Understanding spatial effects of tetrahedral and octahedral cobalt cations on peroxymonosulfate activation for efficient pollution degradation

Identifying the spatial effects of cobalt cations in cobalt-based heterogeneous catalysts contributes to develop effective peroxymonosulfate (PMS) activators in water treatment. Herein, we investigated typical tetrahedral and octahedral cobalt ions in CoAl2O4 and ZnCo2O4 via an inactive cation substitution strategy towards spinel Co3O4. ZnCo2O4 (0.095 min−1) performs remarkably better than CoAl2O4 (0.007 min−1) for degrading rhodamine B, while non-radical 1O2 is the dominant reactive oxygen species. Then, interface kinetics characterized by systemic electrochemical techniques indicate the feasibility of Co2+/Co3+ transformation and charge transfer resistance at catalyst-electrolyte interface determine intrinsic activity. Octahedral cobalt species exhibit superior intrinsic activities comparing with tetrahedral ones on the removal of several dye and aromatic pollutants. Additionally, flat band potentials of cobalt-based oxides reflecting Fermi level positions is a thermodynamic factor to activate PMS. Our work attempts to further understand spatial occupation-activity relationship of cobalt sites to design efficient PMS activators.