Biomedical Engineering Reference
In-Depth Information
3.3
Carbon Aerogels
3.3.1
Synthesis and Characterization of CAs
In the present work, CAs were synthesized from resorcinol (R)
(99.0%), furfural (F) (99.0%), and Hexamethylenetetramine (HMTA)
(99.0%), which were obtained from Sigma Aldrich Pty. Ltd., Australia.
The precursors were mixed in ethanol (E) as a solvent (molar ratio
of E/R = 190) followed by magnetic stirring for 3 h within a sealed
container. The resultant solutions were put in an oven at 75-80°C
for 3-7 days after being first stabilized for at least 24 h at room
temperature. The organic wet gels were then transferred into a
chamber and were subcritically dried for 10 h. The aerogel samples
were carbonized at different temperatures from 250°C to 900°C
at a heating rate of 3°C/min for 3 h under a nitrogen atmosphere
(N
flow rate = 1.5 L/min). The CA samples will be referred to in
the text by CA
2
indicates the carbonization temperature
in degree centigrade, i.e., CA250,
T
, where
T
. The CA900 sample was also
activated by an additional heating process at 900°C for 1 h under
a CO
etc
flow rate = 1.5 L/min), which is referred to
as CA900-A in the text. The synthesis process performed includes
curing, heating, carbonizing, and activating by adopting a method
proposed by Wu
atmosphere (CO
2
2
. [25]. A different pyrolysis schedule at a low
heating rate (1.5°C/min) was employed for thorough decomposition
and chemical reaction between 300°C and 500°C except for CA250.
The proportions of individual raw materials were 1 mol of resorcinol
to 2 mol of furfural, i.e., R/F = 0.5. Initially the molar ratio of R/HMTA
was chosen between 20 and 40 in order to determine the appropriate
HMTA reaction conditions to obtain suitable gel networks. The
molar ratio of R/HMTA was determined to be optimum at 30 after
comparison with microstructures of resultant CA samples [26].
The FTIR spectrum of the resultant organic aerogels (dried and
heated at different stages) shows evidence of the principal reactions
(see Fig. 3.2).
The broad absorption bands between 3471 and 3525 cm
et al
-1
for
-1
-1
the dried sample, 3383 cm
for CA250, and 3525 cm
for CA500
are characteristic of the O
stretching vibrations, which are
assigned to residual organic solvent and absorbed water from the
environment. At higher temperature, only C−C absorption bands at
1576 cm
H
-1
-1
-1
-1
and 1101 cm
for CA750, and 1567 cm
and 1091 cm
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