Tuning intramolecular charge transfer of covalent organic frameworks with triazine structure for enhanced peroxymonosulfate activation performance on the catalytic degradation of organic pollutants under visible light irradiation

As emerging metal-free photocatalysts, covalent organic frameworks with triazine structure (CTFs) hold great potential for refractory organic pollutants removal in the visible-light-induced peroxymonosulfate system (PMS/Vis). In this work, the electron-withdrawing group-ketone structure was introduced into the CTF framework (keto-CTF), aiming to regulate the regional electronic structure of CTF and thus further enhancing its visible-light photocatalytic performance and PMS activation. The results showed that the introduction of ketone greatly enhanced the visible-light utilization, carrier separation and charge transfer capabilities of CTF. Notably, the keto-CTF/PMS/Vis system with resistance to environmental factors exhibited highly efficient and stable catalytic performance for the degradation and mineralization of organic pollutants, which was superior to that of single catalytic system. Indeed, the excellent photocatalytic performance and PMS activation of keto-CTF were attributed to the enriched valence-electron density around O atoms of ketone compared to that of C atoms, which led to a multitude of internal electric fields within the keto-CTF consisting of positive and negative electric centers. These internal electric fields not only promoted the separation and transfer of photogenerated charges but enhanced the adsorption of PMS onto keto-CTF. The adsorbed PMS subsequently captured photogenerated electrons, further reducing electron-hole recombination in keto-CTF and generating various reactive species. Ultimately, the efficient degradation of organic pollutants was achieved via the co-dominance of hole and singlet oxygen with the assistance of the charge-transfer-based non-radical pathway. This work provides new insights into the visible-light-induced multi-path catalytic oxidation mechanism of PMS and provides an effective solution for the removal of refractory organic pollutants from wastewater.