Introducing and Boosting Oxygen Vacancies within CoMn2O4 by Loading on Planar Clay Minerals for Efficient Peroxymonosulfate Activation

Abstract

CoMn₂O₄ (CMO) has been recognized as an effective peroxymonosulfate (PMS) activator; however, it still shows disadvantages such as limited reactive sites and metal leakage. Herein, an effective and environmentally friendly composite catalyst, CMO/Kln, was synthesized by anchoring CMO on kaolinite (Kln), a natural clay mineral with a special lamellar structure, to activate peroxymonosulfate (PMS) for the degradation of residue pharmaceuticals in water. The abundant hydroxyl groups located on the surface of Kln helped induce rich oxygen vacancies (OVs) into composite CMO/Kln, which not only acted as additional active sites but also accelerated working efficiency. In addition, compared with bare CMO, CMO/Kln showed lower crystallinity, and the adoption of the Kln substrate contributed to its structural stability with lower metal leaching after three rounds of reaction. The universal applicability of CMO/Kln was also verified by using three other pharmaceuticals as probes. This work shed light on the adoption of natural clay minerals in modifying CMO catalysts with promoted catalytic activity for the efficient and eco-friendly remediation of pharmaceuticals in wastewater.

Keywords: CoMn2O4; composite catalyst; kaolinite; peroxymonosulfate activation; pharmaceutical degradation.

Figure 1

XRD patterns of bare CMO, Kln, and CMO/Kln (a), and FESEM images of bare CMO, Kln, and CMO/Kln (b–d).

Figure 2

STEM images of raw Kln (a) and CMO/Kln (b,c); SAED pattern of CMO/Kln (d); and EDS mappings of CMO/Kln (e–h).

Figure 3

XPS spectra of survey (a), Co 2p (b), Mn 2p (c), and O 1s (d) for bare CMO and CMO/Kln.

Figure 4

EPR spectra of bare CMO and CMO/Kln.

Figure 5

N₂ adsorption and desorption isotherms and BJH pore size distribution plots for bare CMO, Kln, and CMO/Kln.

Figure 6

(a) Degradation of SMZ in different reaction systems ([CMO+Kln]: 160 mg L⁻¹ CMO+240 mg L⁻¹ Kln), and (b) corresponding pseudo first-order kinetic models. General working conditions: [SMZ] = 20 μmol L⁻¹, [PMS] = 0.1 mmol L⁻¹, [catalyst] = 400 mg L⁻¹, pH = 5.6.

Figure 7

EPR spectra of CMO/Kln: (a) SO₄^·− and OH^·, (b) ¹O₂, and (c) O₂^·−. (d) Effects of scavengers on SMZ degradation. (e) Effect of N₂ plugging on SMZ degradation. General working conditions: [SMZ] = 20 μM, [PMS] = 0.1 mM, [catalyst] = 400 mg L⁻¹, [scavengers] = 10 mM, [spin-trapping reagents] = 0.1 M, pH = 5.6.

Figure 8

(a) SMZ degradation with CMO/Kln after three recycle rounds. (b) XRD pattern of recycled CMO/Kln compared with fresh CMO. General working conditions: [SMZ] = 20 μM, [PMS] = 0.1 mM, [catalyst] = 400 mg L⁻¹, pH = 5.6.

Scheme 1

The crystalline structure of planar kaolinite (Kln) (a) and synthesis route of bare CMO and CMO/Kln (b).