A New Approach to the Preparation of Nitrogen-Doped Titania Visible Light Photocatalyst
Résumé
A new simple method is described, allowing introduction of nitrogen into the TiO2 lattice at low temperatures. The technique is based on the introduction of oxophilic molecules, such as CCl4, into the reaction mixture. The treatment of titanium dioxide powders by NH3-CCl4 mixtures leads to highly dispersed N-doped TiO2. As compared to bare TiO2 or to the same oxide treated with sole NH3, the solids treated with NH3-CCl4 mixtures showed a stronger red shift in optical absorption and enhanced photocatalytic activity under visible light, as demonstrated for two reactions of formic acid oxidation and photocatalytic production of hydrogen from methanol. The nitridation temperature can be significantly decreased by introducing CCl4, because of a favorable change of the reaction thermodynamics. Not only can higher specific surface area of materials be obtained as a result of avoiding sintering but a higher amount of nitrogen is introduced in a position beneficial for the enhanced catalytic activity. The X-ray photoelectron spectroscopy study demonstrated increased surface concentration of nitrogen having N Is binding energy near 399 eV. As established by ESR, the nature of paramagnetic species generated by treatments is strongly dependent on the titania polymorph variety and crystallinity as well as on the treatment conditions, but in all cases the major part of introduced nitrogen remains ESR-silent.