120
7 Molten Salt Conversion of Plastics into Highly Conductive …
The internsity ratio of the D and G bands (I D /I G ) of the soot formed on the anode
and the cathode was calculated to be 0.77 and 0.67, respectively. This indicates
that carbon nanotubes present in the anode soot had a higher degree of structural
defects, which was in agreement with the SEM and TEM results. Since the cathode
soot formed at higher temperatures of the arc plume, where the arcing occurs, the
graphitization level is higher as compared to the soot obtained from the hole of the
anode. It should be mentioned that temperature plays an important role on determining the level of graphitization of carbon nanotubes [63]. In comparison to techniques
such as arc discharge, molten salt-based technologies have the prospect of being
commercially viable due to the advantages of simplicity and cost effectively.
7.4 Molten Salt-Assisted Conversion of PET into Carbon
Nanomaterials
Molten salts can act as diffusion-enhancing medium to promote chemical reactions
[68–70]. For instance, Li et al. [69] reported that the dissolution of SrO in molten
KCl enhances the diffusion of ionic species (Sr
2+ and O
2- ) to the surface of TiO 2
particles immersed in the melt, leading to the facile synthesis of Sr 3 Ti 2 O 7 .
It was also reported that the hydrolysis of molten lithium chloride leads to the
formation of O
2- . The reaction of O
2- and Li
+ with Nb 2 O 5 particles added to the melt
promoted the ultrafast formation of LiNbO 3 , much faster than solid-state synthesis
methods [70]. As discussed in the Chap. 3, the exposure to the molten salt media can
enhance the crystallinity of graphitic materials [71].
These observations imply that molten salts can be able to act as the graphitization
medium to improve the quality of plastic-derived carbons. NaCl is the cheapest salt
and one of the most abundant natural materials. In the following sections, the molten
NaCl-assisted pyrolysis of PET is introduced as a green and cost-effective method
for the preparation of high-quality carbon nanostructures, with interesting properties
such as a high surface area (522 m
2 g
−1 ) and Raman I 2D /I G value (0.52), as well
as a low value of Raman I D /I G (0.47) and an impressive electrical conductivity of
1150 S m
−1 obtained under a compressive pressure of about 6 MPa [24].
7.4.1 Molten Salt Heat Treatment of PET
A mixture of about 10 g PET and 50 g NaCl was heated in air atmosphere up to two
different temperatures of 1100 and 1300 °C, which are above the melting point of
NaCl (801 °C). After cooling down to room temperature, the carbon obtained was
washed with water to remove the NaCl off the product [24]. In the XRD pattern of
the carbon material obtained at 1100 °C (Fig. 7.7), the diffraction peaks arisen from
the hexagonal carbon and also cubic NaCl can be detected. The presence of NaCl
7 Molten Salt Conversion of Plastics into Highly Conductive …
The internsity ratio of the D and G bands (I D /I G ) of the soot formed on the anode
and the cathode was calculated to be 0.77 and 0.67, respectively. This indicates
that carbon nanotubes present in the anode soot had a higher degree of structural
defects, which was in agreement with the SEM and TEM results. Since the cathode
soot formed at higher temperatures of the arc plume, where the arcing occurs, the
graphitization level is higher as compared to the soot obtained from the hole of the
anode. It should be mentioned that temperature plays an important role on determining the level of graphitization of carbon nanotubes [63]. In comparison to techniques
such as arc discharge, molten salt-based technologies have the prospect of being
commercially viable due to the advantages of simplicity and cost effectively.
7.4 Molten Salt-Assisted Conversion of PET into Carbon
Nanomaterials
Molten salts can act as diffusion-enhancing medium to promote chemical reactions
[68–70]. For instance, Li et al. [69] reported that the dissolution of SrO in molten
KCl enhances the diffusion of ionic species (Sr
2+ and O
2- ) to the surface of TiO 2
particles immersed in the melt, leading to the facile synthesis of Sr 3 Ti 2 O 7 .
It was also reported that the hydrolysis of molten lithium chloride leads to the
formation of O
2- . The reaction of O
2- and Li
+ with Nb 2 O 5 particles added to the melt
promoted the ultrafast formation of LiNbO 3 , much faster than solid-state synthesis
methods [70]. As discussed in the Chap. 3, the exposure to the molten salt media can
enhance the crystallinity of graphitic materials [71].
These observations imply that molten salts can be able to act as the graphitization
medium to improve the quality of plastic-derived carbons. NaCl is the cheapest salt
and one of the most abundant natural materials. In the following sections, the molten
NaCl-assisted pyrolysis of PET is introduced as a green and cost-effective method
for the preparation of high-quality carbon nanostructures, with interesting properties
such as a high surface area (522 m
2 g
−1 ) and Raman I 2D /I G value (0.52), as well
as a low value of Raman I D /I G (0.47) and an impressive electrical conductivity of
1150 S m
−1 obtained under a compressive pressure of about 6 MPa [24].
7.4.1 Molten Salt Heat Treatment of PET
A mixture of about 10 g PET and 50 g NaCl was heated in air atmosphere up to two
different temperatures of 1100 and 1300 °C, which are above the melting point of
NaCl (801 °C). After cooling down to room temperature, the carbon obtained was
washed with water to remove the NaCl off the product [24]. In the XRD pattern of
the carbon material obtained at 1100 °C (Fig. 7.7), the diffraction peaks arisen from
the hexagonal carbon and also cubic NaCl can be detected. The presence of NaCl