Characterization of Silica Gels by ²⁹Si MAS NMR and IR Spectroscopic Measurements

Abstract

Abstract The solubility of commercial and synthesized silica gels in a solution of Tetra‐Ethyl‐Ammonium‐Hydroxide (TEAOH) was investigated at room temperature. The state of parent silica frameworks was characterized by BET and SEM. The structural defects were identified both by the Q n group analysis in 29 Si MAS NMR and IR spectroscopic investigation. It was found that the dissolution rate of the samples shows a tendency for growing up with an increasing BET surface. The increase of the internal surface was accompanied by formation of Si(OSi) 3 (OH) (Q 3 ) and Si(OSi) 2 (OH) 2 (Q 2 ) structural units. The higher the number of Q 3 and Q 2 groups observed, the faster the samples were dissolved in TEAOH solution due to the attack of the hydroxide ions on the terminal OH groups of the framework. The asymmetrical TOT valence vibration of the IR spectra was systematically shifted to lower values with increase in the number of Q 3 and Q 2 structure groups.