Abstract
This work unambiguously describes the direct-Zscheme governing the charge carrier separation induced by visible light of the C3N4–ZnO heterojunction.
Highlights
Nowadays, the necessity to find and develop even more powerful systems in the area of heterogeneous photocatalysis is one of the most arduous challenges currently being attempted by researchers
Electron paramagnetic resonance (EPR) spectroscopy analysis coupled with in situ irradiation, performed at 77 K, and supported by accurate simulations, demonstrated that the charge carrier dynamics at the C3N4– ZnO interface is governed by a direct Z-scheme heterojunction mechanism rather than that of a type-II heterojunction system
The experimental results suggest that the photoexcited electrons in the ZnO conduction band annihilate the holes in the C3N4 valence band, as in a solid direct Z-scheme system, allowing an improved charge carrier separation and stabilizing both electrons and holes at the best reductive and oxidative potentials, respectively
Summary
The necessity to find and develop even more powerful systems in the area of heterogeneous photocatalysis is one of the most arduous challenges currently being attempted by researchers. The first study on photoactive materials dates back to the 1920s, but we had to wait until the 1960s to see a systematic study of photoactivity regarding transition metal oxide-based semiconductors.[12,13] The work at that time focused mainly on the fact that wider band gap semiconductors exhibited higher activities concerning the reductive and oxidative redox reactions carried out by electrons and holes. An inherent restriction of this model is that the holes and electrons are not stabilized on semiconductors with the best oxidative and reductive potentials, respectively This problem has recently been overcome by the so called ‘‘direct Z-scheme’’ or ‘‘S-scheme’’ heterojunction, already conceptually theorized by Bard in 1979:23 the first direct Z-scheme-interfaced systems could only be constructed in the liquid phase, since they needed the presence of an electrolytic mediator.[24] In 2006, Tada et al.[25] demonstrated that an all-solid Z-scheme was possible, in which the solid electron mediator was represented by gold particles. To the best of our knowledge, this study provides straightforward and unambiguous proof of the direct Z-scheme or S scheme heterojunction mechanism of the visible photon absorption characterizing the C3N4–ZnO mixed system
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