Synergistic cobalt-nitrogen sites and cobalt nanoparticles in polyethylene terephthalate-derived catalysts for selective singlet oxygen generation: Bridging plastic upcycling and antibiotic mineralization

To confront the synergistic remediation of plastic waste valorization and antibiotic contamination, we engineered cobalt-embedded nitrogen-enriched carbonaceous hybrids (Co@N/PC) via a molten salt-assisted pyrolysis strategy using polyethylene terephthalate (PET) plastics coupled with zeolitic imidazolate framework-67 (ZIF-67) immobilization. These transition metal–carbon composites were methodically optimized as peroxymonosulfate (PMS) activators for enhanced tetracycline (TC) degradation. Kinetic evaluations demonstrated that Co@N/PC-800 exhibited exceptional catalytic performance with a first-order rate constant (k_obs = 0.085 min⁻¹) surpassing conventional ZIF-67-derived counterparts by 2.3-fold. Remarkably, the optimized catalyst sustained 88.16 % TC elimination efficiency within 30 min under environmentally relevant conditions, including elevated ionic strength and natural organic matter interference, confirming robust operational stability. Multidisciplinary characterization (radical scavenging, electron paramagnetic resonance (EPR), and voltametric analyses) identified that Co²⁺/Co³⁺ redox cycling synergistically interacts with graphitic carbon matrices to enhance electron transfer efficiency, while atomically dispersed Co-N catalytic sites specifically drive the generation of singlet oxygen (¹O₂) through a non-radical oxidation mechanism. Density functional theory (DFT) calculations reveal that synergistic coupling between atomically dispersed Co-N sites and metallic Co nanoparticles in carbon-based heterostructures markedly enhances PMS activation. This configuration significantly lowers the activation energy barrier and enhances PMS activation, thereby accelerating interfacial electron transfer and promoting reactive oxygen species (ROS) generation. Molecular orbital analysis further demonstrates that pollutant degradation kinetics correlate with energy level alignment between the highest occupied molecular orbital (HOMO) of contaminants and the lowest unoccupied molecular orbital (LUMO) of ¹O₂. This research develops a bifunctional remediation strategy that integrates plastic upcycling with the deep mineralization of micropollutants, achieved through the rational design of transition metal–carbon heterogeneous interfaces.