Factorial design for the evaluation of the influence of synthesis parameters upon the textural and structural properties of SBA-15 ordered materials

Abstract

A series of well-ordered mesoporous silicas SBA-15 was prepared under various experimental conditions and characterized by N 2 physisorption, small-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of the synthesis conditions on the textural and structural properties of SBA-15 materials was studied using a statistical model built from a full 2 3 factorial design at two levels. The variables chosen were temperature of the reaction of gel formation (synthesis stage), as well as temperature and time of the following hydrothermal treatment of the formed gel (aging stage). Within the experimental conditions, the response equations for surface area, micropore area, total pore volume, mesopore diameter, unit-cell parameter and pore wall thickness show good agreement with the experimental data. The statistical analysis showed that both, synthesis and aging temperatures had a significant influence on the textural and structural properties of SBA-15 materials. Their increase affected in a positive way the BET surface area, total pore volume, pore diameter and unit-cell parameter, producing simultaneously a decrease of micropore area and pore wall thickness. The effect of the gel aging time on the responses studied was not so strong with the exception of micropore area, which continued decreasing with the increase of aging time. Textural and structural differences induced by change in the synthesis conditions are discussed in terms of the mechanism of SBA-15 formation in presence of Pluronic P123.