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 an ovel redox strategy for efficient preparation of ultrathin crystalline amidefunctionalizedc ovalent-triazine-framework nanosheets (CTF NSs) with enhanced visible light absorption. The CTF NSs exhibited photocatalytic hydrogen (512.3 mmol h À1 )a nd oxygen (12.37 mmol h À1 )e volution rates much higher than that of pristine bulk CTF.Photocatalytic overall water splitting could be achieved with efficient stoichiometric H 2 (5.13 mmol h À1 ) and O 2 (2.53 mmol h À1 )e volution 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 asupport as athin film device and demonstrate excellent photocatalytic activity (25.7 mmol h À1 m À2 for hydrogen evolution).

Two-dimensional crystalline covalent triazine frameworks(CTFs) have received much attention because of their unique triazine structure, which endows CTFs with high thermal and chemical stability, high proportion of nitrogen and permanent porosity. Based on this unique structure characteristic, CTFs have shown great potential in energy storage and conversion due to the intrinsically strong conjugated structure, delocalized electron and rich active sites. However, charge carrier(electron, hole or ion) transport can't reach the deep active sites and charge diffusion was impeded by defects in bulk CTFs. Hence, to break through this barrier, increasing attention has been paid to get few layered CTFs or CTFs nanosheets in order to shorten the pathways of charge diffusion and expose more active sites. This review summarizes the synthetic methodologies of CTFs nanosheets and the potential application in ph otocatalytic and electrochemical energy storage and conversion.

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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).