Methylene Blue photocatalysis enabled by strontium titanate nanostructures and structural evolution with influence of hydrothermal reaction duration.

Strontium titanate (SrTiO3) nanoparticles were synthesized via a hydrothermal route at 150 °C for 12, 24, 48 and 72 h to tune their structural, optical and photocatalytic properties. X-ray diffraction confirmed phase-pure cubic perovskite SrTiO3 for all samples, and Williamson-Hall analysis revealed a progressive increase in crystallite size with reduced lattice strain up to 48 h, consistent with enhanced structural ordering by Raman spectroscopy. UV-Visible spectroscopy showed a narrowing of the optical band gap from 3.18 to 3.08 eV with increasing duration, while SEM and HRTEM revealed well-developed polyhedral nanostructures, and XPS confirmed the presence of Ti4+ species and oxygen-vacancy-related surface states. Photoluminescence spectroscopy showed the lowest emission intensity for the 48 h sample, indicating suppressed charge-carrier recombination, consistent with its enhanced photocurrent response in linear sweep voltammetry. Band-edge positions estimated via the Mulliken electronegativity method rationalized the dominance of photogenerated holes and hydroxyl radicals identified through reactive species trapping. The 48 h sample achieved the highest methylene blue degradation efficiency, 89.7%, with a pseudo-first-order rate constant of 0.020 min-1, attributed to synergistic improvements in crystallinity, strain, morphology, and charge-carrier separation. The catalyst retained 80.1% of its initial efficiency after five recycling cycles with negligible structural change, and control experiments showed that direct photolysis (∼22%) and dark adsorption (∼16%) alone accounted for only a minor fraction of dye removal, confirming genuine, reusable photocatalysis. These findings establish hydrothermal duration as a critical, dopant-free lever for tailoring the structural, optical and photocatalytic performance of SrTiO3 nanoparticles.