Increased Covalence and V-center mediated Dark Fenton-Like Reactions in V-doped TiO2: Mechanisms of Enhanced Charge-Transfer

Abstract

Tuning the valence state and electronic structure of catalytically active sites is crucial for improving Fenton and Fenton-like reactions, which rely on the efficient activation of the H2O2 molecule. Pure TiO2, however, has inadequate activity towards the H2O2 activation and is often constrained by the intrinsic electronic limitations of pristine TiO2. Herein, a rational approach has been demonstrated to improve the Fenton-like catalytic performance of TiO2 through multivalent vanadium (V) doping. A comprehensive characterization using X-Ray Diffraction (XRD), Raman spectroscopy, UV-Vis spectroscopy, X-Ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), and Density functional theory (DFT) reveals that V incorporation substantially alters the electronic structure of TiO2. The DFT results, supported by experimental data, indicate that V doping enhances Ti-O covalence and introduces mid-gap states, resulting in a reduced band gap and improved charge transfer. XPS confirms the coexistence of multiple oxidation states of V, which serve as active centres for activating H2O2 and generating OH radicals. As a result, V-doped TiO2 exhibits significantly enhanced dark-catalytic activity in degrading the organic dye Rhodamine B (RhB). Overall, this study provides fundamental insights into multivalent-cation-induced valence state and electronic structure modulation in TiO2, offering a promising strategy for designing high-performance catalysts via defect engineering for sustainable environmental remediation.