Photoreduction of Iron Oxyhydroxides in the Presence of Important Atmospheric Organic Compounds

The photolytic reduction of amorphous iron hydroxide [am-Fe(OH)₃], lepidocrocite (γ-FeOOH), goethite (α-FeOOH), hematite (α-Fe₂O₃), and natural iron-containing aerosol particles in the presence of formaldehyde, formate, acetate, oxalate, and butyrate has been investigated. Important parameters in the photoreduction experiments are the pH, wavelength of the irradiating light, nature of the electron donor, characteristics of the iron phase. The present results show that the fastest rates of photoreduction of Fe(III) to Fe(II) are achieved with am-Fe(OH)₃ as the electron acceptor and formate as the electron donor. Maximum rates of photoreduction were observed at 330 nm with a continuous decrease to 405 nm. Natural ironcontaining aerosol particles show photochemical behavior similar to am-Fe(OH)₃ and γ-FeOOH. These results suggest that a significant fraction of the reactive atmospheric iron in urban aerosol could be present as am-Fe-(OH)₃ and γ-FeOOH. Ambient iron-containing aerosol particles with oxalate as the electron donor resulted in a significant photochemical production of H₂O₂.