Single-atomic Co-N site modulated exciton dissociation and charge transfer on covalent organic frameworks for efficient antibiotics degradation via peroxymonosulfate activation

Abstract

Covalent organic framework (COF) materials have received extensive attention in the field of photocatalysis in recent years, but the strong exciton effect in COF has seriously affected the separation of electron-hole pairs so that limiting the enhancement of the photocatalytic performance. It is of great significance to explore suitable ways to regulate the exciton behavior in COF materials and enhance their electron-hole's separation efficiency. By anchoring Co single-atoms within a silver birch leaf-like COF framework (COF-Cox), the exciton in COF is effectively dissociated by forming Co-N sites, producing massive free electrons and holes. Co-N sites also facilitate photogenerated holes aggregation toward Co single-atoms, which effectively drives the carriers' separation in COF framework. The carrier concentration of COF-Co10 is 2.81 times higher compared with the original COF. The reduced exciton binding energy (E_b) further proves that the the formation of Co-N sites promote the exciton dissociation. Consequently, COF-Cox can well activate peroxymonosulfate (PMS) to degrade tetracycline (TC) pollutants, the reaction rate constant of COF-Co10 (3.65 × 10^-2 min⁻¹) is 5.27 times higher than COF (6.93 × 10^-3 min⁻¹). The possible activation routes and degradation products of TC are also discussed. This study provides a more comprehensive understanding of the exciton behavior for the design of more efficient COF-based catalysts.