Construction of multivariate donor-acceptor heterojunction in covalent organic frameworks for enhanced photocatalytic oxidation: Regulating electron transfer and superoxide radical generation

Covalent organic frameworks (COFs) have attracted attention as photocatalysts, however, low electron transfer and reactive oxygen species (ROS) generation still hinder their photocatalytic application. In this work, we construct multivariate donor-acceptor (D-A) heterojunctions in the covalent organic frameworks by synchronously introducing electron-withdrawing and donating substituents. Importantly, the optoelectronic characteristics and visible-light photocatalytic performance were improved with the increase of the electron donor carbon chains in multivariate D-A COFs. Combining in-situ characterization with theoretical calculations, the charge carrier separation and transfer efficiency, •O₂^– generation and conversion, and the energy barrier of the rate determination steps related to the formation of *OH and *OOH, can be well regulated by the multivariate D-A COFs. More importantly, the ortho-carbon atom of the Br and OCH₃ group-linked benzene rings and the imine bond (–C=N–) in COF-Br@OCH₃ were activated to produce the key *OH and *OOH intermediates for effectively reducing the energy barrier of H₂O oxidation and O₂ reduction. This work provides valuable insights into the precise design and synthesis of COFs-based catalysts and the regulation of electron transfer and ROS generation by modulating the electron-withdrawing and donating substituents for highly efficient visible-light photocatalytic degradation of refractory organic pollutants.