Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C                         3                         N                         4                         /Bi                         2                         MoO                         6                         (010) and g-C                         3                         N                         4                         /Bi                         2                         WO                         6                         (010) heterostructures: A hybrid density functional theory study

Francis Opoku; Krishna Kuben Govender; Cornelia Gertina Catharina Elizabeth van Sittert; Penny Poomani Govender

doi:10.1016/j.apsusc.2017.09.019

Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures: A hybrid density functional theory study

Francis Opoku, Krishna Kuben Govender, Cornelia Gertina Catharina Elizabeth van Sittert, Penny Poomani Govender

Chemical Sciences

Research output: Contribution to journal › Article › peer-review

122 Citations (Scopus)

Abstract

Graphite-like carbon nitride (g-C ₃ N ₄ )-based heterostructures have received much attention due to their prominent photocatalytic activity. The g-C ₃ N ₄ /Bi ₂ WO ₆ and g-C ₃ N ₄ /Bi ₂ MoO ₆ heterostructures, which follow a typical hetero-junction charge transfer mechanisms show a weak potential for hydrogen evolution and reactive radical generation under visible light irradiation. A mediator-free Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures photocatalyst are designed for the first time using first-principles studies. Moreover, theoretical understanding of the underlying mechanism, the effects of interfacial composition and the role the interface play in the overall photoactivity is still unexplained. The calculated band gap of the heterostructures is reduced compared to the bulk Bi ₂ WO ₆ and Bi ₂ MoO ₆ . In this study, we systematically calculated energy band structure, optical properties and charge transfer of the g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures using the hybrid density functional theory approach. The results show that the charge transfer at the interface of the heterostructures induces a built-in potential, which benefits the separation of photogenerated charge carriers. The g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) heterostructure with more negative adhesion energy (−1.10 eVA ⁻² ) is predicted to have a better adsorptive ability and can form more easily compared to the g-C ₃ N ₄ /Bi ₂ WO ₆ (010) interface (−1.16 eVA ⁻² ). Therefore, our results show that the g-C ₃ N ₄ interaction with Bi ₂ MoO ₆ is stronger than Bi ₂ WO ₆ , which is also verified by the smaller vertical separation (3.25 Å) between Bi ₂ MoO ₆ and g-C ₃ N ₄ compared to the g-C ₃ N ₄ /Bi ₂ WO ₆ (010) interface (3.36 Å). The optical absorption verifies that these proposed Z-scheme heterostructures are excellent visible light harvesting semiconductor photocatalyst materials. This enhancement is ascribed to the role of g-C ₃ N ₄ monolayer as an electron acceptor and the direct Z-scheme charge carrier transfer at the interface of the heterostructures. This work is useful for designing new types of Z-scheme photocatalyst and offers new insight into Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.

Original language	English
Pages (from-to)	487-498
Number of pages	12
Journal	Applied Surface Science
Volume	427
DOIs	https://doi.org/10.1016/j.apsusc.2017.09.019
Publication status	Published - 1 Jan 2018

Keywords

Adhesion energy
Bi MoO
Built-in potential
Hybrid density functional theory
Photocatalysis

ASJC Scopus subject areas

General Chemistry
Condensed Matter Physics
General Physics and Astronomy
Surfaces and Interfaces
Surfaces, Coatings and Films

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1016/j.apsusc.2017.09.019

Cite this

Opoku, F., Govender, K. K., Sittert, C. G. C. E. V., & Govender, P. P. (2018). Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures: A hybrid density functional theory study. Applied Surface Science, 427, 487-498. https://doi.org/10.1016/j.apsusc.2017.09.019

Opoku, Francis ; Govender, Krishna Kuben ; Sittert, Cornelia Gertina Catharina Elizabeth van et al. / Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures : A hybrid density functional theory study. In: Applied Surface Science. 2018 ; Vol. 427. pp. 487-498.

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title = "Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures: A hybrid density functional theory study",

abstract = " Graphite-like carbon nitride (g-C 3 N 4 )-based heterostructures have received much attention due to their prominent photocatalytic activity. The g-C 3 N 4 /Bi 2 WO 6 and g-C 3 N 4 /Bi 2 MoO 6 heterostructures, which follow a typical hetero-junction charge transfer mechanisms show a weak potential for hydrogen evolution and reactive radical generation under visible light irradiation. A mediator-free Z-scheme g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures photocatalyst are designed for the first time using first-principles studies. Moreover, theoretical understanding of the underlying mechanism, the effects of interfacial composition and the role the interface play in the overall photoactivity is still unexplained. The calculated band gap of the heterostructures is reduced compared to the bulk Bi 2 WO 6 and Bi 2 MoO 6 . In this study, we systematically calculated energy band structure, optical properties and charge transfer of the g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures using the hybrid density functional theory approach. The results show that the charge transfer at the interface of the heterostructures induces a built-in potential, which benefits the separation of photogenerated charge carriers. The g-C 3 N 4 /Bi 2 MoO 6 (010) heterostructure with more negative adhesion energy (−1.10 eVA −2 ) is predicted to have a better adsorptive ability and can form more easily compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (−1.16 eVA −2 ). Therefore, our results show that the g-C 3 N 4 interaction with Bi 2 MoO 6 is stronger than Bi 2 WO 6 , which is also verified by the smaller vertical separation (3.25 {\AA}) between Bi 2 MoO 6 and g-C 3 N 4 compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (3.36 {\AA}). The optical absorption verifies that these proposed Z-scheme heterostructures are excellent visible light harvesting semiconductor photocatalyst materials. This enhancement is ascribed to the role of g-C 3 N 4 monolayer as an electron acceptor and the direct Z-scheme charge carrier transfer at the interface of the heterostructures. This work is useful for designing new types of Z-scheme photocatalyst and offers new insight into Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.",

keywords = "Adhesion energy, Bi MoO, Built-in potential, Hybrid density functional theory, Photocatalysis",

author = "Francis Opoku and Govender, {Krishna Kuben} and Sittert, {Cornelia Gertina Catharina Elizabeth van} and Govender, {Penny Poomani}",

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Opoku, F, Govender, KK, Sittert, CGCEV & Govender, PP 2018, 'Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures: A hybrid density functional theory study', Applied Surface Science, vol. 427, pp. 487-498. https://doi.org/10.1016/j.apsusc.2017.09.019

Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures: A hybrid density functional theory study. / Opoku, Francis; Govender, Krishna Kuben; Sittert, Cornelia Gertina Catharina Elizabeth van et al.
In: Applied Surface Science, Vol. 427, 01.01.2018, p. 487-498.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures

T2 - A hybrid density functional theory study

AU - Opoku, Francis

AU - Govender, Krishna Kuben

AU - Sittert, Cornelia Gertina Catharina Elizabeth van

AU - Govender, Penny Poomani

PY - 2018/1/1

Y1 - 2018/1/1

N2 - Graphite-like carbon nitride (g-C 3 N 4 )-based heterostructures have received much attention due to their prominent photocatalytic activity. The g-C 3 N 4 /Bi 2 WO 6 and g-C 3 N 4 /Bi 2 MoO 6 heterostructures, which follow a typical hetero-junction charge transfer mechanisms show a weak potential for hydrogen evolution and reactive radical generation under visible light irradiation. A mediator-free Z-scheme g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures photocatalyst are designed for the first time using first-principles studies. Moreover, theoretical understanding of the underlying mechanism, the effects of interfacial composition and the role the interface play in the overall photoactivity is still unexplained. The calculated band gap of the heterostructures is reduced compared to the bulk Bi 2 WO 6 and Bi 2 MoO 6 . In this study, we systematically calculated energy band structure, optical properties and charge transfer of the g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures using the hybrid density functional theory approach. The results show that the charge transfer at the interface of the heterostructures induces a built-in potential, which benefits the separation of photogenerated charge carriers. The g-C 3 N 4 /Bi 2 MoO 6 (010) heterostructure with more negative adhesion energy (−1.10 eVA −2 ) is predicted to have a better adsorptive ability and can form more easily compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (−1.16 eVA −2 ). Therefore, our results show that the g-C 3 N 4 interaction with Bi 2 MoO 6 is stronger than Bi 2 WO 6 , which is also verified by the smaller vertical separation (3.25 Å) between Bi 2 MoO 6 and g-C 3 N 4 compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (3.36 Å). The optical absorption verifies that these proposed Z-scheme heterostructures are excellent visible light harvesting semiconductor photocatalyst materials. This enhancement is ascribed to the role of g-C 3 N 4 monolayer as an electron acceptor and the direct Z-scheme charge carrier transfer at the interface of the heterostructures. This work is useful for designing new types of Z-scheme photocatalyst and offers new insight into Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.

AB - Graphite-like carbon nitride (g-C 3 N 4 )-based heterostructures have received much attention due to their prominent photocatalytic activity. The g-C 3 N 4 /Bi 2 WO 6 and g-C 3 N 4 /Bi 2 MoO 6 heterostructures, which follow a typical hetero-junction charge transfer mechanisms show a weak potential for hydrogen evolution and reactive radical generation under visible light irradiation. A mediator-free Z-scheme g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures photocatalyst are designed for the first time using first-principles studies. Moreover, theoretical understanding of the underlying mechanism, the effects of interfacial composition and the role the interface play in the overall photoactivity is still unexplained. The calculated band gap of the heterostructures is reduced compared to the bulk Bi 2 WO 6 and Bi 2 MoO 6 . In this study, we systematically calculated energy band structure, optical properties and charge transfer of the g-C 3 N 4 /Bi 2 MoO 6 (010) and g-C 3 N 4 /Bi 2 WO 6 (010) heterostructures using the hybrid density functional theory approach. The results show that the charge transfer at the interface of the heterostructures induces a built-in potential, which benefits the separation of photogenerated charge carriers. The g-C 3 N 4 /Bi 2 MoO 6 (010) heterostructure with more negative adhesion energy (−1.10 eVA −2 ) is predicted to have a better adsorptive ability and can form more easily compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (−1.16 eVA −2 ). Therefore, our results show that the g-C 3 N 4 interaction with Bi 2 MoO 6 is stronger than Bi 2 WO 6 , which is also verified by the smaller vertical separation (3.25 Å) between Bi 2 MoO 6 and g-C 3 N 4 compared to the g-C 3 N 4 /Bi 2 WO 6 (010) interface (3.36 Å). The optical absorption verifies that these proposed Z-scheme heterostructures are excellent visible light harvesting semiconductor photocatalyst materials. This enhancement is ascribed to the role of g-C 3 N 4 monolayer as an electron acceptor and the direct Z-scheme charge carrier transfer at the interface of the heterostructures. This work is useful for designing new types of Z-scheme photocatalyst and offers new insight into Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.

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KW - Built-in potential

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Opoku F, Govender KK, Sittert CGCEV, Govender PP. Insights into the photocatalytic mechanism of mediator-free direct Z-scheme g-C ₃ N ₄ /Bi ₂ MoO ₆ (010) and g-C ₃ N ₄ /Bi ₂ WO ₆ (010) heterostructures: A hybrid density functional theory study. Applied Surface Science. 2018 Jan 1;427:487-498. doi: 10.1016/j.apsusc.2017.09.019