Boosting photocatalytic hydrogen production via enhanced exciton dissociation in black phosphorus quantum Dots/TiO2 heterojunction

The Coulomb interactions between excited electrons and holes have a very important influence on the photo-physical processes in 2D semiconductors. Exciton dissociation is one of the key steps that significantly contribute to the efficiency of photocatalysis, but its research in the relevant aspects of photocatalysis has not been in-depth. Herein, the BP/TiO2 heterojunction as a prototypical model system was constructed on the surface of urchin-like TiO2 where black phosphorous (BP) quantum dots (QDs) grew. The BP/TiO2 heterojunction exhibits an improved H-2-production rate of 112 mu mol.h(-1).g(-1) under UV-visible light irradiation without any cocatalysts, which is 2.4 times higher than that of pure TiO2 (47 mu mol.h(-1).g(-1)). As a typical exciton-rich material, BP QDs have special advantages on the charge separation process, because of their prominent many-body effect, short carrier transport distance, and large specific surface with rich reactive sites. The energy difference between the con-duction bands turns out to be the driving force for exciton dissociation in the BP/TiO2 heterojunction. The theoretical calculation implies that the excited electron tends to transfer from BP QD to TiO2. The high catalytic performance of heterojunction contributes to the effective exciton dissociation, interfacial charge separation, and charge-carrier accumulation. This work lays the foundation for the design of the BP QDs based photocatalytic system and its application in photocatalytic hydrogen production and provides an effective reference for increasing the active sites of heterojunctions.