96
forming ternary surface–Lewis base–heavy metal complexation. The adsorbed
amount of particular heavy metal from metal cations and humate mixture solutions
is generally lower than the adsorbed from individual metal ion solutions. Competition
among metal cations reduces the maximum adsorption capacity. But the competition does not affect the adsorption characteristic (Hizal et al. 2016).
The studies showed that the metal ion, having high affinity for permanently negatively charged sites, such as Cd(II), is nearly not affected from competitive adsorption at low pH (Hızal et al. 2009). Hence, Hizal et al. explained the significant
enhancement adsorption of Cd(II) on montmorillonite, comparing the adsorption on
kaolinite, by 2:1 smectite-type structure of montmorillonite (Hizal et al. 2016).
On the other hand, montmorillonite has high affinity for cationic organic dyes.
The adsorption of cationic/basic organic dyes occurs as a result of electrostatic
interaction of positive charges on nitrogen atoms of five-membered cyclic rings
with permanent negatively charged surface of montmorillonite. Because the interaction between montmorillonite surface and cationic organic dye does not include
hydrogen ion exchange, the adsorbed amount of the basic organic dye is not effected
from deprotonation of surface occurred by increasing pH. Erçağ et al. declared that
while the maximum adsorption capacities of dyes on montmorillonite significantly
decreased in the presence of other basic dyes, the Langmurian character of adsorption was maintained as expected (Erçağ et al. 2015).
4.3 Polymer Composites of Montmorillonite
Montmorillonite is the basic and most commonly used clay in production of polymer nanocomposites due to high abundancy and high surface area allowing interfacial interaction between montmorillonite and polymer matrix in nanoscaled size,
besides reduced cost (Sani et al. 2017; Uddin 2018). Generally, two types of polymeric nanocomposites occur: (i) when clay nanoparticle is used, the intercalated
clays form by replacement of polymeric chains into the clay platelets, (ii) or clay
particles can randomly disperse all over polymeric structure, and in this situation,
clay exfoliation occurs.
Montmorillonite particles and polymer matrix interact with each other via
hydroxyl group and permanent negative charge of clay, and the higher interaction
between polymer and clay means stronger mechanical and thermal properties.
Copolymerization and grafting reactive groups or clay organophilization methods
are used in order to enable the interaction of clay and polymer matrix. Generally,
amino acids, alkylammonium, and other organic compounds are used as organophilization agents.
Polymeric composites of montmorillonite have been widely used for heavy metal
removal (Say et al. 2006; Anirudhan and Rijith 2012; Zauro and Vishalakshi 2018).
The composite of extracellular polymeric substances, which was extracted from
Pseudomonas putida X4, with montmorillonite showed high adsorption affinity for
Cu(II). It was suggested by the authors that inner-sphere Cu(II) adsorption onto
J. Hızal and M. Yılmazoğlu
forming ternary surface–Lewis base–heavy metal complexation. The adsorbed
amount of particular heavy metal from metal cations and humate mixture solutions
is generally lower than the adsorbed from individual metal ion solutions. Competition
among metal cations reduces the maximum adsorption capacity. But the competition does not affect the adsorption characteristic (Hizal et al. 2016).
The studies showed that the metal ion, having high affinity for permanently negatively charged sites, such as Cd(II), is nearly not affected from competitive adsorption at low pH (Hızal et al. 2009). Hence, Hizal et al. explained the significant
enhancement adsorption of Cd(II) on montmorillonite, comparing the adsorption on
kaolinite, by 2:1 smectite-type structure of montmorillonite (Hizal et al. 2016).
On the other hand, montmorillonite has high affinity for cationic organic dyes.
The adsorption of cationic/basic organic dyes occurs as a result of electrostatic
interaction of positive charges on nitrogen atoms of five-membered cyclic rings
with permanent negatively charged surface of montmorillonite. Because the interaction between montmorillonite surface and cationic organic dye does not include
hydrogen ion exchange, the adsorbed amount of the basic organic dye is not effected
from deprotonation of surface occurred by increasing pH. Erçağ et al. declared that
while the maximum adsorption capacities of dyes on montmorillonite significantly
decreased in the presence of other basic dyes, the Langmurian character of adsorption was maintained as expected (Erçağ et al. 2015).
4.3 Polymer Composites of Montmorillonite
Montmorillonite is the basic and most commonly used clay in production of polymer nanocomposites due to high abundancy and high surface area allowing interfacial interaction between montmorillonite and polymer matrix in nanoscaled size,
besides reduced cost (Sani et al. 2017; Uddin 2018). Generally, two types of polymeric nanocomposites occur: (i) when clay nanoparticle is used, the intercalated
clays form by replacement of polymeric chains into the clay platelets, (ii) or clay
particles can randomly disperse all over polymeric structure, and in this situation,
clay exfoliation occurs.
Montmorillonite particles and polymer matrix interact with each other via
hydroxyl group and permanent negative charge of clay, and the higher interaction
between polymer and clay means stronger mechanical and thermal properties.
Copolymerization and grafting reactive groups or clay organophilization methods
are used in order to enable the interaction of clay and polymer matrix. Generally,
amino acids, alkylammonium, and other organic compounds are used as organophilization agents.
Polymeric composites of montmorillonite have been widely used for heavy metal
removal (Say et al. 2006; Anirudhan and Rijith 2012; Zauro and Vishalakshi 2018).
The composite of extracellular polymeric substances, which was extracted from
Pseudomonas putida X4, with montmorillonite showed high adsorption affinity for
Cu(II). It was suggested by the authors that inner-sphere Cu(II) adsorption onto
J. Hızal and M. Yılmazoğlu