Microwave-assisted molten-salt rapid synthesis of isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic hydrogen evolution performance

• Published in: Applied catalysis. B, Environmental Environmental, 2017-04, Vol.203, p.300-313
• Main Authors: Liu, Huanhuan, Chen, Deliang, Wang, Zhiqiang, Jing, Huijuan, Zhang, Rui
• Format: Article
• Language: English
• Subjects: Graphitic carbon nitride; Isotype g-C3N4/g-C3N4 heterojunction; Microwave-assisted molten-salt synthesis; Photocatalytic hydrogen evolution; Thermo-polymerization of melamine
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2016.10.014

We first develop a microwave-assisted molten-salt (KCl/LiCl) process to rapidly synthesize isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic activity in hydrogen evolution reaction using melamine as the single-source precursor. [Display omitted] •Isotype g-C3N4 heterojunctions were synthesized using melamine as the single-source precursor.•Microwave-assisted molten-salt process was developed to form the heterojunctions.•The heterojunction consists of isotype triazine-/heptazine based g-C3N4 nanoplates.•The g-C3N4 heterojunctions have highly enhanced photocatalytic activity for HER.•The efficient separation of photogenerated e−–h+ pairs enhanced its photocatalytic performance. Rapid synthesis and construction of graphitic carbon nitride (g-C3N4) based heterojunctions, cost-effective metal-free photocatalysts for hydrogen evolution reaction (HER) under solar irradiation, is of highly practical significance. This work reports a one-pot microwave-assisted molten-salt (mw-ms) process to rapidly synthesize isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic HER performance using melamine as the single-source precursor. The typical sample (mw-ms-g-C3N4) was obtained by thermally polymerizing melamine molecules at 550°C for 30min in the media of eutectic KCl/LiCl salts under microwave irradiation in air. The analyses of phases, chemical compositions and microstructures indicate that the mw-ms-g-C3N4 sample consists of an isotype triazine-/heptazine based g-C3N4 heterojunction, taking on a plate-like morphology with a specific surface area (SBET) of 25.7m2g−1. Comparatively, the g-C3N4 sample synthesized via an electric-resistance molten-salt (er-ms) process at 550°C for 240min is composed of a triazine-based g-C3N4 phase with a SBET of 58.1m2g−1, whereas the samples obtained by electric-resistance heating (er, at 550°C for 240min) and microwave heating (mw, at 550°C for 30min) processes consist of a heptazine-based g-C3N4 phase. The mw-ms-g-C3N4 sample shows a photocatalytic HER rate of 1480μmolg−1h−1, which is 5 times that (300μmolg−1h−1) of the er-ms-g-C3N4 sample, 15 times that (95μmolg−1h−1) of the er-g-C3N4 sample and 23 times that (63μmolg−1h−1) of the mw-g-C3N4 sample, under the similar visible-light (λ≥420nm) irradiation. The typical apparent quantum yield of the mw-ms-g-C3N4 sample at 420nm is up to 10.7%. The UV–vis DR spectra suggest that both the triazine-based g-C3N4 a