Photodissolution of Iron Oxides I: Maghemite in EDTA Solutions

M.I. LITTER; M.A. BLESA

JOURNAL OF COLLOID AND INTERFACE SCIENCE

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Amsterdam; Año: 1988 vol. 125 p. 679 - 687

0021-9797

Dissolution of maghemite (γ-Fe2O3) suspended in ethylenediaminetetraacetic acid (EDTA) aqueous solutions at pH 2 is promoted by UV light. Wavelengths of 254 and 366 nm are effective. Formaldehyde is formed in the course of dissolution, the ratio of quantum yields View the MathML source being close to 2. At 450 nm, neither photodissolution nor EDTA photooxidation takes place. The electronic spectral features are presented and discussed, and used to assess dissolution mechanisms based on the excitation of the semiconductor band or the charge-transfer band in surface FeIII-EDTA complexes. It is concluded that the primary light absorption act involves the generation of (e−, h+) pairs in the solid; however, the ensuing photochemical process is a charge transfer in the surface complexes, akin to the corresponding optical transition. Deviations from the ratio View the MathML source are interpreted in terms of competing events at surface sites, whereby >FeII species may either dissolve or transfer an electron to dissolved species. The relative probability of both processes accounts for the pH dependence.