engleski

Incorporation of large ions in goethite nanorods to manipulate the morphology

Goethite (-FeOOH) is an iron oxyhydroxide with considerable catalytic activity having nominally spherical nanoparticles to submicrometer, acicular particles. The catalitic activity of the goethite is related to its highly hydroxylated surfaces[1]. Thus, the increase of surface to volume ratio could be the parameter for enhancing the catalytic properties. We synthesized the goethite nanorods in a hydrothermal reaction of precipitates prepared by two different precipitation procedures and with the addition of various molar fractions of bismuth ions. In the first procedure the solutions containing both iron and bismuth salts were co-precipitated at high pH before hydrothermal processing. In the second procedure the precipitation of the iron and bismuth salts was carried out separately, prior to mixing in an autoclave for the hydrothermal treatment. The crystal structures were analyzed using X-ray powder diffraction (XRD), while the morphologies and nanostructures were determined using high-resolution transmission electron microscopy (HRTEM) and/or scanning electron microscopy (SEM). The chemical compositions were examined by energy-dispersive X-ray analysis (EDXS). Tailoring the goethite’s morphology in both series of precipitations was observed. Thus, aspect ratio of goethite nanorods increased with an increase in the amount of Bi3+ ions in the reaction (Fig 1). However, with a higher fraction of bismuth other phases (- Fe2O3, BiFeO3, Bi2O3) were also produced (Table 1). Figure 1: Goethite nanorods synthesized in the case of separate precipitation with a) 5 mol% Bi, b) 10 mol% Bi . x (Bi3+) 0 mol % 2 mol % 3.5 mol % 5 mol % 10 mol % co- precip phases (XRD) G G G G, H G, H Average aspect ratio (TEM) 3.2 3.7 6 G: 7.2 H: 1.56 G: 13.9 H: 2 cepar. precip. phases (XRD) G G G G, Bi25FeO4 G, BiFeO3, Bi2O3 Average aspect ratio (TEM) 3.2 G: 4.8 G: 7.7 Table 1: Phases and average aspect ratio in samples prepared by different procedurec. G-goethite, H-hematite In the goethite nanorods synthesized by separate precipitation the content of Bi+3 inbuilt into the structure was larger (1.5–3.5 at %) than in goethite prepared after co-precipitation (0.3–1.5 at %). The influence of the bismuth addition on the goethite morphology and the appearance of other phases will be discussed in terms of the condition of hydrothermal reactions and the ionic radius of bismuth.

nanorods ; goethite ; HRTEM

nije evidentirano