Generation of oxygen vacancies in visible light activated one-dimensional iodine TiO2 photocatalysts

Abstract

A facile and efficient way of generating oxygen vacancies in visible light activated one-dimensional iodine doped TiO₂ photocatalysts was first reported in this work. A two-step hydrothermal synthesis was used to synthesize TiO₂ nanomaterials modified by iodic acid (HIO₃) as a dopant. Detailed analysis was conducted to illustrate the intrinsic doping/reaction mechanisms of iodic acid in the modification of the TiO₂ matrix. The phase and structure evolution were deduced from X-ray diffraction (XRD), Raman, and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was conducted to analyze the generation of oxygen vacancies and the formation of I–O–Ti bonds in the TiO₂ lattice. Multi-valences of iodine, due to the reduction of iodic acid, facilitated the generation of oxygen vacancies and 3d state Ti³⁺ species in the TiO₂ lattice. The visible light absorption and enhanced photocatalytic activity of the TiO₂ nanomaterials were attributed to existing oxygen vacancies, iodine multi-valences in I–O–Ti bonds, and 3d state Ti³⁺ sites in the TiO₂ lattice. The photocatalytic degradation efficiency under visible light (λ > 400 nm) followed a pseudo first-order kinetic model. Rutile nanowires using a two-step synthesis method produced the highest methylene blue (10 mg L⁻¹) degradation rate constant, K_ap, of 7.92 × 10⁻³ min⁻¹ compared to other synthesized nanomaterials. The K_ap value obtained was an order of magnitude greater than commercial P25 (3.87 × 10⁻⁴ min⁻¹) and pristine TiO₂ nanowires (4.18 × 10⁻⁴ min⁻¹). The iodine doped TiO₂ photocatalysts can be used in TiO₂/light irradiation advanced oxidation processes (AOPs) in water treatment using sunlight or a visible light source, rather than an ultraviolet irradiation source.