Renewable Co@MOF-808(C) catalyzed PMS for the efficient degradation of 2,4-D: Performance and mechanism

Abstract

Background

The 2,4-Dichlorophenoxyacetic acid (2,4-D) is widely in agriculture, forestry, and other areas, while it causes environmental pollution problems due to the high chemical stability and poor biodegradability.

Methods

A novel Co₃O₄-loaded MOF-derived carbon catalyst (Co@MOF-808(C)) was prepared and its catalytic performance of peroxymonosulfate (PMS) for 2,4-D degradation was evaluated.

Significant findings

Results indicated Co@MOF-808(C) could effectively degrade 2,4-D by catalyzing PMS. Under the selected conditions of 500 mg·L⁻¹ Co@MOF-808(C), 3 mM PMS, 45 °C, and without pH adjusting, a remarkable degradation rate (97.3 %) and high mineralization rate (88.7 %) were obtained as 2,4-D concentration was 50 mg·L⁻¹. In addition, the existence of H₂PO₄⁻, CO₃²⁻ (5 mM), or SO₄²⁻ (5 mM) could promote the catalytic degradation of 2,4-D, while other ions (including Cl⁻, NO₃⁻, and humic acid) and higher concentration of CO₃²⁻ or SO₄²⁻ inhibited 2,4-D degradation. Reusability experiment of Co@MOF-808(C) indicated the degradation rate was still remained at 89.4 % after five cycles. Quenching experiment, ESR and XPS results demonstrated SO₄⁻· dominated a crucial role in 2,4-D removal and the Co²⁺/Co³⁺ cycle drove the PMS activation. Furthermore, the LC-MS results illustrated the potential degradation pathway for 2,4-D mainly included decarboxylation, dechlorination, hydroxylation, and ring cleavage; and the ecotoxicological results showed an obvious reduction in the toxicity of 2,4-D after degradation. In summary, the stable chemical properties and excellent catalytic effect of Co@MOF-808(C) offered a potential application for 2,4-D elimination form aquatic environment.