Halloysite Nanotubes: An ‘Aluminosilicate Nanosupport’ …
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have disadvantages of having low yields for lighter fuels and therefore require highquality feedstock. Such a process also consumes a high quantity of hydrogen, thus
making it economically limited.
In the past decades, several studies have shown HNT to be used in increasing
the yield output and decreasing the formation of coke during the cracking process
(Abbasov et al. 2013, 2016a, b). In a recent study, NiO and CoO catalysts were
deposited on HNT’s surface for the cracking process. This catalyst allowed the hydrocracking process to occur at lower hydrogen pressure of 1 MPa as compared to the
usual 10–20 MPa. The catalyst had also enhanced the total yield from 52 to 57%
under increasing hydrogen pressure of up to 4 MPa (Abbasov et al. 2016a, b).
HNT have also been used as a template to fabricate cathode catalyst for applications in alkaline fuel cell, which is an alternative for existing fuel sources. Commonly used cathode catalysts are made from noble metals; however, they come with
the limitation of high price and therefore cannot be put into mass production. In
this study, HNT have been used as stencils for the fabrication of nitrogen-doped
carbon nanotubes (N-CNT), which will serve Oxygen Reduction Reaction (ORR)
electro catalysts. Aniline had been loaded on the surface of HNT, which was then
oxidised to form Polyaniline-HNT hybrids. These hybrids were further pyrolyzed
in order to obtain HNT with nitrogen-doped CNTs. These CNTs showed excellent
electrocatalytic performance towards ORR (Liu et al. 2019).
Along with HNT used as a template and a catalyst, they have also been used in the
production of biodiesel production from hybrid feedstocks. In a study, HSO 3 groups
were grafted on the surface of HNT through different methods such as organosilylation, sulfonation, and 2 steps organosilylation and sulfonation. These HNTs were
later used as catalyst for the esterification of fatty acids. The catalysts obtained
through sulfonation showed the highest catalytic activity with a turnover frequency
of 94 h
−1 and a mass normalized activity of 0.08 mol.g
−1 h
−1 (Silva et al. 2018).
4 Conclusion
Nanotechnology-based advancements have emerged as a helping hand for environmental engineers for solving various kinds of issues related to the environment.
However, the toxicity of most of the nanomaterials in addition to the cost involved in
their synthesis has always limited their bulk usage, especially for energy and environmental applications. HNT are naturally occurring aluminosilicate nano-supports
with additional benefits such as being eco-friendly biocompatible and non-toxic, and
these nanotubes have found that their way is an excellent alternative for applications
in the fields of energy and environment.
The nanotube showcases excellent thermal and mechanical properties, along with
an alterable surface chemistry. These properties in addition to the good adsorption
behaviour make HNT a suitable nano-support for various guest molecules. In the
field of environment, commonly used guest molecules include functional reactive
moieties, biomolecules and biopolymers, and nanoparticles. HNT immobilized with
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have disadvantages of having low yields for lighter fuels and therefore require highquality feedstock. Such a process also consumes a high quantity of hydrogen, thus
making it economically limited.
In the past decades, several studies have shown HNT to be used in increasing
the yield output and decreasing the formation of coke during the cracking process
(Abbasov et al. 2013, 2016a, b). In a recent study, NiO and CoO catalysts were
deposited on HNT’s surface for the cracking process. This catalyst allowed the hydrocracking process to occur at lower hydrogen pressure of 1 MPa as compared to the
usual 10–20 MPa. The catalyst had also enhanced the total yield from 52 to 57%
under increasing hydrogen pressure of up to 4 MPa (Abbasov et al. 2016a, b).
HNT have also been used as a template to fabricate cathode catalyst for applications in alkaline fuel cell, which is an alternative for existing fuel sources. Commonly used cathode catalysts are made from noble metals; however, they come with
the limitation of high price and therefore cannot be put into mass production. In
this study, HNT have been used as stencils for the fabrication of nitrogen-doped
carbon nanotubes (N-CNT), which will serve Oxygen Reduction Reaction (ORR)
electro catalysts. Aniline had been loaded on the surface of HNT, which was then
oxidised to form Polyaniline-HNT hybrids. These hybrids were further pyrolyzed
in order to obtain HNT with nitrogen-doped CNTs. These CNTs showed excellent
electrocatalytic performance towards ORR (Liu et al. 2019).
Along with HNT used as a template and a catalyst, they have also been used in the
production of biodiesel production from hybrid feedstocks. In a study, HSO 3 groups
were grafted on the surface of HNT through different methods such as organosilylation, sulfonation, and 2 steps organosilylation and sulfonation. These HNTs were
later used as catalyst for the esterification of fatty acids. The catalysts obtained
through sulfonation showed the highest catalytic activity with a turnover frequency
of 94 h
−1 and a mass normalized activity of 0.08 mol.g
−1 h
−1 (Silva et al. 2018).
4 Conclusion
Nanotechnology-based advancements have emerged as a helping hand for environmental engineers for solving various kinds of issues related to the environment.
However, the toxicity of most of the nanomaterials in addition to the cost involved in
their synthesis has always limited their bulk usage, especially for energy and environmental applications. HNT are naturally occurring aluminosilicate nano-supports
with additional benefits such as being eco-friendly biocompatible and non-toxic, and
these nanotubes have found that their way is an excellent alternative for applications
in the fields of energy and environment.
The nanotube showcases excellent thermal and mechanical properties, along with
an alterable surface chemistry. These properties in addition to the good adsorption
behaviour make HNT a suitable nano-support for various guest molecules. In the
field of environment, commonly used guest molecules include functional reactive
moieties, biomolecules and biopolymers, and nanoparticles. HNT immobilized with