Plasma is a special form of matter that is common in nature and daily life. It is composed of electrons, ions, excited and ground state atoms or molecules, photons, and free radicals, and generally presents an uncharged state. It has a different composition and characteristics from ordinary gases, so it is considered to be another state of matter besides "solid, liquid, and gas", which is the fourth state.

There are many types of plasma, which can be divided into two categories based on the difference in particle temperature: thermal equilibrium state and non-equilibrium state. Thermal equilibrium state refers to a state in which the temperatures of electrons, ions, and neutral particles are similar and reach thermodynamic equilibrium. Non equilibrium state refers to a low-temperature plasma where the electron temperature is much higher than the temperature of ions and neutral particles. The reaction of low-temperature plasma mainly includes three steps: (1) introducing a small amount of gas under low pressure and generating plasma through glow discharge; (2) Excited state particles are unstable and can decompose or collide, leading to morphological changes; (3) The generated free base is unstable and will undergo chemical reactions with other substances to form new compounds. The low-temperature plasma surface treatment process is a dry process with advantages such as energy saving, no pollution, simplicity, and high efficiency. It only acts on a thin layer on the surface of the material and does not affect the internal structure of the material. It has a wide range of applications in surface treatment of polymer materials.

Plasma treatment of porous carbon materials

Plasma treatment, as a technique for surface modification of porous carbon materials, has received increasing attention. During plasma treatment, slow chemical reactions occur on the surface of porous carbon materials, generating some chemically active sites to improve the adsorption performance of carbon materials. But these chemical reactions only occur on the surface of carbon materials and do not change the overall properties of carbon materials. The surface of carbon materials can undergo oxidation, reduction, or no reaction by changing the plasma gas. According to the different plasma gases, corresponding alkaline or acidic functional groups will be generated on the surface of carbon materials. The semi quantitative analysis of surface acidic functional groups shows that the conditions of plasma treatment can affect the quality and quantity of surface functional groups. Plasma oxidation has a relatively small impact on the hydrophilicity of carbon materials. It reduces the surface area of carbon materials, increases the concentration of surface acidic functional groups, and thus improves their adsorption performance. Especially during the discharge process, the generation of weakly acidic functional groups plays a very important role in the adsorption of metal ions. In addition, plasma treatment with nitrogen can significantly alter the distribution of oxygen-containing functional groups on the surface of carbon materials, and also introduce more nitrogen atoms into the aromatic ring.

Compared to traditional modification methods, low-temperature plasma treatment technology is a dry reaction that does not use solvents, avoiding secondary pollution to the environment caused by waste and liquid generated in wet processes. It is an efficient and energy-saving green modification technology.