Naturally occurring 1.4 nm tobermorite and synthetic jennite: Characterization by ²⁷Al and ²⁹Si MASNMR spectroscopy and cation exchange properties

A naturally occurring 1.4 nm tobermorite and a synthetic jennite were characterized by ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy and their cation exchange properties were measured. ²⁷Al MASNMR spectroscopy revealed that both the 1.4 nm tobermorite and synthetic jennite contained trace quantities of Al in tetrahedral coordination. The 1.4 nm tobermorite also contained octahedrally coordinated Al probably due to the presence of an aluminum compound as a trace impurity. The ²⁹Si MASNMR spectrum of 1.4 nm tobermorite exhibited a strong resonance at -85.2 ppm and a small shoulder at -80 ppm which are attributed to chain middle groups (Q²) and end groups (disilicates) respectively. ²⁹Si MASNMR spectroscopy of the synthetic jennite showed a strong resonance at -85.7 ppm and a moderately strong resonance at -81.4 ppm which correspond to single chains and end groups respectively. Jennite showed a considerably larger quantity of end groups than the 1.4 nm tobermorite. The unsubstituted 1.4 nm tobermorite and synthetic jennite exhibited only small cation exchange capacities.