produce graphene film. However, this method is not suitable for the preparation of large-scale graphene macroscopic powders, which limits its application. In addition, the separation of graphene from the substrate is through the method of chemical corrosion of metals, which requires a large amount of acid and will cause huge pollution to the environment, while keeping the cost high. Therefore, how to efficiently and cheaply strip graphene from the substrate to obtain a complete graphene is the main problem facing this method.

REDOX process

REDOX process can be simplified as "oxidation stripping - reduction" three steps and specific for the first use of strong oxidant for graphite oxidation treatment, on the surface of graphite oxide form hydrophilic hydroxyl group, epoxy and carboxyl oxygen containing groups such as, the process can make the graphite layer spacing from 0.34 nm to expand to 0.8 nm, the distance between the layers expand can effectively weaken the interlayer van der Waals attractive, easy to peel; And then the method of using ultrasonic stripping graphite oxide, ultrasonic radiation in the oxidation of graphite slurry density interaction, produce a large number of tiny air bubbles in the liquid, the bubbles in the negative pressure of ultrasonic longitudinal transmission area formation, growth, and in positive pressure area quickly closed, called "cavitation effect" in this process, the closed bubbles can form more than 1.0 x 108 pa of instantaneous high pressure, the high pressure generated continuously like a series of small "explode" constantly impact of graphite oxide, get graphite oxide and quickly stripped the monolayer graphene oxide; Finally, go was reduced at high temperature or in a reducing solution to remove oxygen-containing groups such as hydroxyl groups, epoxy groups and carboxyl groups on the surface of go and restore the perfect two-dimensional sp2 hybrid structure of graphene to obtain graphene products.

The page contains the contents of the machine translation.