Preparation of flexible BOPP/SiOx/TiO2 multilayer film for photodegradation of organic contamination

First a SiOx layer, as a barrier layer between a photo active anatase TiO2 layer and BOPP substrate, was coated on hydroxylated BOPP film by a sol–gel process. Then, TiO2 layer was formed on SiOx surface through liquid phase deposition. Thus a flexible BOPP/SiOx/TiO2 multilayer film which has photocatalytic activity was fabricated. The coating processes were monitored by FT-IR and UV–vis spectroscopy, scanning electron microscopy, atom force microscopy and water contact angle (CA) measurements. The thickness of SiOx and TiO2 layer was about 600 nm and 135 nm, respectively. Root mean square (RMS) roughness of the SiOx layer was about 2–3 nm while the surface of TiO2 layer was much coarse with RMS roughness about 30 nm which offered the large surface area. The TiO2 layer endowed multilayer film photoinduced hydrophilic conversion property evidenced by the fact that its surface water contact angle could reduce to about 5° after 1 h of UV irradiation. The photocatalytic degradation ability of multilayer film was evaluated using methyl orange as model contamination and the results indicating that the degradation is efficient.