Computational investigation of the adsorption and photocleavage of chlorobenzene on anatase TiO2 surfaces

The adsorption and photocleavage of chlorobenzene (CB) molecule on the anatase TiO2 (0 0 1), (1 0 0) and (0 1 0) surfaces are studied with semiempirical SCF MO method, MSINDO. The surfaces have been modeled with two saturated clusters Ti21O58H32 and Ti36O90H36. The dissociative perpendicular adsorption of CB on TiO2 (0 1 0) and (1 0 0) surfaces revealed comparable stabilities and much higher than on the (0 0 1) surface. The aromatic ring cleavage by atomic oxygen, singlet oxygen and superoxide anion molecules has been investigated computationally and relevant mechanisms are proposed. Molecular dynamics (MD) simulations have been implemented for the adsorption models and the early stages of photocleavage mechanisms. The oxygen-type chemistry is involved actively in the water mediated photocleavage step upon excitation. The O2- radical anion dependant ring opening mechanism, through the dioxetane intermediate, is thermodynamically the most favourable.