Fe-doped Bi_4O5Br2 visible light photocatalyst: A first principles investigation

This study employed first principles calculations to investigate Fe-doped Bi_4O5Br 2 as a potential photocatalyst with high efficiency. Based on formation energy calculation, the Fe atoms prefer to replace the Bi atoms with coordination bond of 3, and the optimal concentration for Fe-doping is 6.06wt.%. From surface energy calculations, the (101) surface has the lowest surface energy, and therefore the easiest cleavage facet is {101}. The key factors for the improvement of photocatalytic efficiency after Fe-doped Bi_4O5Br2 are estimated as follows. First, the band gap decreases from 2.63eV in pristine case to 2.40eV in 4 Fe-doped Bi_4O5Br2 case, resulting in the photon absorption edge shift to lower energy range and the absorption coefficient increase. Secondly, the work functions decrease from 5.66 eV (pristine) to 4.92eV (4 Fe-doped Bi_4O5Br2), which facilitate the electrons escaping from the surface. Thirdly, the relative mass ratio of photo-induced electrons and holes increases with Fe concentration. Because the Fe 3d impurity states in the forbidden band gap become wider, the relative ratio increased after Fe-doped Bi_4O5Br2. Finally, the Fe doping process introduces more active sites on the surface, which can effectively improve the capacity of target molecules adsorption. Therefore, it is reasonable to believe that Fe-doped Bi_4O5Br2 can effectively improve the photocatalytic efficiency because the abovementioned key factors have tremendously improved. Our work provides a reasonable reason for choosing Fe as a dopant, which can help our experimental work and provide explanation for photocatalytic efficiency improvement.