Controlling the Crystalline Structure of Mesoporous Silica by Hofmeister Effects
Ming-Chang Liu (劉銘璋)a, Hwo-Shuenn Sheu (許火順)b, Hsin-Yi Lee (李信義)b,
and Soofin Cheng (鄭淑芬)a
a
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
E-mail: chem1031@ccms.ntu.edu.tw; Fax: +886-2-23636359
b
Research Division, National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
For mesoporous silica synthesized by acidic route, the interaction between the cationic
surfactant (S+) and protonated silicate (I+) is proposed to be S+X-I+, where X- is the anion present in
the synthesis gel [1]. This interaction can be modified by varying the X- species. Che et al. [2]
found that four types of well-ordered mesophases were synthesized using cetyltetraethylammonium
(CTEA) ion as the template in various acids. They proposed that the size of the counter anions of
the acids played an important role in micelle formation. Recently, Leontidis [3] disclosed a review
article emphasizing on the Hofmeister effect of the counter anions. The anions were reported to
change the hydrolysis and condensation rates of the silicate precursors. Moreover, the surface
properties, morphologies and the hydrothermal stability of the silica products were affected. In the
present study, we developed a method to fine tune the crystalline structures of the mesoporous silica
by addition of various salt solutions into the silica gels precipitated in acidic environment and using
CTEA as the pore-directing agent. The trend of phase transformation influenced by the anions was
found to follow the Hofmeister series [4]. By the addition of cosmotropic anions, mesostructures of
low packing parameter and high curvature were retained. In contrast, mesophases of high packing
parameter and low curvature were obtained with chaotropic anions. In the experiments of studying
the competition between anion pairs, the results showed that the anions behaved in consistence to
the Hofmeister effect of salting-in.
REFERENCES
[1] Lin HP, Kao CP, Mou CY, Liu SB. J Phys Chem B 2000, 104, 7885.
[2] Che S, Lim S, Kaneda M, Yoshitake H, Terasaki O and Tatsumi T, J. Am. Chem. Soc. 2002, 124,
13962.
[3] Leontidis E, Current Opinion in Colloid & Interface Science 2002, 7, 81.
[4] Cacace MG, Landau EM, Ramsden JJ. Quart Rev Biophys 1997, 30, 241.