The larger the specific surface area of activated carbon the greater the adsorption power must be

Activated carbon is a kind of carbon-containing substance with developed pore structure and huge internal surface area, which is mainly made from natural and man-made organic substances containing carbon elements, processed by a series of processes such as high-temperature thermal decomposition and activator activation. Activated carbon was first discovered and now it is used in every aspect of our life, from large-scale chemical industry, water conservancy project, medicinal color filtration, food project to our daily life to remove odor and formaldehyde, we can see the figure of activated carbon everywhere, and now Food grade activated carbon, Amino acid activated carbon, Medicinal activated carbon and other activated carbons are used in our daily life, Nowadays, Food grade activated carbon, Amino acid activated carbon, Medicinal activated carbon and other activated carbon play an important role in environmental protection, so how much do you know about activated carbon?

Generally speaking, the larger the specific surface area (BET) of activated carbon is, the larger the adsorption power is: but sometimes it is not necessarily so (BET is used as a substitute for specific surface area in the following) BET is a widely used parameter to measure the total surface area of activated carbon by adsorption method of nitrogen or butane. It is logical that the larger the BET, the greater the adsorption capacity. However, this concept has limitations in practical application because the pores of activated carbon are differentiated between macropores, mesopores and micropores, and sometimes only some of the pores are suitable for the adsorbents of a certain size, so the total surface area and pore volume data (e.g., the total surface area is usually about 450~1800 m'/g, and the pore volume is about 0.7~1.8 ml/g) can't be used to evaluate the validity of this adsorption of the activated carbon. The majority of the total surface area belongs to micropores, with typical figures of 1000 m'/g for micropores, 10-100 m'/g for mesopores, and 1 m'/g for macropores.

In liquid phase applications, the adsorption of organic matter usually increases with molecular weight (molecular size). Until the molecule is so large that it cannot enter the pore. Many high molecular weight organics, such as colorants or humus, are excluded from the micropores, which requires the application of activated carbons with many mesopores, whereas microporous carbons with a high total surface area are not useful. The ideal activated carbon is one with a large number of pores that are slightly larger than the adsorbent molecules. If the pores are too small, the adsorbent will not be able to enter; if the pores are too large, the surface area per unit volume will be reduced. It is best to encounter molecules with molecular weights between 300 and 100,000, which corresponds to pore sizes between 0.5 and 4 nm, with darker pigments often being larger molecules.

In gas phase applications, small molecules are adsorbed into the micropores. This is where the concept of total surface area comes into play. Examples are the recovery of solvents from the air or the prevention of gasoline fugitive emissions from automobiles. As for the adsorption of metal complexes by activated carbon, which involves the formation of chemical bonds, the larger the BET, the better. For example, in the case of adsorption of gold cyanide from solution, the activated carbon of the water vapor activation method has a high affinity for gold cyanide, whereas the activated carbon of the chemical activation method has practically no affinity even if it is porous.