Table 3.

Descriptions of isotherm models

Isotherm model	Description
Langmuir [101]	Considers adsorption as a continuous bombardment of molecules onto a surface with their corresponding desorption or evaporation from the surface with no aggregation at the surface
Freundlich [102]	Not limited to monolayer formation and can be applied to formation of multilayers. Adsorption heat does not need to be uniformly distributed on the heterogeneous surface of the isotherm
Redlich–Peterson [103]	Can be applied to heterogenous and homogenous systems as it features both Freundlich and Langmuir models
SIPS or Langmuir–Freundlich (LF) [104]	Combines Langmuir and Freundlich isotherm models to predict the heterogeneity of the system- it localizes the adsorption without adsorbate–adsorbate interaction
Toth [105]	Is a modified version of Langmuir model described for heterogenous system considering both low and high concentration of adsorbate (assuming most sites having lower energy)
Temkin [106]	Considers the interaction between the adsorbent and the adsorbate by ignoring the extremely large and low concentration values- it assumes that adsorption heat of all molecules in the layer declines linearly rather than logarithmically
Dubinin-Radushkevich (DR) [107]	Associates the mechanism of adsorption to the distribution of Gaussian energy onto the heterogeneous surfaces