Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 1, pp. 1−5.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
N.B. Kondrashova, O.G. Vasil’eva, V.A. Val’tsifer, S.A. Astaf’eva, V.N. Strel’nikov, 2009, published in Zhurnal Prikladnoi Khimii, 2009,
Vol. 82, No. 1, pp. 3−7.
AND INDUSTRIAL INORGANIC CHEMISTRY
Preparation of Mesoporous Silicon Dioxide with High Speciﬁ c
N. B. Kondrashova, O. G. Vasil’eva, V. A. Val’tsifer, S. A. Astaf’eva, and V. N. Strel’nikov
Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, Perm, Russia
Received April 1, 2008
Abstract—The influence of the reactant ratio on the specific surface area, total pore volume, and mean pore
diameter of mesoporous silicon dioxide prepared by the sol–gel method was examined. The optimal reactant ratio
for preparing the material with a high specific surface area was determimed.
Mesoporous synthetic materials with pronounced
porous hexagonal structures of the size 2–10 nm and
with a high speciﬁ c surface area (~1000 m
) ﬁ nd
increasing use in various branches of industry, medicine,
and agriculture. Such materials show promise in chemical
and biochemical processes as inorganic sorbents,
catalysts, and catalyst supports. Therefore, preparation
of mesoporous synthetic materials with controllable pore
size is a topical problem.
One of the most efﬁ cient procedures for preparing
nanosized materials with predictable properties of the
final product is chemical liquid-phase condensation
with the formation of difﬁ cultly soluble compounds. By
varying the precipitation conditions (temperature, pH,
component ratio, component concentrations, addition of
surfactants and organic modiﬁ ers), it is possible to vary
in a wide range the phase composition, size, and shape of
the particles formed . Published data on this matter are
contradictory, and therefore it is necessary to optimize the
conditions of preparation of mesoporous silicon dioxide
as support for metal oxide catalysts.
As a source of silicon dioxide we used tetraethoxysilane
(TEOS). Its hydrolysis yields silica gel in accordance with
the following scheme:
O → Si(OH)
Formation of silicon dioxide is accompanied by
various physical processes: phase formation, isothermal
recondensation, coagulation (preparation of sol),
and gelation. The initial synthesis conditions largely
determine the process kinetics, properties of the gels, and
structure of the ﬁ nal materials.
Many methods used for preparing sols with a narrow
particle-size distribution are based on the concepts of
phase formation in supersaturated solutions [2–5].
Nuclei of silica particles are formed during the
induction period. Their concentration does not change the
subsequent steps of particle growth, which is a necessary
condition for preparing sols with a narrow particle-size
distribution . The induction period decreases with
an increase in the total concentration of silica. The
process rate is higher in the system with the higher initial
concentration of silicic acid when a larger number of
nuclei are formed, i.e., when the interface surface area
is higher .
The sol–gel transition involves formation of a three-
dimensional network of chains threading the whole
volume of the sol. The gel strength increases with an
increase in the silica concentration, but the rate of the gel
breakdown increases also .
The effect of pH is also strong. Starting from a small
supersaturation, the polycondensation in the system
occurs only by isothermal recondensation of particles.
Its rate is pH-dependent and grows with an increase
in pH from 3 to 10 . The higher the pH, the lower
the strength of the structure and the earlier it starts to
spontaneously degrade. The structure and properties