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

TiO2 bilayer films with a normal surface (Ns-TiO2), surface defects (Sd-TiO2), and interface defects (Id-TiO2) were successfully prepared by a combination of cold plasma treatment (CPT) and sol gel dip-coating technology. The photodegradation of rhodaminc B (RhB) over these as-prepared TiO2 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-TiO2 films, whereas an efficient degradation (cycloreversion) of RhB occurs over the Sd-TiO2 films. In the RhB/Id-TiO2 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-TiO2 > Sd-TiO2 > Ns-TiO2. It is proposed that the defect sites at the surface or the interface of TiO2 films promote the separation of photogenerated electron holes, leading to a higher photoactivity of defective TiO2 films. Moreover, the higher stability over Id-TiO2 as compared to Sd-TiO2 indicates that the interface defect sites in TiO2 could be applied in environmental photocatalysis.