Photocatalytic activity in graded off-valent cations substituted NaNbO₃

This study investigates the impact of off-valent doping on the photocatalytic properties of NaNbO₃ concerning the degradation of Methylene Blue. Compositions with x values of 0.00 (representing pure NaNbO₃, denoted as NBO) and 0.05 within the material system Na_1-xA_xNbO₃ (where A is K¹⁺, Ba²⁺, La³⁺, abbreviated as K-NBO, Ba-NBO, and La-NBO respectively) were synthesized using the conventional solid-state reaction method. The UV-visible analysis revealed a decrease in the band gap for samples K-NBO and Ba-NBO, while an increase was observed for sample La-NBO. Raman modes of lower wave numbers merged and shifted towards the higher wave number side. The determination of valence band edge and conduction band edge involved computational analysis based on XPS survey scans, and the band gap energy values were derived from UV-Visible spectroscopy results. Examining the band diagram of the samples (NBO, K-NBO, Ba-NBO, and La-NBO) in conjunction with the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of MB dye provided insights into potential degradation mechanisms. Photocatalytic dye degradation experiments for Methylene Blue demonstrated that doping increased the degradation efficiency of samples K-NBO, Ba-NBO, and La-NBO compared to NBO. Among all NaNbO₃ based prepared samples, Ba-NBO exhibited the highest degradation efficiency of 96%, however slightly less than the reference sample P25 TiO₂.