Enhanced Orange II Removal Using Fe/Mn/Mg₂-LDH Activated Peroxymonosulfate: Synergistic Radical Oxidation and Adsorption

Abstract

In this study, Fe/Mn/Mg2-LDH was utilized for the first time as a catalyst for peroxymonosulfate (PMS) activation to facilitate the removal of Orange II. This composite was characterized using various techniques, such as XRD, FTIR, SEM-EDS, BET, and XPS. The results revealed a well-defined lamellar structure of Fe/Mn/Mg2-LDH with a metal molar ratio of Fe/Mn/Mg at 1:1:2. Moreover, the structural stability of Fe/Mn/Mg2-LDH was confirmed through the XRD, FTIR, and SEM. Fe/Mn/Mg2-LDH exhibited a good adsorption capacity towards Orange II and highly efficient PMS activation. The optimal removal efficiency of Orange II (98%) was achieved under the conditions of pH 7.0, [PMS] = 1.0 mmol L−1, [Fe/Mn/Mg₂-LDH] = 1.6 g L−1, and [Orange II] = 50 μM. Additionally, this system demonstrated good adaptability across a wide pH range. The presence of Cl− and humic acids (HA) did not significantly inhibit Orange II removal, whereas inhibitory effects were observed in the presence of CO32− and PO43−. The removal mechanism of Orange II was attributed to a synergy of adsorption and oxidation processes, wherein the generated surface radicals (SO4•−ads and HO•ads) on the surface of the Fe/Mn/Mg2-LDH played a predominant role. Furthermore, the Fe/Mn/Mg2-LDH exhibited good reusability, maintaining a removal rate of 90% over five cycles of recycling. The Fe/Mn/Mg2-LDH/PMS system shows promising potential for the treatment of wastewater contaminated with refractory organic pollutants.

Keywords

• Fe/Mn/Mg₂-LDH
• PMS activation
• adsorption
• Orange II
• surface radicals