Fig. 4, the removal rate of Cu2+ gradually decreases with the
increase of acidic conditions. The Chitosan-Fe-S-C and Chitosan-
Fe-S lose their ability to remove Cu2+ when the pH value is 2 and
for Chitosan-S-C the value is 3. This is because at low pH, the
amine, hydroxyl and other oxygen-containing groups tend to be
protonated, reducing the number of binding sites available for
Cu2+ uptake [32]. Besides, the positively charged adsorbent particles
exert an extra electrostatic repulsion to Cu2+, which prevents
the attachment between the adsorbent and the adsorbate. However,
the sharp decrease of adsorption at strong acidic solutions
illustrates more complex reasons and deserves more exploration.
Fig. 4, the removal rate of Cu2+ gradually decreases with theincrease of acidic conditions. The Chitosan-Fe-S-C and Chitosan-Fe-S lose their ability to remove Cu2+ when the pH value is 2 andfor Chitosan-S-C the value is 3. This is because at low pH, theamine, hydroxyl and other oxygen-containing groups tend to beprotonated, reducing the number of binding sites available forCu2+ uptake [32]. Besides, the positively charged adsorbent particlesexert an extra electrostatic repulsion to Cu2+, which preventsthe attachment between the adsorbent and the adsorbate. However,the sharp decrease of adsorption at strong acidic solutionsillustrates more complex reasons and deserves more exploration.
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