Interfacial OOH* mediated Fe(II) regeneration on the single atom Co-N-C catalyst for efficient Fenton-like processes

Fe(II) regeneration is decisive for highly efficient H2O2-based Fenton-like processes, but the role of cobalt-containing reactive sites in promoting Fe(II) regeneration was overlooked. Herein, a single atom Co-N-C catalyst was employed in Fe(II)/H2O2 system to promote the degradation of diverse organic contaminants. The EPR and quenching experiments indicated Co-N-C significantly enhanced the generation of superoxide species, and accelerated hydroxyl radical generation for pollutant degradation. The electrochemical and surface composition analyses demonstrated the enhanced H2O2 activation and Fe(III)/Fe(II) recycling on the catalyst. Furthermore, in-situ Raman characterization with shell-isolated gold nanoparticles was employed to visualize the interfacial reactive intermediates and their time-resolved interaction. The accumulation of interfacial CoOOH⁎ was confirmed when Co-N-C activated H2O2 alone, but it rapidly transformed into FeOOH⁎ upon Fe(II) addition. Besides, the temporal variation of OOH⁎ intermediates and the relative intensity of Co(III)-O and Co(IV)=O peaks depicted the dynamic interaction of reactive intermediates along the H2O2 consumption. With this basis, we proposed a mechanism of interfacial OOH⁎ mediated Fe(II) regeneration, which overcame the kinetical limitation of Fe(II)/H2O2 system. Therefore, this study provided a primary effort to elucidate the overlooked role of interfacial CoOOH⁎ in the Fenton-like processes, which may inspire the design of more efficient catalysts. H2O2-based Fenton-like processes plays indispensable role in degrading stubborn organic pollutants in industrial wastewater treatment system and natural environment. However, the role of cobalt-containing catalyst was overlooked since they cannot produce ⊡OH from H2O2 or O2 activation directly. Herein, with the aid of in-situ Raman spectroscopy, we observed the CoOOH⁎ intermediate on the surface of single atom Co-N-C and its fast transformation to FeOOH⁎ with Fe(II) and H2O2, demonstrating an efficient Co-mediated Fe(II) regeneration mechanism for efficient Fenton-like processes. These findings should extend the fundamental understanding of Fenton-like processes and inspire the design of new catalyst for efficient pollutant management.