层状Bi2O2CO3可见光催化活性增强机理研究

Enhancing Mechanism of Visible-light Photocatalytic Activity of Bi2O2CO3

基于第一性原理方法,研究Bi2O22+和CO3^2-交替层中氧缺陷生成对晶体结构、能带结构以及光学性质的影响,揭示氧缺陷提高Bi2O2CO3可见光催化活性作用机制。计算结果发现,氧缺陷的存在对Bi2O2CO3的晶胞参数和Bi-O键影响较小,但作为电子施主中心可以向周围原子提供电子,造成Bi2O2CO3电荷分布发生变化,有效减小能带间隙,促进Bi2O2CO3对可见光的吸收,且这种现象随着氧缺陷浓度的升高更加明显。值得注意的是,Bi2O2^2+层和CO32-层氧缺陷的作用不同。CO3^2-层中氧缺陷的形成导致费米能级附近出现缺陷能级,改变了电子的跃迁方式。相较于CO3^2-层,氧缺陷更容易存在于Bi2O2^2+层中,能够更加有效地减小Bi2O2CO3的能带间隙,进一步促进Bi2O2CO3对可见光的吸收。随着Bi2O22+和CO32-层氧缺陷浓度的增加,Bi2O2^2+层氧缺陷的作用愈明显,当浓度达到6.25%时,Bi2O2CO3在可见光区的响应显著增强,有利于提高Bi2O2CO3可见光催化活性。本研究计算结果解释了实验上氧缺陷增强Bi2O2CO3光催化活性现象,并为今后合成其它含氧缺陷Bi基金属氧化物提供理论指导。

This work studied the effect of oxygen vacancies in the Bi2O22+ and CO32- layers on the crystal structures, electronic and optical properties of Bi2O2CO3 with density functional theory(DFT) methods. The cell parameters and Bi-O bond lengths of Bi2O2CO3 before and after the introduction of oxygen vacancies are similar, so the effect of oxygen vacancies on crystal st ructures can be ignored. However,oxygen vacancies as electron donor provide electrons for the surrounding atoms, resulting in the change of charge distributio ns after the introduction of oxygen vacancies. Moreover, oxygen vacancies can reduce the band gap of Bi2O2CO3 and enhance the absorption of visible light. This effect of oxygen vacancies becomes more obvious with the increase of oxygen vacancy concentration. It is notable that the effects of oxygen vacancies in the Bi2O22+ and CO32- layers are different. Once an oxygen vacancy is introduced in the CO32-layer, a defect level appears within the band gap of Bi2O2CO3. The oxygen vacancies in the Bi2O22+ layer are more easily formed in Bi2O2CO3 than in the CO32-layer. Furthermore, the functions of oxygen vacancies in the Bi2O22+ layer for the reduction of band gap and the enhancement of visible light absorption are more effective than that of the oxygen vacancies in the CO32-layer, which is more obvious with the increase of oxygen vacancy concentration. When the concentration of oxygen vacancies in the Bi2O22+ layer reaches to 6.25%, the photoelectric properties of Bi2O2CO3 are the best. The DFT calculation results are consistent with the previous experimental results, and can provide insights into the mechanism for promoting the photoelectric properties of Bi2O2CO3 and other bismuth-based materials.