Formation of ammonium and nitrate ions from photocatalytic oxidation of ring nitrogenous compounds over titanium dioxide

Abstract

The relative concentrations of ammonium and nitrate ions were measured during the photocatalytic oxidation of theophylline, proline, pyridine, and piperidine. It was found that the formation of inorganic nitrogeneous species occurred almost instantaneously upon illumination and at a significantly greater rate than carbon dioxide production, irrespective of whether the nitrogen heteroatom was contained in a saturated or an aromatic ring. The opening of the ring systems was postulated not to be the rate determining step in the formation of these species. The concentration versus time profiles for the formation of carbon dioxide, ammonium and nitrate for each compound indicated that a number of reaction intermediates, referred to here as organic and inorganic nitrogenous intermediates, have to be involved for the photocatalytic conversion of initial organic nitrogen to the inorganic species. A framework is thereby proposed for the formation pathway of these species. Indirect evidence was used to support the existence of such intermediates.