2.2 Synthesis of Goethite
Goethite synthesis followed the procedure reported by Encina et al., with some changes. In resume, 5.5 g of FeSO4.7H2O were dissolved in 100 mL of distilled water. The solution pH was adjusted to 7.0 by the addition of NaOH (1.0 mol L-1) under continuous stirring. Then, the solution was aerated with a constant flow of oxygen for 60 min until the suspended material became reddish. Finally, the solution was centrifuged for 5 min at 4000 rpm separating the solid which was then dried at 60 ºC for 24 h.
2.3 Characterization
Goethite was characterized by Mössbauer spectroscopy at room temperature using a conventional transmission Mössbauer spectrometer in constant acceleration mode equipped with a 0.3 mCi 57CoRh source. Spectrometer was calibrated using a 12 μm thick pure Fe foil. X-ray photoelectron spectroscopy (XPS) analyses were carried out whit XPS Analyzer Kratos model Axis Ultra whit a monochromatic AIKα and charge neutralizer; diffuse reflectance spectroscopy (DRS) samples were recorded using a UV-vis Lambda 35, Perkin-Elmer spectrophotometer equipped with a diffuse reflectance chamber Labsphere RSA-PE-20, N2 adsorption-desorption isotherms at -196 ºC were used for the textural analysis of the goethite, applying the BET method and using Micromeritics ASAP 2020 equipment and X-ray diffraction (XRD) were recorded using Philips PW 1732 diffractometer equipped with CuKα radiation, nickel filter, 20 mA and 40 kV in the high voltage source.