Efficient Tetracycline Hydrochloride Degradation by Urchin-Like Structured MoS2@CoFe2O4 Derived from Steel Pickling Sludge via Peroxymonosulfate Activation

Abstract

Steel pickling sludge serves as a valuable iron source for synthesizing Fe-based catalysts in heterogeneous advanced oxidation processes (AOPs). Here, MoS₂@CoFe₂O₄ catalyst derived from steel pickling sludge was prepared via a facile solvothermal approach and utilized to activate peroxymonosulfate (PMS) for tetracycline hydrochloride (TCH) degradation. Comprehensive characterization using scanning electron microscopy (SEM)-energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) confirmed the supported microstructure, composition, and crystalline structure of the catalyst. Key operational parameters-including catalyst dosage, PMS concentration, and initial solution pH-were systematically optimized, achieving 81% degradation efficiency within 30 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed SO₄^∙- as the primary oxidative species, while the catalyst maintained high stability and reusability across cycles. TCH degradation primarily occurs through hydroxylation, decarbonylation, ring-opening, and oxidation reactions. This study presents a cost-effective strategy for transforming steel pickling sludge into a high-performance Fe-based catalyst, demonstrating its potential for practical AOP applications.

Keywords: MoS2@CoFe2O4 catalyst; degradation; peroxymonosulfate; pickling sludge; tetracycline hydrochloride.

Figure 1

The comparison of degradation efficiencies for TCH by different catalysts (TCH 200 mg/L, PMS 300 mg/L, catalyst dosage 150 mg/L, and initial solution pH 3.5).

Figure 2

SEM images of the prepared MoS₂ (a) and the prepared catalyst 2 (b).

Figure 3

XRD patterns of the prepared MoS₂ and the prepared catalyst 2.

Figure 4

XPS spectra of the prepared MoS₂@CoFe₂O₄: (a) S 2p spectrum; (b) Mo 3d spectrum; (c) Co 2p spectrum; (d) Fe 2p spectrum.

Figure 5

Effects of operational parameters on degradation efficiency: (a) the effect of PMS dosage (TCH 200 mg/L, initial solution pH 6.0, and catalyst 150 mg/L); (b) the effect of catalyst dosage (TCH 200 mg/L, initial solution pH 6.0, and PMS 600 mg/L); (c) the effect of initial pH value (TCH 200 mg/L, PMS 600 mg/L, and catalyst 300 mg/L).

Figure 6

(a) Effects of radical scavengers on degradation efficiency (TCH 200 mg/L, PMS 600 mg/L, catalyst 300 mg/L, and initial solution pH 6.0); (b) DMPO-trapping EPR signals with different reaction times.

Figure 7

Proposed pathways for the oxidative degradation of TCH in the MoS₂@CoFe₂O₄ catalyst/PMS system, with the TCH chemical structure, LUMO and HOMO diagrams.

Figure 8

XPS spectra of the prepared MoS₂@CoFe₂O₄: (a) S 2p spectrum; (b) Mo 3d spectrum; (c) Co 2p spectrum; (d) Fe 2p spectrum after first and third run.

Figure 9

Reusability experiments of MoS₂@CoFe₂O₄ catalyst for the degradation of TCH (TCH 200 mg/L, PMS 600 mg/L, catalyst 300 mg/L, and initial solution pH 6.0).