Adsorbent is a solid substance that can effectively adsorb certain components from gases or liquids. Adsorbent generally has the following characteristics: large specific surface, suitable pore structure and surface structure; strong adsorption capacity for adsorbent; generally do not have a chemical reaction with the adsorbent and the medium; easy to manufacture, easy to regenerate; and good mechanical strength. Adsorbents can be classified according to pore size, particle shape, chemical composition, surface polarity, etc., such as coarse and fine pore adsorbents, powder, granular, strip adsorbents, carbonaceous and oxidative adsorbents, polar and non-polar adsorbents.

Commonly used adsorbents are various activated carbon adsorbents made of carbonaceous materials and metal and non-metal oxide adsorbents (such as silica gel, alumina, molecular sieve, natural clay, etc.).

The main indicators of adsorbent are: adsorption capacity of different gases and impurities, abrasion rate, bulk density, specific surface area, crushing strength and so on. They are used for filtering out poisonous gases, refining petroleum and vegetable oils to prevent viruses and moulds, recovering petrol from natural gas and decolourising sugar and other coloured substances.

Industry commonly used adsorbents are: silica gel, activated alumina, activated carbon, molecular sieve, etc., in addition to selective adsorption for a certain component of the adsorbent material developed. The success of gas adsorption and separation depends greatly on the performance of the adsorbent, so the selection of adsorbent is an important issue to determine the adsorption operation.