Synthesis of Fe(II-III) hydroxysulphate green rust by coprecipitation

摘要

Iron(II-III) hydroxysulphate precipitates were prepared in absence of other compounds by coprecipitation that consists of mixing solutions of iron(II) and iron(III) salts with NaOH solution in adequate proportions. Precipitates were characterised by transmission Mossbauer spectroscopy (TMS), XRD, TEM and AFM. Mossbauer spectrum measured at 15 K was composed of Fe(II) and Fe(III) doublets with δ = 1.33 and 0.51 mm s~(-1), and △ = 2.88 and 0.43 mm s~(-1), respectively. The Fe(II)/Fe(III) ratio of 2 is independent of the solution ratio set at 3 that confirms the composition, [Fe_4~(II)Fe_2~(III) (OH)_(12)]~(2+)·[SO_4~(2-)·m H-2O]~(2-). XRD analysis led to hexagonal unit cell parameters of a_H = b_H = 0.318 ± 0.004 nm and c_H = 1.090 ± 0.004 nm. The value a_H = 0.314 ± 0.002 nm was obtained by TEM diffraction pattern corresponding to (h k 0) planes and displayed a distribution of hexagonal plates (10 < diameter < 500 nm). Sample aged 7 days at 70 ℃ showed larger plates (100 < diameter < 1000 nm). AFM on aged sample allowed to measure the thickness of isolated hexagonal crystallite.