Realizing nitrogen doping in Bi4Ti3O12 via low temperature synthesis and its enhanced photocatalytic performance

Abstract

Nitrogen doping in Bi-based oxides is highly desired due to the band gap tuning and chemisorption ability engineering. While it is rather difficult to incoporate nitrogen into Bi-based oxides because bismuth could be reduced easily during the high temperature synthesis process. In this work, we design a low temperature synthesis route to dope nitrogen into Bi-based Aurivillius phase compound Bi4Ti3O12 (BIT), which is a process of in-situ reaction, and the nitrogen doped Bi4Ti3O12 (N-BIT) particles have a similar morphology and structure to BIT. The positions of the substitutive nitrogen atoms in the N-BIT crystals are predicted to be at the oxygen atoms between the medial [TiO6] octahedron and the [TiO6] octahedron near the [Bi2O2]2+ layers and a smaller band gap of the N-BIT crystals is resulted by the first-principles calculations. The reduced band gap from BIT of 3.04 eV to N-BIT of 2.80 eV is confirmed by the absorption spectra measurements, which is benefical for charge separation under photoexcitaton. Furthermore, oxygen vacancies formed in the N-BIT sample due to the substitution of oxygen atoms with nitrogen atoms, gernerate more chemisorbed oxygens, which could be excited to the superoxide radicals. Therefore, the photocatalytic activity of N-BIT is enhanced after nitrogen doping.