Spectroscopic CW-EPR and HYSCORE investigations of Cu2+ and O2− species in copper doped nanoporous calcium aluminate (12CaO·7Al2O3)

Continuous wave (CW) and pulse electron paramagnetic resonance in a variant of hyperfine sublevel correlation spectroscopy (HYSCORE) were used for obtaining structural information concerning speciation and local environment of alien Cu2+ and native O2− ions encaged in copper doped nanoporous 12CaO·7Al2O3 (mayenite). The samples were prepared by a solid-state reaction and characterized by means of XRD, SEM, and Raman techniques. X-Band CW-EPR spectra showed that three different Cu2+ species together with paramagnetic extraframework O2− anions were present in the mayenite sample, whereas extraframework OH− anions were revealed by Raman spectroscopy. 27Al HYSCORE provided evidence for the interaction of Cu2+ ions with the mayenite framework. Superhyperfine interaction of the Cu2+ ions with proximal (dCu–OH = 2.4 Å) and distal (dCu–OH = 5.0 Å) OH− anions, located in the same and the nearby cage, respectively, was resolved by means of 1H HYSCORE spectra. A different situation held for the encaged O2− radicals found to be sitting on the Ca2+ ions. They exhibited only a weak superhyperfine interaction of 1 MHz with the 27Al3+ framework ions.