One-pot synthesis and characterization of FeII–FeIII hydroxide (green rust) intercalated with C9–C14 linear alkyl carboxylates

Layered FeII–FeIII hydroxides (green rusts, GR) intercalated with monovalent aliphatic carboxylate anions, called GR-carboxylates, possess hydrophobic interlayer regions which can adsorb non-polar organic compounds. GRs are well known reductants and hence GR-carboxylates may have the potential to detoxify adsorbed compounds, such as chlorinated solvents. GR-carboxylates, GRCX, for the first time, were precipitated directly by aerial oxidation of an ethanolic solution containing FeSO4 and linear alkyl carboxylate ions synthesis condition using monovalent carboxylic acids with X, the total number of carbon atoms in the acid, varying from 5 (pentanoic acid) to 14 (tetradecanoic acid), synthesis conditions were tested. GRCX formed for X ≥ 9. The syntheses were carried out at constant pH of 8 using 1 M NaOH as neutralizing agent, and with a maximum duration of 3.5 h. The basal spacings of GRCX increased with X and they were 2.68 nm (GRC9), 2.94 nm (GRC10), 3.59 nm (GRC12) and 4.16 nm (GRC14). The Mössbauer spectra measured at 80 K of different GRC12 synthesized under identical chemical conditions resulted in hyperfine parameters close to those of other GRs. The FeII/FeIII ratios of the final products (R) ranged between 1.4 and 2.8 demonstrating that FeII in GRCX can be partly oxidized without degradation of the structure. R at various stages of the synthesis decreased from 5.2 at the start of the reaction to 2.8 at the end of synthesis. In the specific case of GRC12, the optimum initial solution concentrations were [C12]0 = 25 mM, [FeII]0 = 30 mM and 40% (v/v) EtOH/H2O.