Photocatalytic Degradation of RhB over TiO₂ Bilayer Films: Effect of Defects and Their Location

TiO(2) bilayer films with a normal surface (Ns-TiO(2)), surface defects (Sd-TiO(2)), and interface defects (Id-TiO(2)) were successfully prepared by a combination of cold plasma treatment (CPT) and sol-gel dip-coating technology. The photodegradation of rhodamine B (RhB) over these as-prepared TiO(2) films was investigated via UV-vis irradiation. Results indicate that the three kinds of films exhibit very different photodegradation processes for RhB. A mainly N-deethylation reaction over the Ns-TiO(2) films, whereas an efficient degradation (cycloreversion) of RhB occurs over the Sd-TiO(2) films. In the RhB/Id-TiO(2) system, however, efficient N-deethylation concomitant with the highly efficient cycloreversion of RhB is observed. The efficiency of the complete mineralization of RhB dye follows the order of Id-TiO(2) > Sd-TiO(2) > Ns-TiO(2). It is proposed that the defect sites at the surface or the interface of TiO(2) films promote the separation of photogenerated electron-holes, leading to a higher photoactivity of defective TiO(2) films. Moreover, the higher stability over Id-TiO(2) as compared to Sd-TiO(2) indicates that the interface defect sites in TiO(2) could be applied in environmental photocatalysis.