Synthesis of heterojunction photocatalysts composed of Ag S quantum dots combined with Bi Ti O nanosheets for the degradation of dyes.

Facilitating the separation of photogenerated electron/hole pairs and widening the light-responsive region are crucial to enhance the overall photocatalytic performance of photocatalysts. To achieve this aim, here we have prepared AgS/BiTiO heterojunction composite photocatalysts by assembling AgS quantum dots onto the surface of BiTiO nanosheets. Transmission electron microscopy observation demonstrates that two types of AgS quantum dots separately with size of 40-70 and 7-17 nm are uniformly assembled onto the surface of large-sized BiTiO thin nanosheets. The as-prepared AgS/BiTiO heterojunction composites exhibit much enhanced light absorption (particularly in the visible and near-infrared region) and highly efficient separation of electrons and holes photogenerated in BiTiO. Rhodamine B (RhB) aqueous solution was chosen as the target organic pollutant to evaluate the photocatalytic performance of the samples under simulated sunlight irradiation. It is found that the AgS/BiTiO heterojunction composites manifest significantly enhanced photocatalytic activity toward the RhB degradaton. In particular, the 15wt% AgS/BiTiO composite exhibits the highest photocatalytic activity, which is ca. 2.8 and 4.0 times higher than bare BiTiO and AgS, respectively. The enhanced photocatalytic activity of the composites can be explained as a result of the Z-scheme electron transfer from the conduction band of BiTiO to the valence band of AgS, and thus more photogenerated holes in the valence band of BiTiO and electrons in the conduction band of AgS are able to participate in the photocatalytic reactions. Active species trapping experiments were carried out, from which it is concluded that photogenerated holes and •O radicals play the dominant and secondary role in the photocatalysis, respectively.