Redox-Mediated TEMPO-based D-A Covalent Organic Framework for Efficient Photo-Induced Hydrogen Peroxide Generation.

Abstract

Molecular engineering of covalent organic frameworks (COFs) offers an alternative approach to conventional anthraquinone oxidation via photo-induced H2O2 production from O2 reduction. Despite their potential, reported photocatalysts suffer limited proton mobility, low selectivity, and insufficient charge separation and utilization. Herein, we report a nitroxyl radical (TEMPO) decorated two-dimensional (2D) donor-acceptor (D-A)-COF photocatalyst via a one-pot strategy linking the porphyrin unit. Under visible light irradiation, highly crystalline TAPP-TPDA-TEMPO-COF (TT-T-COF) exhibits a remarkable photocatalytic H2O2 yield of 10066 μmol g-1 h-1 in two-phase water-benzyl alcohol (BA 10%) system through direct two-electron (2e-) pathway. The mechanistic study by DFT calculations and in-situ DRIFT spectra suggests Yeager-type adsorption of O2 on the nitroxyl radical site (N-O•). The efficient photocatalytic performance and stability of TT-T-COF are attributed to the involvement of the nitroxyl radical (N-O•), which enhances selective O2 adsorption, establishes a distinct electron density distribution, and facilitates photogenerated charge carrier (electron-hole) separation compared to TT-HT-COF and TT-COF counterparts. This study uncovers a new perspective for constructing metal-free, redox-mediated radical-based COFs for sustainable energy conversion, storage, and biomedical applications.