Influence of Cr doping on the structural, magnetic, optical and photocatalytic properties of α-Fe2O3 nanorods

Abstract

Pure and Cr-doped hematite (α-(Fe1-xCrx)2O3, x = 0, 0.026, 0.039, 0.085 or 0.135) nanorods were prepared by a simple co-precipitation and calcination method. Influence of different levels of Cr doping on the change of properties of long and thin pure hematite nanorods was investigated. Cr3+-for-Fe3+ substitution in the crystal structure of hematite was proved by measuring a gradual contraction of the unit cell and a gradual decrease of the hyperfine magnetic field by increasing the Cr molar fraction. Cr doping induced an increase in the width and thickness of hematite nanorods, as well as a decrease in the overall surface area. Low temperature 57Fe Mössbauer spectroscopy showed that the Morin transition in hematite was suppressed by Cr doping to temperatures below 80 K. Magnetic measurements confirmed the suppression of the Morin transition in Cr-doped hematite down to 5 K. Infrared spectra of Cr-doped hematite samples showed shifts of IR bands by Cr3+-for-Fe3+ substitution. Optical properties of α-Fe2O3 nanorods changed significantly by Cr doping – the absorption edge was shifted to higher wavelengths, accompanied by a greater absorption in the visible range and narrowed direct and indirect optical band gaps. The improved visible light photocatalytic activity of hematite nanorods in the heterogeneous photo-Fenton process by moderate Cr doping was measured, which can be attributed to the modifications in electronic structure and optical properties.