Preparation of mesoporous aluminum hydroxide and oxide in ionic liquids

Article abstract of DOI:10.1134/S0036023607100051

Mesoporous aluminum hydroxides and oxides were synthesized using ionic liquids (ILs) as templates. The influence of various factors (the nature of the IL, pH, ultrasonication, surfactants, reagent ratio, and the nature of the aluminum precursor) on the sp

Full text of DOI:10.1134/S0036023607100051

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 10, pp. 1511–1513. © Pleiades Publishing, Inc., 2007.
Original Russian Text © L.A. Aslanov, M.A. Zakharov, E.E. Knyazeva, A.V. Yatsenko, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 10, pp. 1613–1615.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Preparation of Mesoporous Aluminum Hydroxide
and Oxide in Ionic Liquids
L. A. Aslanov, M. A. Zakharov, E. E. Knyazeva, and A. V. Yatsenko
Moscow State University, Vorob’evy gory, Moscow, 119992 Russia
Received November 10, 2006
Abstract—Mesoporous aluminum hydroxides and oxides were synthesized using ionic liquids (ILs) as tem-
plates. The influence of various factors (the nature of the IL, pH, ultrasonication, surfactants, reagent ratio, and
the nature of the aluminum precursor) on the specific surface area and pore volume was analyzed.
DOI: 10.1134/S0036023607100051
Ionic liquids (ILs) are used as templates for prepar-
ing mesoporous inorganic oxides [1–7]. However, the
preparation of mesoporous Al O in ILs has not been
Synthesis of bmimNTf2
The synthesis procedure is described in work [10].
BmimNTf , which is incompletely miscible with water,
2
3
2
described. Micellar template is now the main method
was produced by an exchange reaction between
for preparing mesoporous oxides, including Al O [8].
2
2
3
bmimBr and LiNTf in aqueous solution and separated.
2
In particular, mesoporous Al O with S ≥ 550 m /g was
2
3
BmimNTf2 remaining in the aqueous phase was
extracted with methylene chloride in virtually quantita-
tive yield.
prepared by this method [9]. Below, we report the
results of our study of the preparation of mesoporous
Al(éH) · nH O and Al O in systems where the tem-
3
2
2
3
plate used was one of the following ILs: 1-butyl-3-
methylimidazolium bromide (bmimBr), 1-butyl-3-
methylimidazolium bis(trifluoromethylsulfonyl)amide
–
4
Synthesis of an IL Containing AlCl Anions
Inasmuch as bmimAlCl crystallizes at room tem-
perature, we used near-eutectic mixtures of bmimAlCl
and bmimCl that contained 40 or 60 mol % AlCl . To
bmimCl (3 g), a calculated amount of freshly distilled
AlCl was added; the reaction mixture was strongly
4
(
(
bmimNTf ), 1-decyl-3-methylimidazolium bromide
2
4
dmimBr), or 1-butyl-3-methylimidazolium chloride
–
4
–
4
chloroaluminate with varied AlCl concentrations
(
bmimCl and bmimAlCl4).
3
heated, and a clear liquid was formed.
EXPERIMENTAL
Preparation of Mesoporous Al(OH) · nH O
3
2
Synthesis of Halide ILs (bmimCl and bmimBr)
From Al(O-iPr) . Aluminum isopropoxide was dis-
3
solved in benzene. The cosolvent used was freshly pre-
pared and dried acetonitrile or dimethylformamide. The
solutions were mixed with an IL. Then, the solvents
were distilled off in vacuo at temperatures not higher
than 80°ë. Very fine solid particles of aluminum isopro-
poxide were formed and uniformly distributed over the
bulk of in the IL. The particle diameter was not greater
than 100 µm. To this mixture, water was added in an
The synthesis procedure is described in works [10, 11].
Butyl halide taken in a 20% excess was mixed with
N-methylimidazole, and acetonitrile was added to the
mixture in provide uniform boiling. The mixture was
refluxed for 2–4 h, acetonitrile was distilled off in
vacuo, the residue was rinsed three times with equal
volumes of ethyl acetate to remove unreacted reagents,
and finally ethyl acetate and water were removed from
the product in vacuo. The yield was 65–80%; most loss
was during ethyl acetate rinsing.
amount sufficient for Al(OH) formation. The mixture
3
was stirred and left to stand at room temperature for
1
week for hydrolysis and gel formation. Gel formation
Example synthesis: butyl bromide (32.9 g, 0.24 mol), started soon when, after water addition, the mixture of
N-methylimidazole (16.4 g, 0.2 mol), and acetonitrile IL, aluminum isopropoxide, and H O was ultrasoni-
30 mL) were refluxed for 2.5 h. The product was rinsed cated (a UZDN-A instrument, 300 W, 22 ± 1.65 kHz).
2
(
with three 30-mL portions of ethyl acetate. The yield After 7 days, the IL and isopropanol were extracted
was 31.5 g bmimBr (72%). The product was a thick from the gel with acetonitrile or ethanol (two times for
light yellow liquid which crystallized upon standing. 4 h each in a flask with a refluxer). The solid precipitate
Thus-prepared bmimCl was virtually colorless.
was filtered with a porous-bottomed funnel, and the IL
1
511

1
512
ASLANOV et al.
Characteristics of aluminum hydroxide samples
IL + Al-precursor systems
Specific
Run
IL and water amounts per 1.5 g Al(O-iPr)3
Properties of IL
surface area,
pore volume*
Notes
no.
IL volume, mL
H2O (mL)
1
2
3
4
Hydrophilic
325/1.03
326/1.24
606/1.88
423/1.36
bmimBr
1
1
4
4
0.1985
2.0
The same
"
"
2.0
2.0
Ultrasonication during
gel formation
5
6
362/1.10
278/0.66
dmimBr
1
1
0.1985
0.1985
The same
Addition of NH OH
4
to pH 9
7
8
9
Hydrophobic
589/1.75
528/1.14
313/0.67
bmimNTf2
The same
"
1.5
4
0.1985
2.0
1.25 0.1975
Addition of 3 wt %
PEG
1
1
1
0
1
2
Hydrophilic
Hydrophobic
390/0.26
333/0.26
399/0.20
bmimCl : AlCl3,
–
–
Addition of NH OH**
4
AlCl weight fraction = 0.2
3
bmimCl : AlCl3,
The same
AlCl weight fraction = 0.4
3
bmimNTf2
1
0.1985
2
3
Notes: * In the numerator, Al(OH) · nH O specific surface areas (m /g); in the denominator, pore volumes (cm /g) with pore diameters
3
2
less than 40 nm.
* In the amount required for Al(OH) · nH O precipitation.
*
3
2
was recovered. The solid residue was dried in air for
The phase composition of products (Al O · nH O)
2 3 2
1
−2 h at 100–120°ë.
was studied on a DRON-3 diffractometer (2θ = 5°–60°,
CuK radiation).
From AlCl . To the chloride–chloroaluminate IL,
α
3
an aliquot of 25% aqueous ammonia required for
hydrolyzing tetrachloroaluminate ions was added
under vigorous stirring:
RESULTS AND DISCUSSION
–
4
The rate of aluminum isopropoxide hydrolysis in
hydrophilic or hydrophobic ILs was expected to be dif-
ferent because of different solubilities of water in these
ILs. However, one week of structuring led to complete
hydrolysis in all samples. It appeared that from hetero-
–
AlCl + 3NH + 3H O = Al(OH) ↓ + 3NH Cl + Cl .
3
2
3
4
The precipitate was left to age for 1 week; the last
day, it was heated for 4 h to 100°ë to enhance aging,
cooled, and centrifuged. The precipitate was washed
alternately with ethanol and water to remove the IL and
geneous IL + aluminum precursor + H O systems, alu-
2
minum hydroxide was obtained with higher specific
NH Cl and dried at 150°ë.
4
2
surface areas (up to 600 m /g) and greater specific pore
From Al(acac)(O-iPr) . To obtain homogeneous
2
3
volumes (up to 1.88 cm /g) than from initially homoge-
solutions of the aluminum derivative in a hydrophobic
IL, one of the three isopropoxide moieties was substi-
tuted by an acetyl acetone moiety (acac). The resulting
Al(acac)(O-iPr) was dissolved in the bmimNTf IL. The
hydrolysis and separation of porous aluminum hydrox-
ide were performed as with aluminum isopropoxide.
neous IL + aluminum precursor + H O systems; com-
2
pare runs 3 and 7 with runs 10–12 (table). Ultrasonica-
tion in the beginning of gel formation decreased both
the specific surface area and the pore volume, despite
the enhancement of gel formation; compare run 3 with
run 4 (table). When the pH of the system was increased
2
2
The pore-structure parameters for Al(OH) were to 9 by adding aqueous NH in order to complete
3
3
derived from low-temperature nitrogen adsorption/des- hydrolysis, both the specific surface area and the pore
orption isotherms. The isotherms were recorded on an volume decreased; compare runs 5 and 6 (table). Addi-
ASAP 2010 Micromeritics automated sorption meter. tion of 3 wt % PEG decreased the specific surface area
Standard instrumental software was used in isotherm and pore volume; compare runs 7 and 9 (table). The fol-
processing.
lowing fact is interesting. When the ratios between the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007

PREPARATION OF MESOPOROUS ALUMINUM HYDROXIDE
1513
IL and water that gave the best results for hydrophilic
ACKNOWLEDGMENTS
ILs were used for hydrophobic ILs, the pore volume
decreased; compare runs 3, 7, and 8 (table).
The authors are thankful to G.P. Murav’eva and
O.E. Korneichuk for help and I.I. Ivanova for fruitful
discussion.
This work was supported by the Russian Foundation
for Basic Research, project no. 05-03-32760a.
In hydrophilic ILs that formed homogeneous sys-
tems, aqueous ammonia was used for hydrolyzing
AlCl . One could think that the use of aqueous NH is
3
3
the reason of the low specific surface areas and low
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007