The Main Influencing Factor in Activated Carbon Water Treatment Is the Nature of the Adsorbate (Solute or Pollutant)

The adsorption capacity of the same type of activated carbon varies greatly for different pollutants.

(I) Solubility

The solubility of substances within the same family decreases with increasing chain length, while the adsorption capacity increases with increasing homologue number or molecular weight. Lower solubility leads to easier adsorption.

For example, activated carbon adsorbs organic acids from water in the following order: formic acid – acetic acid – propionic acid – butyric acid.

(II) Molecular Structure

The size and chemical structure of the adsorbate molecules also significantly affect adsorption. Because the adsorption rate is influenced by internal diffusion, the size of the adsorbate (solute) molecules is proportional to the pore size of the activated carbon, which is most conducive to adsorption. Among homologues, larger molecules are more easily adsorbed than smaller molecules. Unsaturated organic compounds are more easily adsorbed than saturated ones. Aromatic organic compounds are more easily adsorbed than aliphatic organic compounds.

(III) Polarity

Activated carbon can be considered a non-polar adsorbent, with a greater adsorption capacity for non-polar substances in water than for polar substances. (iv) Adsorption Capacity (Solute)

When the concentration of the adsorbate is within a certain range, the adsorption capacity increases with increasing concentration. Therefore, changes in the concentration of the adsorbate (solute) also affect the adsorption capacity of activated carbon for that adsorbate (solute).