A Study on the Formation Mechanism of SBA-15 Thin Sheet with Perpendicular Nanochannels (SBA(⊥))

A ternary surfactant system C16TMAB/SDS/P123 was empolyed to template the condensation of sodium silicates for SBA(⊥) formation. The study on the formation mechanism is helpful to control direct it for application. SBA(⊥) is characterized as thin sheet with 2D hexagonally arrayed perpendicular nanochannels with open-ends.
We have investigated the formation mechanism by using TEM, SEM, N2 sortion isotherm, powder XRD (X-ray Diffraction), TGA (Thermogravimetric Analysis), DLS (Dynamic Light Scattering), and SAXS (solution SAXS and in-situ SAXS). This studies is organized as four section. In SectionⅠ, we have summarized the results and correlate channel orientation, sheet thickness, and wall thickness to pH and temperature by proposing a vesicle confinement effect. The best recipe for SBA(⊥) synthesis is SDS/C16TMAB=1.5, T≧40oC. In SectionⅡ, the self-assembly process of C16TMAB/SDS/P123 reveals the correlation between the appearance of disk micelles and the silica sheet formation. In SectionⅢ, the co-assembly process of surfactant/silicate hybrids has been investigated. In SectionⅣ, it is found that the assembly behaviors in the late stage of SBA(⊥) formation follow the oriented attachment mechanism. It is confirmed that the sheet form and the perpendicular nanochannels of SBA(⊥) should derive from disk micelle template.