Mesoporos

ISSN 1061 933X, Colloid Journal, 2010, Vol. 72, No. 6, pp. 737–742. © Pleiades Publishing, Ltd., 2010.

Synthesis and Formation of Hierarchical Mesoporous Silica
Network in Acidic Aqueous Solutions of Sodium Silicate
and Cationic Surfactant1
Yi Wang
Center of Analysis and Measurement, Fudan University, Shanghai 200433, People’s Republic of China
e mail: wangyifd@fudan.edu.cn
ReceivedNovember 2, 2009

Abstract—Synthesis and formation of hierarchical mesoporous silica network in acidic aqueous solutions of
commercial sodium silicate and cationic surfactant were studied by SEM, TEM, XRD and nitrogen adsorp
tion–desorption methods. The formation process occurs through several steps, involving (1) formation of
mesoporous silica nanoparticles; (2) aggregation of mesoporous silicananoparticles into blocks; (3) growth
of silica nanorods in closely packed arrays by merging of silica nanoparticles; (4) separation of the nanorods
to form 3D silica network; and (4) shrinking of the mesoporous silica network. The as prepared 3D silica net
work exhibits bimodal morphology constituting mesoporous and macroporous phases.
DOI: 10.1134/S1061933X10060025
1

1. INTRODUCTIONSince the ordered mesoporous materials (FSM 16
and M41S families) was first prepared by Yanagisawa
etc. [1] and Mobil Research [2], respectively, much
attention was paid to the synthesis of mesoporous
molecular sieves with highly controllable structures
and morphologies for the catalytic, adsorption, and
separation applications in industrial processes [3–6].
A wide variety of hierarchicalmesoporous silica mate
rials with desirable microstructures (two or three
dimensional periodic symmetries [7–9]) and macro
scopical morphologies (ropes [10], films [11, 12],
monoliths [13], spheres [14, 15], fibers [16], and rod
like powders [17–19]) were synthesized under acidic
or basic conditions [20, 21]. Further researches [10,
19, 22–24] indicated that the morphologies of meso
porousmaterials resulted from the surfactant micelles
alignments, and hence, the majority of methods for
preparing mesoporous silica with special morphology
needs to use expensive organic silica precursors such as
TEOS [25, 26], or fluoride inducement [27], or rapid
pH adjustment [19] for fine tuning the surfactant
micelles, that sophisticates the synthesis and applica
tion of these materials.Recently, it had been reported
that the growth and evolution of nanoparticles were
related to the structuring of mesoporous SBA 15 [28].
This leads to the important question – is the evolution
of microstructure associated with macroscopical mor
phologies? Zhao et al. [29] applied “Colloidal Phase
Separation Mechanism” to explain the morphologies
and structures of mesoporous materials; thephase
1 The article is published in the original.

separation is, however, too fast to observe the nucle
ation and formation processes. Mokaya [30] also
showed that the morphologies of mesoporous silica
materials can be modified by hydrothermally induced
morphological transformation of nanoparticles,
accompanied with some changes in micro structure,
but the resulting morphologies were hardlypredict
able. It is known that highly cross linked network
materials with a desired porous internal environment
can provide pathways for encapsulation, delivery and
release of drug molecule are of scientific interest [31–
35]; they are, however, rarely synthesized at low cost.
Studying the process of growing mesoporous silica
network would help improve synthesis and under
standing theencapsulation, delivery and release of
drug molecule. Herein, we reported a simple method
to synthesize hierarchical mesoporous silica network
in acidic aqueous solutions of sodium silicate and cat
ionic surfactant (CTAB). The formation of the hierar
chical mesoporous silica network as well as micro
structures was observed and a mechanism of the for
mation of netlike morphology was suggested....