Nanostructural and photocatalytic properties of iron and silver co-doped titanium dioxide nanorods

Iron- and silver-co-doped TiO₂ nanorods (DTNs) were synthesized through a sol–gel-assisted hydrothermal route to investigate the influence of calcination temperature on their nanostructural evolution, optical properties, and photocatalytic performance toward methylene blue degradation. The uncalcined sample exhibited the smallest crystallite size, the highest estimated surface area, the lowest optical bandgap, and the highest Urbach energy, indicating the presence of abundant defect-related electronic states that promoted visible-light absorption and charge transfer. Increasing the calcination temperature progressively reduced lattice defects and estimated surface area while increasing crystallite size and bandgap energy, resulting in lower photocatalytic activity. Among all samples, the uncalcined DTNs achieved the highest degradation efficiency (75.84%) and the largest pseudo-first-order rate constant (0.022 min⁻¹) after 60 min of UV irradiation. These findings demonstrate that suppressing excessive thermal growth preserves defect-assisted charge separation and active surface sites, providing an effective strategy for improving the photocatalytic performance of Fe/Ag co-doped TiO₂ nanorods for dye-contaminated wastewater treatment.