How to get graphene products

Graphite interpolation method

The method uses natural scale graphite as raw material, alkali metal element as interlayer agent, and the graphite interlayer compound is obtained by mixing interlayer agent with graphite. The graphite interlayer compound accelerates the graphite stripping process from two aspects. First, the insertion of the interlayer increases the interlayer distance of the graphite and weakens the van der Waals force between the graphite layers. Second, after the insertion of alkali metals such as lithium, potassium, and cesium, an electron is input into the Shimojingge, so that the crystal surface is negatively charged, resulting in electrostatic repulsion, making the graphite crystal prone to stripping. Finally, graphene tablets are obtained by ultrasound and centrifugation.

However, the graphene tablets prepared by this method are multi-layer(> 10 layers) with a thickness greater than a few tens of nanometers, and the addition of intercalated materials will destroy the SP2 hybrid structure of graphene, making graphene physically and chemically. Properties are affected.

Solution stripping method

Solvent stripping method is to disperse graphite in the solvent to form a low concentration of dispersion liquid, use ultrasound or high-speed shear to weaken the van der Waals force between the graphite layers, insert the solvent between the graphite layers, and peel it off layer by layer to produce graphene. In 2014, Paton et al. first dispersed graphite in N-methylpyrrolidone(NMP) solvents, used simple high-speed shear to achieve rapid and efficient stripping of graphite, obtained a small layer of graphene stable dispersion, and proposed an effective way to achieve graphene large-scale production.

The liquid-phase stripping method can produce high-quality graphene. The entire liquid-phase stripping process does not introduce chemical reactions, 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 it is not suitable for large-scale production and commercial applications.

Chemical vapor deposition(CVD) method

This method is the main method of preparing semiconductor membrane materials on a large scale in industry by chemical reaction of the reaction material at a higher temperature and annealing to form solid material deposited on the surface of the metal matrix. The preparation of graphene by CVD method is heated at high temperature, the gas is decomposed into carbon atoms and hydrogen atoms, and the carbon atoms are deposited on the base surface to form graphene by annealing, and the metal base is finally removed by chemical corrosion. In 2009, Hong et al. deposited graphene with a thickness of 6 to 10 atomic layers on the nickel layer for the first time using the CVD method. In 2013, Bharathi et al. prepared large-sized monocrystalline graphene with a diameter of about 1cm by CVD method.

The CVD method is considered to be the most promising method for the preparation of high-quality, large-area graphene, and is the most promising industrial method for the production of graphene membranes. However, this method is not suitable for the preparation of large-scale graphene macropowders, which limits its application. In addition, the separation of graphene from the substrate is a method of chemically corroding metals, requiring a large amount of acid, which will cause huge pollution to the environment and at the same time keep the cost high. Therefore, how to obtain the complete graphene from the substrate is the main problem.

Oxidation and reduction method

The Redox method can be simplified into three steps: "oxidizing, stripping, reducing". Specifically, the graphite is first oxidized with a strong oxidant to form hydrophilic hydroxyl groups, epoxy groups, and carboxyl groups on the surface of the graphite. Oxygen groups, This process will increase the layer spacing of graphite from the original 0.34 nm to 0.8 nm. The expansion of the inter-layer distance can effectively weaken the van der Waals attraction between layers and is easy to peel off; Then the graphite oxide was stripped by ultrasonic method. Ultrasonic radiation in the graphite oxide suspension produced a large number of tiny bubbles in the liquid. These bubbles formed and grew in the negative pressure region of the ultrasonic longitudinal propagation, and in the positive pressure area. Close quickly, In this process known as the "cavitation" effect, bubble closure can form an instantaneous high pressure of more than 1.0 × 108 Pa, and the continuous high pressure generated is like a series of small "explosions" that continuously impact graphite oxides. The graphite oxide sheet is rapidly stripped to give a single layer of graphene oxide; Finally, graphene oxide is reduced at high temperatures or in a reducing solution, and oxygen-containing groups such as hydroxyl groups, epoxides, and carboxyl groups on the surface of graphene oxide are removed by reduction to restore graphene's perfect two-dimensional SP2 hybrid structure. Graphene products.

The page contains the contents of the machine translation.