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Structural and Optical Properties of Tin-doped Hematite (alfa-Fe2O3) Nanorods

Due to their high stability, low toxicity, abundance and low cost, iron oxides are desirable materials for different applications. Hematite (α-Fe2O3) is an especially stable iron oxide compound and a semiconducting material (Eg = 2.2 eV) with strong absorption of UV and visible light with λ < 600 nm. Hematite can be regarded as suitable material for application as a photoelectrode for hydrogen production by water splitting using solar energy [2] or as a photocatalyst for decomposition of toxic compounds [3]. Photoelectrochemical and photocatalytic properties of hematite can be significantly improved by doping with various metal cations and/or by morphology modification [2, 4]. A significant effect of tin doping on the photoactivity of hematite photoanodes for photoeletrochemical water splitting was reported in several recent publications [5-8]. This effect was explained by modification of optical, electronic and electrical properties of hematite by incorporation of Sn4+ ions as an n-type dopant. Also, a strong effect of nanoparticles morphology on the hematite photocatalytic activity has been reported. A higher activity of hematite nanorods compared to nanocubes or nanoplates was observed in decomposition of rhodamine B dye by heterogeneous photo Fenton reaction [4]. In the present work, structural and optical properties of hematite nanoparticles of elongated shape (nanorods) doped with tin were investigated. Sn-doped hematite nanorods were prepared by calcination of Sn-doped goethite nanorods obtained by precipitation in alkaline aqueous solution. Influence of Sn doping on the structural properties of hematite was studied using X-ray powder diffraction (XRPD), field emission scanning electron microscopy (FE-SEM) and Mössbauer spectroscopy. Incorporation of tin into the crystal structure of hematite was confirmed by measuring unit cell expansion by XRPD and hyperfine magnetic field reduction by Mössbauer spectroscopy. Also, the size and shape of hematite nanorods significantly changed by Sn doping. Optical properties were investigated using diffuse reflectance UV-Vis- NIR spectroscopy. A shift of absorption edge to higher wavelengths by Sn doping was observed in recorded spectra. A reduced direct and indirect optical band gap in Sn-doped hematite were estimated using Tauc plots.

Hematite ; Sn dopant ; Mössbauer spectroscopy ; Optical band gap

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