کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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6454461 | 1418817 | 2017 | 14 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Microwave-assisted molten-salt rapid synthesis of isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic hydrogen evolution performance Microwave-assisted molten-salt rapid synthesis of isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic hydrogen evolution performance](/preview/png/6454461.png)
- 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 eâ-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 30 min 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 25.7 m2 gâ1. Comparatively, the g-C3N4 sample synthesized via an electric-resistance molten-salt (er-ms) process at 550 °C for 240 min is composed of a triazine-based g-C3N4 phase with a SBET of 58.1 m2 gâ1, whereas the samples obtained by electric-resistance heating (er, at 550 °C for 240 min) and microwave heating (mw, at 550 °C for 30 min) processes consist of a heptazine-based g-C3N4 phase. The mw-ms-g-C3N4 sample shows a photocatalytic HER rate of 1480 μmol gâ1 hâ1, which is 5 times that (300 μmol gâ1 hâ1) of the er-ms-g-C3N4 sample, 15 times that (95 μmol gâ1 hâ1) of the er-g-C3N4 sample and 23 times that (63 μmol gâ1 hâ1) of the mw-g-C3N4 sample, under the similar visible-light (λ â¥Â 420 nm) irradiation. The typical apparent quantum yield of the mw-ms-g-C3N4 sample at 420 nm is up to 10.7%. The UV-vis DR spectra suggest that both the triazine-based g-C3N4 and heptazine-based g-C3N4 phases have a similar bandgap of â¼2.66 eV, whereas the Mott-Schottky analysis indicates that the triazine-based g-C3N4 phase has a more positive flat conductive potential (â0.90 V) than the triazine-based g-C3N4 phase (â1.22 V). Due to the suitable alignment of their energy bandgap structures, the isotype triazine-/heptazine based g-C3N4 hybrids in the mw-ms-g-C3N4 sample form a type II heterojunction of semiconductor/semiconductor, which provides a convenient carrier transfer path and leads to more efficient separation of photo-generated electron-hole pairs than the other samples. The synergistic effects of microwave heating and molten-salt liquid polycondensation provide a robust platform for rapid and large-scale construction of isotype g-C3N4/g-C3N4 heterojunctions as metal-free high-performance HER photocatalysts using a simple single-source precursor.
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.310
Journal: Applied Catalysis B: Environmental - Volume 203, April 2017, Pages 300-313