Insights into Excitonic Behavior in Single-Atom Covalent Organic Frameworks for Efficient Photo-Fenton-Like Pollutant Degradation

The generation of radicals with strong oxidizing properties through photo-Fenton-like reactions has demonstrated significant potential for the efficient remediation of emerging organic contaminants (EOCs) in complex aqueous environments. However, the excitonic effect, induced by strong Coulomb interactions between photoexcited electrons and holes, significantly impairs the carrier utilization efficiency in photo-Fenton-like systems and has been largely neglected. In this study, we developed Cu single-atom-loaded covalent organic frameworks (CuSA/COFs), which serve as ideal models to modulate excitonic effects. Temperature-dependent photoluminescence spectroscopy revealed that the incorporation of acenaphthene units into linker (CuSA/Ace-COF) significantly reduced the intrinsic exciton binding energy (Eb). The ultrafast dynamic of carriers in CuSA/Ace-COF was further corroborated by femtosecond time-resolved transient absorption spectra. This modification not only enhances PMS adsorption at the Cu active sites but also facilitates rapid electron transfer from the active sites to the adsorbed PMS, thereby promoting the selective generation of hydroxyl radicals. Compared to the degradation kinetics of sulfamethoxazole (SMX) using CuSA/Obq-COF (Eb = 25.6 meV), the pseudo-first-order rate constant for SMX degradation with CuSA/Ace-COF (Eb = 12.2 meV) was 0.434 min⁻¹, representing a 39.5-fold enhancement. This work elucidates the critical role of excitonic behavior in the degradation of EOCs by photo-Fenton-activated PMS and offers novel insights into modulating the excitonic effect of single-atom catalysts through linker engineering.