3D variable Co species carbon foam enhanced reactive oxygen species generation and ensured long-term stability for water purification

Cobalt (Co) and oxides are the most common catalysts for activating peroxymonosulfate (PMS). However, practical applications of Co-based PMS-advanced oxidation processes are difficult to realize the degradation of the targeted pollutants due to poor yield of reactive oxygen species (ROS) and inaccessible active sites. Here, we designed 3D oxygen vacancy-rich (V_o-rich) variable Co species@carbon foam (Co_xO_y@CF) via coupling solvent-free and pyrolysis strategies for degrading tetracycline by PMS activation. The kinetic rate of optimized (Co@CoO) Co_xO_y@CF-1.0 (1.0 presented the molar ratio of Co²⁺ and 2-methylimidazole) enhanced by an order of magnitude compared to that of ZIFs derivatives (ZIFs-500) (0.073 vs 0.155 min⁻¹) due to the special structure. The flow-through unit maintained over 90% removal within 12 h, which was far better than that of ZIFs-500/PMS system. We used electrochemical analysis, quenching experiment, in-situ FTIR and Raman spectra to further investigate the possible mechanism of the 3D Co_xO_y@CF-1.0/PMS system. 3D Co_xO_y@CF-1.0 stimulated the production of the metastable catalyst-PMS* complex obtained O₂^•− as intermediates accompanied by the redox cycling of Co²⁺/Co³⁺, which created the dominant ROS (more ¹O₂) in the presence of V_o, which was completely different for ZIFs-500/PMS with coordinated and dominant radical and non-radical pathways. This study could large-scale generate variable cobalt-based catalysts for enhanced ROS generation, leading the new insight for boosting practical applications.