Influence of pretreatment on the properties of alpha-Fe2O3 and the effect on photocatalytic degradation of methylene blue under visible light

摘要

The hematite (alpha-Fe2O3) nanostructures were synthesized by thermal oxidation of metal at 500 degrees C under atmospheric pressure. We studied the effect of the electrochemical pretreatment of the substrate before calcinations and its impact on the morphology, crystalline structure, lattice microstructural, and optical properties of alpha-Fe2O3. Uniform nanosheets were observed on the sample surface after calcination; their dimension and morphology were accentuated by the pretreatment, as confirmed by the SEM images. The characteristics of the nanostructures, analyzed by X-ray diffraction (XRD), revealed a rhombohedral symmetry with the space group R-3c and lattice constants: a = 0.5034 nm and c = 1.375 nm. The average crystallite size and strain, determined from the Williamson-Hall (W-H) plot, showed substantial variations after the substrate pretreatment. The Raman spectroscopy confirmed the changes in the crystal properties of the hematite submitted to pretreatment. The diffuse reflectance allowed to evaluate the optical gap which lies between 1.2 and 1.97 eV, induced by the electrochemical processing. The photocatalytic activity of alpha-Fe2O3 films was assessed by the degradation of methylene blue (MB) under LED light; 15 enhancement of the degradation for the pretreated specimens was noticed.