Structural variations of MCF and SBA-15-like mesoporous materials as a result of differences in synthesis solution pH

This work illustrated the significance of synthesis solution pH on the structural characteristics of MCF and SBA-15-like mesoporous materials. SBA-15 and MCF-like materials synthesized at pH ≪1.0 and pH values higher than 1.0 showed highly different structural and morphological properties. XRD, TEM and nitrogen adsorption–desorption isotherms of the synthesized materials showed that the long range order of mesopores of SBA-15 and the cage-window structure of MCF were significantly distorted at higher synthesis solution pH values (all acidic). A totally amorphous material with no ordered pores was obtained at a pH value of 2.0. Surface area and micropore contribution to the total pore volume significantly increased, while average mesopore diameter was decreased by increasing the synthesis pH value to 1.5. This was considered to be due to the increased contribution of corona region and bridging of the mesopores by secondary pores at higher pH. Pore structures of the MCF and SBA-15-like materials prepared at pH 1.5 were rather complex and interconnected. SEM, FT-IR and pyridine adsorbed FT-IR analysis of the materials also showed the importance of synthesis solution pH on the morphology, structure and acidic characteristics of the synthesized materials.

► Different structure/morphology of SBA-15 and MCF synthesized at pH 1.5 and pH ≪1.0.
► Distorted SBA-15 mesopore long range order and MCF cage-window structure at pH 1.5.
► Significant increase in micropore contribution and surface area at pH 1.5.
► Increased corona contribution and bridging of mesopores by secondary pores at pH 1.5.
► Complex interconnected pores with short range order at pH 1.5.