Influence of V ions on the structural and electronic properties of V_xTi_1−xO₂ nanostructures and their photocatalytic performance

The growing presence of emerging contaminants in aquatic environments has intensified the need for efficient and sustainable water treatment technologies. In this context, heterogeneous photocatalysis based on semiconductor nanostructures has emerged as a promising approach for pollutant degradation. This work investigates the effect of vanadium incorporation on the structural, electronic, adsorption, and photocatalytic properties of V_xTi_1−xO₂ nanostructures synthesized via a hydrothermal method at 200 °C. X-ray diffraction (XRD) confirms that all samples crystallize in the anatase TiO₂ phase without detectable secondary phases. Raman spectroscopy indicates systematic shifts and broadening of the E_g mode with increasing V content, revealing enhanced structural disorder. X-ray absorption near edge structure spectra (XANES) further evidence local structural distortion around Ti centers, including an increased contribution of TiO₅-like units. Electron energy loss spectroscopy (EELS) demonstrates that vanadium (V) is predominantly incorporated as V³⁺ substituting Ti⁴⁺ sites, which promotes charge compensation via oxygen vacancy formation. High-resolution Transmission Electron Microscopy (HRTEM) confirms homogeneous distribution of V within the TiO₂ lattice without segregation. Photocatalytic and adsorption studies using methylene blue (MB) show that V incorporation significantly improves surface reactivity. Prior to irradiation, all samples exhibit strong adsorption capacity, with V_0.40Ti_0.60O₂ reaching an equilibrium adsorption capacity of approximately 220 mg g^-1, well described by the Langmuir isotherm. Under UV light, the materials follow pseudo-first-order degradation kinetics, with enhanced performance attributed to improved charge separation and defect-mediated active sites. Overall, vanadium doping effectively tunes the structural and electronic properties of TiO₂, enhancing both adsorption and photocatalytic efficiency through defect engineering and modified electronic structure.