Hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide and its application in heavy metal removal and solar-induced photocatalytic degradation

Abstract

In this study, hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide nanostructures (3D-Fe₂O₃) were synthesized by a facile and rapid ultrasound irradiation method. Additives, templates, inert gas atmosphere, pH regulation, and other complicated procedures were not required. Dense 3D-Fe₂O₃ with a relatively large Brunauer-Emmett-Teller (BET) surface area of 129.4 m²/g was synthesized within 23 min, and the BET surface area was further improved to 282.7 m²/g by a post heat-treatment process. In addition, this post processing led to phase changes from maghemite (γ phase) to hematite (α phase) Fe₂O₃. Subsequent characterization suggested that the growth mechanism of the 3D-Fe₂O₃ follows self-assembly and oriented attachment. The prepared 3D-Fe₂O₃ was applied to wastewater purification. Ultrasound-irradiated 3D-Fe₂O₃ can eliminate a As(V) and Cr(VI) from water with 25 times faster removal rate by using a one third smaller amount than commercial α-Fe₂O₃. This was attributed to the inter-particle pores and relatively positively charged surface of the nanostructure. In addition, post heat treatment on ultrasound-irradiated 3D-Fe₂O₃ significantly influenced the photocatalytic degradation of methylene blue and phenol, with a 25 times higher removal efficiency than that of commercial α-Fe₂O₃, because of both high BET surface area and good crystallization of the prepared samples.

Keywords: Heavy metal adsorption; Iron oxide (Fe(2)O(3)); Photocatalytic activity; Three-dimensional (3D) hierarchical architectures of metal oxides; Ultrasound irradiation.