Vamsi krishna Liu et al ; J.Am.Chem.Soc., 2009, 131,

Introduction :  The surfactant-templated mesoporous materials of uniformly arranged pores with tunable pore diameter of nm and very high surface areas.  It is important to understand the interaction between theorganic templates and the inorganic matrix in the formation of surfactant-templated mesoporous materials.  The surfactant-templated synthesis of the mesoporous silica was mainly divided into two routes: the alkaline synthesis of M41S families and the acidic synthesis of SBA phases. Mesoporous acidic materials synthesis is driven by electrostatic interactions, and the “charge density matching” model, S + X - I + type interaction.  The framework of mesostructured silica templated by CTEA micelles is relatively delicate in comparison to that made by CTMA, due to less degree of silica condensation  The packing parameter (g) is calculated by the equation g = V/(aol), where V is the volume of the hydrocarbon part of the surfactant, l is the lengthof the extended all-trans alkyl tail, and ao is the effective surface area of the headgroup. cubic (Pm3n, etc.) and 3D hexagonal (P6 3 /mmc) with g < 1/3, 2D hexagonal (p6mm) with 1/3 < g < 1/2, cubic(Ia3d) with 1/2 < g < 2/3, and lamellar with g= 1.

TEOS/CTEABr/acid/H 2 O = 1:0.13:3.0:125 CTEABr + H 2 O + acid (H 2 SO 4, HCl, and HNO 3 ) Stirred for 1 h at R.T Cooled to 0 0 C, stirred for 1h Pre cooled TEOS Stirred for 10 min Aged at 0 0 C for 3h Precipitate Filtered Aqueous solutions of salts Experimental Section 0.29 ml of 1.03mM pyrene in ethanol Evaporation of ethanol 100 ml of M CTEABr Stirred at 30 0 C for 12 h (H 2 SO 4, HCl, and HNO 3 ) Cooled to 0 0 C, stirred for 1h Pre cooled TEOS Stirred for 10 min Aged at 0 0 C for 3h Precipitate Filtered Aqueous solutions of salts CTEABr/Py/ TEOS/acid/H2O = 0.13:(6.7 × 10-6):1:3:125. (NaHSO 4, NaH 2 PO 4, NaCl, NaBr, NaNO 3, and NaSCN)

Phase Transformation Studied by In Situ Small-Angle X-ray Scattering 2D hexagonal Bi continous cubic(MCM-48) Cubic(SBA-1) 3D hexagonal

2D hexagonal Bi continous cubic(MCM-48) Cubic(SBA-1) 3D hexagonal HSO 4 - < H 2 PO 4 - ∼ Cl - < Br - ∼ NO 3 - < SCN -, Hofmeister series Right side of series: Kosmotropic ions, Salting out ions. Decreases solubility Left side of series : chaotropic ions, Salting in ions. Increases Solubility

Morphology Changes of Silica with Interfacial Anion Exchange.

 The interfacial anions not only affect the pore structures formed but also influence the architecture of silica framework and the morphology of the silica material.

Interfacial Anion Exchange Probed by Pyrene Fluorescence. is the concentration of excited state molecules at time t, is the initial concentration and Γ is the decay rate or the inverse of the fluorescence lifetime

CBr 3 COO - < HSO 4 - <CH 3 COO - < Cl - < NO 3 - < CCl 3 COO - ∼ CF 3 COO - ∼ SCN -.

 The anions present in the interfacial space between the poredirecting CTEA micelle and the silica wall of mesostructured silica are ready to be exchanged, accompanied by phase transformation and morphology change.  The anion exchange proceeds very fast and there is an equilibrium distribution between interfacial anion and the counter anion in the interface.  The crystallographic phase as well as the morphology of mesostructured silica tends to transform from higher pore curvature toward lower one, which follows the Hofmeister series of salting-in.  The pyrene luminescence study demonstrates that the hydrated anions instead of the net anions should be considered in their binding strength to the head groups of the surfactants.  The mesophase transformation induced by the interfacial anion exchange provides a unique technique to study anions which are not yet included in the Hofmeister series.  mesoporous silica of cubic Ia3d phase, which is not readily formed in mineral acids, can be easily prepared by ion exchange with anions of strongest salting-in power. Conclusions :