Bifunctional N-Doped Mesoporous TiO₂ Photocatalysts

Abstract

We have successfully prepared visible-light-active mesoporous N-doped TiO₂ (N-TiO₂) photocatalysts by the precipitation of titanyl oxalate complex ([TiO(C₂O₄)₂]²⁻) by ammonium hydroxide at a low temperature followed by calcination at different temperatures. The structures of N-TiO₂ photocatalysts have been characterized in detail by means of powder X-ray diffraction, N₂ adsorption−desorption isotherms, infrared spectroscopy, diffuse reflectance UV−vis spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscope. The calcination process of the catalyst precursor was also studied by means of temperature-programmed reaction spectroscopy. N-TiO₂ photocatalysts exhibit comparable UV-light activity and visible-light activity in the photodegradation of methyl orange. The doped N species locates at the interstitial sites in TiO₂, which leads to the band gap narrowing of TiO₂. A novel and interesting result is that N-doped TiO₂ calcined at 400 °C (N-TiO₂-400) has Brönsted acid sites arising from covalently bonded dicarboxyl groups, which greatly enhances the adsorption capacity for methyl orange. The N-TiO₂-400 catalyst is a promising adsorption−photodegradation integration catalyst; meanwhile, it is also a promising acid catalysis−photocatalysis bifunctional catalyst.