Hen Feather: A Remarkable Adsorbent for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 424

affected significantly by pH due to its dependence on the surface binding
site of the adsorbent and the ionization process of the dye molecule. In both
cases the adsorption was found to decrease almost linearly with the increase
in pH. It may be noted that for both dyes the maximum uptake of the dye
takes place at around pH 2.0, and beyond pH 4.0 the adsorption of the dye
was almost negligible. Thus, pH 2.0 was selected for all subsequent studies.
The higher adsorption of the dye at low pH may be due to increased
protonation by neutralization of the negative charge at the surface of the
adsorbents. This phenomenon helps in the preference of the dye for active
sites and facilitates the diffusion process in the working solution. While,
with an increase in alkaline conditions or pH, protonation is reduced and
electrostatic repulsive force becomes operative, which thereby retards dif-
fusion and adsorption.

11.4.2.2 Effect of Adsorbate Concentration

Different concentrations of the Azo dyes have been investigated with fixed
amount of adsorbents by increasing the temperature from 30 to 50 C. The
concentration study reveals that for both the Azo dyes an increase in con-
centration of the dye solution increases the extent of adsorption almost
linearly over Hen Feathers (Figures 11.2 and 11.3). The amount of dye

Figure 11.2 Effect of concentration of Amaranth (pH = 2.0) on adsorption over
0.01 g/25 mL Hen Feathers at different temperatures.