A novel dual S-scheme heterojunction photocatalyst -Bi₂O₃/NiAl-LDH/-Bi₂O₃ induced by phase-transformed bismuth oxide for efficient degradation of antibiotics in full-spectrum: Degradation pathway, DFT calculation and mechanism insight

We report for the first time a novel dual step-scheme (S-scheme) heterojunction photocatalyst alpha beta-Bi2O3/NiAlLDH (BN), composed of phase-transformed bismuth oxide (alpha beta-Bi2O3) and layered double hydroxide (LDH). When the mass ratio of LDH reached 20%, alpha beta-Bi(2)O(3)3/20 %NiAl-LDH (BN3) exhibited the highest degradation rate. With 120 min visible light exposure, the photodegradation efficiency of BN3 for tetracycline (TC) reached 96.17%, which was 1.46 and 2.18 times higher than alpha beta-Bi2O3 and LDH, respectively, and 94.81% norfloxacin (NOR) was decomposed by BN3 within 180 min. In addition, two degradation pathways of TC were presented via LC-MS tests. A dual S-scheme heterojunction was presented based on experimental, in-situ XPS test and DFT calculations. The S-scheme heterostructure formation leads to the construction of internal electric fields (IEFs) between the interfaces and the bending of the band edges, which is very favored for the photogenerated carriers' separation and lifetime extension. More significantly, holes in the higher valence band (VB) of alpha beta-Bi2O3 and electrons on the lower conduction band (CB) of LDH have stronger redox capabilities, which can produce more powerful reactive species ((OH)-O-center dot, O-center dot(2)- and h(+)). This research offers a novel insight into the construction of dual S-scheme heterojunctions and suggests a possible method to treat antibiotic wastewater.