Hierarchical Porous alpha-Fe2O3 Formation by Thermal Oxidation of Iron as Catalyst for Cr(Vi) Reduction

alpha-Fe2O3 is a semiconductor photocatalyst that can adsorb and reduce heavy metal ions from contaminated water. Here, hierarchical porous structured alpha-Fe2O3 was synthesised by thermal oxidation of iron wire at 400 degrees C - 700 degrees C in the presence of water vapour for 1 hour. The mechanism of formation of the iron oxide nanowires is proposed to follow stress-driven mechanism and when the nanowires merged, nanoblades resulted hierarchical porous structure. Field emission electron microscope (FESEM) images of the oxidized iron had shown the formation of surface oxide comprising of a hierarchical porous structures. High resolution transmission electron microscope (HRTEM) and Raman spectroscopy results confirmed that the iron oxide is consisted of alpha-Fe2O3 in the surface whereas Fe2O3 and FeO are in the inner layer. The oxides were immersed in Cr(VI) solution and illuminated under sunlight to produce reducing electrons. The highest reduction precentage of Cr(VI) at pH 2 on the hierarchical porous structure is 80.78% for synthesized sample at 500 degrees C. It may be due to the higher surface area of the porous hierarchical structure which provide more catalytic reaction sites hence improving the photocatalytic activity.