DFT+U predictions: The effect of oxygen vacancy on the structural, electronic and photocatalytic properties of Mn-doped BiOCl

In order to provide fundamental understanding and guidance for the effective Mn doping BiOCl and enhanced physicochemical properties derived from the interplay between Mn dopant and oxygen defect, the density functional theory (DFT)+U calculations were adopted to evaluate the effects of Mn doping and oxygen vacancy defects on the geometric structure, electronic property, optical absorption, Mulliken charge and effective mass of BiOCl. The suitable theoretical models were built up and their relaxed structural parameters agree well with the experiment values. It is found that both substitutional and interstitial Mn doping BiOCl not only are energetically favorable but also modify band structures to achieve remarkable optical red-shift of BiOCl, and the substitutional Mn-doped BiOCl show better feasible Mn doping behavior due to the beneficial p-type doping characteristic and p–d hybridization between substitutional Mn and adjacent Bi (or O) atoms in the CB (or VBM). The occurrence of oxygen vacancy in BiOCl crystal significantly influences the neighboring Bi 6p states, forming a capture center of photo-excited electrons in the forbidden band, which enhances the efficient mobility of photo-generated carriers and improves the effective separation rate of electron–hole pairs. The better negative formation energy of substitutional Mn-doped BiOCl with oxygen vacancy (BiOCl:VO) demonstrates thermodynamically its favorable structural stability. Besides, the higher relative ratio value for the effective masses of activated holes and electrons in the Mn-doped BiOCl:VO system implies the lower recombination rate of electron–hole pairs. Furthermore, our calculated optical absorption spectra exhibit that the spectral absorption edge of BiOCl is obviously red-shifted and extends to visible, red and infrared light region by the synergistic effect of oxygen vacancy and Mn dopant. Therefore, we theoretically predicted that Mn-doped BiOCl:VO system is expected to become highly promising semiconductor material applied in photocatalytic field for effectively photochemical decomposition of organics or water splitting under the sunlight irradiation.

► DFT+U study of electronic structures of Mn-doped BiOCl with and without VO defect.
► Occurrence of VO defect has great influence on the Bi 6p states of Mn-doped BiOCl.
► Synergistic effect of VO and Mn dopant leads to an obvious red-shift of BiOCl.
► A p–d hybridization of Bi 6p and Mn 3d states reduces charge carrier recombination.
► Mn-doped BiOCl:VO theoretically has enhanced visible light photocatalytic property.