Absorption vs Adsorption
Sorption is the process where one substance takes up or holds another substance. This can be a chemical phenomenon, since there are chemical bonds involved in taking up and holding two substances. Sorption can be advantageous in some occasions, but it can be disadvantageous too. For example, ground level water contamination is reduced due to sorption. When contaminants are added to the soil, they are attracted to soil; thus, their movement to underground soil layers is slowed down, which will result in low contamination. As sorption reactions occur quickly, it takes less time. Sorption can be of two types, absorption and adsorption. The two types are described below.
In absorbance, one substance is taken up into the physical structure of the other substance. The substance, which is absorbing into another substance, is known as the “absorbate.” The substance which absorbs the absorbate is known as the “absorbent.” For example, if an organic molecule goes inside a solid particle (soil particle), then the organic molecule is the absorbate, and the soil particle is the absorbent. Absorbent can be a gas, liquid or a solid, whereas the absorbate can be an atom, ion or a molecule. Normally, absorbate and the absorbent are in two different phases. Absorption property of chemicals is used in various occasions. For example, this is the principle behind liquid-liquid extraction. Here, a solute can be extracted from one liquid to another liquid, because the solute is more absorbed to one liquid than the other when they are in the same container. In order to absorb, the absorbent should have a porous structure or enough space in which the absorbate can be accommodated. The absorbate molecule should also be of a suitable size, to go inside the absorbent structure. Further, there should be attractive forces between two to facilitate the absorption process. Same as masses are absorbed; energy also can be absorbed into substances. This is the foundation behind spectrophotometry. There, light is absorbed by the atoms, molecules or another species.
In adsorption, a substance or energy is attracted to a surface of another matter. The attracted substance is called an “adsorbate”, and the surface is called the “adsorbent.” Attraction between organic materials and activated charcoal is an example of adsorption. Organic material is the adsorbate in this occasion, and the adsorbent is activated charcoal. Another example of adsorption is attracting protein onto biomaterial. Adsorption can be of three types, physical adsorption, chemisorption, and electrostatic adsorption. In physical adsorption, weak van der Waals forces are the attracting forces. In chemisorption, the attraction is taking place via a chemical reaction between the adsorbent and the adsorbate. As the name suggests, in electrostatic adsorption, electrostatic interactions are forming between ions and the surfaces.
What is the difference between Absorption and Adsorption?
• In absorption, one substance (matter or energy) is taken into another substance. But in adsorption only the surface level interactions are taking place.
• The two substances involved in absorption are known as the absorbate and the absorbent; whereas, in adsorption, two substances are known as adsorbate and the adsorbent.