Highly Visible Light Activity of Nitrogen Doped TiO2 Prepared by Sol–Gel Approach

A simple approach was explored to prepare N-doped anatase TiO₂ nanoparticles (N-TiO₂ NPs) from titanium chloride (TiCl₄) and ammonia (NH₃) via sol–gel method. The effects of important process parameters such as calcination temperatures, NH₃/TiCl₄ molar ratio (R_N) on crystallite size, structure, phase transformation, and photocatalytic activity of titanium dioxide (TiO₂) were thoroughly investigated. The as-prepared samples were characterized by ultraviolet–visible spectroscopy, x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated upon the degradation of methylene blue aqueous solution under visible-light irradiation. The results demonstrated that both calcination temperatures and NH₃/TiCl₄ molar ratios had significant impacts on the formation of crystallite nanostructures, physicochemical, as well as catalytic properties of the obtained TiO₂. Under the studied conditions, calcination temperature of 600°C and NH₃/TiCl₄ molar ratio of 4.2 produced N-TiO₂ with the best crystallinity and photocatalytic activity. The high visible light activity of the N-TiO₂ nanomaterials was ascribed to the interstitial nitrogen atoms within TiO₂ lattice units. These findings could provide a practical pathway capable of large-scale production of a visible light-active N-TiO₂ photocatalyst.