Oxygen vacancies assisted photocatalytic dye degradation and photoelectrochemical water splitting performance in Ag and Mg-modified NaNbO₃

A lead-free Na_0.85Ag_0.15Nb_0.95Mg_0.05O₃ (AM-NN) polycrystalline ceramic was synthesized using the conventional solid-state reaction method, and its structural, dielectric, impedance, and optical properties were thoroughly investigated. X-ray diffraction (XRD) and Rietveld refinement of AM-NN confirmed that the material adopts a perovskite-type orthorhombic structure with the <i>P</i>2₁<i>ma</i> space group. Introducing oxygen vacancies through AgO resulted in spectral changes observed in Raman spectroscopy and Photoluminescence. Dielectric and complex impedance measurements, taken from 10²-10⁶ Hz and room temperature to 500 °C, exhibited non-Debye behavior. AM-NN presented a reduced band gap of 3.12 eV compared to pure NaNbO₃ (NN) (3.4 eV) as obtained from UV-vis spectroscopy. AM-NN demonstrated a superior photocatalytic dye degradation percentage of 99% methylene blue (MB), 95% crystal violet (CV) and 60% congo red (CR) at 300 min with the rate constant (<i>k</i>) of 0.0128 min^-1 (MB), 0.0138 min^-1 (CV) and 0.0027 min^-1 (CR), respectively. PEC water splitting showed that the photoanode fabricated with AM-NN exhibits enriched photocurrent density (1.11 mA cm^-2). XRD showed no secondary phase after dye degradation, indicating the system's reusability. A detailed investigation into the electrical properties and photocatalytic mechanism was provided to account for the observed improvements in dye degradation and water splitting applications.