[Zurück]

O. Diwald, E. Knözinger:
"Intermolecular electron transfer on the surface of MgO nanoparticles";
Journal of Physical Chemistry B, 106 (2002), S. 3495 - 3502.

A systematic study of electron transfer reactions on the surface of MgO nanoparticles, exposed to H2/O2 atmosphere in the dark, was performed. The evolving products are two different types of surface
complexes consisting each of a paramagnetic superoxide anion (O2-) on a Mg2+ cation and an adjacent infrared active hydroxyl group (OH). Via the electronic (H-bond-like) influence of O2- on the OH group (red
shift of the respective IR signal) the process of O2- evolution can be monitored IR spectroscopically on a time scale of minutes. Additional structural information on the complexes is obtained via the magnetic
influence of the OH proton on O2- (superhyperfine splitting) of the respective electron paramagnetic resonance (EPR) signals. Based on these data as well as on a kinetic evaluation of the time-dependent IR
and EPR signals, a description of two local surface structures involved in the complicated reaction scheme was obtained: two hydride groups as intermediate products are constituents of a low coordinated anion vacancy or of a (110) microplane, respectively. A fraction of the products (O2-...HO) is located on ion pairs adjacent to or in these structure elements. Because of an intermediately produced mobile H radical, further product evolves on similar ion pairs (same coordination), but remote from the local surface structures where
H2 may be split.

http://pubs.acs.org/journals/jpcbfk/article.cgi/jpcbfk/2002/106/i13/pdf/jp011049+.pdf