engleski

Influence of Zn-doping on the properties of synthetic goethite

The influence of Zn-doping on the properties of alpha-FeOOH was investigated by X-ray powder diffraction, Fourier transform infrared and 57Fe Mössbauer spectroscopies. alpha-FeOOH was synthesized at a highly alkaline pH by precipitation from the FeCl3 solution with the addition of tetramethylammonium hydroxide and autoclaving at 160 &ordm ; C [S. Krehula, S. Popović, S. Musić, Mater, Lett. 54 (2002) 108]. The Zn-doped samples with nominal molar ratio values (expressed as 100×[Zn]/([Zn]+[Fe])) equal to 0.99, 1.96, 2.91, 4.76, 6.98, 9.09, 11.11 and 13.04 mole % were precipitated in the same way, but in the presence of varying ZnCl2 concentrations. XRD patterns showed the presence of an alpha-FeOOH-related phase (solid solution of the type alpha-(Fe, Zn)OOH) as a single phase up to 9.09 mole % Zn. Upon increasing the amount of Zn-dopant XRD lines were gradually broadened. Upon doping, small shifts in diffraction lines were observed, dependent on the Miller indices, indicating an anisotropy in lattice expansion. XRD pattern of the sample with 13.04 mole % Zn showed the presence of ZnFe2O4 and alpha-Fe2O3, besides the dominant phase having the structure type of alpha-FeOOH. FT-IR spectra showed a clear influence of the amount of Zn-dopant in the alpha-FeOOH structure on the positions of the bands. O-H in-plane bending (delta O-H) band shifted from 893 to 888 cm-1, O-H out-of-plane bending (gama O-H) band shifted from 796 to 800 cm-1, whereas Fe-O stretching band shifted from 638 to 629 cm-1 with nominal molar ratio value increased up to 11.11 mole % Zn. RT Mössbauer spectra of undoped alpha-FeOOH and Zn-doped alpha-FeOOH samples showed a distribution of the hyperfine magnetic field. mm decreased from 34.9 T for an undoped alpha-FeOOH to 25.5 T for a Zn-doped alpha-FeOOH with 9.09 mole % Zn. Mössbauer spectra of samples with higher nominal molar ratio values showed the presence of ZnFe2O4 (sample with 11.11 mole % Zn) and additionally alpha-Fe2O3 (sample with 13.04 mole % Zn).

Zn-dopant; tetramethylammonium hydroxide; alpha-FeOOH; alpha-Fe2O3; ZnFe2O4; XRD; 57Fe Mössbauer; FT-IR; FE SEM; EDS

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