Site-Specific Spin State Modulation in Spinel Oxides for Enhanced Nonradical Oxidation

Spinel oxides hold tremendous potential for driving advanced oxidation processes, yet the underlying mechanism for maximizing their activity remains unclear. In this study, we leverage tetrahedral and octahedral site interactions in Mn_xCo_3-xO₄ to modulate the spin states, specifically spin alignment and spin moment, thereby enhancing periodate (PI) activation and catalytic performance in contaminant degradation. Through combined experimental and density functional theory (DFT) analyses, we elucidate the role of spin alignment at synergetic tetrahedral and octahedral sites in facilitating quantum spin exchange interactions (QSEI) with an efficient electronic spin channel for charge transfer. Meanwhile, the engineered high spin configuration in CoMn₂O₄ raises the d-band center, favoring stable PI* surface complex formation and accelerating the rate-determining desorption of IO₃⁻ with a lower-ICOHP value during the catalytic degradation of ciprofloxacin. As a result, the fine-tuned spin state of CoMn₂O₄ leads to enhanced overall reaction kinetics, with a 2.5-fold increase compared to MnCo₂O₄ and up to 22-fold increase compared to the octahedrally-active only catalysts. Such a site-specific modulation has been found applicable to other spinel oxides, enlightening fine-tuned electronic structure for maximizing catalytic performance.