Nitrogen photofixation on nanostructured iron titanate films.

A nanostructured iron titanate thin film has been prepared by a sol-gel method from iron(III) chloride and titanium tetraisopropylate. Energy-dispersive X-ray analysis and Mössbauer spectroscopy suggest the presence of a Fe(2)Ti(2)O(7) phase, which was previously obtained as an intermediary phase upon heating ilmenite. In the presence of ethanol or humic acids and traces of oxygen, the novel film photocatalyzes the fixation of dinitrogen to ammonia (17 microM) and nitrate (45 microM). In the first observable reaction step, hydrazine is produced and then undergoes further photoreduction to ammonia. Oxidation of the latter by oxygen affords nitrate as the final product. Since the reaction occurs also in air and with visible light (lambda>455 nm), and since the iron titanate phase may be formed by the weathering of ilmenite minerals, it may be a model for mutual nonenzymatic nitrogen fixation in nature.