Adsorption is a process, similar to absorption, by which a substance in a gas or liquid becomes attached to a solid. The substance can be a pollutant, called an adsorbate, which is attracted to the surface of a special solid. Adsorption occurs naturally, but industrialists have perfected adsorption methods to clean up hazardous waste or purify drinking water.
Tiny chemical particles suspended in another phase of matter, meaning in the air as a gas or in water as a liquid, are sometimes considered contaminants. These tiny particles can be separated from that phase, called the adsorbent, to enter a different phase. A material of another phase, like the solid carbon, preferentially targets these particles and bonds the adsorbate to its surface. The remaining air or liquid has been purified. This differs from absorption where the particles never change phase, but enter pores of the solid along with the accompanying air or water.
Natural or organic methods of adsorption take place all the time. For example, the ocean adsorbs carbon dioxide in the atmosphere, which effects climate and atmospheric temperature. Early humans observed that if they charred a piece of bone all the way through, they could put the bone in food mixtures, like sugar water, and it would collect polluting particles that weren't edible, thereby purifying the food. Particles colored in our visible spectrum, as well as those with strong odors, are easiest to adsorb.
It's important to harness the power of adsorption in battling modern chemical hazards. Some solids are ideal for adsorption. They have a lot of surface area for their volume because they are pockmarked with micropores. Industrial and commercial uses for adsorption filters vary. For example, carbon makes cold drinking water taste better. A carbon filter can be heated to clean the surface of adsorbates and reused. Activated alumina removes harmful chemicals like fluoride and arsenic from liquids. Synthetic resins can clean up highly hazardous spills, such as nerve gas, in areas that might have high temperatures, like near explosives.