Browsing by Author "Wang, Guanshi"

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Electronic and optical performances of (Cu, N) codoped TiO2/g-C3N4 heterostructure photocatalyst: A spin-polarized DFT plus U study
(2018-03-01)
Zhao, Yali
;
Lin, Yanming
;
Wang, Guanshi
;
Jiang, Zhenyi
;
Zhang, Ruiqin
The geometrical, electronic and optical properties of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure systems have been investigated systematically on the basis of spin-polarized density functional theory calculations. Our calculated results indicate that the band gap of TiO2/g-C3N4 heterostructure has an obvious narrowing compared with pure TiO2 (1 0 1) surface, and (Cu, N) codoping can induce some impurity states of N 2p and hybridized states of Cu 3d and N 2p appearing in the forbidden gap of TiO2/g-C3N4 heterostructure, which lead to a decrease of the photon excitation energy and an obvious redshift of the optical absorption edge. Moreover, the charge density difference calculations of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure systems show that the excited electrons and holes will eventually accumulate in (co)doping TiO2 (1 0 1) surface and g-C3N4 monolayer, respectively, which can effectively reduce the recombination of the photogenerated electron-hole pairs by the interfacial coupling of between TiO2 (1 01) surface and g-C3N4 monolayer. This work not only investigates systematically the electronic and optical properties of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure, but also suggests that (Cu, N) codoped TiO2/g-C3N4 heterostructure is a preferable visible-light photocatalyst.
Enhanced optical absorption and photocatalytic H-2 production activity of g-C3N4/TiO2 heterostructure by interfacial coupling: A DFT plus U study
(2017-04-13)
Lin, Yanming
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Shi, Hailong
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Jiang, Zhenyi
;
Wang, Guanshi
;
Zhang, Xiaodong
The electronic and optical properties of g-C3N4/TiO2 heterostructure are investigated using spin-polarized DFT+U calculations. The equilibrium spacing (1.94 angstrom) and binding energy (24 meV/angstrom(2)) show that g-C3N4/TiO2 is a van der Waals heterostructure. And the calculated band gap of g-C3N4/TiO2 is significantly reduced compared with TiO2. Therefore, the visible light response of g-C3N4/TiO2 heterostructure is remarkably improved. Besides, the predicted type II band alignment would ensure that the electrons can migrate from g-C3N4 monolayer to anatase TiO2 (101) surface, which leads oxidation and redox reactions can occur on g-C3N4 and TiO2, respectively. Finally, a built-in electric field within the interface region will be set. Above processes can benefit the separation of photoexcited carriers and enhance the hydrogen-evolution activity. In addition, compared with TiO2, g-C3N4/TiO2 with higher conduction band minimum energy can effectively produce higher-energy electrons to reduce hydrogen ions. Moreover, the influence of composite distance and the number of g-C3N4 layers are also investigated systematically. The results indicate that the optical absorption is enhanced over the whole spectrum with the increase of the number of g-C3N4 layers. Similar visible light enhancing is also found when the composite distance is decreased. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Photocatalytic water splitting of (F, Ti) codoped heptazine/triazine based g-C3N4 heterostructure: A hybrid DFT study
(2019-01-01)
Zhao, Yali
;
Lin, Yanming
;
Wang, Guanshi
;
Jiang, Zhenyi
;
Zhang, Ruiqin
Graphitic carbon nitride (g-C3N4) has been widely investigated as a metal-free photocatalyst for water splitting. However, the rapid recombination of photoexcited carriers and narrow visible-light response region substantially limit its performance. In this work, we have systematically studied the geometrical, electronic, optical, charge transfer and photocatalytic mechanism of (F, Ti) codoped heptazine/triazine based g-C3N4 heterostructure using hybrid density functional approach. The interface interaction between heptazine and triazine gC(3)N(4) shows heptazine and triazine g-C3N4 form a Van Der Waals heterostructure. The bandgap of (F, Ti) codoped heptazine/triazine based g-C3N4 heterostructure is narrow (2.39 eV), which enhances the absorption of visible light and leads to an obvious redshift of absorption edge. A type-II heterostructure is formed at the interface of (F, Ti) codoped heptazine/triazine based g-C3N4 heterostructure, and leads to high photocatalytic activity. Furthermore, Bader charge and charge density difference indicate that the internal electric field promotes the separation of electron-hole pairs in the heptazine/triazine g-C3N4 interface and inhibits carrier recombination. Meanwhile, electrons in the conduction band of triazine g-C3N4 and holes in the valence band of (F, Ti) codoped heptazine g-C3N4 have enough redox ability. This work is helpful in understanding the mechanism of photocatalytic water splitting and relevant experimental observations.