High-valent metal-oxo species in catalytic oxidations for environmental remediation and energy conversion

Advanced oxidation processes based on transition metals (TMs) have been extensively applied to eliminate organic contaminants from water bodies. In addition to the long-recognized radicals, another emerging class of reactive intermediates, high-valent metal-oxo species (HVMSs), have recently been discovered to participate in or even dominate the contaminant degradation during these TM-based catalytic processes. This paper systematically reviewed the latest research progress of HVMSs in the field of environmental catalysis in the past decade. The formation and importance of representative high-valent Fe(IV)/Fe(V), Co(IV), and Mn(V)/Mn(VI) intermediates as active oxidants in different catalytic systems for organics removal were mainly summarized, with detailed discussion on the characteristics of HVMSs (selective oxidation, strong anti-interference ability, and highly affected by solution pH). Then, we specifically introduced the identification and validation methods of HVMSs (including chemical probes, 18O isotope-labeling, spectroscopic techniques, density functional theory calculation, and kinetic modeling), while discussing the applicability and limitations of each method. Moreover, the applications of HVMSs in contaminant degradation, water splitting, and organic synthesis were further summarized. Finally, based on the analyses of the current shortcomings and challenges in this field, some suggestions and prospects for the future development of HVMS-driven catalytic processes were proposed. Overall, we hope this review can supply some reference and enlightenment for further research and practical applications of HVMSs in environmental remediation and energy conversion.