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G. Pandey et al.
on HNT in order to impart mussel-inspired properties to the nanotube to develop
a novel core@double shelled structure, consisting of HNT modified with PDA and
KH550, which is an organosilane that attaches amino groups on the surface, along
with magnetite nanoparticles (Fe 3 O 4 ). This core@double shell structure showed a
high adsorption capacity by removing 714.23 mg/g of Methylene Blue (MB) from
aqueous solutions at 318.15 K. Such a high adsorption capacity was contributed by the
Fe 3 O 4 nanoparticles as well, which enhanced the surface area of the structure. These
nanoparticles also imparted magnetic property to the structure, thereby ensuring their
easy separation from aqueous solutions. This structure also showed high reusability
even after 5 cycles of adsorption and desorption of MB (Wan et al. 2017). Another
study had reported the use of chitosan and HNT based hydrogel beads for the removal
of MB and Malachite Green (MG). The incorporation of HNT into the beads formed
a rough surface which in turn increased the number of adsorption sites. This along
with the abundance of amine groups contributed by chitosan allowed adsorption of
the dyes up to 92% for MB and up to 97% for MG ( Peng et al. 2015).
In addition to adsorption, dyes have also been removed through photocatalytic
degradation of HNT based nanocomposites. A study had reported photodegradation
of Aniline by HNT that had been chemically activated by incorporating titanium
dioxide (TiO 2 ). The chemical activation allowed the reduction of amorphous part of
HNT, and an upsurge in the amount of Halloysite and Kaolinite. This catalyst showed
a reaction rate constant of up to 0.431 ± 0.003 for concentrations of aniline kept at
0.04 mg/cm
3 (Szczepanik and Słomkiewicz 2016).
3.1.2 Heavy Metal Remediation
The chief reasons for pollution caused by heavy metals are industrial activities,
agricultural runoffs, and traffic emission. Heavy metals are non-biodegradable and
are present in the environment for longer periods of time. The persistent exposure
of heavy metals may cause adverse effects on living beings. In recent years, the use
of HNT-based nanocomposites for the removal of heavy metals such as chromium
Cr(VI)) and lead (Pb(II)) has gained attention. The different ways of removal of
heavy metals have been through adsorption, filtration, SPE and reduction (Gidlow
2015; Mason et al. 2014).
In another work, quaternary ammonium ions (NH 4
+ ) were grafted onto HNT’s
surface through treatment by Hexadecyltrimethylammonium bromide (HDTMA),
which is a surfactant for the removal of Cr (VI) ions. The adsorbent showed high
adsorption capacity by removing 90% of chromates within 5 min. Factors such as
ionic strength and pH deemed to be a heavy influence on the adsorption by HNT,
which was confirmed by the decrease observed in the rate of adsorption upon increasing the ionic strength and pH (Jinhua et al. 2010). The negatively charged chromate
ions get attracted to the positively charged surface of HNT, thus resulting in enhanced
adsorption of the metal ions. Apart from NH 4
+ ions, amine groups have been grafted
on HNT’s surface though treatment by Polyethyleneimine (PEI) for the removal of Cr
(VI). These nanocomposites showed excellent adsorption rate, which was deemed to
G. Pandey et al.
on HNT in order to impart mussel-inspired properties to the nanotube to develop
a novel core@double shelled structure, consisting of HNT modified with PDA and
KH550, which is an organosilane that attaches amino groups on the surface, along
with magnetite nanoparticles (Fe 3 O 4 ). This core@double shell structure showed a
high adsorption capacity by removing 714.23 mg/g of Methylene Blue (MB) from
aqueous solutions at 318.15 K. Such a high adsorption capacity was contributed by the
Fe 3 O 4 nanoparticles as well, which enhanced the surface area of the structure. These
nanoparticles also imparted magnetic property to the structure, thereby ensuring their
easy separation from aqueous solutions. This structure also showed high reusability
even after 5 cycles of adsorption and desorption of MB (Wan et al. 2017). Another
study had reported the use of chitosan and HNT based hydrogel beads for the removal
of MB and Malachite Green (MG). The incorporation of HNT into the beads formed
a rough surface which in turn increased the number of adsorption sites. This along
with the abundance of amine groups contributed by chitosan allowed adsorption of
the dyes up to 92% for MB and up to 97% for MG ( Peng et al. 2015).
In addition to adsorption, dyes have also been removed through photocatalytic
degradation of HNT based nanocomposites. A study had reported photodegradation
of Aniline by HNT that had been chemically activated by incorporating titanium
dioxide (TiO 2 ). The chemical activation allowed the reduction of amorphous part of
HNT, and an upsurge in the amount of Halloysite and Kaolinite. This catalyst showed
a reaction rate constant of up to 0.431 ± 0.003 for concentrations of aniline kept at
0.04 mg/cm
3 (Szczepanik and Słomkiewicz 2016).
3.1.2 Heavy Metal Remediation
The chief reasons for pollution caused by heavy metals are industrial activities,
agricultural runoffs, and traffic emission. Heavy metals are non-biodegradable and
are present in the environment for longer periods of time. The persistent exposure
of heavy metals may cause adverse effects on living beings. In recent years, the use
of HNT-based nanocomposites for the removal of heavy metals such as chromium
Cr(VI)) and lead (Pb(II)) has gained attention. The different ways of removal of
heavy metals have been through adsorption, filtration, SPE and reduction (Gidlow
2015; Mason et al. 2014).
In another work, quaternary ammonium ions (NH 4
+ ) were grafted onto HNT’s
surface through treatment by Hexadecyltrimethylammonium bromide (HDTMA),
which is a surfactant for the removal of Cr (VI) ions. The adsorbent showed high
adsorption capacity by removing 90% of chromates within 5 min. Factors such as
ionic strength and pH deemed to be a heavy influence on the adsorption by HNT,
which was confirmed by the decrease observed in the rate of adsorption upon increasing the ionic strength and pH (Jinhua et al. 2010). The negatively charged chromate
ions get attracted to the positively charged surface of HNT, thus resulting in enhanced
adsorption of the metal ions. Apart from NH 4
+ ions, amine groups have been grafted
on HNT’s surface though treatment by Polyethyleneimine (PEI) for the removal of Cr
(VI). These nanocomposites showed excellent adsorption rate, which was deemed to