Region 1 is usually observed in the low adsorbate concentrations meaning that adsorption increases linearly.
Region 2 could be interpreted by the Temkin or Langmuir isotherms, including only monolayer surface aggregate formation. At high concentrations the third region was observed due to molecular association on the surface. With respect to the characteristics of phosphate, bilayer adsorption does not happen on the surface of LDHs.