1H MAS NMR studies of hydroxyl groups in aluminium-free H-boralites

Abstract

1 H MAS NMR spectra of H-boralites contain seven lines at 1.0, 1.4, 1.7, 2.3, 2.6, 4.7 and 6.7 ppm with intensities dependent on the activation temperature. The lines at 6.7, 4.7 and 1.7 ppm are assigned to residual ammonium ions, residual water and terminal Si-OH groups, respectively. The prominent line at 2.3 ppm comes from bridging Si-O(H)-B hydroxyls. The lines at 1.0,1.4 and 2.6 ppm are tentatively assigned to B-OH, B-OH⋯O and Si-OH⋯O protons, respectively. The assignment has been assisted by the proton spectra of partially hydrated B2O3 and SiO2, and by infrared measurements.