A computational study on the adsorption and OH initiated photochemical and photocatalytic primary oxidation of aniline

In this work, a computational technique based on semiempirical SCF MO method MSINDO, has been used for the investigation of adsorption and initial oxidation step for the photodegradation of aniline on anatase TiO2 (1 0 0) surface. This surface has been chosen because it is present in TiO2 powders used in the adsorption experiments. Molecular dynamics (MD) simulations for the adsorption behavior of aniline have revealed a planar orientation of the aromatic ring to the surface linked via amino nitrogen with the surface lattice titanium ion. With the intention of predicting the primary photochemical and photocatalytic OH initiated oxidation intermediates, two different theoretical approaches, frontier electron theory and Wheland localization theory, have been applied. Based on our results, all isomers, para-, ortho- and meta-hydroxyaminocyclohexadienyl radicals, could be present in the case of photochemical oxidation, but the para- and ortho-positions are energetically more favorable than meta-position. Whereas, for the photocatalytic oxidation, where the aniline is adsorbed onto the TiO2 surface via amino group, the para- and meta-isomers are energetically more stable than the ortho-isomer, which is mainly influenced by steric hindrance.