Enhanced Fenton Degradation of Tetracycline over Cerium-Doped MIL88-A/g-C3N4: Catalytic Performance and Mechanism

Abstract

Since enormous amounts of antibiotics are consumed daily by millions of patients all over the world, tons of pharmaceutical residuals reach aquatic bodies. Accordingly, our study adopted the Fenton catalytic degradation approach to conquer such detrimental pollutants. (Ce_0.33Fe) MIL-88A was fabricated by the hydrothermal method; then, it was supported on the surface of g-C₃N₄ sheets using the post-synthetic approach to yield a heterogeneous Fenton-like (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst for degrading the tetracycline hydrochloride drug. The physicochemical characteristics of the catalyst were analyzed using FT-IR, SEM-EDX, XRD, BET, SEM, and XPS. The pH level, the H₂O₂ concentration, the reaction temperature, the catalyst dose, and the initial TC concentration were all examined as influencing factors of TC degradation efficiency. Approximately 92.44% of the TC was degraded within 100 min under optimal conditions: pH = 7, catalyst dosage = 0.01 g, H₂O₂ concentration = 100 mg/L, temperature = 25 °C, and TC concentration = 50 mg/L. It is noteworthy that the practical outcomes revealed how the Fenton-like process and adsorption work together. The degradation data were well-inspected by first-order and second-order models to define the reaction rate. The synergistic interaction between the (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ components produces a continuous redox cycle of two active metal species and the electron-rich source of g-C₃N₄. The quenching test demonstrates that ^•OH is the primary active species for degrading TC in the H₂O₂-(Ce_0.33Fe) MIL-88A/10%g-C₃N₄ system. The GC-MS spectrum elucidates the yielded intermediates from degrading the TC molecules.

Keywords: Ce-doping; Fenton-like degradation; GC-MS; XPS; degradation mechanism.

Scheme 1

The simple representation of the synthesis process of (Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 1

(A) FTIR, (B) XRD of MIL-88A, (Ce_0.33Fe) MIL-88A, g-C₃N₄, and (Ce_0.33Fe) MIL-88A/10%g-C₃N₄, and (C) N₂ adsorption/desorption hysteresis loop of (Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 2

XPS spectra of the (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst: (A) survey, (B) carbon, (C) nitrogen, (D) oxygen, (E) iron, and (F) cerium.

Figure 3

SEM images of (A) MIL-88A, (B) (Ce_0.33Fe) MIL-88A, (C) g-C₃N₄, and (D) (Ce_0.33Fe) MIL-88A/10%g-C₃N₄, (E–I) elemental mapping of (Ce_0.33Fe) MIL-88A/10%g-C₃N₄, and (J) SEM-EDX pattern of (Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 4

The optimization of (A) the Ce-doping proportion and (B) the g-C₃N₄ proportion in (Ce_0.33Fe) MIL-88A/g-C₃N₄, and (C) comparison test between the degradation aptitude of H₂O₂, MIL-88A, (Ce_0.33Fe) MIL-88A, g-C₃N₄, and (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ towards the TC molecules.

Figure 5

Effects of (A) pH, (B) catalyst doses, (C) temperature, and (D) oxidant concentration on the Fenton-like degradation % of TC by (Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 6

(A) The Fenton-like degradation of the TC molecules during 200 min and (B) first order and (C) second order of TC degradation by H₂O₂–(Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 7

(A) Quenching test of the (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst during the Fenton-like degradation process of TC and XPS of the used (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst; (B) survey, (C) Fe2p3, (D) Ce3d, and (E) N1s.

Figure 8

The schematic representation of the degradation of TC by (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ throughout the adsorption and Fenton-like processes.

Figure 9

The yielded intermediates during the Fenton-like degradation of the TC molecules by (Ce_0.33Fe) MIL-88A/10%g-C₃N₄.

Figure 10

(A) Recycling test of the (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst during sequential five Fenton-like degradation cycles of the TC molecules, (B) SEM, and (C) SEM-EDX of the used (Ce_0.33Fe) MIL-88A/10%g-C₃N₄ catalyst.