98
model (Irani et al. 2014). Kinetic and thermodynamic properties of Co(II) adsorption onto chitosan–montmorillonite composite were searched by Wang et al. (Wang
et al. 2014). It was mentioned that the maximum Co(II) adsorption was obtained for
chitosan–montmorillonite composite having 1:4 chitosan–montmorillonite ratio,
and it was concluded that the multilayer Co(II) adsorption onto composite is endothermic chemisorption (Wang et al. 2014).
Vieira et al. used the chitosan/acid-activated montmorillonite composite hydrogel for the removal of Pb(II) and Ni(II) ions by adsorption process (Vieira et al.
2018). The chitosan hydrogel was synthesized by using acrylic acid and N,N′methylenebisacrylamide. The presence of montmorillonite did not significantly
change the adsorption capacities of chitosan hydrogel. This situation was attributed
to the increase in hydrogen bonds and cross-linking points after incorporating montmorillonite (Vieira et al. 2018).
4.4 Metal Oxide Composites of Montmorillonite
Many types of iron and iron oxides such as Fe 2 O 3 or Fe 3 O 4 have been widely used
as a part of montmorillonite composite (Wang et al. 2010; Hua et al. 2012; Egirani
et al. 2019). Zn(II), Cd(II), and Ni(II) adsorption onto bentonite and magnetic iron
oxide–bentonite composite was studied by Mockovčiaková et al. The studied composites were obtained at different bentonite–iron oxide ratios and at different temperatures. As a result, obtained composites had higher specific surface area and pore
volume comparing those of natural bentonite. It was determined that the zeta potential of composite suspension was negative at all pHs. Heavy metal adsorptions did
not significantly change with respect to adsorption onto natural bentonite. Zn(II)
and Cd(II) adsorptions showed Langmuir character, while the Freundlich model
better described the Ni(II) adsorption on bentonite–iron oxide composites better
(Mockovčiaková et al. 2010).
The composite, obtained by N-[3-(trimethoxysilyl)propyl]ethylenediaminetriacetic acid sodium salt addition after mesoporous silica and ferric oxide–montmorillonite composite was formed, was used to adsorb Cu(II), Ni(II), Cd(II), Zn(II),
Fe(III), and Pb(IV) ions. Because N-[3-(trimethoxysilyl)propyl]ethylenediaminetriacetic acid is a EDTA-like chelating agent for heavy metals, adsorption capacities
for all metal ions enhanced. Although clay minerals cannot adsorb unhydrolyzed
metal cations from acidic solution because of positive charge, chelating agent
grafted composite retained the heavy metals at low pH. The authors declared that
the fabricated composite was successfully used to uptake heavy metals from individual and mixture solutions and showed preferable adsorption for Fe(III) cations
(Addy et al. 2012).
Another iron source for formation of composite is nanoscale zero-valent iron.
The nanoscale zero-valent iron has been widely used for environmental remediation due to having many advantages such as controllable particle size and abundant surface sites (Zou et al. 2016) It is known that the composite shows high
J. Hızal and M. Yılmazoğlu
model (Irani et al. 2014). Kinetic and thermodynamic properties of Co(II) adsorption onto chitosan–montmorillonite composite were searched by Wang et al. (Wang
et al. 2014). It was mentioned that the maximum Co(II) adsorption was obtained for
chitosan–montmorillonite composite having 1:4 chitosan–montmorillonite ratio,
and it was concluded that the multilayer Co(II) adsorption onto composite is endothermic chemisorption (Wang et al. 2014).
Vieira et al. used the chitosan/acid-activated montmorillonite composite hydrogel for the removal of Pb(II) and Ni(II) ions by adsorption process (Vieira et al.
2018). The chitosan hydrogel was synthesized by using acrylic acid and N,N′methylenebisacrylamide. The presence of montmorillonite did not significantly
change the adsorption capacities of chitosan hydrogel. This situation was attributed
to the increase in hydrogen bonds and cross-linking points after incorporating montmorillonite (Vieira et al. 2018).
4.4 Metal Oxide Composites of Montmorillonite
Many types of iron and iron oxides such as Fe 2 O 3 or Fe 3 O 4 have been widely used
as a part of montmorillonite composite (Wang et al. 2010; Hua et al. 2012; Egirani
et al. 2019). Zn(II), Cd(II), and Ni(II) adsorption onto bentonite and magnetic iron
oxide–bentonite composite was studied by Mockovčiaková et al. The studied composites were obtained at different bentonite–iron oxide ratios and at different temperatures. As a result, obtained composites had higher specific surface area and pore
volume comparing those of natural bentonite. It was determined that the zeta potential of composite suspension was negative at all pHs. Heavy metal adsorptions did
not significantly change with respect to adsorption onto natural bentonite. Zn(II)
and Cd(II) adsorptions showed Langmuir character, while the Freundlich model
better described the Ni(II) adsorption on bentonite–iron oxide composites better
(Mockovčiaková et al. 2010).
The composite, obtained by N-[3-(trimethoxysilyl)propyl]ethylenediaminetriacetic acid sodium salt addition after mesoporous silica and ferric oxide–montmorillonite composite was formed, was used to adsorb Cu(II), Ni(II), Cd(II), Zn(II),
Fe(III), and Pb(IV) ions. Because N-[3-(trimethoxysilyl)propyl]ethylenediaminetriacetic acid is a EDTA-like chelating agent for heavy metals, adsorption capacities
for all metal ions enhanced. Although clay minerals cannot adsorb unhydrolyzed
metal cations from acidic solution because of positive charge, chelating agent
grafted composite retained the heavy metals at low pH. The authors declared that
the fabricated composite was successfully used to uptake heavy metals from individual and mixture solutions and showed preferable adsorption for Fe(III) cations
(Addy et al. 2012).
Another iron source for formation of composite is nanoscale zero-valent iron.
The nanoscale zero-valent iron has been widely used for environmental remediation due to having many advantages such as controllable particle size and abundant surface sites (Zou et al. 2016) It is known that the composite shows high
J. Hızal and M. Yılmazoğlu