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Band alignment tuning of heptazine-g-C3N4/g-ZnO vdW heterostructure as a promising water-splitting photocatalyst

Rahimi, K ; Sharif University of Technology | 2021

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  1. Type of Document: Article
  2. DOI: 10.1039/d1cp02911h
  3. Publisher: Royal Society of Chemistry , 2021
  4. Abstract:
  5. Van der Waals (vdW) heterostructures of two-dimensional monolayers are a relatively new class of materials with highly tunable band alignment, bandgap energy, and bandgap transition type. In this study, we performed density functional theory calculations to investigate how a vdW heterostructure of heptazine-based graphitic carbon nitride (hg-C3N4) and graphitic zinc oxide (g-ZnO) monolayers is formed (hg-C3N4/g-ZnO). This heterostructure is a potential solar-driven photocatalyst for the water-splitting reaction. Upon the formation of the heterostructure, a type-I indirect bandgap (Eg = 2.08 eV) is created with appropriate conduction band minimum and valence band maximum levels relative to the oxidation/reduction potentials for the water-splitting reaction. In addition, a very large electrostatic potential difference of 11.18 eV is generated across the heterostructure, leading to a large, naturally-formed, built-in electric field directing from hg-C3N4 to g-ZnO. The produced electric field forces photogenerated electrons in g-ZnO to transfer toward hg-C3N4, leading to a decrease in the electron-hole recombination rate. We also found that both g-ZnO and hg-C3N4 synergistically lead to higher light absorption of the heterostructure (λmax = 387 nm). Furthermore, band alignment, bandgap energy, and transition type of the heterostructure can be tuned by applying external perpendicular electric fields and biaxial strains. It was found that a strain of +2% leads to a Z-scheme band alignment (Eg = 2.34 eV, direct) and an electric field of 1 V Å-1 leads to a type-II heterostructure (Eg = 2.29 eV, indirect), which are both beneficial for efficient water-splitting photocatalysis. This journal is © the Owner Societies
  6. Keywords:
  7. Carbon nitride ; Density functional theory ; Electric fields ; Energy gap ; II-VI semiconductors ; Light absorption ; Monolayers ; Strain ; Zinc oxide ; Band alignments ; Band gap energy ; Band gap transition ; Density-functional theory calculations ; Energy transitions ; Tunables ; Two-dimensional ; Van der Waal ; Water splitting ; Water splitting reactions ; Van der Waals forces
  8. Source: Physical Chemistry Chemical Physics ; Volume 23, Issue 36 , 2021 , Pages 20675-20685 ; 14639076 (ISSN)
  9. URL: https://pubs.rsc.org/en/content/articlelanding/2021/cp/d1cp02911h