Phase transformation and room temperature stabilization of various Bi₂O₃ nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

Abstract

The air annealing induced grain growth from nano to microscale and a transformation sequence from Bi → β-Bi2O3 → γ-Bi2O3 → α-Bi2O3 was evident. All the annealed samples are oxygen-deficient, resulting in the appearance of a strong red emission band.

Plasmonic Bismuth Nanoparticles: Thiolate Pyrolysis Synthesis, Size-Dependent LSPR Property, and Their Oxidation Behavior

“…At low laser power (0.5 and 1 mW), only the E g and A 1g peaks for rhombohedral Bi are visible, whereas with an increase of laser power (2, 3, and 5 mW), the strong E g vibration for elemental Bi damps out and three Raman peaks at 91, 121, and 308 cm –1 appear and become more obvious (Figure a). They fit well with the Raman signature from β-Bi 2 O 3 with a tetragonal crystal phase. ,, This result is consistent with the thermal oxidation of Bi NPs in an air-flow TG–DSC heating process, which converts Bi NPs into pure-phase β-Bi 2 O 3 NPs (confirmed by XRD and Raman spectrum and discussed later).…”

“…Similar surface components were also detected in other Bi NP samples (65 nm) on the basis of the XPS results. As displayed in Figure S6, a quite weak S 2s XPS signal is detectable, indicating the presence of surface Bi–S components (i.e., bismuth thiolate); at the same time, there are two peaks with BEs of 529.4 and 531.0 eV in the O 1s region, which are consistent with the characteristic positions for Bi–O (Bi 2 O 3 ) ,, and surface O–H hydrated species, , respectively. The oxidation of Bi to Bi 2 O 3 , that is, 4Bi(s) + 3O 2 (g) → 2Bi 2 O 3 (s), is a thermodynamically favorable reaction due to its negative Gibbs free energy .…”

“…The oxidation of Bi to Bi 2 O 3 , that is, 4Bi(s) + 3O 2 (g) → 2Bi 2 O 3 (s), is a thermodynamically favorable reaction due to its negative Gibbs free energy . Accordingly, Bi is easily oxidized and even forms a shell layer of native oxide on the surface as exposed to an oxygen-containing environment, especially upon electric or laser heating. − ,,,− However, thiols are a kind of robust reducing agents and capping ligands ,, and thus are able to not only reduce surface bismuth oxide to zero-valent Bi but also protect Bi NPs from reoxidation by forming a thiol-adsorbed layer on the surface (Figure b), thus generating Bi NPs with high quality that is favorable for the investigations on their intrinsic physical and chemical properties.…”

“…Similar to noble-metal Au and Ag NPs, bismuth NPs (Bi NPs) are found to exhibit LSPR optical bands and extinction spectra highly sensitive to their grain sizes, shapes, and surrounding dielectric media [especially the solvents of different relative dielectric constants (ε)]. − , For spherical NPs, an increase in the size of Bi NPs would cause a red shift of LSPR bands, doublet or multiple resonance bands, enhanced light scattering, and bandwidth broadening in the ultraviolet–visible–near-infrared (UV–vis–NIR) extinction spectra. − , Unlike Au and Ag NPs, however, the synthesis of monodisperse Bi NPs with tunable average sizes is rather difficult, ,− so that a comprehensive experimental investigation concerning the size effect on their LSPR optical properties is significantly limited. On the other side, the oxidation of metallic Bi would produce thin films or particulates of bismuth oxide (Bi 2 O 3 ), − which is known as a versatile material that exhibits rich polymorphism and phase-dependent physical and chemical properties. , Recently, it has been found that controlling the surface oxidation level of liquid Bi droplets could successfully make atomically thin Bi 2 O 3 monolayer sheets, opening up a novel route to 2D materials of nonlayered oxides. , In this context, further investigations and mechanistic insights are required in order to reveal and regulate the oxidation behaviors of liquid or solid Bi NPs as well as the polymorphism in so-formed Bi 2 O 3 .…”

Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2O3 and Fe2O3

“…Bismuth oxide exists in several polymorphs. They are α‐Bi 2 O 3 (monoclinic), β‐Bi 2 O 3 (tetragonal), γ‐Bi 2 O 3 (bcc), δ‐Bi 2 O 3 (cubic), and ε‐Bi 2 O 3 (triclinic) (Gandhi et al, 2020b; Gandhi, Cheng, & Wu, 2020a; Liu et al, 2016).…”