Optically Switchable Photocatalysis in Ultrathin Black Phosphorus Nanosheets

Recently low-dimensional materials hold great potential in the field of photocatalysis, whereas the concomitantly promoted many-body effects have long been ignored. Such Coulomb interaction mediated effects would lead to some intriguing, nontrivial band structures, thus promising versatile photocatalytic performances and optimized strategies. Here, we demonstrate that ultrathin black phosphorus (BP) nanosheets exhibit an exotic, excitation-energy dependent, optical switching effect in photocatalytic reactive oxygen species (ROS) generation. It is, for the first time, observed that singlet oxygen (O-1(2)) and hydroxyl radical (center dot OH) are the dominant ROS products under visible- and ultraviolet-light excitations, respectively. Such an effect can be understood as a result of subband structure, where energy-transfer and charge-transfer processes are feasible under excitations in the first and second subband systems, respectively. This work not only establishes an in-depth understanding on the influence of many-body effects on photocatalysis but also paves the way for optimizing catalytic performances via controllable photoexcitation.