Generation of singlet oxygen on the surface of metal oxides

Generation of singlet oxygen on the surface of metal oxides is studied. It is shown that, under conditions of heterogeneous photo-catalysis, along with the conventional mechanism of singlet oxygen formation due to the formation of electron–hole pairs in the oxide structure, there is an additional and more efficient mechanism involving direct optical excitation of molecular oxygen adsorbed on the oxide surface. The excited adsorbate molecule then interacts with the surface or with other adsorbate molecules. It is shown that, with respect to singlet oxygen generation, yttrium oxide is more than an order of magnitude more efficient than other oxides, including titanium dioxide.