Construction of a novel S-type γ-Bi₂O₃/CeO₂ heterojunction for highly efficient photocatalytic degradation of antibiotics

Abstract

Cubic nanoparticles of CeO₂ were partly covered on the tetrahedron surface of γ-Bi₂O₃ through a hydrothermal reaction and then a calcination process to construct a novel S-type γ-Bi₂O₃/CeO₂ heterojunction. The optimized sample removed 96% of lomefloxacin and 81% of tetracycline. During the cycling test, the photocatalytic efficiency of lomefloxacin and tetracycline was maintained above 87% and 80%, respectively, for five consecutive cycles. According to XRD and Raman spectra characterization, the sample after cycling held a stable crystal structure. Holes, OH^-˙, O₂˙, and electrons participated in the degradation of lomefloxacin, while tetracycline was removed <i>via</i> the effect of the former three active substances. Based on theoretical calculation and experimental tests, the excellent photocatalytic activity of γ-Bi₂O₃/CeO₂ came from the fast transfer of charge carriers along the S-type path. Moreover, the CB electrons of γ-Bi₂O₃ and VB holes of CeO₂ were preserved to generate free radicals for antibiotic degradation. The colony numbers of <i>Escherichia coli</i> were 1.50 × 10^-6 CFU mL^-1 and 1.39 × 10^-6 CFU mL^-1 in solutions after the degradation of the two pollutants, which represents the non-toxicity of the final products. The γ-Bi₂O₃/CeO₂ sample has a potential application for antibiotic removal from modern sewage.