Theory for adsorption from solution

Liquid phase adsorption methods depend on the establishment of an equilibrium between adsorbed and unadsorbed solute molecules. Adsorption of solute on to the surface of a solid continues until it reaches a saturation point giving a clear plateau in the isotherm. As the isotherm usuaUy tends towards a limiting value, the limit has often been taken to correspond to the covering of the surface with a monolayer of solute. The equation derived for monolayer coverage is  

For K much greater than unity and for low concentrations of component me. this reduces to Langmuir s equation. Alternatively, the Langmuir equation, replacing p vnth concentration of solution c. has been used to determine the limiting value [19,20]. 

Thus a plot of dx versus c should give a straight line of slope Mxm and intercept MKXfn. 

Three things are required for the determination of specific surface, namely  

The point on the isotherm where a complete monolayer has been 

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The potential theory introduced by Polanyi for adsorption of gases and vapors has been discussed in detail elsewhere in this book. For a single gas or vapor, the adsorption potential s has been defined as equal to the work done in bringing one mole of the adsorbate from infinity to a specified distance from the surface. Polanyi modified the theory for adsorption from solutions of sparingly soluble solutes. The sigifificance of this approach is that it is not essential to postulate a thickness for the adsorbed layer. This modified equation can be written as... 

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