Synthesis and properties of Sn-doped α-FeOOH nanoparticles

Pure and Sn-doped goethite (α-FeOOH) nanoparticles with good uniformity were synthesized by a facile precipitation method. The effects of Sn doping on the particle size and shape, structural, thermal, vibrational, optical and photocatalytic properties of prepared goethite nanoparticles were investigated. The Sn4+-for-Fe3+ substitution in the crystal structure of goethite was proved by determination of a significant unit cell expansion (the effect of larger Sn4+ ions) and a substantial reduction of the hyperfine magnetic field (the effect of magnetic dilution by non-magnetic Sn4+ ions). Sn doping induced a decrease in length and an increase in thickness of goethite nanocrystallites and nanoparticles, i.e., the change in particle shape from thin goethite nanorods to shorter and thicker Sn-doped goethite nanoellipsoids and nanocuboids. Thermal dehydroxylation of goethite was shifted to significantly higher temperatures by the Sn4+-for-Fe3+ substitution. The optical band gap of goethite nanoparticles narrowed with the increased Sn4+-for-Fe3+ substitution. The visible light photocatalytic efficiency for rhodamine B (RhB) degradation by a heterogeneous photo-Fenton process was gradually enhanced by Sn doping from 38% for pure goethite nanorods to 55% for Sn-doped nanoellipsoids and 70% for Sn-doped goethite nanocuboids.