Surface reactivity of nanostructured tin oxide and Pt-doped tin oxide as studied by EPR and XPS spectroscopies

Nanostructured (3–6 nm) thin films (80 nm) of SnO2 and Pt-doped SnO2 were obtained by a new sol–gel route using tetra(tert-butoxy)tin(IV) and bis(acetylacetonato)platinum(II) as precursors. EPR and XPS investigations, performed on thin films after interaction with CO, demonstrated that singly ionized oxygen vacancies (Vo) fully transferred their electrons to the noble metal and reduced Pt(IV) to Pt(II). Contact with air at room temperature led to the reduction of O2 to O2−, therefore, re-oxidizing metal centers. The reaction mechanism concords with the high electrical sensitivity of this material.