Phase transformation from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:mrow><mml:mi mathvariant="normal">α</mml:mi></mml:mrow></mml:math>-Bi2O3 needles to petal-shaped β-Bi2O3 nanoparticles via ball milling for boosted photocatalytic activity of rhodamine B dye
Divya Janardhana, Shivaramu Nagarasanakote Jayaramu, Harris Richard Anthony, H.C. Swart
Abstract
Tetragonal bismuth oxide (β-Bi 2 O 3 ) is regarded as a promising heterogeneous photocatalyst for the degradation of organic dye molecules in polluted water, owing to its high surface area , wide absorption band edge, effective exciton separation, and abundant oxygen vacancies . Here, we propose a phase transformation from needle-shaped monoclinic (α) Bi 2 O 3 to petal-shaped β-Bi 2 O 3 nanoparticles through a ball milling process. The α-Bi 2 O 3 and β-Bi 2 O 3 materials were extensively characterized through various techniques to investigate their structural, morphological, surface chemicals, and optical properties . X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HR-TEM), and selected-area electron diffraction (SAED) patterns reveal that the ball-milled α-Bi 2 O 3 has a polycrystalline structure and identify the (201) and (101) planes, which correspond to the β-Bi 2 O 3 phase. The Tauc plot yields band gaps of 2.9 eV for α-Bi 2 O 3 and 2.5 eV for β-Bi 2 O 3 . Furthermore, β-Bi 2 O 3 exhibited a broad absorption band from UV to 540 nm. This finding suggests that β-Bi 2 O 3 has an enhanced ability to absorb UV–visible light, thereby improving photon utilization efficiency. The petal-shaped β-Bi 2 O 3 nanoparticles demonstrated improved UV–visible light absorption, enhanced charge carrier separation, and superior photocatalytic properties. The petal-shaped β-Bi 2 O 3 nanoparticles exhibited excellent photocatalytic activity for the degradation of Rhodamine B in aqueous phase under UV–visible light and solar simulator irradiation. Notably, the β-Bi 2 O 3 system achieved 97 % degradation in 75 min under UV–visible light and 91 % degradation in 150 min under the solar simulator. Both catalytic reactions followed pseudo-first-order kinetics, with kinetic constants (k) registering at 8.7 ± 0.6 × 10 −3 and 48.1 ± 4.7 × 10 −3 min −1 for Rhodamine B (RhB) under UV–vis light. Additionally, by expanding the number of reactive sites and oxygen vacancies , the catalyst's large surface area boosted electron-hole separation and its photocatalytic performance.