Defect engineering boosting PMS activation activity on cobalt polyphthalocyanine: Promoting Co(IV)=O formation and enhancing 1O2 selectivity

Abstract

The use of unsaturated Co-N₄ coordinated cobalt polyphthalocyanine (CoPPc) in activating peroxymonosulfate (PMS) for the degradation of organic pollutants has potential applications, but the π-π stacking structure limits the axial electron transfer, hindering the activation of PMS. In this research, a simple hydrothermal modification method was proposed to introduce structural defects into CoPPc. Structural defects can serve as channels for axial electron transfer, which not only reduces the electron transfer resistance but also lowers the oxidation–reduction potential of the central Co ion, favoring the formation of high-valent metal-oxo species (Co(Ⅳ)=O). Additionally, the formation of graphitic carbon, graphitic N, and carbonyl groups during the modification of defective cobalt polyphthalocyanine (D-CoPPc) enhances the selectivity of generating singlet oxygen (¹O₂) during the activation of PMS. Therefore, the degradation efficiency of tetracycline (TC) in the D-CoPPc/PMS system, with dual non-radicals (Co(Ⅳ)=O and ¹O₂) as the main pathway and ${\text{SO}}_{\text{4}}^{·-}$ as auxiliary pathway, increased from 68.0 % to 95.9 %. The outcomes of the experiment demonstrated that D-CoPPc/PMS is also feasible for withstanding natural water bodies, pH variations, and the interference of anions. This study provides new insights into the modification of cobalt polyphthalocyanine and proves its huge potential in organic pollutant degradation.