1、 Root of the problem: Where do impurities in graphene come from and what are their hazards?

Main sources of impurities:
Chemical preparation (such as oxidation-reduction method): This is the main source of problems. During the preparation process, a large number of oxygen-containing functional groups (such as epoxy groups, carboxyl groups, hydroxyl groups) and residual metal ions (such as K, Na, S, Ca, etc.) will be introduced.
Chemical Vapor Deposition (CVD): During the transfer of graphene from a metal substrate (such as copper foil) to a target substrate, residual transfer media (such as PMMA) and metal contaminants may remain.
Physical methods (such as mechanical exfoliation): Although the purity is high, it also faces problems of environmental adsorption (water vapor, oxygen) and structural defects.

The deadly effects of impurities:
Disrupting electrical performance: Oxygen functional groups and defects can severely scatter electrons, leading to a sharp decrease in conductivity and electron mobility, making it unsuitable for applications in high-frequency transistors, high-end sensors, and other fields.
Deterioration of thermal performance: Impurities and defects can hinder the transmission of phonons, making it impossible to reflect the theoretical ultra-high thermal conductivity (~5300 W/mK) of graphene, and greatly reducing the heat dissipation effect.
Weakening mechanical performance: Defect points will become stress concentration points, becoming the starting point of material fracture under stress, making it unable to reach theoretical strength.
Causing chemical instability: Residual functional groups make it more prone to unnecessary chemical reactions in subsequent processing or applications, affecting product life and reliability.

2、 Technical core: How to "accurately remove" impurities in high-temperature purification?

The mechanism of high temperature action:
Temperature range: usually needs to be carried out within the range of 1500 ℃ to 3000 ℃. The clearance targets vary at different temperatures:
Low to medium temperature range (below~500 ℃): mainly used for removing adsorbed water and some organic residues.
High temperature range (500 ℃ -1500 ℃): Most oxygen-containing functional groups (such as C=O, C-OH) undergo thermal decomposition in this temperature range, escaping in the form of gases such as CO and CO ₂.
Ultra high temperature range (above 1500 ℃): This is the key to achieving high performance. At this temperature, the most stubborn oxygen-containing groups and carbides are completely removed. At the same time, the extremely high energy provides the driving force for the lattice repair of graphene, allowing carbon atoms to gain sufficient mobility to move to defect sites, making the hexagonal ring lattice structure more complete.

The role of vacuum/controlled atmosphere:
High vacuum (such as 10 ⁻³ Pa to 10 ⁻⁵ Pa): The core function is to quickly remove the gas products (CO, CO ₂) generated by the reaction, promoting the decomposition reaction to continue to the right (Le Chatelier principle). At the same time, create an oxygen free and water free ultra clean environment to prevent graphene from undergoing secondary oxidation at high temperatures.
Protective/reactive atmosphere (such as high-purity Ar, H ₂):
Inert gas (Ar): Provides physical protection to prevent oxidation.
Reductive gas (H ₂): Hydrogen can act as an auxiliary reducing agent, react with oxygen-containing groups to generate water vapor, enhance purification efficiency, and have a slight etching repair effect on graphene edges.

3、Application scenarios: Which graphene products must undergo high-temperature purification?
Graphene conductive film: used for touch screens and transparent electrodes, requiring extremely high conductivity and transparency.
Graphene heat dissipation film: used for mobile phones, 5G base stations, LED heat dissipation, requiring maximum thermal conductivity.
Graphene based RF devices: transistors, detectors, etc., require extremely high electron mobility.
High end composite materials: As reinforcements, perfect interface bonding with the matrix is required, and impurities can become weak points at the interface.