Facile Fabrication of Tunable Bi₂O₃ Self-Assembly and Its Visible Light Photocatalytic Activity

Abstract

In this article, we report the fabrication of various morphological bismuth oxides (α-Bi2O3) by a self-assembly process using bismuth oxalates as precursors. Barlike Bi2(C2O4)3·7H2O and microrod-like (BiOHC2O4)2·H2O were synthesized by using bismuth nitrate with oxalic acid in a simple mixing and hydrothermal process and are hereafter referred to as bismuth oxalate-1 and bismuth oxalate-2, respectively. The thermal decomposition of bismuth oxalate-2 at 300 and 400 °C for 2 h yields aggregate-free honeycomb brushlike and wormlike morphological Bi2O3, respectively. We first report the formation of both the above-mentioned novel morphological bismuth oxides. However, the decomposition of bismuth oxalate-1 results in microspheres with bundle-shaped particles and wormlike bundles with microflower morphologies at 300 and 400 °C, respectively. The influences of hydrothermal temperature, time, and bismuth precursor on the formation of bismuth oxalate-2 were investigated. The synthesized bismuth oxalates and Bi2O3 were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and nitrogen adsorption analysis. The XRD patterns indicated that well-crystallized α-Bi2O3 was formed in the thermal decomposition process from both precursors. The FE-SEM images indicated the formation of well-organized honeycomb brush-like and worm-like morphologies. The photocatalytic degradation of Acid Orange 7 (AO7) dye by using the synthesized bismuth oxides was investigated, and the results showed superior photocatalytic activity of the honeycomb brushlike Bi2O3. We propose a plausible mechanism for the formation of various morphologies of Bi2O3.