Hexagonal, cubic and lamellar aluminoborate mesophases containing octahedral aluminium and tetrahedral boron are prepared and characterized for the first time

Ayyappan, S.

Rao, C. N. R.

English

Indian Academy of Sciences

 
2015105
2θ (Cu-Kα) / °
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Mesoporous aluminoborates
S. Ayyappan and C. N. R. Rao*
CSIR Centre of Excellence in Chemistry and Materials Research Centre, Indian Institute of Science, Bangalore 560 012, India and
Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India
Hexagonal, cubic and lamellar aluminoborate mesophases
containing octahedral aluminium and tetrahedral boron are
prepared and characterized for the first time.
Since the first synthesis of mesoporous silica,1 there has been
intense activity in the design and synthesis of a variety of
mesoporous solids.2–4 These studies have also unravelled the
mechanism of formation of these materials by means of
supramolecular templating involving an unusual combination
of surfactant aggregates and anionic silicate species.4,5 By
varying the pH or the surfactant to silica ratio, hexagonal, cubic
and lamellar forms of silica mesophases have been prepared.6
Besides ionic surfactants, neutral amines7 and polyalkene
oxides8 have been employed to synthesise the mesophases. The
strategy to prepare silica-based mesophases has been extended
to prepare a variety of mesoporous metal oxides such as Al2O3,8
TiO29,10 and ZrO211 and Nb2O5.12 AlPO4 which is isoelectronic
with SiO2 has provided the basis for a distinct family of
microporous materials.13 However, efforts to make hexagonal
mesoporous AlPO4 have not been successful; instead, only
lamellar AlPO4 has been obtained.14 We considered it most
worthwhile to explore the synthesis of the mesoporous phases
of the analogous aluminoborates containing the AlBO422
species. There has been some effort15 to make microporous
aluminoborates with different B/Al ratios, but the products do
not seem to have been adequately characterized. Here, we report
the first successful synthesis and characterization of mesopor-
ous aluminoborate phases in hexagonal, cubic and lamellar
forms. It has been possible to remove the surfactant from the
hexagonal phase and expand the pore size of the hexagonal
phase by using aliphatic hydrocarbons as solubilizing agents.
Mesoporous aluminoborate phases could not be obtained
when cationic surfactants or long-chain amines were employed
for the synthesis. They could however be prepared by
employing sodium dodecyl sulfate (SDS) as the surfactant. In a
typical preparation, to a solution containing Ca, Al and B in
1 : 1 : 1 molar ratio, prepared by dissolving appropriate quan-
tities of CaO and Al(NO3)3 and boric acid in aqueous nitric acid,
sodium dodecyl sulfate (1.0 mol with respect to Ca or Al) was
added under stirring. Ammonia was added to the resulting
turbid solution under constant stirring to reach the desired value
of pH. The resultant gel was maintained at room temperature for
48 h. The product so obtained was washed several times with
distilled water and dried at 100 °C in a hot air oven. X-Ray
diffraction (XRD) patterns of the dried solids were recorded
with a Rich–Seifert (model XRD 3000TT) instrument. Fig. 1
shows the XRD patterns of the products obtained at different pH
values. The XRD pattern of the product obtained at pH 2
[Fig. 1(a)] is characteristic of a hexagonal phase with a d100
value of 36.1 Å (a0 = 41.7 Å). The XRD pattern of the product
Fig. 1 X-Ray diffraction patterns of the aluminoborate mesophases: (a)
hexagonal, (b) cubic and (c) lamellar
Fig. 2 TEM images of (a) hexagonal and (b) lamellar aluminoborate
mesophases
Chem. Commun., 1997 575
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–400–2000300400
δ (11B)
δ (27Al)
200 100 0 –100 –200
(b)
(a)
obtained at a pH of 3.5 [Fig. 1(b)] corresponds to that of a cubic
phase. This pattern could be indexed with a = 83.5 Å. The XRD
pattern of the product obtained at pH ca. 5.5 [Fig. 1(c)] is
characteristic of a lamellar phase and accordingly exhibits the
various 00l reflections (d001 = 32.5 Å). The scanning electron
micrographs of the hexagonal and lamellar phases exhibit
characteristic differences in morphology, the lamellar form
showing the flaky structure. The transmission electron micro-
scope (TEM) image (recorded with a JEOL JEM 3010
microscope) reveals the presence of disordered hexagonal pores
with an opening of ca. 32 Å with a wall thickness of ca. 11 Å
[Fig. 2(a)]. The TEM image of the lamellar phase shows an
interlayer separation of ca. 32 Å [Fig. 2(b)].
EDAX analysis of the aluminoborate mesophases showed the
Ca : Al molar ratio to be 1 : 1, while an ICP analysis gave a Al : B
molar ratio of 1 : 1. Thermogravimetry showed the loss of water
by 150 °C and of the surfactant by 600 °C. Based on the mass
loss data and assuming the Ca : Al : B molar ratio to be 1 : 1 : 1,
the composition of the aluminoborate–surfactant adduct works
out to be CaO·0.5Al2O3·0.5B2O3·0.6SDS·1.5H2O. The %mass
of boron from the ICP analysis (3.15 ± 0.25%) is also consistent
with the theoretical value of 3.2% based on the empirical
formula. The IR spectrum of this adduct showed a boron–
oxygen stretching band in the region 900–1100 cm21 due to
BO4 tetrahedra. The IR band characteristic of BO3 units in the
region 1200–1400 cm21 was absent. Significant structural
information was obtained by means of 27Al and 11B MAS NMR
spectra (recorded with a Bruker MSL-300 spectrometer) of the
hexagonal aluminoborate mesophase. The 27Al NMR signal is
centred around d 0.0 [Fig. 3(a)], characteristic of an octahedral
environment of Al.16 The 11B NMR signal is also centred
around d 0.0 [Fig. 3(b)] suggesting a tetrahedral environment
for boron.17
By heating the as-prepared hexagonal mesophase to 300 °C,
we could remove some of the surfactant without destroying the
structure. Thus, the XRD pattern of the resulting product shows
the mesoporous structure with a d100 value of 35.2 Å. We could
however remove the surfactant by refluxing the hexagonal
mesophase with acidified ethanol for 3 h. The removal of the
template was confirmed by the absence of mass loss over the
temperature range where the template is normally removed as
well as by the XRD pattern. The removal of the surfactant from
the hexagonal phase was confirmed by the IR spectra,which
showed the near-absence of bands arising from CH2 groups.
Accordingly, the surface area of the hexagonal aluminoborate
obtained by calcination was ca. 100 m2 g21 and that of the
sample obtained by alcohol extraction was 470 m2 g21; their
XRD patterns were not identical.
We have been able to expand the pore size of the hexagonal
mesoporous aluminoborate by the use of n-alkanes as solubiliz-
ing agents. For this purpose, we added the alkane along with the
surfactant solution to the acidic solution containing Ca, Al and
B, maintaining the molar ratio of the alkane to the surfactant to
be 1 : 1. This molar ratio was found to be optimal for expanding
the pore size. The XRD patterns gave d100 values of 49.0 and
56.6 Å respectively with n-octane and n-hexadecane, compared
to the value of 36.1 Å obtained in the absence of the alkanes.
We have also varied the Al : B ratio and obtained hexagonal
mesoporous phases with Al : B ratios down to 0.5 : 1.5. By using
Na+ as the cation instead of Ca2+, a hexagonal mesoporous
phase with a Na : Al : B ratio of 2 : 1 : 1 was obtained with a d100
value of 35.5 Å.
References
1 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge,
K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Sheppard,
S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc.,
1992, 114, 10 834.
2 P. Behrens and G. D. Stucky, Angew. Chem., Int. Ed. Engl., 1993, 32,
696.
3 P. Behrens, Angew. Chem., Int. Ed. Engl., 1996, 35, 515.
4 J. S. Beck and J. C. Vartuli, Curr. Opinion Solid State Mater. Sci., 1996,
1, 76.
5 Q. Huo, D. I. Margolese, U. Ciesla, D. G. Demuth, P. Feng, T. E. Gier,
P. Sieger, A. Firouzi, B. F. Chmelka, F. Schüth and G. D. Stucky, Chem.
Mater., 1994, 6, 1176; Q. Huo, D. Margolese and G. D. Stucky, Chem.
Mater., 1996, 8, 1147.
6 A. Monnier, F. Schüth, Q. Huo, D. Kumar, D. Margolese, R. S.
Maxwell, G. D. Stucky, M. Krishnamurty, P. Petroff, A. Firouzi,
M. Janicke and B. F. Chmelka, Science, 1993, 261, 1299; J. C. Vartuli,
K. D. Schmitt, C. T. Kresge, W. J. Roth, M. E. Leonowicz,
S. B. McCullen, S. D. Helbring, J. S. Beck, J. S. Schlenker, D. H. Olson
and E. W. Sheppard, Chem. Mater., 1994, 6, 2317.
7 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 365.
8 S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem., Int. Ed. Engl., 1996,
35, 1102.
9 D. M. Antonelli and J. Y. Ying, Angew. Chem., Int. Ed. Engl., 1995, 34,
2014.
10 N. Ulagappan and C. N. R. Rao, Chem. Commun., 1996, 1685.
11 U. Ciesla, S. Schacht, G. D. Stucky, K. K. Unger and F. Schüth, Angew.
Chem., Int. Ed. Engl., 1996, 35, 426; N. Ulagappan, Neeraj,
B. V. N. Raju and C. N. R. Rao, Chem. Commun., 1996, 2243.
12 D. M. Antonelli and J. Y. Ying, Angew. Chem., Int. Ed. Engl., 1996, 35,
426.
13 S. T. Wilson, B. M. Lok, C. A. Messina, T. R. Connan and
E. M. Flanigan, J. Am. Chem. Soc., 1982, 104, 1176.
14 A. Sayari, V. R. Karra, J. S. Reddy and I. L. Moudrakovski, Chem.
Commun., 1996, 411.
15 J. Wang, S. Feng and R. Xu, J. Chem. Soc., Chem. Commun., 1989, 265;
J. Yu, K. Tu and R. Xu, in Zeolites and Related Microporous Materials:
State of the Art, ed. J. Weitkamp, H. G. Karge, H. Pfeifer and W.
Hölderich, Elsevier, Amsterdam, 1994.
16 C. A. Fyfe, G. C. Gobbi, J. Klinowski, J. M. Thomas and S. Ramdas,
Nature, 1982, 96, 530.
17 C. A. Fyfe, L. Berni, H. G. Clark, J. A. Davies, G. C. Cobbi,
J. S. Hartman, P. J. Hayes and R. E. Wasilyshen, Adv. Chem. Ser., 1983,
211, 405.
Received, 18th November 1996; Com. 6/07782J
Fig. 3 MAS NMR spectra of mesoporous aluminoborate: (a) 27Al spectrum
and (b) 11B spectrum
576 Chem. Commun., 1997
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Mesoporous aluminoborates

Publications of the IAS Fellows

 2015105
2θ (Cu-Kα) / °
In
te
ns
ity
 (a
.u.
)
(10
0)
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0)
(21
1)
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(00
2)
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(00
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(00
7)
(a)
(b)
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Mesoporous aluminoborates
S. Ayyappan and C. N. R. Rao*
CSIR Centre of Excellence in Chemistry and Materials Research Centre, Indian Institute of Science, Bangalore 560 012, India and
Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India
Hexagonal, cubic and lamellar aluminoborate mesophases
containing octahedral aluminium and tetrahedral boron are
prepared and characterized for the first time.
Since the first synthesis of mesoporous silica,1 there has been
intense activity in the design and synthesis of a variety of
mesoporous solids.2–4 These studies have also unravelled the
mechanism of formation of these materials by means of
supramolecular templating involving an unusual combination
of surfactant aggregates and anionic silicate species.4,5 By
varying the pH or the surfactant to silica ratio, hexagonal, cubic
and lamellar forms of silica mesophases have been prepared.6
Besides ionic surfactants, neutral amines7 and polyalkene
oxides8 have been employed to synthesise the mesophases. The
strategy to prepare silica-based mesophases has been extended
to prepare a variety of mesoporous metal oxides such as Al2O3,8
TiO29,10 and ZrO211 and Nb2O5.12 AlPO4 which is isoelectronic
with SiO2 has provided the basis for a distinct family of
microporous materials.13 However, efforts to make hexagonal
mesoporous AlPO4 have not been successful; instead, only
lamellar AlPO4 has been obtained.14 We considered it most
worthwhile to explore the synthesis of the mesoporous phases
of the analogous aluminoborates containing the AlBO422
species. There has been some effort15 to make microporous
aluminoborates with different B/Al ratios, but the products do
not seem to have been adequately characterized. Here, we report
the first successful synthesis and characterization of mesopor-
ous aluminoborate phases in hexagonal, cubic and lamellar
forms. It has been possible to remove the surfactant from the
hexagonal phase and expand the pore size of the hexagonal
phase by using aliphatic hydrocarbons as solubilizing agents.
Mesoporous aluminoborate phases could not be obtained
when cationic surfactants or long-chain amines were employed
for the synthesis. They could however be prepared by
employing sodium dodecyl sulfate (SDS) as the surfactant. In a
typical preparation, to a solution containing Ca, Al and B in
1 : 1 : 1 molar ratio, prepared by dissolving appropriate quan-
tities of CaO and Al(NO3)3 and boric acid in aqueous nitric acid,
sodium dodecyl sulfate (1.0 mol with respect to Ca or Al) was
added under stirring. Ammonia was added to the resulting
turbid solution under constant stirring to reach the desired value
of pH. The resultant gel was maintained at room temperature for
48 h. The product so obtained was washed several times with
distilled water and dried at 100 °C in a hot air oven. X-Ray
diffraction (XRD) patterns of the dried solids were recorded
with a Rich–Seifert (model XRD 3000TT) instrument. Fig. 1
shows the XRD patterns of the products obtained at different pH
values. The XRD pattern of the product obtained at pH 2
[Fig. 1(a)] is characteristic of a hexagonal phase with a d100
value of 36.1 Å (a0 = 41.7 Å). The XRD pattern of the product
Fig. 1 X-Ray diffraction patterns of the aluminoborate mesophases: (a)
hexagonal, (b) cubic and (c) lamellar
Fig. 2 TEM images of (a) hexagonal and (b) lamellar aluminoborate
mesophases
Chem. Commun., 1997 575
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–400–2000300400
δ (11B)
δ (27Al)
200 100 0 –100 –200
(b)
(a)
obtained at a pH of 3.5 [Fig. 1(b)] corresponds to that of a cubic
phase. This pattern could be indexed with a = 83.5 Å. The XRD
pattern of the product obtained at pH ca. 5.5 [Fig. 1(c)] is
characteristic of a lamellar phase and accordingly exhibits the
various 00l reflections (d001 = 32.5 Å). The scanning electron
micrographs of the hexagonal and lamellar phases exhibit
characteristic differences in morphology, the lamellar form
showing the flaky structure. The transmission electron micro-
scope (TEM) image (recorded with a JEOL JEM 3010
microscope) reveals the presence of disordered hexagonal pores
with an opening of ca. 32 Å with a wall thickness of ca. 11 Å
[Fig. 2(a)]. The TEM image of the lamellar phase shows an
interlayer separation of ca. 32 Å [Fig. 2(b)].
EDAX analysis of the aluminoborate mesophases showed the
Ca : Al molar ratio to be 1 : 1, while an ICP analysis gave a Al : B
molar ratio of 1 : 1. Thermogravimetry showed the loss of water
by 150 °C and of the surfactant by 600 °C. Based on the mass
loss data and assuming the Ca : Al : B molar ratio to be 1 : 1 : 1,
the composition of the aluminoborate–surfactant adduct works
out to be CaO·0.5Al2O3·0.5B2O3·0.6SDS·1.5H2O. The %mass
of boron from the ICP analysis (3.15 ± 0.25%) is also consistent
with the theoretical value of 3.2% based on the empirical
formula. The IR spectrum of this adduct showed a boron–
oxygen stretching band in the region 900–1100 cm21 due to
BO4 tetrahedra. The IR band characteristic of BO3 units in the
region 1200–1400 cm21 was absent. Significant structural
information was obtained by means of 27Al and 11B MAS NMR
spectra (recorded with a Bruker MSL-300 spectrometer) of the
hexagonal aluminoborate mesophase. The 27Al NMR signal is
centred around d 0.0 [Fig. 3(a)], characteristic of an octahedral
environment of Al.16 The 11B NMR signal is also centred
around d 0.0 [Fig. 3(b)] suggesting a tetrahedral environment
for boron.17
By heating the as-prepared hexagonal mesophase to 300 °C,
we could remove some of the surfactant without destroying the
structure. Thus, the XRD pattern of the resulting product shows
the mesoporous structure with a d100 value of 35.2 Å. We could
however remove the surfactant by refluxing the hexagonal
mesophase with acidified ethanol for 3 h. The removal of the
template was confirmed by the absence of mass loss over the
temperature range where the template is normally removed as
well as by the XRD pattern. The removal of the surfactant from
the hexagonal phase was confirmed by the IR spectra,which
showed the near-absence of bands arising from CH2 groups.
Accordingly, the surface area of the hexagonal aluminoborate
obtained by calcination was ca. 100 m2 g21 and that of the
sample obtained by alcohol extraction was 470 m2 g21; their
XRD patterns were not identical.
We have been able to expand the pore size of the hexagonal
mesoporous aluminoborate by the use of n-alkanes as solubiliz-
ing agents. For this purpose, we added the alkane along with the
surfactant solution to the acidic solution containing Ca, Al and
B, maintaining the molar ratio of the alkane to the surfactant to
be 1 : 1. This molar ratio was found to be optimal for expanding
the pore size. The XRD patterns gave d100 values of 49.0 and
56.6 Å respectively with n-octane and n-hexadecane, compared
to the value of 36.1 Å obtained in the absence of the alkanes.
We have also varied the Al : B ratio and obtained hexagonal
mesoporous phases with Al : B ratios down to 0.5 : 1.5. By using
Na+ as the cation instead of Ca2+, a hexagonal mesoporous
phase with a Na : Al : B ratio of 2 : 1 : 1 was obtained with a d100
value of 35.5 Å.
References
1 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge,
K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Sheppard,
S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc.,
1992, 114, 10 834.
2 P. Behrens and G. D. Stucky, Angew. Chem., Int. Ed. Engl., 1993, 32,
696.
3 P. Behrens, Angew. Chem., Int. Ed. Engl., 1996, 35, 515.
4 J. S. Beck and J. C. Vartuli, Curr. Opinion Solid State Mater. Sci., 1996,
1, 76.
5 Q. Huo, D. I. Margolese, U. Ciesla, D. G. Demuth, P. Feng, T. E. Gier,
P. Sieger, A. Firouzi, B. F. Chmelka, F. Schu¨th and G. D. Stucky, Chem.
Mater., 1994, 6, 1176; Q. Huo, D. Margolese and G. D. Stucky, Chem.
Mater., 1996, 8, 1147.
6 A. Monnier, F. Schu¨th, Q. Huo, D. Kumar, D. Margolese, R. S.
Maxwell, G. D. Stucky, M. Krishnamurty, P. Petroff, A. Firouzi,
M. Janicke and B. F. Chmelka, Science, 1993, 261, 1299; J. C. Vartuli,
K. D. Schmitt, C. T. Kresge, W. J. Roth, M. E. Leonowicz,
S. B. McCullen, S. D. Helbring, J. S. Beck, J. S. Schlenker, D. H. Olson
and E. W. Sheppard, Chem. Mater., 1994, 6, 2317.
7 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 365.
8 S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem., Int. Ed. Engl., 1996,
35, 1102.
9 D. M. Antonelli and J. Y. Ying, Angew. Chem., Int. Ed. Engl., 1995, 34,
2014.
10 N. Ulagappan and C. N. R. Rao, Chem. Commun., 1996, 1685.
11 U. Ciesla, S. Schacht, G. D. Stucky, K. K. Unger and F. Schu¨th, Angew.
Chem., Int. Ed. Engl., 1996, 35, 426; N. Ulagappan, Neeraj,
B. V. N. Raju and C. N. R. Rao, Chem. Commun., 1996, 2243.
12 D. M. Antonelli and J. Y. Ying, Angew. Chem., Int. Ed. Engl., 1996, 35,
426.
13 S. T. Wilson, B. M. Lok, C. A. Messina, T. R. Connan and
E. M. Flanigan, J. Am. Chem. Soc., 1982, 104, 1176.
14 A. Sayari, V. R. Karra, J. S. Reddy and I. L. Moudrakovski, Chem.
Commun., 1996, 411.
15 J. Wang, S. Feng and R. Xu, J. Chem. Soc., Chem. Commun., 1989, 265;
J. Yu, K. Tu and R. Xu, in Zeolites and Related Microporous Materials:
State of the Art, ed. J. Weitkamp, H. G. Karge, H. Pfeifer and W.
Ho¨lderich, Elsevier, Amsterdam, 1994.
16 C. A. Fyfe, G. C. Gobbi, J. Klinowski, J. M. Thomas and S. Ramdas,
Nature, 1982, 96, 530.
17 C. A. Fyfe, L. Berni, H. G. Clark, J. A. Davies, G. C. Cobbi,
J. S. Hartman, P. J. Hayes and R. E. Wasilyshen, Adv. Chem. Ser., 1983,
211, 405.
Received, 18th November 1996; Com. 6/07782J
Fig. 3 MAS NMR spectra of mesoporous aluminoborate: (a) 27Al spectrum
and (b) 11B spectrum
576 Chem. Commun., 1997
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Mesoporous aluminoborates

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