Adsorption finds extensive applications both in research laboratory and in industry. A few applications are discussed below:
In preserving vacuum:
In Dewar flasks activated charcoal is placed between the walls of the flask so that any gas which enters into the annular space either due to glass imperfection or diffusion though glass is adsorbed.
In glass masks:
All gas masks are devices containing suitable adsorbent so that the poisonous gases present in the atmosphere are preferentially adsorbed and the air for breathing is purified.
In clarification of sugar:
Sugar is decolorized by treating sugar solution with charcoal powder. The latter adsorbs the undesirable colors present.
In paint industry:
The paint should not contain dissolved gases as otherwise the paint does not adhere well to the surface to be painted and thus will have a poor covering power. The dissolved gases are therefore, removed by suitable adsorbents during manufacture. Further, all surfaces are covered with layers of gaseous, liquid or solid films. These have to be removed before the paint is applied. This is done by suitable liquids which adsorbs these films. Such liquids are called wetting agents. The use of spirit as wetting agent in furniture painting is well known.
In chromatographic analysis:
The selective adsorbent of certain substances from a solution by a particular solid adsorbent has helped to develop technique for the separation of the components of the mixture. This technique is called chromatographic analysis. For example: in column chromatography a long and wide vertical tube is filled with a suitable adsorbent and the solution of the mixture poured from the top and then collected one by one from the bottom.
The action of certain solids as catalysts is best explained in terms of adsorption. The theory is called adsorption theory. According to this theory, the gaseous reactants are adsorbed on the surface of the solid catalyst. As a result, the concentration of the reactants increases on the surface and hence the rate of reaction increases. The theory is also able to explain the greater efficiency of the catalyst in the finely divided state, the action of catalyst promoters and poisons.
In adsorption indicators:
Various dyes which owe their use to adsorption have been introduced as indicators particularly in precipitation titrations. For example: KBr is easily titrated with AgNO3 using eosin as an indicator.
In softening of hard water:
The use of ion exchangers for softening of hard water is based upon the principle of competing adsorption just as in chromatography.
In removing moisture from air in the storage of delicate instruments:
Such instruments which may be harmed by contact with the moist air are kept out of contact with moisture using silica gel.