What Are The Physical Properties Of Adsorbents?

The good adsorption performance of the adsorbent is due to its dense pore structure. The physical properties related to the pores of the adsorbent are:
a. Pore volume (VP): The volume of micropores in the adsorbent is called pore volume, which is usually expressed as the volume of the adsorbent micropores per unit weight of the adsorbent (cm3/g). Pore volume is the effective volume of the adsorbent, It is a value calculated from the saturated adsorption capacity, which is the volume that the adsorbent can accommodate the adsorbate, so the larger the pore volume is, the better. The pore volume (Vk) of the adsorbent is not necessarily equal to the pore volume (VP). Only the micropores in the adsorbent have adsorption effect, so VP does not include coarse pores. Vk includes the volume of all holes, which is generally larger than VP.
b. Specific surface area: that is, the surface area per unit weight of the adsorbent. The common unit is m2/g. The surface area of adsorbent ranges from hundreds to more than a thousand square meters per gram. The surface area of the adsorbent is mainly the surface of the micropore wall, and the outer surface of the adsorbent is very small.
c. Pore size and pore size distribution: In the adsorbent, the shape of the pores is extremely irregular, and the pore sizes also vary. Pores with a diameter of several angstroms (A0) to tens of angstroms are called fine pores, and pores with a diameter of several hundred angstroms or more are called coarse pores. The more pores, the larger the pore volume and the larger the specific surface area, which is conducive to the adsorption of adsorbate. The function of coarse pores is to provide pathways for adsorbate molecules to enter the adsorbent. The relationship between coarse pores and fine pores is like streets and alleys. Foreign molecules can quickly reach the depths of the adsorbent through the coarse pores. Therefore, coarse holes should also occupy an appropriate proportion. The coarse and fine pores in adsorbents such as activated carbon and silica gel are formed during the manufacturing process. Zeolite molecular sieves form crystals with a diameter of several microns during synthesis, with only uniform fine pores, and coarse pores between crystals are formed during molding.