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.