Modulation of the electronic structure of Fe/Co 2D-MOFs by amination for the promotion of 1O2 generation through hydrogen bonding with H2O2: the hitherto overlooked role of ligands

Abstract

Singlet oxygen (¹O₂) generation has attracted attention for the selective degradation of contaminants in Fenton-like reactions. However, it is still a challenge to improve catalytic activity for ¹O₂ generation via H₂O₂-based Fenton-like reactions because of the symmetrical structure of H₂O₂. Metal–organic frameworks (MOFs) are usually reported as catalysts in Fenton-like reactions with metal atoms as active sites. Nevertheless, the contribution of the ligand to the catalytic activity is always overlooked. Herein, two-dimensional (2D) MOFs (Fe/Co as the metal node, terephthalic acid/amino-terephthalic acid as the ligand) were synthesized as catalysts to activate H₂O₂, in which the amino-terephthalic acid displays catalytic activity to activate H₂O₂ for ¹O₂ generation under neutral and alkaline conditions, as reported here for the first time. The experimental results indicated that an O–H bond in H₂O₂ was broken at the catalyst surface instead of the conventional O–O bond. Moreover, density functional theory (DFT) calculations further illustrated that hydrogen bonding (N⋯H) formation between –NH₂ and H₂O₂ affected the electronic configuration of the adjacent C, resulting in the acceleration of electron transfer and improvement in catalytic activity for ¹O₂ generation. The contribution of ¹O₂ reached about 93%. The degradation pathway for methylene blue (MB) was proposed according to mass spectrometry and DFT calculations, following a non-radical pathway with the majority of intermediates being non-toxic. This study provided a strategy for catalyst synthesis and ¹O₂ selective generation in H₂O₂-based Fenton-like reactions.