Structural, morphological, optical, and electrochemical studies of α-Bi₂O₃ and CuBi₂O₄ photocathode materials

Herein, we synthesized tetragonal CuBi₂O₄ powder from raw Bi₂O₃ and CuO powders by the combination of hand-milling and ball-milling and subsequent sintering at 750 °C for 4 h in air. The structural, morphological, optical, and physicochemical properties of Bi₂O₃ and CuBi₂O₄ powder samples were examined by a variety of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), UV-Vis-NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical workstation. The combined XRD and Raman data analyses confirmed the monoclinic (P2₁/c) and tetragonal (P4/ncc) phases of α-Bi₂O₃ and CuBi₂O₄, respectively. The average crystallite domain size was estimated to be ~ 72 nm for α-Bi₂O₃ and ~ 50 nm for CuBi₂O₄. SEM micrographs exhibit microrod-like morphologies for α-Bi₂O₃ and spherical nanograin-like morphologies for CuBi₂O₄. XPS studies revealed the Bi 4f peak split into Bi 4f_5/2 and Bi 4f_7/2 and the presence of Bi³⁺ valence states for both α-Bi₂O₃ and CuBi₂O₄, whereas Cu²⁺ valence state for CuBi₂O₄. The optical bandgap was estimated from diffuse reflection data and found to be ~ 2.62 and ~ 1.77 eV for α-Bi₂O₃ and CuBi₂O₄, respectively. Finally, Cyclic Voltammetry and (Photo)Electrochemical Impedance studies of α-Bi₂O₃ and CuBi₂O₄ slurries atop the screen-printed gold electrode with aqueous Na₂SO₄ electrolyte were conducted and compared to demonstrate a quick assessment technique of their photocatalytic performance.