3.6. Effect of coexisting metal ions
The competitive adsorption of coexisting ions to the binding
sites is usually a severe problem when using conventional adsorbents
for removal of heavy metals. To investigate the effect of
coexisting ions, the uptake capacities of SH-mSi@Fe3O4 in different
water matrices with mixed heavy metal ions were tested.
Fig. 7 shows the competitive adsorption between Hg2+, Pb2+,
Ag+ and Cu2+ in different water matrices. The residue concentration
of Cu2+ was higher than that of other three metal ions because
of its weak affinity to thiol group. However, the removal efficiency
of Cu2+ was still more than 70% which was higher than that in natural
water matrices with single metal ion in the same experimental
condition. This suggested that coexisting heavy metals facilitated
the adsorption of Cu2+ to SH-mSi@Fe3O4. This phenomenon can be
explained as below: the organic moieties embedded in the pore
walls endue the adsorbent surface with hydrophobic characteristic.
While upon vigorous shaking, contact between the adsorbent
and the bulk solution occurred. The heavy metal ions with strong
affinity to –SH such as Hg2+ and Ag+ first bind with –SH groups near
the orifice of the pores and created a hydrophilic threshold leading
to more aqueous solution entering into the pores [45]. Therefore,
more –SH binding sites become accessible even to those ions with
weaker affinity. The other reason may be the inherent random networks
with broad pore size distribution of the organic–inorganic hybrid mesoporous materials, which lead to an increase in entropy
and thus benefit the diffusion of the metal ions [21].
3.6. Effect of coexisting metal ionsThe competitive adsorption of coexisting ions to the bindingsites is usually a severe problem when using conventional adsorbentsfor removal of heavy metals. To investigate the effect ofcoexisting ions, the uptake capacities of SH-mSi@Fe3O4 in differentwater matrices with mixed heavy metal ions were tested.Fig. 7 shows the competitive adsorption between Hg2+, Pb2+,Ag+ and Cu2+ in different water matrices. The residue concentrationof Cu2+ was higher than that of other three metal ions becauseof its weak affinity to thiol group. However, the removal efficiencyof Cu2+ was still more than 70% which was higher than that in naturalwater matrices with single metal ion in the same experimentalcondition. This suggested that coexisting heavy metals facilitatedthe adsorption of Cu2+ to SH-mSi@Fe3O4. This phenomenon can beexplained as below: the organic moieties embedded in the porewalls endue the adsorbent surface with hydrophobic characteristic.While upon vigorous shaking, contact between the adsorbentand the bulk solution occurred. The heavy metal ions with strongaffinity to –SH such as Hg2+ and Ag+ first bind with –SH groups nearthe orifice of the pores and created a hydrophilic threshold leadingto more aqueous solution entering into the pores [45]. Therefore,more –SH binding sites become accessible even to those ions withweaker affinity. The other reason may be the inherent random networkswith broad pore size distribution of the organic–inorganic hybrid mesoporous materials, which lead to an increase in entropyand thus benefit the diffusion of the metal ions [21].
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