An N-doped anatase/rutile TiO2 hybrid from low-temperature direct nitridization: enhanced photoactivity under UV-/visible-light

Abstract

Colloidal N-doped TiO₂ nanocrystals are successfully synthesized by low-temperature direct nitridization in triethylamine solution during hydrolysis of tetrabutyl titanate, followed by acidic peptization at 70 °C. Through adjusting the acid concentration and peptization time, the N-doped samples consisting of different proportions of anatase and rutile phases are obtained. Several characterization techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy are employed to determine the crystal phase, morphology, degree of nitrogen incorporation and optical properties of the products. The high resolution XPS spectrum of the N 1s region confirms the substitutional nitrogen doping of lattice oxygen in TiO₂ crystals. For comparison, it is found that most of the N species are chemisorbed on the surface of TiO₂ particles if the N-source is introduced after crystallization. The light response in the range of 400–500 nm is obviously improved by N doping, which facilitates the absorption of photons to produce e⁻–h⁺ pairs under visible irradiation. On the other hand, nitrogen doping also inhibits the recombination of the photoinduced carriers and therefore increases the quantum efficiency of the TiO₂ photocatalyst. As a result, the as-synthesized N-doped TiO₂ nanomaterials exhibit higher photocatalytic activity both in the UV- and visible-light region in contrast to the non-doped TiO₂. The hybrid containing 63.1% anatase shows the highest photocatalytic activity, which is due to a synergistic effect between anatase and rutile.