Green and Scalable Synthesis of Atomic-Thin Crystalline Two-Dimensional Triazine Polymers with Ultrahigh Photocatalytic Properties

Abstract

Scalable and eco-friendly synthesis of crystalline two-dimensional (2D) polymers with proper band gap and singlelayer thickness is highly desired for the fundamental research and practical applications of 2D polymers; however, it remains a considerable and unresolved challenge. Herein, we report a convenient and robust method to synthesize a series of crystalline covalent triazine framework nanosheets (CTF NSs) with a thickness of ∼80 nm via a new solvent-free salt-catalyzed nitrile cyclotrimerization process, which enables the cost-effective largescale preparation of crystalline CTF NSs at the hundred-gram level. Theoretical calculations and detailed experiments revealed for the first time that the conventional salts such as KCl can not only act as physical templates as traditionally believed but also more importantly can efficiently catalyze the cyclotrimerization reaction of carbonitrile monomers as a new kind of green solid catalysts to achieve crystalline CTF NSs. Upon simple liquid-phase sonication, these CTF NSs can be easily further exfoliated into abundant single-layer crystalline 2D triazine polymers (2D-TPs) in high yields. The obtained atomically thin crystalline 2D-TPs with a band gap of 2.36 eV and rich triazine active groups exhibited a remarkable photocatalytic hydrogen evolution rate of 1321 μmol h −1 under visible light irradiation with an apparent quantum yield up to 29.5% at 420 nm and excellent photocatalytic overall water splitting activity with a solar-to-hydrogen efficiency up to 0.35%, which exceed all molecular framework materials and are among the best metal-free photocatalysts ever reported. Moreover, the processable 2D-TPs could be readily assembled on a support as a photocatalytic film device, which demonstrated superior photocatalytic performance (135.2 mmol h −1 m −2 for hydrogen evolution).

Hydrothermal Synthesis of Highly Crystalline Zwitterionic Vinylene-Linked Covalent Organic Frameworks with Exceptional Photocatalytic Properties

“…As exhibited in Figure d, a high AQY of 47.1% at 420 nm was achieved for ZVCOF-1, and then the AQY decreased with increasing wavelength of irradiation light, which was consistent with the light absorption properties of ZVCOF-1. Interestingly, even when ZVCOF-1 was irradiated with 650 nm red light, it could still achieve a high AQY of 1.6%, demonstrating its high efficiency in photocatalytic H 2 production. , Meanwhile, the AQY of ZVCOF-2 was 24.0% at 420 nm (Figure S38), which was relatively lower than that of ZVCOF-1. We also compared ZVCOF-1 with other COFs reported in the literature in terms of HER performance and AQY values (Figure e and Table S3) and found ZVCOF-1 to be one of the highest among all the COFs reported so far.…”

Recent progress in polymer nanosheets for photocatalysis

“…5a). 108 Common salts (KCl, etc. ) could not only facilitate the formation of a nanosheet morphology but also act as a kind of green solid catalyst to catalyze the cyclotrimerization reaction of carbonitrile monomers.…”

“…High crystallinity and hydrophilicity are the key factors to obtain photocatalytic overall water splitting activity. Besides the amide-functionalized CTF nanosheets and atomically thin crystalline 2D-TPs prepared by Xu et al 105,108 the crystalline CTF nanosheets with high hydrophilicity (denoted as CTF-HUST-A1) prepared by Jin et al also exhibited photocatalytic overall water splitting activity. 111 The crystalline CTF-HUST-A1 nanosheets were synthesized using p -xylylenediamine as the monomer and a strong base as the catalyst.…”

Fluorescent covalent organic frameworks for environmental pollutant detection sensors and enrichment sorbents: a mini-review

“…CTFs constructed by aromatic triazine bonding have unique properties such as excellent chemical and thermal stability, two-dimensional conjugated structure and abundant reactive triazine groups, thus exhibiting great potential for photocatalysis, detection, adsorption and energy storage. 11 In 2019, Tang et al 10 have synthesized two fluorescent CTFs (F-CTFs) via a condensation reaction between 4′,4′′′,4′′′′′,4′′′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1′-biphenyl]-4-carbaldehyde)) (ETTC) monomers with phenamidine hydrochloride (PAHC) and diphenamidine hydrochloride (DPHC), respectively (Fig. 2H).…”

“…Covalent organic frameworks (COFs) are a class of crystalline organic porous materials formed by the interconnection of two or more organic molecular building blocks via strong covalent bonds ( e.g. , CN bonds, 1–3 B–O bonds, 4–6 CC bonds, 7,8 and triazinyl bonds 9–11 ) that extend in an ordered two-dimensional (2D) or three-dimensional (3D) manner. Originally, in 2005, Côté et al 12 synthesized honeycomb structured porous COFs connected by boron ester rings and extended in 2D planes forming fully overlapping stacks for the first time.…”