High-resolution Si-29 solid-state NMR study of silicon functionality distribution on the surface of silicas

Si-29 solid-state NMR allows us to distinguish silicon atoms involved in siloxane bridges (Q(4)), Single silanol (Q(3)) and geminal silanol groups (Q(2)) On the surface of silica. The relative proportions of each species can be obtained by Magic Angle Spinning (MAS) associated with H-1 --> Si-29 crosspolarization (CP/MAS), This preliminary study deals with the silicon functionality of MCM-41, a purely siliceous, amorphous and mesoporous silica, From the Si-29 spectra the relative proportions are estimated to be 3.7% Q(2) 27.3% Q(3) and 69.0% Q(4), while the ratio Q(2)/(Q(2) + Q(3)) is 0.12. These results are found to be in perfect agreement with a binomial probability distribution of sites. Copyright (C) 1996 Elsevier Science Inc.