ZnMn2O4 nanorods: an effective Fenton-like heterogeneous catalyst with t2g3eg1 electronic configuration

Abstract

Fenton-like catalysis is promising in the treatment of organic-containing wastewater owing to easy separation of solid catalysts, wide working pH range, and high efficiency. Although α-Mn₂O₃ with Mn³⁺ in t_2g³e_g¹ electronic configuration displays high activity in photocatalytic oxidation of water, it is not preferred as a Fenton-like catalyst due to its low phase-transition temperature. Herein, we developed a Fenton-like catalyst with both high activity and stability. Two catalysts, namely, spinel ZnMn₂O₄ and ZnMnO₃ nanorods were synthesized by a facile co-precipitation method. Experimental results indicate that the two Mn-containing catalysts have similar rod-like morphology, but with different crystallographic structures and oxidation states of Mn. DFT calculations suggest t_2g³e_g¹ electron configuration of Mn in ZnMn₂O₄ with strong Jahn–Teller distortion of MnO₆ units. ZnMn₂O₄ nanorod Fenton-like catalyst displays high activity in the degradation of methyl violet with a degradation ratio of 100% at 120 min and a TOC removal rate near 90% after 240 min. ˙OH and ˙OOH/˙O₂⁻ reactive radicals generated in the catalytic system were studied by EPR spectroscopy. The ZnMn₂O₄ nanorods exhibited much better catalytic performance than ZnMnO₃ nanorods. The t_2g³e_g¹ configuration of Mn in spinel ZnMn₂O₄, facilitating the dissociation of various oxygen-containing radicals through strong JT distortion, is responsible for its higher catalytic activity.