Isotherms | Isotherm Equation | Uses and notes | Ref. |
One-Parameter Isotherm | |||
Henry’s |
| Simplest adsorption isotherm | |
Two-Parameter Isotherm | |||
Hill-Deboer | Math_9# | o Defines the case where there is mobile adsorption and lateral interaction and K2 is the energetic constant of the interaction between adsorbed molecules (kJ∙mol−1) | [47] |
Fowler- Guggenheim | Math_11# | o Side contact between adsorbed molecules and the heat of adsorption (w) varies linearly with loading. If attractive, w = positive, repulsive w = negative and w = 0 no interaction between absorbate. But applicable only if θ < 0.6 | [47] |
Langmuir |
| o Homogeneous binding sites (same affinities), alike sorption energies, and no interactions between adsorbed species. RL is separation aspect which decides whether the adsorption is un-favorable when its value is >1, linear (=1), favourable (0 < RL < 1), and irreversible (RL = 0) | [48] |
Freundlich |
| o Heterogonous surfaces(varied affinities), 1/n (adsorption intensity) that specifies the energy and the heterogeneity of the adsorbent sites (1/n < 1= Langmuir, 1/n > 1cooperative adsorption and generally, n in b/n 2 - 10 indicates good favorability of sorption | [49] |