Platinum Single Atoms Anchored on a Covalent Organic Framework: Boosting Active Sites for Photocatalytic Hydrogen Evolution

It is of great importance to explore and achieve a more effective approach toward the controllable synthesis of single-atom-based photocatalysts with high metal content and long-term durability. Herein, single-atom platinum (Pt) with high loading content anchored on the pore walls of two-dimensional β-ketoenamine-linked covalent organic frameworks (TpPa-1-COF) is presented. Aided by advanced characterization techniques of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, it has been demonstrated that atomically dispersed Pt is formed on the TpPa-1-COF support through a six-coordinated C3N–Pt–Cl2 species. The optimized Pt1@TpPa-1 catalyst exhibits a high photocatalytic H2 evolution rate of 719 μmol g–1 h–1 under visible-light irradiation, a high actual Pt loading content of 0.72 wt %, and a large turnover frequency (TOF) of 19.5 h–1, with activity equivalent to 3.9 and 48 times higher than those of Pt nanoparticles/TpPa-1 and bare TpPa-1, respectively. The improved photocatalytic performance for H2 evolution is ascribed to the effective photogenerated charge separation and migration and well-dispersed active sites of single-atom Pt. Moreover, density functional theory (DFT) calculations further reveal the role of Pt single atoms in the enhanced photocatalytic activity for H2 evolution. Overall, this work provides some inspiration for designing single-atom-based photocatalysts with outstanding stability and efficiency using COFs as the support.