Diminishing photoactivity in microwave-synthesized vanadium-doped TiO2: Resolving the paradox of defect-mediated charge recombination

Abstract

Vanadium-doped TiO₂ photocatalysts with varying V concentrations (0–2 mol%) were synthesized via a microwave-assisted solution chemistry method and subsequently calcined at 300 °C. The structural, morphological, and optical properties of TiO₂ and V doped-TiO₂ at a concentration of 0.5–2 mol% were systematically analyzed using XRD, SEM, FT-IR, UV–Vis, and PL spectroscopy. XRD analysis confirmed the formation of the anatase TiO₂ phase, while dislocation density (δ) and strain (ε) calculations revealed an increase in structural defects with higher V doping levels, affecting crystallinity. Band gap analysis indicated a reduction from 3.11 eV (TiO₂) to 2.81 eV (2 mol% V–TiO₂), attributed to the introduction of localized defect states. Photocatalytic degradation of Rhodamine B (RhB) under UV light for 240 min showed that pure TiO₂ exhibited the highest degradation efficiency (96.97 %), followed by 0.5 mol% V–TiO₂ (95.14 %) and 2 mol% V–TiO₂ (75.75 %). PL analysis further confirmed that moderate V doping enhanced charge carrier separation, whereas excessive doping promoted tunneling-mediated recombination. These findings provide valuable insights into the defect-driven charge dynamics in V-doped TiO₂, emphasizing the significant impact of dopant concentration on enhancing photocatalytic efficiency.