Construction of Bi/Polyoxometalate doped TiO2 composite with efficient visible-light photocatalytic performance: Mechanism insight, degradation pathway and toxicity evaluation

Exploration of visible-light-responsive, efficient and durable photocatalysts is of great concern for removing organic dyes and antibiotics from the wastewater. Herein, a series of mesoporous TiO2-doped with polyoxometalates [H3PMo12O40] (PMo12) and loaded with Bi nanoparticles (NPs) composites were fabricated through a convenient electrospinning/calcination and hydrothermal methods, which was labelled as x wt% Bi/PMo12 doped TiO2 (abbr. x% Bi/PT, x = 10, 20 and 30, respectively). In these composites, polyoxometalate PMo12 acts as a dopant to reduce the band gap value of TiO2, effectively expanding its visible light absorption and enhance its photocatalytic redox ability. Moreover, the Schottky junction between Bi NPs and PT further promotes the separation efficiency of the photoinduced carriers. Therefore, these as-prepared catalysts demonstrated outstanding and persistent photocatalytic activity for removing tetracycline (TC), enrofloxacin (EFA) and methyl orange (MO) with visible-light (lambda > 420 nm) illumination. Especially, 20 % Bi/PT specimen presented the optimal catalytic performance, whose degradation efficiencies for TC, EFA and MO reached 86.0 %, 90.9 % and 92.5 % with k = 0.03019, 0.01275 and 0.01199 min(-1), respectively. The superoxide radical (center dot O-2(-)), hydroxyl radical (center dot OH) and holes (h(+)) were proved to be the dominating active species in contaminants degradation through the trapping tests and electron spin resonance (ESR) measurements. Furthermore, the possible TC degradation pathways were established based on the identification of degradation products by high performance liquid chromatography-mass spectrometry (HPLC-MS). The toxicity of intermediates was also assessed through QSAR prediction. According to the energy band structure analysis, the corresponding photocatalytic mechanism was revealed. The current work provides several new insights for the design and preparation of low cost, efficient, stable and versatile photocatalysts.