8.3 Conversion of CO 2 into Diamond Nanocrystals
153
(Sect. 4.6). The heat treatment of this nanostructure led to the formation of nanodiamonds. The process has been summarized in Fig. 8.7. The cathodic exfoliation
of a graphite electrode (Fig. 8.7a) under a moist CO 2 flow led to the formation of
a nanostructured hybrid material containing a high fraction of carbon-encapsulated
Li 2 CO 3 (Fig. 8.7b). This hybrid material was heated at a heating rate of 40 °C min
−1
in an airflow rate of 100 mL min
−1 to 440 °C, and heated material was rapidly
cooled down to the room temperature by a flow of air providing a cooling rate of
Fig. 8.7 Molten salt conversion of CO 2 into diamond crystals. a SEM micrograph of the graphite
cathode used. This material was consumed together with CO 2 in the molten salt process to produce
a hybrid nanostructure containing mostly nanoparticles of less than 50 nm as can be seen in (b-left
panel). (b-right panel) A HRTEM micrograph from the hybrid nanostructure, in which Li 2 CO 3
nanoparticles are encapsulated into graphitic layers. These nanostructures can act as high-pressure
nanovessels during the air heat treatment of the material. (c-left panel) A low magnification SEM
image from the heat-treated sample (to 530 °C), indicating the presence of diamond crystals in large
carbon particles. (c-middle panel) A higher magnification SEM image showing a diamond crystal.
(c-right panel) A HRTEM image from the heat-treated sample, exhibiting a number of diamond
nanocrystals. The inset is a fast Fourier transformation of the area indicated by rectangle on the
HRTEM image, exhibiting the (111) crystal planes of diamond with a lattice spacing of 0.2 nm.
d The schematic summary of the process, in which CO 2 , graphite, water and LiCl are consumed and
the product contains diamond crystals, reproduced from Ref. [68], copyright 2019, with permission
from Elsevier
153
(Sect. 4.6). The heat treatment of this nanostructure led to the formation of nanodiamonds. The process has been summarized in Fig. 8.7. The cathodic exfoliation
of a graphite electrode (Fig. 8.7a) under a moist CO 2 flow led to the formation of
a nanostructured hybrid material containing a high fraction of carbon-encapsulated
Li 2 CO 3 (Fig. 8.7b). This hybrid material was heated at a heating rate of 40 °C min
−1
in an airflow rate of 100 mL min
−1 to 440 °C, and heated material was rapidly
cooled down to the room temperature by a flow of air providing a cooling rate of
Fig. 8.7 Molten salt conversion of CO 2 into diamond crystals. a SEM micrograph of the graphite
cathode used. This material was consumed together with CO 2 in the molten salt process to produce
a hybrid nanostructure containing mostly nanoparticles of less than 50 nm as can be seen in (b-left
panel). (b-right panel) A HRTEM micrograph from the hybrid nanostructure, in which Li 2 CO 3
nanoparticles are encapsulated into graphitic layers. These nanostructures can act as high-pressure
nanovessels during the air heat treatment of the material. (c-left panel) A low magnification SEM
image from the heat-treated sample (to 530 °C), indicating the presence of diamond crystals in large
carbon particles. (c-middle panel) A higher magnification SEM image showing a diamond crystal.
(c-right panel) A HRTEM image from the heat-treated sample, exhibiting a number of diamond
nanocrystals. The inset is a fast Fourier transformation of the area indicated by rectangle on the
HRTEM image, exhibiting the (111) crystal planes of diamond with a lattice spacing of 0.2 nm.
d The schematic summary of the process, in which CO 2 , graphite, water and LiCl are consumed and
the product contains diamond crystals, reproduced from Ref. [68], copyright 2019, with permission
from Elsevier