Fabrication of black TiO2/TiO2 homojunction for enhanced photocatalytic degradation

Photocatalysis is a promising technology for removing contaminant in water. However, the rapid recombination of photogenerated charge carriers limits the performance of photocatalysis in water treatment. Here, a novel light response B/W-TiO2 homojunction catalyst based on the black TiO2 (B-TiO2) and TiO2 (W-TiO2) was successfully synthesized by a facile hydrothermal method. The mass ratio of B-TiO2 to W-TiO2 was tuned to study its effect on homojunction formation and photocatalytic performance. Beneficial from the band difference between B-TiO2 and W-TiO2, the conduction band (CB) electrons of W-TiO2 can migrate to the CB of B-TiO2 and the valence band (VB) holes of B-TiO2 transfer to the VB of W-TiO2, hence effectively promoting the separation of photogenerated charge carriers. The formation of homojunction can dramatically improve the photocatalytic ability of B/W-TiO2; the kinetic constant of rhodamine B degradation of B/W-TiO2 with optimal mass ratio is nearly 3.9 and 5.2 times higher than that of B-TiO2 and W-TiO2, respectively. Moreover, the superoxide radical (O2 center dot-) and hydroxyl radicals (center dot OH) species play a crucial role in the photodegradation process. The enhancement of photocatalytic activity is attributed to the construction of B/W-TiO2 homojunction, which is beneficial to improve the separation efficiency of photogenerated electron-holes.