4. Conclusions
Activated carbon with a large surface area (820 m2/g) and
a modest surface charge density (0.54 group/nm2) was shown
to be effective in removing anionic reactive dyes from solution.
At pH 7.0 and 298 K, the maximum adsorption values
as described using the Langmuir equilibrium isotherm model
were 0.27, 0.24, and 0.11 mmol/g for C.I. Reactive Blue 2,
C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes, respectively.
The formation of a complete monolayer was not
achieved and the fraction of surface coverage was calculated
as 0.45, 0.42, and 0.22 for C.I. Reactive Blue 2, C.I. Reactive
Yellow 2 and C.I. Reactive Red 4 dyes, respectively.
The adsorption capacity of the dyes on activated carbon increased
in acidic solutions, but decreased in basic solutions.
The adsorption capacity of the dyes increased when increasing
the ionic strength of solution, this was attributed to dye
aggregation in solution. Adsorption of reactive dyes was
found to be spontaneous at the temperatures under investigation
(298e328 K) as indicated from the negative values of
free energy (DGads).