BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 57

1.1.10.2 TEMPLATE METHODS
Microporous carbons, of which the highest surface area and pore volume were ap-
proximately 4000 g −1 and 1.8 mL/g, respectively, were prepared through the car-
bonization of a carbon precursor in nano channels of zeolite, with the procedure
called as template carbonization technique. Since the size and shape of the chan-
nels in zeolites are strictly defined by their crystal structures and the pores formed
in the resultant carbon are inherited from their channels, micropores formed in
the resultant carbon are homogeneous in both size and morphology. Impregna-
tion of furufuly alcohol (FA) into the channels of a zeolite was carried out under
vacuum at a low temperature, followed by washing excess FA attached on physi-
cal surface of zeolite particles with mesitylene. The composite particles of FA/
zeolite thus obtained were heated at 150°C for 8 h to polymerize FAs (PFA/zeolite
composite). The composites were carbonized at 700°C, followed by dissolution
of the template zeolite by 46-48% HF solution. The relation of zeolite cage to
the resultant pores in carbon. Detailed preparation procedure for these highly mi-
croporous carbons was reviewed. High resolution TEM images show that regu-
lar alignment of super cages with the size of 1.4 nm is inherited in the resultant
carbon as the periodicity of approximately 1.3 nm. The carbon gives a diffraction
peak at an angle of approximately 6° in 20 of CuKa X-rays, just as the template
zeolite does, which corresponds to the periodicity of approximately 1.3-1.4 nm
due to superstructure. Very high surface area indicates the presence of the curved
carbon surfaces, which was predicted by grand canonical Monte Carlo simulation.
Mesoporous carbons were also prepared by template method using mesoporous
silica. By coupling with an activation process, micropores could be easily intro-
duced into these mesoporous carbons [21, 40].
A simple heat treatment of thermoplastic precursors, such as poly(vinyl alco-
hol) PVA, hydroxyl propyl cellulose HPC, polyethylene terephthalate) PET, and
pitch in the coexistence of various ceramics, was able to coat ceramic particles by
porous carbon. Using MgO particles as substrate ceramics, it was experimentally
proved that the carbons formed from PVA at 900°C were experimentally shown
to have larger surface area after the substrate MgO was dissolved out by a di-
luted acid to isolate carbon. The carbons have high S BET , particularly the carbons
obtained from the mixtures prepared from Mg acetate and citrate with PVA in
their aqueous solutions (solution mixing). Most of carbons show a relatively high
external surface area Sext, which is known to be mostly due to mesopores. Meso-
pores formed in the carbon was known to have almost the same size as MgO par-
ticles, which were formed by the thermal decomposition of Mg compounds in ad-
vance of the thermal decomposition and carbonization of carbon precursor. When
MgO particles with rectangular morphology were used, the rectangular pores
with the same size were observed under SEM in the resultant carbons. Therefore,
it was concluded that MgO works as a template for mesopore formation. Pore
size distributions in micropore and mesopore ranges measured by DFT and BJH