Active sites on mesoporous and amorphous silica materials and their photocatalytic activity: An investigation by FTIR, ESR, VUV-UV and photoluminescence spectroscopies

Active sites for photometathesis on mesoporous silica materials, FSM-16 and MCM-41, and amorphous silica, which are generated by dehydroxylation of surface isolated hydroxyl groups at high temperature above 673 K, were investigated by some spectroscopies such as FTIR, ESR, VUV-UV, and photoluminescence. FTIR study revealed that the catalytic active sites are the sites exhibiting the IR bands at 891 and 910 cm(-1), which are known as a "strained siloxane bridge". The catalytic active sites generated on three kinds of silica materials have uniform activity, and higher activity over FSM-16 than MCM-41 and amorphous silica is attributed to the larger amount of active sites generated. ESR study suggested that the IR bands would be assigned to the radical sites, dropSi-0(.) (NBOHC, which would be generated together with (.)Sidrop (E' center) by the dehydroxylation at high temperature, and the NBOHC photoexcited under UV light below ca. 390 nm would cause the photometathesis.