BP@Au undergoes rapid degradation and releases singlet oxygen under dark conditions: Doping effect and detrimental effects on superoxide-producing marine algae

Black phosphorus (BP) shows encouraging utility in many fields, and metal doping has been suggested as an efficient way to improve stability. However, controversial results and inconsistent mechanisms have been reported for doping modulation and stability change. We observed the unforeseen evolution of singlet oxygen (O-1(2)) from BP integrated with gold nanoparticles (BP@Au) under dark conditions, and this led to rapid BP deterioration, even though enhanced stability is commonly thought via surface doping. Briefly, the BP reacted with oxygen and water to yield superoxide (O-2(center dot-)) and hydrogen peroxide. Au-0 acted as an enzyme mimic and catalyzed the conversion of these derivatives, and Au-0 was converted to a mixture of Au3+ and Au+. The O-2(center dot-) was converted to O-1(2) via direct donation of electrons to the Au3+/+. The Au-catalyzed redox reactions accelerated the degradation of the BP nanosheets. BP@Au showed significant toxicity toward marine alga that produce O-2(center dot-) in the dark, as indicated by a more than 30% reduction in cell viability after 12 h of incubation with 7.56 mg/L BP@Au. The novelty of this work lies in the demonstration of a dopant-related degradation pathway of BP that shows unrevealed toxicity toward O-2(center dot-)-producing marine algae.