Ruthenium(platinum)-doped tin dioxide inverted opals for gas sensors: Synthesis, electron paramagnetic resonance, Mossbauer, and electrical investigation

Tin dioxide and ruthenium(platinum)-doped tin dioxide were synthesized in the form of inverted opals, aiming to investigate the interaction of these materials with CO reducing gas. The results of electron paramagnetic resonance (EPR) investigation allowed us to conclude that CO interaction causes the formation of singly ionized oxygen vacancies located in the subsurface region. These ones transfer their electrons to transition metal centers, Ru or Pt, enhancing the SnO2 surface reactivity toward CO. The reduction of Ru4+ and Pt4+ was assessed both by EPR and Mossbauer spectroscopy. Resistance measurements showed that the materials are well-suitable for use in CO sensor devices because of their reproducible and fast electrical response; this was related to the homogeneous and high dispersion of Ru and Pt centers in the oxide matrix and to the subsurface location of the species active in the electron-transfer processes.