Direct synthesis of hydrothermally stable micro–mesoporous silicas templated by unsaturated α-linolenic acid self-assemblies under high temperature hydrothermal conditions

Abstract

Herein, we report the direct synthesis of micro–mesoporous silicas using unsaturated anionic surfactant α-linolenic acid as mesophase template. The self-assembly of α-linolenic acid, which could transform to a rigid mesophase template via inner-micellar polymerization when heated, was successfully leveraged to fabricate hydrothermally stable mesoporous silicas at high temperature, which retained a BET surface area of 678 m 2 g −1 after hydrothermal treatment in boiling water for 5 days. Different analysis methods, e.g. X-ray diffraction, nitrogen physisorption, the non-local density functional theory (NLDFT) analysis and transmission electron microscopy, were employed to investigate the mesostructure of as-synthesized samples, which revealed a micro- and mesopores hybrid in one phase. 1H NMR was applied to characterize the α-linolenic acid micellar structure and confirmed that C C bonds have been opened up and polymerization occurred within micelles. The 29Si MAS NMR spectra indicated Q 4 silicon is the dominating species, which explains well the high hydrothermal stability of the materials.