Aqueous Sol-Gel Synthesis of Ta-, V-, and Nb-Doped TiO₂ Photocatalysts for Superior Degradation of Refractory Pollutants under UV-Visible Light

In the quest for efficient, sustainable water treatment solutions, advanced oxidation processes like photocatalysis offer immense promise for degrading refractory organic contaminants. This study introduces an innovative, low-temperature aqueous sol-gel method to synthesize crystalline TiO₂-based photocatalysts doped with tantalum (Ta), vanadium (V), or niobium (Nb) at varying molar ratios (0.1–16 mol%), eliminating the need for energy-intensive calcination steps. This eco-friendly approach yields high-surface-area materials (up to 292 m²/g) with biphasic anatase-brookite structures, as confirmed by XRD, TEM, and BET analyses. ICP-AES, EDX, and XPS verify dopant incorporation, revealing nitrogen co-doping in undoped TiO₂ and oxidation states like Ta⁵⁺, V⁵⁺, and Nb⁵⁺. UV-Vis diffuse reflectance spectroscopy demonstrates bandgap narrowing, particularly with V-doping (from 2.95 eV to 1.88 eV), enabling visible-light activation.
Photocatalytic screening on p-nitrophenol (PNP) degradation under UV-visible (300–800 nm) and visible light (395–800 nm) highlights dopant-dependent enhancements: Ta and Nb doping boost visible-light efficiency to 37% and 55% (vs. 22% for undoped TiO₂), while V-doping reduces it to 3–12%. Kinetic studies, scavenger experiments, and recycling tests (up to 120 h) confirm stability and radical-driven mechanisms. Pioneering electrophotocatalytic tests in a custom setup show Nb-doped TiO₂ coatings on Pt anodes achieving 94% PNP mineralization under UV (vs. 72% uncoated), underscoring synergistic electro-photo effects.
This sol-gel innovation advances TiO₂ photocatalysts beyond commercial benchmarks like Evonik P25, offering scalable, cost-effective materials for quaternary wastewater treatment and solar-driven purification.