High-resolution solid-state magic angle spinning nuclear magnetic resonance investigations of surface hydroxy groups on modified silica gel

Abstract

¹ H, ²⁹Si and ³¹P magic angle spinning nuclear magnetic resonance measurements have been performed on silica gel and its phosphorus-containing modification. It was possible to separate the proton resonance lines of silanol groups and of phosphorus hydroxy groups at the surface. From the resonance shifts it follows that the latter species possess a remarkably higher acidity. The phosphorus atoms at the surface were found to exist in the pentavalent state. According to the ²⁹Si resonance shifts the silicon atoms of a modified sample have a coordination number of six. The process of partial dehydroxylation and rehydroxylation of the modified surface leads to drastic changes in the phosphorus resonance signals.