Ultrathin Crystalline Covalent-Triazine-Framework Nanosheets with Electron Donor Groups for Synergistically Enhanced Photocatalytic Water Splitting.

Ultrathin nanosheets have great potential for photocatalytic applications, however, suffer from enlarged band gap and narrowed visible-light-responsive range due to the quantum confinement effect. Herein, we report a novel redox strategy for efficient preparation of ultrathin crystalline amide-functionalized covalent-triazine-framework nanosheets (CTF NSs) with enhanced visible light absorption. The CTF NSs exhibited photocatalytic hydrogen (512.3 μmol h-1 ) and oxygen (12.37 μmol h-1 ) evolution rates much higher than that of pristine bulk CTF. Photocatalytic overall water splitting could be achieved with efficient stoichiometric H2 (5.13 μmol h-1 ) and O2 (2.53 μmol h-1 ) evolution rates under visible light irradiation. Experimental and theoretical analysis revealed that introduction of amide groups as electron donor optimized the band structure and improve its visible-light absorption, hydrophilicity and carrier separation efficiency, thus resulting in the enhanced photocatalytic performance. The well-dispersed CTF NSs could be easily cast onto a support as a thin film device and demonstrate excellent photocatalytic activity (25.7 mmol h-1  m-2 for hydrogen evolution).