Identifying the role of tetrahedral sites in Fe-based spinel oxides for Fenton-like catalysis

Engineering the electronic structure of active centers located at the octahedral sites in spinel oxides has been widely recognized as an effective strategy for enhancing their performance in Fenton-like catalysis. However, the role of tetrahedral site during the catalytic process between octahedral active site and oxidant molecule remains to be unrevealed. In this study, a series of Fe-based spinel oxides with the substitution of different tetrahedral sites (AFe 2 O 4 , A = Zn, Ni, Co, Mn, Cu) were synthesized by the sol-gel method, and the critical role of tetrahedral site in the peroxymonosulfate (PMS) activation process was systematically investigated. The Fe-based spinel oxide with Co occupying the tetrahedral site (CoFe 2 O 4 ) exhibited high activity and stability in Fenton-like catalysis. Remarkably, the degradation efficiency of bisphenol A (BPA) reached 100 % within 40 min, with a corresponding kinetic rate constant of 0.107 min -1 . The density functional theory calculations reveal that the substitution at the tetrahedral site could regulate the occupation of electron filling in d orbital, and thereby lead to a modulation of the electronic structure accompanied with the shift of d-band center. Co atom at the tetrahedral site modulates the d-band center of Fe closer to the Fermi level, which optimizes the interaction between PMS molecule and Fe active center, thereby facilitating BPA degradation via a fast electron transfer process.