First Principles Calculation Of Doped CeO₂

Rare earth cerium dioxide?CeO₂?is a typically wide forbidden band semiconductor.Under the condition of different atmosphere and temperature,phase transition of CeO₂ was easy to happen.Thus Ce O₂ was widely applied in ultraviolet?UV?absorption catalysis and pollutant degradation like vehicle exhaust purification and other fields.Because of large forbidden band width for CeO₂,its visible light photo-catalytic efficiency is very low.Thus the energy gaps of bulk CeO₂ and?110?surface configuration were tuned by Ce and O sites doping with the help of the first-principle calculation.This research can give a theoretical guidance to prepare high efficiency visible light catalysis CeO₂ materials in experiment.Firstly,we construct three models such as different concentrations of S-doping model,C/N co-doped model and oxygen vacancy?VO?model under poor-oxygen conditions by doping S,N and C into O site.Through the theoretical simulations,the geometry crystal structure,local energy bands and density of states,optical adsorption spectra were tuned due to the effect of impurities and vacancy defects.Moreover,the VO in the CeO₂ powder was easily formed in the preparation process.For the VO models,the charge density redistribution and oxygen vacancy formation energy were calculated to further mimic the experimental results.The increment of S doping concentration can enhance hydrogen-production efficiency of water decomposition in the visible light irradiation.The visible-light absorption wavelength range was enlarged by single-and co-doping C or N into the O site.Due to local charge balance in co-doping model,the catalytic effect may be more significant.The VO formation energy in bulk CeO₂ was approximate 0.1eV under the poor-oxygen condition and the oxygen atoms easily formed oxygen molecular to escape from the lattice sites,which further confirmed the experiment results.The O 2p?Ce 4f forbidden transitions were transferred to allowed transition because of the local lattice distortion induced by the VO appearance,which increased visible light absorption efficiency.Secondly,Sr/F and Fe/N co-doping model were constructed using metal like Sr or Fe and non-metallic like F or N to occupy Ce and O sites.Different lattice sites occupancy can lead different electronic properties.Some new impurities energy levels appeared in the valence and conduction band in the Sr/F co-doping model.The local impurity levels increased the energy band numbers and UV absorption coefficient.The local charge imbalance in Fe/N co-doped model induced new local states near the intrinsic energy level and spectral red shift phenomenon.The visible light absorption efficiency in Fe/N co-doping model was more than that of single Fe and N doping model,and thus Fe/N co-doping CeO₂ material may have good photo-catalytic performance.Finally,we studied the formation energy of VO,chemical bonds and electronic structure of CeO₂?110?active surfaces because the catalysis effect mainly happened in the crystal surfaces.Compared to the formation energy of VO in bulk CeO₂,this value in the CeO₂?110?surface reduced to-0.7eV,indicating that the VO formed easily in the?110?active surface.The binding force of Ce-O bond near the VO was enhanced by the analysis of covalent.The CeO₂?110?band gap became narrow by calculating the energy gap between the valence and conduction band edges.Therefore,the visible light photo-catalytic activity of CeO₂?110?surface could be enhanced by controlling the VO concentration.