Preparation of Visible-Light-Responsive TiO_(2-x)N_x Photocatalyst by a Sol-Gel Method:Analysis of the Active Center on TiO_2 that Reacts with NH_3

摘要

Active reaction centers for ammonia on titanium oxyhydroxide were explored to direct the search for an efficient sol-gel method for the synthesis of a titanium oxynitride (TiO_(2-x)N_x) sample with an efficient responsiveness to the visible light constituting a main part of the solar spectrum.The results lead to the conclusion that the site giving IR bands at around 2195 cm~(-1) for the adsorbed CO molecules at 300 K is a reactive site and behaves as Lewis acid site in the coordination environment of distorted five-coordinate Ti~(4+) ions.Ammonia molecules are adsorbed on such a site to form -NH_2 and -OH species during the heat treatments at a temperature above 373 K,and they are ultimately incorporated into the TiO_2 lattice as nitride through the dehydration at higher temperatures of up to 723 K,resulting in the formation of an anatase type of TiO_(2-x)N_x.