Novel Bi2Sn2O7 quantum dots/TiO2 nanotube arrays S-scheme heterojunction for enhanced photoelectrocatalytic degradation of sulfamethazine

The step-scheme (S-scheme) heterojunction of Bi2Sn2O7 quantum dots (QDs)/TiO2 nanotube arrays (NTAs) photoanodes were prepared for efficient and stable photoelectrocatalytic (PEC) degradation of sulfamethazine (SMT) at low potential and light-emitting diode (LED) illumination. In the Bi2Sn2O7/TiO2 NTAs system, the synergistic factor of photocatalysis (PC) and electrocatalysis (EC) reached 10.1. The elevated performance was attributed to improved light-harvest capability by the decorated TiO2 NTAs with Bi2Sn2O7 QDs, lower charge transfer resistance, more efficient photoexcited charge separation, and higher redox ability to produce photogenerated holes (h+) and reactive oxygen species (ROS) with great efficiency. The possible PEC mechanism of S-scheme Bi2Sn2O7/TiO2 NTAs was elucidated by experimental studies and density functional theory (DFT) calculations, which confirmed the establishment of the internal electric field (IEF) promoted carrier separation and transport. This research provides a feasible approach for fabricating superior PEC photoanodes as well as new insights into heterojunction design.