Hydrolysis of Fe(III) in the presence of mixed anions and promoters

Forced hydrolyses in the precipitation systems (a) Fe(NO 3 ) 3 /Fe 2 (SO 4 ) 3 and FeCl 3 /Fe 2 (SO 4 ) 3 and (b) FeCl 3 /N-guanylurea sulphate were investigated using 57 Fe Mössbauer and FT-IR spectroscopies and scanning electron microscopy (FE SEM). Forced hydrolyses of Fe(NO 3 ) 3 /Fe 2 (SO 4 ) 3 solutions at 90 °C yielded superparamagnetic goethite nanorods, whereas in the case of FeCl 3 /Fe 2 (SO 4 ) 3 solutions the clusters of akaganéite nanoneedles were formed. With a prolonged heating time at 90 °C the conversion of these akaganéite nanoneedles into goethite nanorods was observed. Forced hydrolysis in the system FeCl 3 /N-guanylurea sulphate at 160 °C generated only hematite and goethite phases and their fractions depended on the concentration of FeCl 3 and the amount of N-guanylurea sulphate in the solution. Different shapes of iron(III) oxyhydroxides and hematite in dependence on the experimental conditions were monitored with FE SEM. Specifically adsorbed sulphates on these particles, as shown by FT-IR spectroscopy, served as directing agents in the particle/crystal growth.