The following is a detailed introduction to the pore size and adsorption principle of activated carbon:
First, the pore size of activated carbon
Activated carbon is a kind of porous carbonaceous material with highly developed pore structure. These pores can be divided into the following categories according to their radius:
Micropore: radius less than 2nm (also said to be less than 150nm). The surface area of activated carbon is mainly provided by micropores, which allows the activated carbon to have a huge specific surface area, so that it is easy to achieve the purpose of absorbing and collecting impurities.
Mesopore (or transition pore) : radius between 250nm (also said to be 15020000nm). Mesopores play an important role as channels in the adsorption process of activated carbon, which is conducive to the diffusion and adsorption of gas molecules.
Large hole: radius greater than 50nm (also said to be greater than 20000nm). Macropores mainly serve as channels for gas molecules to enter the interior of activated carbon, making it easier for gas molecules to access micropores and mesopores.
The pore size distribution of activated carbon has an important effect on its adsorption performance. Different pore sizes are able to adsorb molecules of different sizes; therefore, efficient adsorption of specific molecules can be achieved by adjusting the pore size distribution of activated carbon.
Two, the adsorption principle of activated carbon
The adsorption principle of activated carbon is mainly divided into two kinds of physical adsorption and chemical adsorption:
Physical adsorption:
Principle: Physical adsorption is based on the gravitational interaction between molecules. The large number of molecules on the wall of the activated carbon pore can generate a strong gravitational force to attract impurities in the medium into the pore diameter. This adsorption is not selective, as long as the adsorbed impurity molecular diameter is smaller than the pore size of activated carbon, it is possible to be adsorbed.
Characteristics: Physical adsorption is reversible, when the external conditions (such as temperature, pressure) change, the adsorbed molecules may be desorbed.
Chemical adsorption:
Principle: In addition to physical adsorption, chemical reactions also often occur on the surface of activated carbon. Activated carbon not only contains carbon, but also contains a small amount of chemically combined, functional group forms of oxygen and hydrogen on its surface, such as carboxyl, hydroxyl, phenols, lipids, quinones, ethers, etc. The oxides or complexes on these surfaces can chemically react with the adsorbed substances, thereby combining with the adsorbed substances and collecting to the surface of activated carbon.
Characteristics: Chemisorption is selective, usually for some specific chemical substances or functional groups of adsorption. In addition, chemisorption is usually irreversible, and a chemical bond is formed between the adsorbed material and the activated carbon, which is difficult to desorb by simple physical methods.
In practice, the adsorption process of activated carbon is often the result of physical adsorption and chemical adsorption. Efficient adsorption and removal of specific contaminants can be achieved by rational pore size design and surface chemical modification.