Tailoring properties of SBA-15 materials by controlling conditions of hydrothermal synthesis

Abstract

The influence of synthesis time and temperature on the properties of SBA-15 is investigated for the samples prepared by using two different silica sources, tetraethylorthosilicate (TEOS) and sodium metasilicate. The samples studied were obtained via two-step synthesis, which involved an initial self-assembly of polymer and silica species at 40 °C for 2 hours followed by longer hydrothermal treatment at higher temperatures. The SBA-15 samples obtained from both silica sources were highly ordered as evidenced by SAXS spectra showing up to seven reflection peaks characteristic of the P6mm symmetry group. While for the samples studied the specific surface area decreased with increasing time and temperature of the hydrothermal treatment, their mesopore size distributions became narrower and their mesopore widths and mesopore volumes showed a tendency to increase. In contrast, a slight decrease in the mesopore wall thickness and micropore volume was observed with increasing time of this treatment. Also, the samples obtained from sodium metasilicate exhibited thicker mesopore walls than those prepared from TEOS. It was shown that the adsorption properties of SBA-15 can be tailored by adjusting the time and temperature of the hydrothermal treatment and simultaneously reducing the time of the initial self-assembly process from 24 h to 2 h.