Naslov
Influence of cobalt ions on the precipitation of goethite in highly alkaline media

Autori
Krehula, Stjepko ; Musić, Svetozar

Izvornik
Clay minerals (0009-8558) 43 (2008), 1; 95-105

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
cobalt ions ; goethite ; cobalt ferrite ; XRD ; Mossbauer ; FTIR ; FE-SEM ; EDS

Sažetak
The effects of cobalt ions on the precipitation of goethite in highly alkaline media were monitored using X-ray diffraction (XRD), Mossbauer, Fourier transform infrared (FTIR) and energy dispersive X-ray (EDS) spectroscopies and field emission scanning electron microscopy (FE-SEM)techniques. Tetramethylammonium hydroxide was used as a precipitating agent. The precipitates were collected after heating of the precipitation systems at 160 º ; ; C for 2 h. The XRD results showed the formation of goethite structure as a single phase up to r = 6.98 (where r = 100· ; ; [Co]/([Co]+[Fe])). Cobalt ferrite was found as an additional phase in the precipitates obtained at r = 9.09 and 13.04. Mossbauer spectroscopy showed the formation of solid solutions of a-(Fe, Co)OOH. The incorporation of cobalt ions into the goethite crystal structure was monitored by a decrease in the average hyperfine magnetic field (Bhf). The value Bhf i decreased linearly up to r = 5.66, whereas a nonlinear dependence was obtained at r = 6.98 to 13.04. Infrared (IR) bands corresponding to the bending vibrations dOH and gOH were shifted from 892 to 903 cm-1 and from 797 to 800 cm-1, respectively, up to r = 6.98. Fourier transform infrared spectroscopy lacked the sensitivity to monitor the effects of cobalt ions, demonstrated by the Mo¨ssbauer analysis. Cobalt incorporation into the crystal structure of goethite induced a gradual elongation of a-(Fe, Co)OOH particles along the crystallographic c axis. The formation of a-(Fe, Co)OOH nanowires was shown at r 56.98. These nanowires were ~700 nm long, whereas their diameter was ~15-20 nm. The majority of the cobalt ferrite particles were in the nanosize range, as observed by FE-SEM. On the basis of the Co/Fe ratio measured by EDS, it appears that the cobalt ferrite particles were not fully stoichiometric.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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