XPS study of Fe(II)Fe(III) (oxy)hydroxycarbonate green rust compounds

Abstract The oxidation behaviour of Fe(II)Fe(III) hydroxysalt green rust (GR) compounds was investigated using XPS. Stoichiometric GR(CO 3 2− ), i.e. Fe(II) 4 Fe(III) 2 (OH) 12 CO 3 3H 2 O was prepared by co‐precipitating Fe(II) and Fe(III) ions in carbonate‐containing solution under an inert atmosphere. Fast oxidation of stoichiometric GR(CO 3 2− ) by hydrogen peroxide in aqueous medium resulted in GR(CO 3 2− )* of various composition, i.e. Fe(II) 6(1− x ) Fe(III) 6 x O 12 H 2(7−3 x ) CO 3 with 1/3 ≤ x ≤1, where x is the Fe(III) molar fraction [Fe(III)]/[Fe(total)] of positively charged hydroxide sheets. The Fe(2p 3/2 ) spectra of GRs of various composition were well fitted using Gupta and Sen multiplet peaks and additional broad satellite and surface features. The oxidation of Fe(II) in the GR structure is accompanied by deprotonation of hydroxyl groups as evidenced by the O(1s) spectra. The deprotonation of the hydroxyl groups compensated for the presence of excess positive charge that resulted from the oxidation of Fe(II) in the GR structure. In addition, the fully ferric GR(CO 3 2− )* at x = 1 was coated on a sand substrate and the quality of the GR coating was investigated by XPS imaging. Copyright © 2008 John Wiley & Sons, Ltd.