Visible-Light Photocatalytic Abatement of Diclofenac Potassium over Bismuth Sulfoiodide

The growing presence of pharmaceutical residues in aquatic systems underscores the need for effective and efficient treatment processes capable of eliminating persistent contaminants under mild conditions. In this study, bismuth sulfoiodide (BiSI) was investigated as a visible-light-responsive photocatalyst for the abatement of diclofenac potassium from aqueous media. Orthorhombic bismuth sulfoiodide nanorods were synthesized via a solution-phase method and comprehensively characterized using multiple analytical techniques. Powder X-ray diffraction (PXRD) confirmed the phase purity of crystalline BiSI, whereas UV-vis diffuse reflectance spectroscopy (UV-vis DRS) revealed strong visible-light absorption with an optical band gap of 1.65 eV. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) images showed uniform nanorod morphology with an average width of 148 ± 46 nm and an average length of 2.84 ± 1.37 μm, indicating a high aspect ratio. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the elemental composition of the material. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Bi³⁺, S^2-, and I^- ions, consistent with the BiSI lattice structure. The photocatalyst demonstrated excellent performance under visible-light irradiation, achieving 95.2% removal of the parent diclofenac potassium, as determined by UV-vis spectroscopic analysis, within 120 min. The reaction was described by a pseudo-first-order Langmuir-Hinshelwood model with an apparent rate constant of 2.999 × 10^-2 min^-1; however, the moderate fitting indicates that this model does not represent ideal pseudo-first-order kinetic behavior.