Preparation of α-Fe2O3 hollow spheres, nanotubes, nanoplates and nanorings as highly efficient Cr(vi) adsorbents

Abstract

α-Fe₂O₃ nanoparticles with different morphologies, such as hollow spheres, nanotubes with a limited amount of the {0001} plane exposed, and nanoplates and nanorings with the {0001} plane predominantly exposed, have been synthesised by using NaH₂PO₄ and urea in a facile hydrothermal method. The mechanism of the morphology evolution from hollow sphere to nanoring has been investigated. It is proposed that the polymerisation of Fe³⁺/H₂PO₄⁻ plays an important role in the formation of these morphologies. The adsorption of Cr(VI) from aqueous solution onto these α-Fe₂O₃ nanoparticles showed that the α-Fe₂O₃ with nanoring morphology has the highest removal efficiency, and the adsorption capacity reached 16.9 mg g⁻¹. These results indicate that the adsorption mechanism of Cr(VI) onto hematite nanoparticles is a chemisorption process through doubly and triply coordinated hydroxyl groups on the outer surface of α-Fe₂O₃.