Heterogeneous activation of peroxymonosulfate by bimetallic MOFs for efficient degradation of phenanthrene: Synthesis, performance, kinetics, and mechanisms

Abstract

The performance of metal–organic frameworks (MOFs) in removal of hazardous contaminants is a topic of great significance for aqueous environments. In this study, bimetallic MOFs (FeCo-MOF-74) based on the organic linker 2,5-dihydroxy-1,4-benzene dicarboxylate (DHTA) and divalent cations (Fe and Co) were successfully synthesized for degradation of phenanthrene (PHE). The crystallinity, morphology, and chemical valence state of the synthesized FeCo-MOF-74 were analyzed using XRD, SEM, TEM, and XPS, respectively. Moreover, effects of the preparation parameters, including the synthetic temperature and loading dosage were evaluated. The results demonstrated that Fe1Co1-MOF-74 with a low dosage (50.0 mg/L) could efficiently activate PMS to achieve 100% removal of PHE. PHE degradation followed the pseudo-first-order kinetic well with the rate constants ranging from 0.053 to 0.124 min−1 depending on the synthetic conditions of FeCo-MOF-74. More importantly, EPR studies revealed that sulfate (SO4−), hydroxyl (OH), and singlet oxygen (1O2) were the dominant oxidants responsible for PHE degradation. The coexistence of radical and non-radical species was originated from the interaction of FeCo-MOF-74 and PMS. Frontier orbitals and Fukui functions were calculated to reveal the most reactive sites (C10 and C23) in PHE for radical attack. The intermediates and degradation mechanism of PHE were also investigated. This work proposed a new idea for the development of novel bimetallic MOFs that could be potentially used for the catalytic oxidation of refractory organic pollutants.