Enhanced Photo-Fenton Removal of Oxytetracycline Hydrochloride via BP/Bi2MoO6 Z-Scheme Heterojunction Photocatalyst

Abstract

Fenton oxidation technology utilizing hydrogen peroxide is recognized as an effective method for producing reactive oxygen species (ROS) to facilitate the degradation of antibiotics. However, the requirement for strongly acidic conditions during this process significantly restricts its broader applicability. In this study, we synthesized black phosphorus (BP) nanosheets by exposing the {010} crystal planes and then constructed a 0D/2D BP/Bi₂MoO₆ (PBMO) heterojunction to function as a Fenton catalyst. The PBMO-75 heterojunction exhibited a remarkable increase in photo-Fenton catalytic activity towards oxytetracycline (OTC) under neutral conditions, achieving catalytic efficiencies that were 20 and 8 times greater than those of BP and Bi₂MoO₆ (BMO), respectively. This can be attributed to its strong absorption of visible light, the establishment of an internal electric field (IEF) at the interface, and the implementation of a Z-scheme catalytic mechanism. Additionally, the photo-Fenton system was further improved in OTC degradation through the continuous conversion of Mo⁶⁺/Mo⁵⁺ under visible light irradiation in conjunction with H₂O₂. Based on ERS, XPS, and active species trapping experiments, we propose a Z-scheme charge transfer mechanism for PBMO. This research offers compelling evidence that 0D/2D Z-scheme heterojunctions are promising candidates for the photo-Fenton treatment of antibiotic contaminants.

Keywords: BP/Bi2MoO6; Z-scheme heterojunction; oxytetracycline; photo-Fenton degradation.

Figure 1

(a) XRD patterns and (b) a partially enlarged plot of the BP, BMO, and PBMO heterojunctions.

Figure 2

(a) TEM and (b) HRTEM images of BP; (c) TEM and (d) HRTEM images of the PBMO-75 heterojunction.

Figure 3

High-resolution XPS spectra of BP, BMO, and the PBMO-75 heterojunction: (a) P 2p, (b) Bi 4f, (c) Mo 3d, and (d) O 1s.

Figure 4

(a) Control experiments of the photo-Fenton degradation reaction; (b) the associated apparent rate constants for the degradation of OTC utilizing the PBMO-75 heterojunction; (c) the photo-Fenton degradation process of OTC under 40 W LED irradiation, with an OTC concentration of 20.0 mg/L, a volume of 200 mL, an initial pH of 7.0, and a H₂O₂ concentration of 50.0 mM; and (d) the corresponding apparent rate constants.

Figure 5

The influence of various parameters on the efficiency of visible light-assisted Fenton degradation of OTC over the PBMO-75 heterojunction includes (a) the concentration of H₂O₂ with a catalyst dosage of 0.5 g/L, an OTC concentration of 20.0 mg/L, and a pH of 5.0; (b) the initial pH of the solution, maintaining H₂O₂ at 10.0 mM, a catalyst dosage of 0.5 g/L, and an OTC concentration of 20.0 mg/L; (c) the catalyst dosages while keeping H₂O₂ at 10.0 mM, OTC at 20.0 mg/L, and the initial pH at 5.0; and (d) the concentration of OTC, with H₂O₂ set at 10.0 mM, a catalyst dosage of 0.5 g/L, and pH at 5.0.

Figure 6

(a) UV–Vis DRS spectra of the as-prepared BMO, BP, and PBMO heterojunctions; VB XPS spectra for (b) BMO, (c) BP, and (d) PBMO-75; Mott–Schottky curves for (e) BMO and (f) BP.

Figure 7

(a) EIS Nyquist plots; (b) transient photocurrent curves; (c) PL spectra of the synthesized BMO, BP, and PBMO-75 heterojunctions; and the influence of radical scavengers on the photo-Fenton degradation of OTC over (d) BP, (e) BMO, and (f) PBMO-75 heterojunctions under the irradiation of a 40 W LED.

Figure 8

ESR spectra for (a) DMPO-•OH in aqueous solution and (b) DMPO-•O₂⁻ in methanol, utilizing BMO, BP, and PBMO-75 within photo-Fenton systems; ESR spectra for (c) DMPO-•OH in aqueous solution and (d) DMPO-•O₂⁻ in methanol over PBMO-75 across various systems; (e) PL of TAOH at 426 nm with an excitation wavelength of 312 nm; and (f) the absorbance of NBT at 259 nm.

Figure 9

(a) The energy levels EC, EV, and EF of BMO and BP before contact; (b) the IEF and band bending at the interface of BMO and BP after contact; and (c) the Z-scheme transfer mechanism of photogenerated charge carriers between BMO and BP under visible light irradiation.

Figure 10

Schematic illustration of the photo-Fenton degradation of OTC over PBMO-75 under 40 W LED irradiation.