3.4. Adsorption isotherms
Adsorption isotherms is an important part of this study, as they
can provide the information about adsorption capacity as well as
the surface properties and affinity of the adsorbent, providing a
better understanding on how an adsorption system can be
improved [33]. The Cu2+ adsorption isotherm at pH 6.0 is shown
in Fig. 5. Here we introduce two common isotherm models to fit
the experimental data and the parameters are summarized in
Table 2. The first model is the Langmuir isotherm, which describes
the monolayer adsorption that happened on a solid phase where
all sites are equivalent and independent, while Freundlich isotherm
interprets adsorption occurred on heterogeneous surfaces
or surfaces supporting sites of varied affinities [34]. Their linear
forms are expressed as followed: