First principles study on band gap modulation of TiO2 (112) surface for enhancing optical properties

Abstract

Anatase TiO2 is widely used in solar photocatalysis. However, the optical properties are limited by its ability to capture visible light and its poor activity. In order to obtain ideal material properties, GGA + U method based on density functional theory is used to study the electronic structure and optical properties of anatase phase TiO2 and its (112) surface and Cr and Co-doped TiO2 (112) surface. The results show that the transition metal Cr-doped system is more stable than the Co-doped system. The four systems exhibit semiconducting properties. The indirect band gap value of intrinsic TiO2 is 3.245 eV, and the impurity bands appear in the spin-up energy bands after Cr, Co doping. The impurity states of the doped system spin split, which transforms the non-magnetic semiconductor into a semiconductor with net magnetic moments of 2 μB and 3 μB, respectively. In addition, the Cr, Co-doped systems show excellent optical properties, and the absorption coefficients are red-shifted in the range of (0–3 eV) with higher optical absorptivities. Through the investigation, it is evident that doping results in different degree of band gap change. As the conduction band moves towards the lower energy level, an impurity band is generated near the Fermi level. The presence of the impurity band fundamentally alters the initial transition mode of the electron, making the transition require less energy, thus enabling enhanced optical properties. The doping system enhances the lepton threshold of electrons and light absorption by changing the mode of inter-band leaps and decreasing the reflectivity, making them candidates in the field of optoelectronics and photocatalysis.