Biomedical Engineering Reference
In-Depth Information
reactive sites into the carbon-based nanoporous structures by
doping nanoscaled metal particles (as catalysts) or to polymerize
unsaturated functionalized complexes to modify the carbon surface.
Extensive physisorption and chemisorption (hydrogen absorption)
characterization was performed to determine the uptake of hydrogen
in these materials.
The nitrogen adsorption isotherm was measured gravimetrically
with a TriStar 3000 at 77 K using a computer-aided apparatus.
The samples were evacuated to 1 mPa at 110°C for 2 h prior to the
adsorption measurements. It took 3 h to attain each adsorption or
desorption equilibrium upon measuring the hysteresis. The specific
surface area obtained via N
adsorption was determined by the
standard Brunauer, Emmett, and Teller (BET) analysis. The Brunauer-
Joyner-Halenda (BJH) method was used to determine mesopore
information and the Dubinin-Radushkevich (DR) method was used
to determine micropore information. Small-angle X-ray scattering
(SAXS) was also employed to determine the aerogel micropore size
via the Guinier equation. CA powder samples were mounted between
thin polymer films for the SAXS measurements. The SAXS patterns
were obtained from a Bruker NanoSTAR SAXS instrument.
Data was recorded at a sample to detector distance of 65 cm,
using a wavelength,
2
) with a 2-D multiwire
detector. The raw data was radially averaged, background subtracted,
and put on an absolute scale by calibrating against a known standard
via the method of Spalla
λ
= 0.15418 nm (CuK
α
[8]. The conversion of the SAXS data onto
an absolute scale was performed assuming that the samples were
pure carbon with a true density of 1.9 g/cm
et al.
3
. TEM was performed
with a JOEL-2000FX microscope operating at 200 kV. Samples were
deposited from an ethanol suspension onto copper grids. Some
powders were scraped from the bulk CA samples and dispersed with
ethanol onto a copper grid for microscopic examination.
Hydrogen sorption experiments were performed in a Sieverts
manometric apparatus. For ambient temperatures, the Hemmes
equation of state [22] was used following the method of McLennan
and Gray [23] to account for the compressibility of hydrogen. For
T
= 77 K, the NIST Standard Reference Database Number 69 was
used [24]. The manometric apparatus used can achieve hydrogen
sorption measurements at a maximum temperature of 800 K and
maximum pressure of 15 MPa.
