Size and shape controlled of α-Fe2O3 nanoparticles prepared via sol-gel technique and their photocatalytic activity

Haematite (alpha-Fe2O3) nanoparticles (NPs) of different sizes and morphologies were prepared from two different iron precursors (iron acetate (A) and iron nitrate (N)) using the sol-gel technique, through a reaction with oxalic acid. A pure alpha-Fe2O3 phase (rhombohedral) that contained particles of different sizes and shapes were obtained from both iron precursors. Transmission electron microscope measurements showed average sizes of 23 +/- 2 and 30 +/- 2 nm for alpha-Fe2O3 (A) and alpha-Fe2O3 (N) formed NPs, respectively. The observed uniform spherical shape for the alpha-Fe2O3 (A) formed NPs is due to the presence of carboxylic acid (acetic acid) used to control the nucleation and growth process of alpha-Fe2O3 NPs. However, quasi-spherical particle shapes for alpha-Fe2O3 (N) were produced in the presence of a mineral acid (nitric acid), which caused the particles to be constrained during their growth step. However, the optical analysis showed that the band gaps of alpha-Fe2O3 (A) and alpha-Fe2O3 (N) as 2.63 and 2.60 eV were found, respectively. The surface area results exhibited that both alpha-Fe2O3 NPs were a porous material with a higher area for alpha-Fe2O3 (A), which resulted from the uniform shape and smaller size of particles. The magnetic properties were observed to be slightly different for both alpha-Fe2O3 NPs, which were also attributed to the different particle size of the NPs. Higher photocatalytic activity for congo red dye and 4-chlorophenol degradation under sunlight was achieved by alpha-Fe2O3 (A), which was attributed to the smaller size and higher surface area compared to alpha-Fe2O3 (N) NPs. [GRAPHICS]