Plasma cleaning technology utilizes ionization to generate reactive particles, which, through the combination of high-energy particle physical bombardment and chemical reactions, break down the large molecule hydrocarbon pollutants adsorbed on the material surface and generate small molecule gaseous organic pollutants. Small molecules escape from the surface of the material, achieving the removal of organic pollutants.

In the face of residual organic pollutants on the surface of materials, plasma cleaning technology can generate large-area dispersed reactive particles to remove deep organic pollutants with complex morphologies. Plasma has the characteristics of high electron energy and low ion temperature, making it very suitable for chemical reactions with organic pollutants. After plasma cleaning, the object does not require drying treatment to avoid secondary pollution, and can be specifically removed for different substrate materials and pollutants. It can improve surface properties such as wetting and adhesion, and the cleaning product is environmentally friendly gas molecules with high cleaning efficiency, which can remove particles and organic pollutants.

Principle of plasma cleaning to remove residual organic matter on the surface of materials

In the low-pressure chamber of a plasma cleaning machine, activated oxygen atoms, nitrogen atoms, free electrons, and unreacted gases are excited by a radio frequency power supply to form a plasma. When these plasmas bombard the material surface, in addition to the physical process of impact, ionized oxygen gas and ionized oxygen atoms undergo chemical oxidation reactions with residual organic matter on the material surface, thereby achieving the removal of molecular level stains containing organic pollutants on the material surface

The plasma cleaning process can be divided into the following steps:

Plasma generation: By exciting gas molecules with an electric or electromagnetic field, plasma is formed. Gas plasma contains electrons, ions, and neutral particles.

Surface reaction: High energy particles in plasma undergo chemical reactions or physical bombardment with surface organic pollutants, causing the pollutants to dissociate and undergo oxidation reactions, forming volatile products.

Pollutant removal: The volatile products formed are discharged through a vacuum system to achieve cleaning effect.

In the process of plasma cleaning organic pollutants, oxygen plays a major role due to its high activity and strong oxidizing properties. During the plasma cleaning process, organic matter is transformed into carbon dioxide and water molecules, which are discharged from the material surface. The interaction between electrons and oxygen molecules produces excited oxygen, which is unstable. The excited oxygen atoms produced will combine with hydrogen atoms in organic matter and form hydroxyl groups. The remaining organic matter will continue to react with high-energy oxygen molecules, generating chemical single or double bond oxygen groups, changing the structural stability of organic matter, promoting organic matter decomposition, and ultimately carbon containing organic molecules will generate carbon dioxide and water under the action of high-energy oxygen atoms and oxygen free radicals, and be discharged from the surface, achieving the removal of organic matter. The reaction that occurred is shown in Figure 1 below:

Figure 1: Chemical reaction equation for plasma cleaning of organic matter

The plasma cleaning process involves many chemical reaction pathways, and Figure 2 shows the main reaction pathways through which organic molecules are destroyed by oxygen free radicals. Oxygen free radicals first capture hydrogen atoms from unsaturated carbon chains on organic molecules, and further oxidize carbon atoms to form aldehyde groups. At the same time, the hydrogen atom in the hexagonal carbon ring is also taken away by the oxygen atom. Compared with other chemical bonds, the C-H bond in organic molecules is the easiest to break. After losing three hydrogen atoms, the six membered carbon ring structure loses its conjugated stability and is disrupted to form a new carbon chain. Oxygen atoms obtain a hydrogen atom from organic compounds to form a hydroxyl group, which further oxidizes to form water molecules. In the end, all C-H bonds are broken, and carbon atoms are oxidized into carbonyl groups, which dissociate into CO and CO2 molecular clusters. These small molecule clusters have weak adsorption capacity on the surface of the material and are desorbed from the surface, collected by a vacuum system, and ultimately achieve the removal of organic residual pollutants on the surface of the material.

The reaction pathway of oxygen free radicals disrupting organic molecules