130
G. Pandey et al.
the different energy and environmental applications of HNT are discussed, while
giving special emphasis on the effect, the guest molecules have on the nanotube and
thereby on its applicability. Table 1 depicts the different guest molecules, which are
immobilized on HNTs for different kinds of energy and environmental applications.
3.1 Environmental Applications
Surplus pollutants present in water bodies require immediate treatment to prevent
hazardous effects on nearby flora and fauna. In recent years, HNT has garnered
worldwide attention through its use as a unique nano-support for the remediation
of environmental pollutants. Their non-toxic and biocompatible nature further aides
their applicability in such fields. Over the years, HNT have been utilized for the
remediation of dyes such as auramine yellow and orange (Khatri et al. 2016b), heavy
metals, drugs, pesticides and even nanoparticles such as silver (AgNP). HNT immobilized with various guest molecules have also been employed for such purposes. This
section highlights the utilization of HNT immobilized with various guest molecules
for environmental remediation.
3.1.1 Dye Remediation
Contamination of water bodies with dyes largely results from the runoff of synthetic
dyes from industries of textile, cosmetics, plastic making or other manufacturing
units. When the effluent discharge from such industries is not monitored properly,
it results in release of copious amounts of toxic dyes, which pose a serious risk
to life in the waterbody and its environment. Some of the dye components have
also proven to be mutagenic or carcinogenic, and therefore, their remediation is
highly essential. Over the years, waste water treatment methods such as primary
and secondary treatments which involve techniques such as flocculation (Lee et al.
2014), catalytic degradation (Pirilä et al. 2015), and filtration (Li et al. 2017a, 2017b)
have served the purpose. However, such treatments are economically difficult to
implement, and come with additional difficulties such as high-operational cost and
energy requirements.
HNT due to their tubular structure, biocompatibility and non-toxic nature along
with high physical and chemical stability are exceedingly suitable to be used either as
adsorbents in order to remove harmful dyes, or as support for immobilizing various
guest molecules to impart catalytic properties to the nanotube. The guest molecules
can also be selected in such a way that they enhance the adsorption property of
the HNT as well. When HNT is used as an adsorbent, factors such as dosage of
the adsorbent, pH and temperature of the solution, and contact time have to be
contemplated (Anastopoulos et al. 2018). Based on such factors, the types of guest
molecules that can be immobilized on the surface of HNT can be considered.
G. Pandey et al.
the different energy and environmental applications of HNT are discussed, while
giving special emphasis on the effect, the guest molecules have on the nanotube and
thereby on its applicability. Table 1 depicts the different guest molecules, which are
immobilized on HNTs for different kinds of energy and environmental applications.
3.1 Environmental Applications
Surplus pollutants present in water bodies require immediate treatment to prevent
hazardous effects on nearby flora and fauna. In recent years, HNT has garnered
worldwide attention through its use as a unique nano-support for the remediation
of environmental pollutants. Their non-toxic and biocompatible nature further aides
their applicability in such fields. Over the years, HNT have been utilized for the
remediation of dyes such as auramine yellow and orange (Khatri et al. 2016b), heavy
metals, drugs, pesticides and even nanoparticles such as silver (AgNP). HNT immobilized with various guest molecules have also been employed for such purposes. This
section highlights the utilization of HNT immobilized with various guest molecules
for environmental remediation.
3.1.1 Dye Remediation
Contamination of water bodies with dyes largely results from the runoff of synthetic
dyes from industries of textile, cosmetics, plastic making or other manufacturing
units. When the effluent discharge from such industries is not monitored properly,
it results in release of copious amounts of toxic dyes, which pose a serious risk
to life in the waterbody and its environment. Some of the dye components have
also proven to be mutagenic or carcinogenic, and therefore, their remediation is
highly essential. Over the years, waste water treatment methods such as primary
and secondary treatments which involve techniques such as flocculation (Lee et al.
2014), catalytic degradation (Pirilä et al. 2015), and filtration (Li et al. 2017a, 2017b)
have served the purpose. However, such treatments are economically difficult to
implement, and come with additional difficulties such as high-operational cost and
energy requirements.
HNT due to their tubular structure, biocompatibility and non-toxic nature along
with high physical and chemical stability are exceedingly suitable to be used either as
adsorbents in order to remove harmful dyes, or as support for immobilizing various
guest molecules to impart catalytic properties to the nanotube. The guest molecules
can also be selected in such a way that they enhance the adsorption property of
the HNT as well. When HNT is used as an adsorbent, factors such as dosage of
the adsorbent, pH and temperature of the solution, and contact time have to be
contemplated (Anastopoulos et al. 2018). Based on such factors, the types of guest
molecules that can be immobilized on the surface of HNT can be considered.