where qm and KL are constants related to the capacity and energy of
adsorption process, while Kf is a measure of adsorption capacity and
n stands for the heterogeneity.
From Table 2, it can be found that the Freundlich model shows
low correlation coefficients and thus is considered incompetent to
describe the adsorption behaviors. Whereas the Langmuir model
gives a satisfactory fitting with high correlation coefficients more
than 0.999, which means a monolayer adsorption with chemical
nature happened between the adsorbents and Cu2+. It is worth
noted that in comparison with Cu2+ adsorption capacities of various
adsorbents reported in the literature (Table 3), the calculated
qm of Chitosan-Fe-S-C is up to 413.2 mg/g, and is much larger than
Chitosan-Fe-S (303.0 mg/g), Chitosan-S-C (270.3 mg/g) as well as