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Fig. 3. (a)
Point of zero charge of CRHC, (b) Effects of pH on Diamine Green B
(DG-B), Acid Black 24 (AB-24) and Congo Red (CR) adsorption onto CRHC.
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Fig. 4. The possible molecular mechanism of Diamine Green B (DG-B), Acid Black
24 (AB-24) and Congo Red (CR) adsorption onto CRHC
The electrolyte in the dye bath will block the coulomb
charge between the dye
and the adsorbent, resulting in a decrease in the electrostatic interaction force, which
will increase or decrease the adsorption capacity of the dye onto the adsorbent. Fig. 5a
shows the effect of ionic strength on the adsorption capacity of Diamine Green B
(DG-B), Acid Black 24 (AB-24) and Congo Red (CR). As can be seen from Fig. 5a,
the adsorption capacity of three dyes increased with the increasing of sodium chloride
concentration, indicating that electrostatic interaction
force is not the only force
between the dye and the adsorbent, Van der Waals force and hydrogen bonding force
may still exist. Moreover, the salting-out effect leads to a decrease in the solubility of
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the dye and a decrease in the hydrophilicity of the dye, which leads to an increase in
the adsorption of the dye by the hydrophobic effect [35]. So, the higher ionic strength
thus improves the dye adsorption capacity onto CRHC.
Fig. 5. Effect of ionic strength on the adsorption of Diamine Green B (DG-B), Acid
Black 24 (AB-24) and Congo Red (CR).
3.4 Reusability
From a practical point of view, the reusable experiments are of great significance
for the practical application of the adsorbents. The adsorption-desorption
cycle was
repeated five times and the results are shown in Fig.5b. The adsorption capacity was
decreased with the increasing of cycle times. However, the regenerated CRHC still
possessed a high adsorption capacity for Diamine Green B (DG-B), Acid Black 24
(AB-24) and Congo Red (CR), and the decrease in
adsorption capacity is not
significant. It is recommended that the CRHC has a good reusability and high
adsorption performance for dye removal.
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