Enhanced photocatalytic performance of K-doped NaNbO3 correlated with structural defects, optical and polar properties

The swift pace of industrialization in the modern world has intensified the global energy crisis while exacerbating the challenges of water pollution, posing significant threats to the environmental sustainability and human well-being. Substantial endeavors have been undertaken to protect the environment from the detrimental impacts of methylene blue in the wastewater. This study shows the photocatalytic performance of eco-friendly K-modified NaNbO₃ catalysts in the degradation of methylene blue dye. Compositions with x = 0, 0.05, 0.10, 0.15, and 0.20 have been synthesized using solid-state reaction method. The XRD patterns for all the compositions demonstrate the formation of a single-phase orthorhombic structure with Pbcm space group symmetry. Analysis of the UV–Visible spectra indicates a trend of decreasing band gap from 3.21 eV for x = 0 to 3.01 eV for x = 0.20. High-resolution XPS scans show the presence of additional Nb⁴⁺ state along with Nb⁵⁺ state for doped samples. The edges of the valence and conduction bands using XPS and UV–Visible spectra, have been determined for each of the samples. The composition with x = 0.10 has shown a maximum degradation efficiency of 96% under UV radiations (300 W Xenon lamp) that aligns with the lowest photoluminescence intensity observed for this sample. An appropriate defect model with the help of band diagrams of these compositions for MB dye degradation and a suitable electron transfer mechanism have been proposed. The scavenger test has been found to validate the role of superoxide ions in the photocatalytic degradation of MB dye.