Journal of Alloys and Compounds
Synthesis and structure of cage-like mesoporous silica using different precursors
M.C.A. Fantinia,∗, C.F. Kanagussukoa, G.J.M. Ziliotia, T.S. Martinsb
a Instituto de Física, Universidade de São Paulo, Rua do Matão, Travessa R 187, 05508-090, São Paulo, SP, Brazil
b Departamento de Ciências Exatas e da Terra, Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo, Rua Prof. Artur Riedel 275, 09972-270,
Diadema, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2010
Received in revised form 13 January 2011
Accepted 16 January 2011
Available online 22 January 2011
In this work the synthesis of cubic, FDU-1 type, ordered mesoporous silica (OMS) was developed from two
types of silicon source, tetraethyl orthosilicate (TEOS) and a less expensive compound, sodium silicate
(Na2Si3O7), in the presence of a new triblock copolymer template Vorasurf 504 (EO38BO46EO38). For both
silicon precursors the synthesis temperature was evaluated. For TEOS the effect of polymer dissolution
in methanol and the acid solution (HCl and HBr) on the material structure was analyzed. For Na2Si3O7
the influence of the polymer mass and the hydrothermal treatment time were the explored experimental
parameters. The samples were examined by Small Angle X-ray Scattering (SAXS) and Nitrogen Sorption.
For both precursors the decrease on the synthesis temperature from ambient, −25 ◦C, to −15 ◦C improved
the ordered porous structure. For TEOS, the SAXS results showed that there is an optimum amount of
hydrophobic methanol that contributed to dissolve the polymer but did not provoke structural disorder.
The less electronegative Br− ions, when compared to Cl−, induced a more ordered porous structure, higher
surface areas and larger lattice parameters. For Na2Si3O7 the increase on the hydrothermal treatment time
as well as the use of an optimized amount of polymer promoted a better ordered porous structure.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Mesoporous silica
SAXS
Nitrogen sorption
1. Introduction
504 is not yet fully optimized; therefore, this work aimed to find out
the influence ofsome experimentalconditions on thestructuraland
Ordered mesoporous silica (OMS) with a cage like structure, tai-
lored pore size [1] and amorphous walls can be used as adjuvant for
specific antigen delivery [2], among other interesting applications.
Also, OMS are appropriate hosts for catalytic purposes due to their
morphological properties like high specific surface area, large pore
size and uniform pore distribution. Ordered mesoporous structures
can be obtained combining triblock copolymer templates with a
silicon source. More hydrophobic templates are used to obtain
cage-like structures. In particular, FDU-1 type of amorphous silica
with a cage-like mesoporous Fm3m cubic structure has outstanding
figures such as its superficial area (ca. 740 m2 cm−1), wall thickness
(2.9–7.4 nm), pore volume (−0.8 cm3 g−1) and pore size (−12 nm),
that is larger than those of previously reported materials [3].
In this work the synthesis of FDU-1 type OMS was developed
from two types of silicon source, tetraethyl orthosilicate (TEOS) and
a less expensive compound, sodium silicate (Na2Si3O7), in the pres-
ence of a new triblock copolymer, Vorasurf 504 (EO38BO46EO38),
produced by Dow Chemicals, in substitution of the former B50-
6600 (EO39BO47EO39) [3–6]. The synthesis process using Vorasurf
morphological properties of the mesoporous material. For both sil-
icon precursors the synthesis temperature was evaluated. For TEOS
the effects of polymer dissolution in methanol and the acid solu-
tion (HCl and HBr) on the material structure were analyzed. For
Na2Si3O7, the influence of the polymer mass and the hydrothermal
treatment time were the explored experimental parameters. The
samples were examined by Small Angle X-ray Scattering (SAXS)
2. Materials and methods
2.1. Synthesis
In the synthesis with TEOS, 2.5 g of Vorasurf 504 (EO38BO46EO38) was dissolved
in analytical grade methanol (5 ml or 12.5 ml) and then, mixed with HCl or HBr
(2 mol L−1). TEOS (8.9 ml) was added to the first solution after 15 min of intense
magnetic stirring. The final solution stayed in magnetic stirring for 24 h. The temper-
ature of the syntheses was tested, such that samples were prepared: (i) at constant
ambient temperature of 25 ◦C, (ii) at constant temperature of 15 ◦C in the first 3 h of
stirring and (iii) with the homogenized copolymer after a heat treatment for 1 h at
50 ◦C before the alcohol dissolution. The hydrothermal treatment was performed in
a pressure vessel inside a conventional oven at 100 ◦C for 12 h.
The synthesis with Na2Si3O7 used different amounts of Vorasurf 504 (0.5–3.0 g)
and fixed ethanol (2 ml) and water (40 ml) dilution. Small quantities of sodium sil-
icate were added while the solution stayed in magnetic stirring for 6 h. At the last
hour of stirring concentrated HCl (40 ml) was added to the solution. The synthesis
temperature was also tested, such that samples were prepared: (i) at constant ambi-
ent temperature of 25 ◦C and (ii) at constant temperature of 15 ◦C. The hydrothermal
∗
Corresponding author at: Departamento de Física Aplicada. Instituto de Física
da Universidade de São Paulo, P.O. Box 66318, São Paulo 05314-970, SP. Brazil.
Tel.: +55 11 30916882; fax: +55 11 30916749.
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.