Major types of adsorbents in use are: activated alumina, silica gel, activated carbon, carbon molecular sieve, zeolite molecular sieve and polymeric adsorbents.
Most adsorbents are manufactured (such as activated carbons), but a few, such as some zeolites, occur naturally. Each material has its own characteristics such as porosity, pore structure and nature of its adsorbing surfaces.
Pore sizes in adsorbents may be distributed throughout the solid. Pore sizes are classified generally into 3 ranges: macro pores have "diameters" in excess of 50 nm, meso pores (also known as transitional pores) have "diameters" in the range 2 - 50 nm, and micro pores have "diameters" which are smaller than 2 nm.
Many adsorbent materials, such as activated carbons, silica gels and activated alumina, are amorphous and contain complex networks of inter-connected micro pores, meso pores and macro pores. In contrast, pores in zeolite adsorbents have precise dimensions.
Typical applications of commercial adsorbents:
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