Study of the Formation of the Mesoporous Material SBA-15 by EPR Spectroscopy

Abstract

SBA-15 is an hexagonal mesoporous material which is synthesized with nonionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers (Pluronics, EOyPOxEOy), templates. Pore diameters in the range of 2−30 nm can be obtained with a relatively thick silica wall (up to 6 nm). This material possesses both large, uniform, and ordered channels, along with a complementary net of micropores which provides connectivity between the ordered channels through the silica. This study focuses on the investigation of the formation mechanism of SBA-15 with emphasis on the PEO interactions with the silica and the initiation of the micropores. This was achieved using in situ X-band EPR spectroscopy in combination with electron spin−echo envelope modulation (ESEEM) experiments. The paramagnetic centers were introduced as spin-labeled Pluronic L62 (EO6PO30EO6) where nitroxides replace the OH groups at the end of the polypropylene oxide (PEO) blocks (L62-NO). Initially, the acidic reaction conditions we...