Bifunctional N-Doped Mesoporous TiO₂ Photocatalysts

We have successfully prepared visible-light-active mesoporous N-doped TiO 2 (N-TiO 2 ) photocatalysts by the precipitation of titanyl oxalate complex ([TiO(C 2 O 4 ) 2 ] 2− ) by ammonium hydroxide at a low temperature followed by calcination at different temperatures. The structures of N-TiO 2 photocatalysts have been characterized in detail by means of powder X-ray diffraction, N 2 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-TiO 2 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 TiO 2, which leads to the band gap narrowing of TiO 2 . A novel and interesting result is that N-doped TiO 2 calcined at 400 °C (N-TiO 2 -400) has Brönsted acid sites arising from covalently bonded dicarboxyl groups, which greatly enhances the adsorption capacity for methyl orange. The N-TiO 2 -400 catalyst is a promising adsorption−photodegradation integration catalyst; meanwhile, it is also a promising acid catalysis−photocatalysis bifunctional catalyst.