Constructing Bi2WO6-decorated TiO2 composite films for photocathodic protection of 304 stainless steel

Bi2WO6 nanoplate/TiO2 nanowire and Bi2WO6 nanoflower/TiO2 nanowire composite films were successfully prepared using a hydrothermal method. The results show that the light absorption for Bi2WO6/TiO2 composite films is extended to the visible region after Bi2WO6 nanoplates and nanoflowers are assembled onto TiO2 nanowires. Furthermore, Bi2WO6 nanoflower/TiO2 nanowire composite film exhibits a better absorption property compared to Bi2WO6 nanoplate/TiO2 nanowire film, which is mainly ascribed to the narrower bandgap of Bi2WO6 nanoflower compared to that of Bi2WO6 nanoplate. The photocurrent density for Bi2WO6 nanoflower/TiO2 nanowire and Bi2WO6 nanoplate/TiO2 nanowire composite films can reach 95 and 62.5 μA cm−2, respectively, which are much higher than that obtained for a pure TiO2 nanowire film (25 μA cm−2). Meanwhile, under illumination, the pure TiO2 nanowire, Bi2WO6 nanoplate/TiO2 nanowire and Bi2WO6 nanoflower/TiO2 nanowire films can reduce the potential of the coupled 304 stainless steel in 3.5 wt.% NaCl solution by 299, 719 and 739 mV, respectively. Thus, Bi2WO6 nanoflower/TiO2 nanowire film is found to provide the best effective photocathodic protection for 304 stainless steel. This work not only provides an example of shape-dependent photocathodic protection based on Bi2WO6 but also opens up new possibilities to design an ideal microstructure on the basis of semiconductor materials for future applications of photocathodic protection.