Question

For modelling protein adsorption, what adsorption model is better: Langmuir or Freundlich and why?

Answer 1

The Langmuir model is theoretical model which had many drawbacks such as:

1. The equationn is valid only under low pressure as it considers that the adsorbed gas behaves like an ideal gas.

2. For the Langmuir equation to exist it is based on an assumption that the solid surface is homogenous in nature i.e all the sites on the solid surface are equivalent in size and shape and have equal affinity towards the adsorbated molecules.

3. It is assumed that only a monomolecular layer is adsorbed at the maximum coverage. This means that there is no stackin  of adsorbed molecules.

The Freundlich model is the modification of Langmuir model to overcome the limitation of the model.The Freundlich isotherm is a multisite adsorption isotherm which involves the existence of heterogenous surfaces including the rough surfaces which will overcome the restriction of monomolecular layer by inducing stacking of adsorbate and eventually increasing the efficiency. Moreover the Freundlich equation is applicable at low as well as high pressure.

Therefore, it can be concluded that Freundlich isotherm is better than Langmuir.