Singlet oxygen-driven degradation of microcystin-LR using a sustainable donor-acceptor-acceptor covalent organic framework

Eutrophication-driven cyanobacterial blooms release microcystin-LR (MC-LR), a potent hepatotoxin, posing severe environmental and public health risks. Effective, safe MC-LR degradation is critical for water remediation. Herein, we propose a rationally designed unique donor–acceptor–acceptor (D-A1-A2) structural strategy to synthesize a covalent organic framework (COF-TFP-TAPT-Me) for visible-light-driven, controllable 1 O₂-mediated MC-LR photocatalysis. Structural/optoelectronic characterization confirmed triazine-based A2 (Melem) incorporation narrowed the parent D-A1 COF's band gap to 1.15 eV (vs. 1.38 eV) and enhanced charge separation via forming continuous π-conjugation, ordered π-π stacking, and a multi-level energy structure that promotes directional electron transfer (1.6-fold higher photocurrent than the parent COF). COF-TFP-TAPT-Me nearly completely degraded MC-LR in 25 min, with a pseudo-first-order rate constant 1.66-fold higher than the parent COF and outperforming benchmarks like P25 and PCN. Mechanistically, its D-A1-A2 configuration effectively enables highly selective and dominant 1 O₂ generation in metal-free COFs (in contrast to mixed ROS in the parent COF) via photosensitized energy transfer, selectively attacking MC-LR's Adda chain (UPLC–MS verified). The catalyst retains >95 % activity after 5 cycles, is stable in natural water, and shows >80 % cell viability in cytotoxicity assays. This work highlights a novel D-A1-A2 framework for regulating 1 O₂-dominated degradation, offering a trinity of high efficiency, stability, and low toxicity strategy for water purification.