engleski

Influence of Ni-dopant on the properties of synthetic goethite

The influence of Ni-dopand on the properties of alpha-FeOOH was investigated by XRD, FT-IR, 57Fe Mössbauer spectroscopy and transmission electron microscopy. alpha-FeOOH was synthesized at a highly alkaline pH by precipitation from the FeCl3 solution with the addition of tetramethylammonium hydroxide and autoclaving at 160º C. The samples doped with Ni2+ ions were precipitated in the same way, but in the presence of varying concentrations of NiCl2. Solid solutions, having the structure of alpha-FeOOH, were observed in samples with the Ni/Fe ratio up to 0.05. Upon increasing the amount of Ni-dopand the XRD lines were gradually broadened. The sample with the ratio Ni/Fe = 0.10 showed NiFe2O4, besides the dominant phase having the structure type of alpha-FeOOH. Shifts of IR bands at 892 and 796 cm-1 were not observed in all samples doped with Ni. For the ratio Ni/Fe = 0.10, the IR bands centered at 631 and 404 cm-1 were significantly broadened. RT Mössbauer spectrum of undoped alpha-FeOOH and Ni-doped alpha-FeOOH showed distributions of hyperfine magnetic fields. Bhf decreased from 35.1 T for an undoped alpha-FeOOH to 32.1 T for alpha-FeOOH containing Ni2+ ions (Ni/Fe = 0.05). The saturation of the alpha-FeOOH structure with Ni2+ ions in amounts higher than ~ 5 mol % was also observed by Mössbauer spectroscopy. The particle size (length) of acicular alpha-FeOOH particles with a maximum in the interval 180-220 nm was slightly decreased with Ni-doping, but the distribution of the length/width ratio showed no change, having a maximum at 4 to 5. TEM photographs additionally showed small populations of cubic-shaped or pseudocubic particles of ~ 10 nm in size for the ratio Ni/Fe = 0.05 and about 10 to 20 nm in size for the ratio Ni/Fe = 0.10. These particles were assigned to NiFe2O4.

Ni-doping ; alpha-FeOOH ; XRD ; FT-IR ; 57Fe Mössbauer ; TEM

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