Phase Domain of the Cubic Im3̄m Mesoporous Silica in the EO106PO70EO106−Butanol−H2O System

Abstract

n-butanol has been chosen as an organic additive in the SiO(2)-EO(106)PO(70)EO(106)-H(2)O system at low HCl concentrations, for the generation of large-pore mesoporous silicas with easily tailored textural and structural properties. As opposed to previous reports on syntheses of cubic mesoporous silica that are usually performed in a very narrow composition range, we report now the possibility of preparing large-pore cagelike mesoporous silicas in a wide range of synthesis mixture compositions. Particularly, the cubic Imm silica with large interconnected cagelike pores (SBA-16) can easily be synthesized with controlled pore sizes and wall thicknesses, depending upon the synthesis mixture composition. The primary mesopore volume of the SBA-16 cages can be tuned from 0.27 to 0.56 cm(3) g(-)(1), and the mesopore size is shown to range from 4.7 to 7.2 nm, by performing a simple adjustment of the starting mixture composition. With the synthesis parameters varied, we describe the first complete diagram of the product phase domains obtained for silica mesophases in a SiO(2)-EO(106)PO(70)EO(106)-butanol-H(2)O system. Other ordered mesophases also observed in this system are the face-centered cubic Fmm silica mesophase and a 2D hexagonal-like mesostructure. Importantly here, the use of a low acid catalyst concentration regime allowed the preparation of silica mesophases in almost thermodynamically controlled conditions because of slow condensation kinetics of the inorganics. Such conditions enabled the introduction of n-butanol as the phase-controlling agent in the system, providing efficient tuning of the mesophase topology. The description of the phase domains provides a future basis for the design of large-pore mesoporous silicas with tailored textural and structural properties. Mesoporous samples obtained within the composition ranges of the phase domains are characterized by powder X-ray diffraction (PXRD) and nitrogen physisorption measurements.