BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 60

structure in the resultant carbons was found to depend on pH- value in the solu-
tion, which was changed by mixing ratio of R/C. Pore volumes of the resultant
carbon aerogels after 800°C carbonization with pH of 8.0 (R/C = 25), no porous
carbon is obtained. Porous carbons are formed in the pH range of 7.0-8.0, par-
ticularly mesopore-rich in the pH range of 7.3-7.7. Carbon aerogels were used as
a template for the preparation of highly crystalline zeolite with uniform mesopo-
rous channels [1, 2, 39].
1.1.10.5 POLYMER BLEND METHOD
Polymer blend method was proposed to synthesize various types of carbons, mix-
ing two different polymers, one having a high carbon yield, such as polyfurufuryl
alcohol, and the other, a low carbon yield, such as polyethylene. The scheme
of polymer blend method to get carbon balloons, carbon beads, and also porous
carbons is shown in Fig. 1.2. By applying spinning on blended polymer, certain
success in obtaining carbon nanofibers was reported. Through the synthesis of
polyurethane-imide films and their carbonization, carbon films were obtained, of
which macropore structure was controlled by changing the molecular structure of
polyurethane. Prepolymer poly(urethane-imide) films were prepared by blending
polyamide acid giving polyimide (PI) with polyurethane (PU). Polyurethane-im-
ide films after heating up to 200°C showed phase separation of PI and PU, where
the former polymer formed a matrix and the latter formed small islands. By heat
treatment up to 400°C, PU component was pyrolyzed to gases and resulted in
porous PI films, which can be converted easily to porous carbon films by carbon-
ization. Pore sizes in these carbon films were controlled by the blending ratio of
PI to PU and also by the molecular structure of PU [1, 2].
1.1.10.6 SELECTION OF SPECIFIC PRECURSORS
1.1.10.6.1 DERIVATIVES OF BUTADIYNYLENE
Poly(phenylene butadiynylene) were found to give very high carbon yield of
more than 90 wt.% after the heat treatment at 900°C, very close to theoretical
yield, whose molecular structure are determined. The resultant carbons are amor-
phous state and microporous, having total surface area of 1 330 rn 2 /g microporous
surface area of 1 300 rn 2 /g and micropore volume of 0 49 mLg −1 . Their pyrolysis
behavior was characterized by a very sharp exothermic peak at around 200°C
without accompanying any mass change, which was due to 1, 4-polymerization
of butadiynylene moiety and resulted in cross-linking between molecules, and a
little but gradual mass loss of approximately 600°C. The material heat-treated
above 200°C was so highly and strongly cross linked that the hydrogen atoms
that remained were mostly stripped off as hydrogen molecules, which is the main
reason to give high carbon yield. The derivatives with methyl radicals on benzene
ring gave also high carbon yields, close to 80 wt.% of carbon content [1].