Nitrogen Photofixation at Nanostructured Iron Titanate Films

Abstract

A nanostructured iron titanate thin film on glass is prepared by a sol-gel method from iron(III) chloride and titanium tetraisopropylate. Energy dispersive X-ray analysis, Mößbauer spectroscopy, and wavelength dependent measurements of the quasi-Fermi level suggest the presence of an Fe2Ti2O7 phase having n-type semiconductor characteristics. In the presence of ethanol or humic acids and traces of oxygen, the film photocatalyzes the fixation of dinitrogen to ammonia and nitrate under ultraviolet or visible light irradiation. In the first observable reaction step, hydrazine is produced, which then undergoes further photoreduction to ammonia. Oxidation of the latter by oxygen yields nitrate as the final product. Since the reaction also occurs in air and with visible light (λ > 455 nm), and since the iron titanate phase can be formed by weathering of ilmenite minerals, the system may be a model for a previously unknown non-enzymatic nitrogen fixation in nature.