Defect‐Driven Charge Separation in Ba‐Doped SrTiO ₃ : Correlating Photoelectrochemical Performance With Dye‐Selective Photocatalysis

Ba x Sr 1‐x TiO 3 (x = 0, 0.05, 0.1, 0.25, and 0.5) perovskite nanoparticles were synthesized via a hydrothermal route to investigate the effect of Ba substitution on the structural, photoelectrochemical (PEC), and photocatalytic properties of SrTiO 3 . X‐ray diffraction confirmed the formation of a single‐phase perovskite structure with systematic lattice expansion upon Ba incorporation, while Williamson–Hall analysis and Raman spectroscopy revealed enhanced lattice distortion and local structural modifications. Optical studies indicated slight band‐gap narrowing and improved visible‐light absorption, accompanied by defect‐related electronic perturbations. X‐ray photoelectron spectroscopy suggested the presence of defect‐related states, whereas photoluminescence and time‐resolved photoluminescence analyses indicated suppressed charge‐carrier recombination and prolonged carrier lifetime. PEC measurements demonstrated significantly improved charge‐transfer characteristics, with Ba 0.5 Sr 0.5 TiO 3 exhibiting a photocurrent density approximately 3.2 times higher than that of pristine SrTiO 3 . Photocatalytic studies under visible‐light irradiation showed that Ba 0.5 Sr 0.5 TiO 3 achieved ∼95% degradation of methylene blue and nearly complete degradation of Congo red within 180 min, following pseudo‐first‐order kinetics. Reactive‐species trapping experiments revealed dye‐dependent degradation pathways governed by •OH radicals and photogenerated holes. The optimized photocatalyst retained ∼93% of its activity after five cycles. The enhanced performance is attributed to the synergistic effects of lattice distortion, defect‐assisted charge separation, and improved interfacial charge transfer.