BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 61

1.1.10.6.2 FLUORINATED POLYAMIDES
Microporous carbon films were prepared from aromatic polyamides synthesized
from different dianhydrides and diamines with different molecular structures by
carbonization. Structures of repeating unit in polyimides are reported. They were
characterized by the presence of pending groups, -CH, and-CF, and number of
phenyl rings in the repeating unit. Highly microporous carbon films were ob-
tained without any activation process, of which microporous surface area was
closely related to the contents of phenyl ring [1, 2].
1.1.10.6.3 METAL CARBIDES
Various metal carbides were found to give highly microporous carbon through
the heat treatment in a flow of carbide-derived carbons. S BET was reported to be
1000-2000 m 2 /g −1 , depending on the precursor carbide and heat treatment tem-
perature. The carbide-derived carbons gave a relatively sharp distribution in pore
size and their predominant pore size depends mostly on the precursor carbide;
SiC, TiC and Al 4 C 3 gave 0.7-0.8 nm, and B 4 TiC approximately 1.3 nm and Ti 3 SiC 2
0.5-0.6 nm. From ZrC 098 , however, the carbons were obtained with a sharp size
distribution of approximately 0.7 nm after the heat treatment at 300-600°C, but
with a broad distribution ranging from 0.6 to 3 nm after the heat treatment at
800-1200°C. These carbide-derived microporous carbons were used as the elec-
trode of electric double layer capacitors.
1.1.10.6.4 BIOMASSES
The cores of kenaf plant (Hibiscus cannabinus) were found to give a high S BET as
high as 2700 m 2 /g by the heat treatment, without any additional activation process.
This high surface area was supposed to be due to the departure of metallic impuri-
ties (mostly K), which were originally included in the cores, during carbonization.
Porous carbons were successfully prepared from chips of cypress (Cupressus) by
the heat treatment under a flow of superheated steam. Pore structure in cypress
charcoals could be controlled by changing carbonization conditions (temperature
of superheated steam, and supplying and transferring rates of chips).
1.1.10.7 SELECTION OF PREPARATION CONDITIONS
1.1.10.7.1 MOLECULAR SIEVING CARBON FILMS
Carbon membranes with molecular sieving performance were successfully pre-
pared by the carbonization of commercially available polyimide films with the
thickness of 0.1 mm. adsorbed amounts of gas molecules with different sizes are
shown on the carbon films heat treated at different temperatures, ethane C 2 H 6
with the size of 0.40 nm permeating in a large amount through the film heated up
to 700°C, but with very small amount through the one heated up to 1000°C. This
result suggested a strong dependence of pore sizes in carbon films on carboniza-