Co-Doped Bismuth Oxide Nanomaterials for Enhanced Visible-Light Photocatalytic Degradation of Persistent Pollutants

Pure Bi2O3 is a favorable photocatalyst for visible-light-driven processes; however, the rapid recombination of photogenerated charge carriers limits its practical performance. In this work, Co-doped Bi2O3 nanoparticles, CoxBi2−xO3 (x = 0–0.1), were produced through a sol–gel combustion route to enhance their visible-light photocatalytic activity. As demonstrated by XRD analysis, Co was successfully incorporated into the Bi2O3 lattice, along with changes to the crystal structure, crystallite size (up to ~88 nm), and lattice strain. Optical measurements revealed that Co-doping induces a clear absorption edge’s red shift, resulting in a systematic reduction of the optical band gap from 3.9 eV for pure Bi2O3 to approximately 3.1 eV for the doped samples. This band gap narrowing enhances visible-light absorption and improves photocatalytic efficiency. Photocatalytic activity was assessed by measuring the degradation of MB under visible-light irradiation. Incorporation of Co consistently enhanced the performance across all doped samples compared to the pristine oxide counterpart. The Co0.1Bi1.9O3 composition demonstrated the best performance, achieving a removal efficiency of 94.5% within 120 min, compared with 73.0% for pure Bi2O3. Kinetic analysis indicated pseudo-first-order behavior, with the optimal sample showing a rate constant of 0.0240 min−1—more than twice that of the undoped material (0.0105 min−1). These results validate that Co-doping is an actual approach for engineering the electronic structure of Bi2O3, leading to enhanced visible-light absorption, improved charge-carrier separation, and significantly higher photocatalytic efficiency for environmental remediation applications.