P-doped BiOCl for visible light photodegradation of tetracycline: An insight from experiment and calculation

A novel n-type phosphorus-doped bismuth oxychloride (P-BiOCl) photocatalyst was synthesized through facile one-step hydrothermal approach with sodium hypophosphite (NaH2PO2) addition, which is of extraordinarily high efficiency for tetracycline (TC) degradation under visible light. The physicochemical properties of the P-BiOCl sample were characterized by XRD, Raman, FTIR, XPS, AFM and (HR)TEM. The inorganic phosphorus sources and P/Bi ratios were optimized, and P-BiOCl remained high TC photodegradation efficiency after six cycles under visible light. The experimental and calculational results were combined to investigate the underline mechanisms: P atoms entered into the lattice of BiOCl by partially replacing Cl atoms, and then formed a midgap impurity level. The introduction of P heteroatom broadens bandgap, generates a new electron channel to facilitate electron transfer and inhibit carrier recombination. Moreover, P-doping enlarges specific surface area, increases oxygen adsorption and alters the conduction band position more negative, thus producing more active O2·- for TC degradation. Additionally, the photodegradation pathway of TC is proposed based on the results of Fukui index and LC-MS/MS.