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M.J. Baniamerian, S.E. Moradi / Journal of Alloys and Compounds 509 (2011) 6307–6310
have been demonstrated to have an excellent catalytic effect on
hydrogen storage in metal based alloys by enhancing the hydrogen
diffusion in M–C systems [28,29].
600
500
In this work, we prepared novel high-specific-surface area Al–Ga
modified mesoporous carbon from highly ordered mesoporous
carbon host, and demonstrated Al–Ga–OMC system that exhibit
ultrafast hydrogenation kinetics with very high capacity.
400
300
200
100
0
2. Experimental
OMC
Al-Ga-OMC
2.1. Materials
The reactants used in this study were tetraethoxysilane (TEOS, 98%, Acros) as a
silica source, non-ionic oligomeric alkyl-ethylene oxide surfactant (Pluronic 123) as
a surfactant, HCl (35 wt%), ethanol and deionized water for synthesis of mesoporous
silica (SBA-15), sucrose as a carbon source, sulfuric acid as a catalyst for synthesis of
mesoporous carbon, Al2(SO4)3 and gallium as fictionalization agents. All chemicals
were of analytical grade from Merck.
0
0.2
0.4
0.6
0.8
1
1.2
Relative Pressure (P/Po)
Fig. 1. Adsorption–desorption isotherms of nitrogen at 77 K on OMC and
Al–Ga–OMC.
2
2
.2. Nanomaterials preparation
.2.1. Mesoporous silica and unmodified mesoporous carbon samples
SBA-15 silica was prepared according to the procedure reported by Zhao et al.
[
30] by using a non-ionic oligomeric alkyl-ethylene oxide surfactant (Pluronic 123)
the measuring experimental set-up was used. It consisted of a temperature con-
trolled glass reactor connected with a water-filled burette for hydrogen collection.
The aluminum powder (0.07–0.4 g) was added in a glass reactor (100 cm ) with
water (50 ml) heated to a predetermined temperature. Hydrogen evolving reaction
started when aluminum powder came into contact with water. Hydrogen was cooled
to the ambient temperature by bubbling through water in a filled burette. Evolving
hydrogen was collected in a water burette to measure the quantity of hydrogen.
as a structure directing agent, after that template removal by means of calcina-
tions at 773 K in flowing air. Ordered porous carbon was synthesized via a two step
impregnation of the mesopores of SBA-15 with a solution of sucrose using an incip-
ient wetness method [31]. Briefly, 1.0 g of the as-prepared SBA-15 was impregnated
with an aqueous solution obtained by dissolving 1.1 g of sucrose and 0.14 g of H2SO4
in 5.0 g of deionized water. The mixture was then dried at 373 K for 6 h, and sub-
sequently at 433 K for 6 h. The silica sample, containing partially polymerized and
carbonized sucrose, was treated again at 373 and 433 K after the addition of 0.65 g of
sucrose, 90 mg of H2SO4 and 5.0 g of deionized water. The sucrose–silica composite
was then heated at 1173 K for 4 h under nitrogen to complete the carbonization.
The silica template was dissolved with 5 wt% hydrofluoric acid at room temper-
ature. The template-free carbon product thus obtained was filtered, washed with
deionized water and ethanol, and dried.
3
3. Results and discussion
3.1. Textural characterization
2.2.2. Aluminum modified mesoporous carbon
Pore textural properties of the pure ordered mesoporous car-
Aluminum was loaded on mesoporous carbon surface according to the proce-
bon and aluminum–gallium modified mesoporous carbon were
calculated from the nitrogen adsorption and desorption isotherms
shown in Fig. 1., it can be seen that after modification the obtained
carbons still have type IV isotherms, indicating that mesoporosity
is still preserved. However, the modification leads to a decrease
in the total uptake of the mesoporous carbon, which reflects the
decrease of the total pore volume resulting from Al–Ga alloy modi-
fications. Interestingly, the modified nanoporous carbon essentially
keeps the bimodal pore size distribution, which is characteristic of
the parent mesoporous carbon. The textural parameters of porous
materials listed in Table 1 clearly confirm the structural changes of
OMC to Al–Ga–OMC. Especially, the variations of the surface area
and pore volume are significant by Al–Ga alloy loading.
In order to check the structural degradation, XRD data of car-
bonaceous samples were obtained on Philips 1830 diffractometer
using Cu K␣ radiation of wavelength 0.154 nm. Fig. 2 reports low
angle XRD patterns of the parent mesoporous silica and of samples
OMC and Al–Ga–OMC. With SBA-15, three well-resolved peaks are
observed, corresponding to the (1 0 0), (1 1 0) and (2 0 0) reflections
typical of the 2D hexagonal space group p6mm. With all repli-
cas, the main reflection peak is well maintained, indicating that
rather ordered mesoporous materials with hexagonal structures
were obtained. With respect to the parent silica, a shift of the d1 0 0
peak towards higher 2ꢀ values is observed, in agreement with the
literature [30].
dure reported by Oh and Park [32]. The mesoporous carbon was heated first at 773 K
for burn-off, then physically activated with water vapor in 1323 K. For treatment,
Al2(SO4)3 used as received. For pretreatment with acid, 5 g of activated carbon was
dipped into 100 mL of 0.01 M phosphoric acid solution and stirred for 24 h at room
temperature. Air and bubbles in the solutions were removed under a pressure of
ca. 1.33 Pa for 20 min, and then the solution was discarded. The samples were dried
at 383 K for 48 h in an air atmosphere. For metal treatment, 5 g of activated car-
bons were dipped into 100 mL of 0.05–0.1 M aqueous aluminum sulfate and stirred
for 12 h at room temperature. After removal of the liquid, samples treated with
aluminum were dried completely in an oven.
2
.2.3. Aluminum–gallium alloy preparation
Alloys in amounts of up to 1 g were melted in glassy graphite crucibles under a
layer of a fluxing agent consisting of cryolite with additives of calcium and aluminum
fluorides in a gradientless tubular furnace [33]. The starting mixture containing
Al–OMC of reagent grade and gallium was heated to 1173 K under N2 gas flow
(
10 ml/min) and kept at this temperature for 15 min, after which the crucible was
rapidly (3–5 min) cooled to 303–313 K under an inert atmosphere. After cooling,
a weighed sample of the alloy (0.1–0.2 g) was treated with distilled water in a
temperature-controlled flask attached to a gas burette graduated in 0.1 mL incre-
ments.
2
.2.4. Textural and structural studies
The porous structure of the surface modified samples was estimated by powder
XRD (Philips 1830 diffractometer) using graphite monochromated Cu K␣ radiation.
Adsorption isotherms of the mesoporous carbon samples were obtained using a N2
gas microporosimeter (micromeritics model ASAP 2010 sorptometer) at 77 K. Pore
size distribution and specific surface area were calculated by Dollimore–Heal [34]
and BET [35] methods. Pore volume was estimated from the amount of adsorbed N2
gas at 0.963 in relative pressure, which derives from 25 nm radii pores. Micropore
volume was calculated by t-plot.
2.3. H2 measurement
Table 1
Textural parameters of the OMC and Al–Ga–OMC employed in this study.
The kinetics of interactions between aluminum and water was investigated by
−1
Vp (cm3
g )
−1
a volumetric method. The measurements of hydrogen volumes at room tempera-
ture were accomplished with tenfold stoichiometric surplus of water to minimize
the influence of the temperature factor. To carry out the reaction at a high tem-
perature, the reactor was located in water bath. To quantify the evolving hydrogen
Adsorbent
d spacing (nm)
ABET (m2
g
)
OMC
Al–Ga–OMC
3.7
3.43
1530
1362.4
0.73
0.58
Baniamerian
