Biomedical Engineering Reference
In-Depth Information
A TEM micrograph of CA-Co-I is shown in Fig. 3.11, which
displays metal-containing particles well dispersed in the CA with
particles sizes between 2 and 8 nm.
The microstructure of the pure CA and its pores can also be seen
in this image as an interconnected bead structure analogous to that
of typical aerogels prepared by Pekala [6]. These beads are generally
several nanometers in size, and many micropores can be found with
pore sizes in the range of 1-2 nm (determined via a pixel counting
method using Digital Micrograph software (Gatan, USA)), which
agree with SAXS average pore size measurements [26].
The specific surface area obtained via N
adsorption was
determined by the standard BET analysis, and the D
-
R model
was used to determine micropore information [26, 30]. From the
Gurvitsch rule (i.e., cumulative volume of nitrogen adsorbed to
2
p
/
p
= 0.975 corresponding to the absorbed volume plateau) the total
volume (per gram of sample) of nitrogen adsorbed is determined.
The pore structure properties are shown in Table 3.6.
0
Table 3.6
The pore structure properties as determined by nitrogen
adsorption at 77 K
Surface
area
S
BET
(m
2
/
g�
H
2
(wt.%�
per 500
m
2
/
g
Total pore
volume
(cm
3
/
g�
Micropore
volume
(cm
3
/
g�
Max. H
2
(wt.%�
(77 K�
Sample
CA
2206 1.32 ± 0.02 0.70 ± 0.02 4.88 (4.6 MPa) 1.1
CA-Co-I
1667 0.70 ± 0.01 0.60 ± 0.01 4.38 (4.6 MPa) 1.3
CA-Co-II
518 0.92 ± 0.01 0.20 ± 0.01 1.82 (3.8 MPa) 1.8
Hydrogen sorption measurements were performed at both
room temperature and at cryogenic temperature (77 K), with results
presented in Fig. 3.12.
The hydrogen sorption at room temperature is much lower
than at 77 K because physisorption is a function of van der Waals
forces which are not as dominant at higher temperatures. The
hydrogen adsorption isotherm of the CAs at room temperature show
near-linear behavior between hydrogen uptake and equilibrium
pressure. The hydrogen adsorption for CA-Co-I displays a high level
