理论计算研究二维/二维BP/g-C_(3)N_(4)异质结的光催化CO_(2)还原性能

2D/2D Black Phosphorus/g-C_(3)N_(4) S-Scheme Heterojunction Photocatalysts for CO_(2) Reduction Investigated using DFT Calculations

光催化二氧化碳还原成烃类化合物是解决能源短缺和环境污染的重要途径。而构建复合物光催化剂可以有效地解决单一光催化剂的缺点,并且提高二氧化碳还原活性。尽管对复合物光催化剂已经做了很多研究,然而对其活性增强的内在机制还缺乏理论认识。本文采用密度泛函理论计算方法研究了二维/二维BP/g-C_(3)N_(4)复合模型的电子性质和CO_(2)还原反应过程。通过对能带位置和界面电子相互作用的综合分析发现,在BP/g-C_(3)N_(4)异质结中,光生载流子的迁移遵循S型异质结光催化机制。与单一的g-C_(3)N_(4)相比,这种异质结可以实现光生载流子的高效分离并且拥有良好的氧化还原能力。此外,通过对比研究CO_(2)在g-C_(3)N_(4)和BP/g-C_(3)N_(4)还原反应过程发现,异质结使CO_(2)还原反应的最大能垒从1.48 e V降低到1.22e V。因此,BP/g-C_(3)N_(4)异质结在理论上被证明是一种优良的CO_(2)还原光催化剂。这项工作有助于了解BP改性对g-C_(3)N_(4)光催化活性的影响,也为其他高性能CO_(2)还原光催化剂的设计提供理论依据。

Photocatalytic reduction of CO_(2) to hydrocarbon compounds is a promising method for addressing energy shortages and environmental pollution.Considerable efforts have been devoted to exploring valid strategies to enhance photocatalytic efficiency.Among various modification methods,the hybridization of different photocatalysts is effective for addressing the shortcomings of a single photocatalyst and enhancing its CO_(2) reduction performance.In addition,metal-free materials such as g-C_(3)N_(4) and black phosphorus(BP)are attractive because of their unique structures and electronic properties.Many experimental results have verified the superior photocatalytic activity of a BP/g-C_(3)N_(4) composite.However,theoretical understanding of the intrinsic mechanism of the activity enhancement is still lacking.Herein,the geometric structures,optical absorption,electronic properties,and CO_(2) reduction reaction processes of 2D/2D BP/g-C_(3)N_(4) composite models are investigated using density functional theory calculations.The composite model consists of a monolayer of BP and a tri-s-triazine-based monolayer of g-C_(3)N_(4).Based on the calculated work function,it is inferred that electrons transfer from g-C_(3)N_(4) to BP owing to the higher Fermi level of g-C_(3)N_(4) compared with that of BP.Furthermore,the charge density difference suggests the formation of a built-in electric field at the interface,which is conducive to the separation of photogenerated electron-hole pairs.The optical absorption coefficient demonstrates that the light absorption of the composite is significantly higher than that of its singlecomponent counterpart.Integrated analysis of the band edge potential and interfacial electronic interaction indicates that the migration of photogenerated charge carriers in the BP/g-C_(3)N_(4) hybrid follows the S-scheme photocatalytic mechanism.Under visible-light irradiation,the photogenerated electrons on BP recombine with the photogenerated holes on g-C_(3)N_(4),leaving photogenerated electrons and holes in the conduction band of g-C_(3)N_(4) and the valence band of BP,respectively.Compared with pristine g-C_(3)N_(4),this S-scheme heterojunction allows efficient separation of photogenerated charge carriers while effectively preserving strong redox abilities.Additionally,the possible reaction path for CO_(2) reduction on g-C_(3)N_(4) and BP/g-C_(3)N_(4) is discussed by computing the free energy of each step.It was found that CO_(2) reduction on the composite occurs most readily on the g-C_(3)N_(4) side.The reaction path on the composite is different from that on g-C_(3)N_(4).The heterojunction reduces the maximum energy barrier for CO_(2) reduction from 1.48 to 1.22 e V,following the optimal reaction path.Consequently,the BP/g-C_(3)N_(4) heterojunction is theoretically proven to be an excellent CO_(2) reduction photocatalyst.This work is helpful for understanding the effect of BP modification on the photocatalytic activity of g-C_(3)N_(4).It also provides a theoretical basis for the design of other high-performance CO_(2) reduction photocatalysts.