III International Conference

PP-I-3PHOTOCATALYSIS OF OXIDATION REACTIONS AS NATURAL PHENOMENONZakharenko V.Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail: zakh@catalysis.nsk.suAn analysis of own and literary data was made to understand nature and mechanism ofphotocatalysis phenomenon. Physical and chemical stages of photocatalitic oxidation reactionon metal oxides are considered. It is shown that the quantum efficiency of photocatalyticreaction on metal oxides, the top level of whose valence band is formed by 2p - orbital ofoxygen depends upon the bond energy of surface lattice oxygen. It may be assumed that therelated to semiconductor metal photocatalytic oxidation reaction does not require an activesurface center.The studies of photocatalytic oxidation reactions had vastly been supported byG.K. Boreskov. He had suggested that an investigation of photocatalysis mechanism wouldthrow light upon the catalytic action nature and mechanism of catalytic oxidation reactions.Photocatalytic reactions are characterized by formation of “free” mobile electrons in theconductivity band and simultaneously “free” mobile holes in the valence band, after theabsorption of radiation quanta with energy exceeding the width of the solid band gap [1]. Ourdata evidence that in the fundamental absorption region of semiconductor metal oxides (ZnO,SnO 2 , TiO 2 , Sc 2 O 3 , In 2 O 3 , V 2 O 5 , and MoO 3 ) the quantum yields of photocatalytic oxidationvary in a wide range from 30 % to 0.01 % under the same conditions of metal oxidepretreatment and quantum yield measurement [2]. Such considerable distinction can not onlybe explained by different physical characteristic of used metal oxides. These characteristicsare energy structure and state density of conductivity and valence bands, size of photocatalystmicro crystals, mobility of lighted charge carriers, recombination rate, near surface electricfields and so on.It was confirmed experimentally that photocatalytic activity is inherent in metal oxides,the top level of whose valence band is formed by 2p - orbital of oxygen (ZnO, SnO 2 , TiO 2 ,Sc 2 O 3 , In 2 O 3 , V 2 O 5 , and MoO 3 ). As distinct from transition metal oxides (Fe 2 O 3 , Co 3 O 4 , andNiO), which have the top valence band formed 3d - orbital of metal and do not show aphotocatalytic activity.11