Molecular Heptazine–Triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Abstract

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 (H2O2) 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 H2O2 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 H2O2 production, which opens potential applications for enhancing PCN‐based photocatalytic redox reactions.This article is protected by copyright. All rights reserved

Unraveling Precise Locations of Indium Atoms in g‐C3N4 for Ameliorating Hydrogen Peroxide Piezo‐Photogeneration

“…[16] Moreover, the presence of metallic salts in the synthetic process can regulate the formation of unique g-C 3 N 4 structures with heptazine and triazine junctions, which can boost the generation of H 2 O 2 . [17] Besides that, with a bunch of nitrogen functional groups in the structures, g-C 3 N 4 is an ideal candidate to decorate single metallic atoms via coordination with stabilized structures. [18] Additionally, single-atom sites can help reduce the energy barriers for reactant adsorption and activation processes during catalytic conditions.…”

Recent developments in photocatalytic production of hydrogen peroxide

“…PCN as a visible-light responsive organic semiconductor material is also known as g-C 3 N 4 . 39,40 Since the first report on PCN for the photosynthesis of H 2 O 2 in 2014, 7 various strategies to enhance photocatalytic activity have been developed over the past few decades, such as creating heterojunctions, [41][42][43][44][45][46] defect (vacancies or functional groups) engineering, [47][48][49][50][51][52][53] heteroatom doping, [54][55][56][57][58] morphological control, 22,[59][60][61][62] loading metals (nanoparticles or single atoms), 19,[63][64][65][66][67][68][69][70] extended conjugation tuning, 71 crystallinity modulation, 72 creating homojunctions 73,74 and building a dipole field. 75 As reported, PCN constructs heterojunctions with pyromellitic diimide (PDI), 41 biphenyl diimide (BDI), 42 reduced graphene oxide (rGO), 43 black phosphorus (BP), 44 polyethylenimine (PEI),…”

“…Zhang et al constructed an internal molecular heptazine/triazine homojunction by a LiCl/KCl molten salt method. 74 Zhu and coworkers reported the synthesis of nitrogen-rich C 3 N 5 with an asymmetric structure and a strong dipole field using triazole and triazine frameworks. 75 C 3 N 5 achieves an H 2 O 2 production rate of 3809.5 mmol g À1 h À1 through the two-electron ORR under simulated sunlight and ultrasonic forces.…”

“…PCN as a visible-light responsive organic semiconductor material is also known as g-C 3 N 4 . 39,40 Since the first report on PCN for the photosynthesis of H 2 O 2 in 2014, 7 various strategies to enhance photocatalytic activity have been developed over the past few decades, such as creating heterojunctions, 41–46 defect (vacancies or functional groups) engineering, 47–53 heteroatom doping, 54–58 morphological control, 22,59–62 loading metals (nanoparticles or single atoms), 19,63–70 extended conjugation tuning, 71 crystallinity modulation, 72 creating homojunctions 73,74 and building a dipole field. 75…”

Enhancing Photosynthesis Efficiency of Hydrogen Peroxide by Modulating Side Chains to Facilitate Water Oxidation at Low‐Energy Barrier Sites

“…However, current photosynthetic systems of H 2 O 2 predominantly utilize the oxygen reduction half-reaction, failing to fully exploit the water oxidation halfreaction. [8][9][10][11][12] This severely hinders the application of this techology in natural water, where the dissolved oxygen concentration is typically below 10 mg L −1 and even lower in polluted water. To address this issue, enhancing the efficiency of water oxidation reaction (WOR) to generate O 2 or directly generate H 2 O 2 becomes a practical solution.…”