Computational modeling of the adsorption and (*)OH initiated photochemical and photocatalytic primary oxidation of nitrobenzene.

The adsorption and primary oxidation step for the photodegradation of nitrobenzene (NB) have been studied computationally using MSINDO SCF MO method. The method performs efficiently for extended surface models such as Ti(36)O(90)H(36). Molecular dynamics simulations have revealed that NB is linked to TiO(2) surface at the titanium ion via the oxygen atoms of NO(2) group. In addition, the computed vibrational density of states for the adsorbed NB molecule is in reasonably good agreement with the available experimental data and theoretical results. In order to identify the primary photochemical and photocatalytic (*)OH initiated photooxidation intermediates, we have employed two different theoretical approaches, frontier orbital theory and Wheland localization theory. It has been found that the meta- hydroxynitrocyclohexadienyl radical is energetically more favored than para- and ortho-hydroxynitrocyclohexadienyl radicals for the photochemical photolysis, whereas in the case of photocatalysis, the (*)OH radical attack is unselective and all three possible isomers have comparable stabilities.