Molecular Heptazine-triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide.

Revealing the photocatalytic mechanism between various junctions and catalytic activities has become the hotspot in photocatalytic system. Herein, an internal molecular heptazine/triazine (H/T) junction in crystalline carbon nitride (HTCN) was constructed and devoted to selective two-electron oxygen reduction reaction (2e - ORR) for efficient hydrogen peroxide (H 2 O 2 ) production. In-situ XRD spectra under various temperature authenticated the successful formation of molecular H/T junction in HTCN during the calcining process rather than physically mixing. The increased surface photovoltage (SPV) and transient photovoltage (TPV) signals, and the decreased exciton binding energy (Eb) undoubtably elucidated that an obvious increasement of carrier density and diffusion capability of photogenerated electrons were realized over HTCN. Additionally, the analyses of in-situ photoirradiated Kelvin probe force microscopy (KPFM) and femto-second transient absorption spectra (fs-TAS) revealed the successful construction of the strong internal built-in-electric field and existence of the majority of long-lived shallow trapped electrons associated with molecular H/T junction over HTCN, respectively. Benefiting from these, the photocatalytic results exhibited an incredible improvement (96.5-fold) for H 2 O 2 production. This novel work provides a comprehensive understanding of the long-lived reactive charges in molecular H/T junction for strengthening the driving-force for photocatalytic H 2 O 2 production, which opens potential applications for enhancing PCN-based photocatalytic redox reactions. This article is protected by copyright. All rights reserved.