DFT Study on Regulating the Electronic Structure and CO2 Reduction Reaction in BiOBr/Sulphur-Doped G-C3N4 S-Scheme Heterojunctions

Xingang Fei,Liuyang Zhang,Jiaguo Yu,Bicheng Zhu

doi:10.3389/fnano.2021.698351

Abstract

Photocatalytic CO2 reduction is a promising method to mitigate the greenhouse effect and energy shortage problem. Development of effective photocatalysts is vital in achieving high photocatalytic activity. Herein, the S-scheme heterojunctions composed by BiOBr and g-C3N4 with or without S doping are thoroughly investigated for CO2 reduction by density functional theory (DFT) calculation. Work function and charge density difference demonstrate the existence of a built-in electric field in the system, which contributes to the separation of photogenerated electron-hole pairs. Enhanced strength of a built-in electric field is revealed by analysis of Bader charge and electric field intensity. The results indicate that S doping can tailor the electronic structures and thus improve the photocatalytic activity. According to the change in absorption coefficient, system doping can also endow the heterojunction with increased visible light absorption. The in-depth investigation indicates that the superior CO2 reduction activity is ascribed to low rate-determining energy. And both of the heterojunctions are inclined to generate CH3OH rather than CH4. Furthermore, S doping can further reduce the energy from 1.23 to 0.44 eV, indicating S doping is predicted to be an efficient photocatalyst for reducing CO2 into CH3OH. Therefore, this paper provides a theoretical basis for designing appropriate catalysts through element doping and heterojunction construction.

Highlights

With the development of society, the greenhouse effect has posed a great threat to human life due to excessive CO2 emission
The equilibrium distance of these two heterojunctions exhibits the feature of van der Waals heterojunction, indicating that a vdW interaction is established between (S-doped) g-C3N4 and BiOBr
It can be seen clearly that the g-C3N4 in both heterojunctions changes from a planar structure to a curved structure, indicating there is an interaction between g-C3N4 and BiOBr

Summary

INTRODUCTION

With the development of society, the greenhouse effect has posed a great threat to human life due to excessive CO2 emission. It can be deduced that appropriate element doping and heterojunction building is fruitful in regulating the electronic structures and improving the photocatalytic performance. BiOBr is deemed to be a prominent candidate for constructing a heterojunction with g-C3N4 It has appropriate bandgap and layered structure where one (Bi2O2) slab is surrounded by the upper and lower chlorine atoms. The effect of sulfur doping on the BiOBr/g-C3N4 heterojunction is investigated by exploring electronic, optical properties, and CO2 reduction reaction. (Han and Sohn, 2005; Yan et al, 2016), which is expressed by the following equation: ΔG ΔH − TΔS + ZPE (1) In this formula, ΔH denotes the energy difference of each reaction step gained from DFT calculation. T represents the temperature at 298.15 K ΔS and ZPE are the change of entropy and zero-point energy, respectively

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT