Nonradical Photocatalysis for Micropollutant Degradation: Mechanism Insights and Environmental Toxicity Evaluation

The tunable structure of covalent organic frameworks (COFs) and their sensitivity to subtle structural modifications make them highly versatile for addressing water contamination challenges in non-homogeneous phase catalysis. However, integrating solid-liquid phase interactions and enhancing the overall efficiency of non-homogeneous catalysis remain substantial challenges. In this study, we synthesized a COF material, TPCOF-2, with an optimized pore size and strong in-plane conjugation. TPCOF-2 can efficiently remove 7 prevalent trace-level sulfonamides (SAs) from water within 30 min through a direct electron transfer pathway. Among SAs, sulfachloropyridazine (SCP) showed the fastest removal rate due to its small molecular volume, narrow HOMO-LUMO gap and high surface electrostatic potential. Degradation intermediates and pathways were characterized using high-resolution mass spectrometry. Toxicity assessments based on the ECOSAR program, alongside mineralization experiments, revealed that although certain intermediates initially exhibited higher toxicity than the parent compound, they were progressively transformed into less toxic species and eventually mineralized. These findings indicate that detoxification is achieved gradually, with a time-dependent reduction in toxicities of both the parent compound and intermediates throughout the treatment process. This study provides an efficient and sustainable strategy for removing trace amounts of complex organic pollutants from wastewater.