The γ-MnO₂/NF mediated peroxymonosulfate activation for expeditious 2,4,6-trichlorophenol degradation: performance, pathways, and mechanism

Abstract

Designing efficient and sustainable catalyst for peroxymonosulfate (PMS) activation and refractory 2,4,6-trichlorophenol (2,4,6-TCP) removal is an imminent task. This study synthesized a novel γ-MnO₂/NF catalyst, which has advantages in saving manganese dioxide demand and reducing manganese leaching. The γ-MnO₂/NF + PMS oxidation system achieved a 0.219 min⁻¹ 2,4,6-TCP apparent rate constant at 20 °C, and removed > 90% of 2,4,6-TCP at the 5th cycle. Both free radical identification and DFT calculations revealed that •OH and SO₄•⁻, rather than ¹O₂, were the dominant reactive species during γ-MnO₂/NF + PMS oxidation. The results indicated that the inner-sphere complexation between γ-MnO₂/NF and PMS facilitated the formation of •OH and SO₄•⁻. To fill the research gap in the molecular-level dissimilarities between •OH and SO₄•⁻ in 2,4,6-TCP degradation mechanism, experimental testing and quantum chemical analysis methods were used. The DFT calculation found that the HAA reaction at H13 site and RAF reaction at C1 site were more favorable for both •OH and SO₄•⁻. For most reaction sites, SO₄•⁻ demonstrates greater energy barriers and substrate selectivity than •OH, attributed to steric constraints. The •OH acted as the predominant oxidative agents responsible for 2,4,6-TCP decomposition. Combining DFT calculation and intermediate identification, potential degradation routes of 2,4,6-TCP were proposed. The ecotoxicity assays verified a substantial reduction in acute toxicity of the treated 2,4,6-TCP solution. This study opens up new avenues for activating PMS with γ-MnO₂/NF, and helps to select preferred radical oxidation processes for optimal 2,4,6-TCP removal in practical engineering.

Graphical abstract

Keywords

γ-MnO ₂/NF / Peroxymonosulfate activation / Catalytic oxidation mechanism / DFT calculation / 2 / 4 / 6-TCP removal

Highlight

	● The designed γ -MnO2/Ni catalyst shows high activation efficiency and stability.
	● The oxidation kinetics and mechanisms of γ -MnO2/Ni + PMS system are proposed.
	● SO4•− exhibits higher energy barriers than •OH during the first-step oxidation.
	● Radical addition on benzene ring is the most favorable route for •OH and SO4•−.

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