Adsorption principle of silica gel.

Silica gel is a highly porous substance – meaning that countless pores are distributed across its entire surface.

Formed into small spheres, it creates a granulate where just 1g offers a surface area nearly the size of three tennis courts. It is primarily used to remove unwanted, high levels of humidity from the air.

Water molecules are actively held on the surface through physical interactions, all without the spheres changing their shape.

Adsorption principle of molecular sieves.

A molecular sieve consists of zeolite, a crystal permeated by tiny pores. Unlike those in silica gel, these pores are all exactly the same size, much like the holes in a sieve.

The unique feature: only molecules small enough can pass through the pores. Water molecules, for instance, are tiny and slip inside, while larger molecules remain on the outside.

Molecular sieves come in various types with different pore sizes, allowing for the targeted adsorption of specific substances.

Once inside, the molecules are held in place by physical forces, all while the beads themselves retain their original shape. Molecules with a polar charge are particularly likely to be captured in this way.

Adsorption principle of activated alumina.

Activated alumina is a highly robust, porous material. Its interior is permeated by countless tiny channels and pores, somewhat like a sponge, though much firmer.

On the internal surface of these pores, there are so-called hydroxyl groups (-OH). These can form bonds with specific ions and polar molecules, effectively "holding" them in place.

In this way, the material uses physical forces to bind various substances to its surface, all while the spheres themselves retain their original shape.

Examples of such substances include water molecules, fluoride ions, and hydrogen sulfide.