The influence of substituting metals (Ti, V, Cr, Mn, Co and Ni) on the thermal stability of magnetite

Abstract

In this paper, a systematic study on the influence of substituting metals on the thermal stability of magnetite was carried out. Six series of substituted magnetite (Fe 3-x M x O 4 , M = Ti, V, Cr, Mn, Co and Ni) and Ti-V co-doped magnetite were prepared by a precipitationoxidation method, followed by the characterization of X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) spectroscopy and thermogravimetry and differential scanning calorimetry (TG-DSC) analyses. XRD patterns confirmed the formation of samples with spinel structure and XANES probed the valence and site occupancy of the substituting ions. From the TG-DSC analysis results, the substitution of Ti 4? , Mn 2? , Co 2? and Ni 2? stabilizes the magnetite structure, while V 3? and Cr 3? do not show such an effect. For the thermal stability of maghemite, V 3? has a negative effect while the other studied ions show a positive effect. In Ti-V co-doped magnetites, the influence of Ti 4? and V 3? on the thermal stability of magnetite is similar to the case of their singlemetal-substituted magnetites. The mechanism about the thermal stability change of magnetite by metal substitution was also discussed. The obtained results will be of high importance for the industrial applications of magnetite.

The UV/Fenton Degradation of Tetrabromobisphenol A Catalyzed by Nanocrystalline Chromium Substituted Magnetite

“…The detailed discussion for X-ray absorption near-edge spectrum (XANSE) of Fe 2 04 Cr 0 96 O 4 has been presented elsewhere. 32 The Cr atoms in (EXAFS) analysis was performed to determine the local atomic structure of Cr in Fe 2 04 Cr 0 96 O 4 . Figure 2 shows the Fourier Transform (FT) curve and the best fitting characteristic of Fe 2 04 Cr 0 96 O 4 .…”

A comparative study about the effects of isomorphous substitution of transition metals (Ti, Cr, Mn, Co and Ni) on the UV/Fenton catalytic activity of magnetite

“…The magnetite samples Fe 3−x M x O 4 (M = Fe, Ti, Cr, Mn, Co and Ni) were synthesized by a precipitation-oxidation method as described in literatures [8,15,21]. The concentration ratio between iron and substituting metal (Fe:M) was about 2:1 in the initial acid solution.…”

“…[28][29][30][31][32][33][34][35][36][37][38][39] • and the shift of peaks at ca. 35.5 • toward lower diffraction angle indicate the incorporation of substituting metals into inverse spinel structure, which is resulted from the difference in ionic radii between iron and substituting metal cations (Table 1) [21]. According to the isomorphous replacement principle, Ti 4+ replaced Fe 3+ with the same amount of Fe 3+ changed to Fe 2+ for electrovalence equilibrium [25].…”

“…Moreover, some substitutions changed the surface properties of magnetite, e.g. specific surface area and surface hydroxyl amount [21]. This enhanced the adsorption of organic pollutants and H 2 O 2 , which also accelerated the degradation process.…”

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

“…The adsorption mechanism includes surface site binding [32], electrostatic interaction [33], modified ligand combination [34] and oxidation-reduction interaction [35,36]. Some substitutions have made obvious variations on the physicochemical properties of magnetite surface [26,37]. For instance, some substituting cations (e.g., Cr 3+ and Ti 4+ ) increase the surface hydroxyl amount of magnetite.…”