Facile fabrication of tunable Bi ₂O ₃ self-assembly and its visible light photocatalytic activity

In this article, we report the fabrication of various morphological bismuth oxides (α-Bi ₂O ₃) by a self-assembly process using bismuth oxalates as precursors. Barlike Bi ₂(C ₂O ₄) ₃·7H ₂O and microrod-like (BiOHC ₂O ₄) ₂·H ₂O 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 Bi ₂O ₃, 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 Bi ₂O ₃ 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-Bi ₂O ₃ 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 Bi ₂O ₃. We propose a plausible mechanism for the formation of various morphologies of Bi ₂O ₃.