Sonochemical synthesis of cobalt-doped barium titanate nanoparticles for visible-light applications: catalytic and antimicrobial properties

Cobalt-doped barium titanate (Co-doped BaTiO₃, Co-BTO) nanoparticles with promising electronic characteristics are synthesized via a sonochemical method. Microstructural analysis by TEM, XRD, and Raman spectroscopy demonstrates uniform quasi-spherical particles (20–30 nm) and a tetragonal crystal phase. Co-doping leads to a transition from a purely tetragonal lattice to a mixed tetragonal/pseudo-cubic structure. XPS analysis reveals that the substitution of Co²⁺ into the BaTiO₃ (BTO) perovskite lattice alters Ti and O oxidation states and increases oxygen-vacancy concentration. Optical characterization by UV–Vis DRS and PL measurements shows that Co-doping narrows the band gap from 3.29 to 2.69 eV at 4 mol % Co and suppresses electron-hole recombination by over 69 %. First-principles calculations reveal that cobalt incorporation into the BTO lattice creates new states below the conduction band, reducing the band gap to ≈ 2.2 eV and extending light absorption into the visible region. Photocatalytic tests demonstrate a 2.4-fold increase in the methylene blue degradation rate constant for 4 mol % Co-BTO compared to undoped BTO. Co-BTO achieves > 50 %, > 85 %, and > 96 % inactivation of Escherichia coli, Staphylococcus aureus, and MS2 bacteriophage under light irradiation, respectively. Sonochemical synthesis of Co-BTO nanoparticles demonstrates their potential as perovskite-based visible-light photocatalysts.