X/g-C_(3)N_(4)(X=g-C_(3)N_(4)、AlN及GaN)异质结光催化活性的理论研究

Theoretical Study on Photocatalytic Activity of X/g-C_(3)N_(4)(X=g-C_(3)N_(4),AlN and GaN)Heterojunction

本文采用基于密度泛函理论的第一性原理平面波超软赝势方法,研究了单层g-C_(3)N_(4)以及X/g-C_(3)N_(4)(X=g-C_(3)N_(4)、AlN及GaN)异质结的稳定性、电子结构、功函数及光学性质。结果表明,X/g-C_(3)N_(4)异质结的晶格失配率和晶格失配能极低,说明X/g-C_(3)N_(4)具有优异的稳定性。与单层g-C_(3)N_(4)相比,X/g-C_(3)N_(4)的带隙均减小,态密度的波峰和波谷均大幅提高且出现了红移现象,处于激发态的电子数量增加,使得电子跃迁变得更为容易,表明构建异质结有利于提高体系对可见光的响应能力。此外,X/g-C_(3)N_(4)的功函数均减小且在界面处形成了内建电场,有效抑制了光生电子-空穴对的复合,这对载流子的迁移以及光催化能力的提高大有裨益。其中,GaN/g-C_(3)N_(4)的功函数最小,在界面处存在电势差形成了内建电场且红移现象最明显,可推测GaN/g-C_(3)N_(4)的光催化性能最好。因此,本文提出的构建异质结是提高体系光催化活性的有效手段。

The stability,electronic structures,work function,and optical properties of single-layer g-C_(3)N_(4) and X/g-C_(3)N_(4)(X=g-C_(3)N_(4),AlN and GaN)heterostructures were investigated using plane-wave density functional theory with ultra-soft pseudopotentials.The results show that the lattice mismatch ratio and lattice mismatch energy of X/g-C_(3)N_(4) heterojunction are very low,indicating that X/g-C_(3)N_(4) heterojunction has excellent stability.Compared with the single-layer g-C_(3)N_(4),the bandgap of the X/g-C_(3)N_(4) all reduces,and the peaks and troughs of the density of states greatly improves.At the same time,X/g-C_(3)N_(4) has a redshift,which leds to an increase in the number of electrons in the excited state,making electronic transitions easier.It shows that the heterojunction is beneficial to improves the response-ability of the system to visible light,and effectively improves the photocatalytic activity of the system.Further calculations show that the work function of X/g-C_(3)N_(4) reduces and a built-in electric field is formed at the interface,which inhibits the recombination of photo-generated electron-hole pairs.This is of great benefit to the migration of carriers and the improvement of photocatalytic ability.Among them,the GaN/g-C_(3)N_(4) heterojunction has the smallest work function,the potential difference at the interface formed a built-in electric field and the redshift is the most obvious.It can be inferred that the GaN/g-C_(3)N_(4) heterojunction has the best photocatalytic activity.Therefore,the heterojunction proposed in this paper is an effective means to improve the photocatalytic activity of the system.