Halloysite Nanotubes: An ‘Aluminosilicate Nanosupport’ …
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3.1.4 Gas Separation
Gas separation is often required in cases where multiple products or a single purified
product is required. Over the years, methods using adsorbents (zeolites, activated
charcoals) have been developed. However, the most commonly used and the most
efficient method is through membranes. Mixed Matrix Membranes (MMM) are a
polymeric hybrid system consisting of the adsorbents as fillers in a flexible polymeric
base. Proper dispersion of such fillers can enhance the free volume in the membranes,
thus bringing an increase in membrane permeability.
A couple of studies have incorporated HNTs as fillers in the development of
MMM. By using HNT as a filler and by ensuring its proper dispersion in the membrane, high permeability and selectivity can be imparted to it. In a study, HNTs which
had been surface etched through alkali had been further subjected to treatment by
APTES in order to immobilize of amine groups. These HNTs were later used as a
filler in a 6FDA-durene polyimide polymer. The presence of HNT had significantly
increased the gas permeability and the presence of amine groups had a major effect
on the selectivity of the membrane towards the gas (here, CO 2 ) by showing an adsorption capacity of 6.1 cm
3 /g (STP) at a pressure of 120 kPa at 298 K (Ge et al. 2017).
Similarly, N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEAPTMS) was used to
treat HNT for the grafting of amine groups on its surface. The studies showed an
enhancement in the adsorption capacity with increment in the amine groups. However, after a certain concentration of the amount of amine groups on HNT’s surface,
the adsorption had decreased. The reason behind this is touted to be the blocking of
pores by the groups (Hashemifard et al. 2011).
3.2 Energy Applications
With rising depletion in natural non-renewable sources, finding an alternative source
of energy or implementing ‘greener’ improvements in current techniques are necessary in order to improve life all over the world. Over the years, several techniques have
been developed that can decrease the consumption of energy, increase its production
or find alternative methods that can produce greener fuels such as biodiesel.
In the past few years, HNT has been utilized for energy storage and development
of green fuels. In this section, the use of HNT in energy applications and the effect of
immobilization of newer guest molecules on the surface of HNT for such applications
has been discoursed.
3.2.1 Energy Storage
A common method of energy storage is through the use of supercapacitors due to
their long cycling life, enhanced power delivery, increased power density and low
137
3.1.4 Gas Separation
Gas separation is often required in cases where multiple products or a single purified
product is required. Over the years, methods using adsorbents (zeolites, activated
charcoals) have been developed. However, the most commonly used and the most
efficient method is through membranes. Mixed Matrix Membranes (MMM) are a
polymeric hybrid system consisting of the adsorbents as fillers in a flexible polymeric
base. Proper dispersion of such fillers can enhance the free volume in the membranes,
thus bringing an increase in membrane permeability.
A couple of studies have incorporated HNTs as fillers in the development of
MMM. By using HNT as a filler and by ensuring its proper dispersion in the membrane, high permeability and selectivity can be imparted to it. In a study, HNTs which
had been surface etched through alkali had been further subjected to treatment by
APTES in order to immobilize of amine groups. These HNTs were later used as a
filler in a 6FDA-durene polyimide polymer. The presence of HNT had significantly
increased the gas permeability and the presence of amine groups had a major effect
on the selectivity of the membrane towards the gas (here, CO 2 ) by showing an adsorption capacity of 6.1 cm
3 /g (STP) at a pressure of 120 kPa at 298 K (Ge et al. 2017).
Similarly, N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEAPTMS) was used to
treat HNT for the grafting of amine groups on its surface. The studies showed an
enhancement in the adsorption capacity with increment in the amine groups. However, after a certain concentration of the amount of amine groups on HNT’s surface,
the adsorption had decreased. The reason behind this is touted to be the blocking of
pores by the groups (Hashemifard et al. 2011).
3.2 Energy Applications
With rising depletion in natural non-renewable sources, finding an alternative source
of energy or implementing ‘greener’ improvements in current techniques are necessary in order to improve life all over the world. Over the years, several techniques have
been developed that can decrease the consumption of energy, increase its production
or find alternative methods that can produce greener fuels such as biodiesel.
In the past few years, HNT has been utilized for energy storage and development
of green fuels. In this section, the use of HNT in energy applications and the effect of
immobilization of newer guest molecules on the surface of HNT for such applications
has been discoursed.
3.2.1 Energy Storage
A common method of energy storage is through the use of supercapacitors due to
their long cycling life, enhanced power delivery, increased power density and low