Acetic acid-assisted fabrication of hierarchical flower-like Bi₂O₃ for photocatalytic degradation of sulfamethoxazole and rhodamine B under solar irradiation

With the assistance of acetic acid (CH₃COOH), a novel 3D flower-like Bi₂O₃ was synthesized via hydrothermal process followed by calcination. For the first time, the role of CH₃COOH as a capping agent in the formation of flower-like structure was investigated. The as-prepared flower-like Bi₂O₃ had a high activity on the degradation of sulfamethoxazole (SMX) under simulated solar light irradiation due to the narrow band gap of 2.69 eV, high percentage of β-Bi₂O₃ as well as high intensity of polar facets (1 2 0) and (2 0 0). Meanwhile, the photocatalytic degradation followed apparent pseudo-first-order kinetics. The rate constant (k) increased from 0.7 × 10⁻² to 3.0 × 10⁻² min⁻¹ with the catalyst loading varying from 0.5 to 2.0 g L⁻¹. Increasing pH values from 3 to 11 led to the decrease of k from 2.2 × 10⁻² to 0.2 × 10⁻² min⁻¹, which could be attributed to the electrostatic adsorption between SMX molecules and Bi₂O₃. The radical quenching experiments showed both direct (h⁺) and indirect oxidation (OH and O₂ ^-) happened in this process.