engleski

Structural, Optical and Photocatalytic Properties of Elongated Cu-, Co- and Sn-doped Goethite and Hematite Nanoparticles

Iron(III) oxides are inexpensive, non-toxic and stable compounds which are extensively investigated for different applications. They can incorporate significant levels of various metal ions into the crystal structure, which can have a positive effect on different properties [1]. Due to significant absorption of solar radiation, iron(III) oxide nanoparticles and nanostructures are investigated for possible application as photocatalysts for decomposition of toxic compounds [2] and photoelectrodes for hydrogen production by water splitting [3]. Heterogeneous photo-Fenton reaction using iron oxide photocatalysts has emerged as a promising way for decomposition of toxic organic compounds by visible light [4]. Size and shape of iron oxide nanoparticles were shown to be very important for photocatalytic activity in heterogeneous photo-Fenton reaction [5, 6]. However, the effect of doping on the photocatalytic activity of iron oxides has been much less investigated. In the present work, the effects of Cu, Co and Sn ions doping on different properties (unit cell size, crystallite size, particle size and shape, hyperfine magnetic field, optical and visible light photocatalytic properties) of elongated goethite (α-FeOOH) and hematite (α- Fe2O3) nanoparticles were investigated. Elongated goethite nanoparticles doped with Cu, Co and Sn ions were synthesized by the coprecipitation of mixed Fe(NO3)3 and Cu(NO3)2, CoCl2 or SnCl4 aqueous solutions using a strong organic alkali tetramethylammonium hydroxide (TMAH). Elongated hematite nanoparticles (pure and doped) were produced by calcination of corresponding goethite nanoparticles. Incorporation of metal cations in the crystal structure of goethite and hematite was confirmed from the change in unit cell size (determined by XRPD) and from the reduction of hyperfine magnetic field (determined by Mössbauer spectroscopy). Also, a strong effect of doping on the nanoparticle size and shape was observed by FE-SEM. Diffuse reflectance UV- Vis-NIR spectroscopy showed a significant influence of doping on the position of goethite and hematite absorption edge. Optical band gaps in samples were estimated using Tauc plots. A significant reduction of direct and indirect optical band gaps in goethite and hematite nanoparticles by Cu, Co and Sn doping was observed. Visible light photocatalytic performances were examined by decomposition of rhodamine B dye in the presence of iron oxide photocatalyst and H2O2 under visible light illumination. Generally, hematite nanoparticles showed higher photocatalytic activities than goethite nanoparticles due to higher absorption of visible light. Photocatalytic activities of goethite nanoparticles were ranked as Cu-doped > Sn-doped > Co-doped > undoped, while photocatalytic activities of hematite nanoparticles were ranked as Cu-doped > Sn- doped > undoped > Co-doped. The high photocatalytic activity of elongated Cu-doped hematite nanoparticles can be explained by a combined effect of an enhanced separation and transfer of photogenerated charges (due to Cu doping) and their short distance from the particle surface (due to nanoneedle morphology).

Hematite ; Co dopant ; Cu dopant ; Sn dopant ; Mössbauer spectroscopy ; Optical band gap ; Photocatalytic activity

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