Visible-light-switched radical/non-radical bichannel degradation mechanism via round-the-clock synergistic CDs-BiO1-xCl/PS system

In order to achieve efficient degradation of organic pollutants (OPs) and to avoid interference from co-existing anions and natural organic matter, a synergistic CDs-BiO_1-xCl/PS system is designed, which is capable of functioning under both dark and visible-light-controlled conditions, enabling round-the-clock operation. A novel nano photocatalyst CDs-BiO_1-xCl was constructed by modifying the surface oxygen vacancy (O_v) rich bismuth oxychloride (BiO_1-xCl) with carbon quantum dots (CDs). The key role of the edge carbon atoms (C) of CDs in CDs-BiO_1-xCl photocatalyst for PS (persulfate) activation was revealed. Electron paramagnetic resonance spectroscopy, In-situ Raman, quenching experiments and density functional theory (DFT) analysis indicated that the C-edge atoms in the photocatalyst acted as an electron donor which facilitated the complexes formation with PS under dark conditions, and the complexes participated in organic pollutants degradation via electron transfer (non-free radical) pathways subsequently. The system cleverly utilizes the “on-off” of light to achieve the controlled triggering of free radical and non-free radical pathways for PS activation. Upon light irradiation, photogenerated carriers migrate toward CDs, promoting further decomposition of its surface complexes to produce sulfate radicals (·SO₄^-). Hence, this optimized light-controlled synergistic system showed complete removal of BPA (10 mg/L) in the presence of 2 mM PS within 15 min via free radical and non-free radical pathways. The visible-light-driven system did not produce any toxic byproducts and showed excellent stability under various reaction conditions. Therefore, the round-the-clock and photo-switching-regulated high-efficiency CDs-BiO_1-xCl/PS system demonstrates promising application prospects for removing organic pollutants in complex water bodies.