High-activity black phosphorus quantum dots/Au/TiO2 ternary heterojunction for efficient levofloxacin removal: Pathways, toxicity assessment, mechanism and DFT calculations

Black phosphorus quantum dots (BPQDs) have attracted extensive attention for different photocatalytic appli-cations, but their fast charge recombination limits their application prospects. It is ideal to improve the pho-tocatalytic activity to acquire effective carrier separation by using precious metals as carrier transport relays and surface plasmon resonance (SPR) motivators. In this study, a highly active ternary heterojunction BPQDs/Au/ TiO2 was prepared to achieve efficient levofloxacin degradation. The results indicated that the decomposition efficiency of levofloxacin reached 93.7%, and the reaction rate constant (K alpha) was as high as 0.03266 min-1. Based on the results obtained from both density functional theory (DFT) calculations and experiments, three possible decomposition pathways of levofloxacin were suggested. Moreover, photocatalysis can effectively decrease the toxicity of the intermediates. The outstanding activity of BPQDs/Au/TiO2 is due to the cooperative effect of all the components. First, Au, as an SPR motivator, can offer many high-energy electrons during the catalytic process. Second, the indirect interfacial electron transport mode from BPQDs to Au and then to TiO2 promotes the separation of photoinduced carriers, which prolongs the lifetime of e--h+ pairs and significantly improves the performance. Third, the good light-capture ability of BPQDs is an important feature. In summary, this study suggests a possible direction for the construction of heterojunction catalysts with excellent perfor-mance in advanced oxidation processes.