Structural Stability of Si–C Bonds in Periodic Mesoporous Thiophene-Silicas Prepared under Acidic Conditions

Abstract

Periodic mesoporous thiophene-silicas with hexagonal (p6mm) symmetry were synthesized using a 2,5-bis(triethoxysilyl)thiophene (BTET) precursor in the presence of Pluronic P123 (EO20PO70EO20) and PLGE (EO17(L28G7)EO17) triblock copolymers at different acidic conditions. P123-templated mesoporous thiophene-silicas with p6mm ordered structure were prepared in the presence of hydrochloric acid and iron(III) chloride hexahydrate used as acid catalysts. However, it was found that a relatively large fraction of the Si–C bonds in thiophene-bridging groups were decomposed during the synthesis process. On the other hand, thiophene-silicas synthesized at lower acidic conditions were disordered and nonporous structures. In contrast, PLGE-templated thiophene-silicas with p6mm ordered mesostructure were prepared using copper(II) perchlorate hexahydrate and boric acid as well as hydrochloric acid. Importantly, up to 97.3% of the Si–C bonds in mesoporous thiophene-silica prepared in the presence of boric acid were retained. Solid state 29Si MAS NMR clearly showed that the structural stability of the Si–C bond is dependent on the acidity and time of the initial self-assembly stage. Also, the thermal stability of the thiophene-bridging groups was shown to be dependent on the acidity of the synthesis gel.