1. INTRODUCTION
In the past few decades, increasing concerns had been paid for energy
crisis and environmental pollution issues,
and
photocatalysis technology, as a promising route for renewable energy
development and environmental governance, has drawn more and more
attentions[1]. BiOBr, was deemed as the most
promising photocatalyst due to the special structure-dependent
photocatalytic performance, excellent chemical stability and
environmental-friendly quality[2], it possessed a
lamellar structure, which can offer enough space for polarizing the
corresponding atoms and orbitals and provide self-built internal
electric field (IEF), and consequently, obtaining that the induced
dipole could accelerate efficiently the separation and migration of
photoinduced electron-hole
(e- -h +) pairs,
improving the photocatalytic performance[3-5].
More importantly, BiOBr shows an appropriate indirect band gap, implies
that photogenerated e- must cross a certaink- space to be emitted to CB, further to prevent the recombination
rates of photoexcitede- -h +pairs[5,
6]. Nevertheless, there exist low quantum efficiency and fast
photoexcitede- -h +pairs
recombination rates as the “bottleneck” for satisfying with the
requirement of practical applications[7, 8].
Therefore, it is rather critical to explore novel strategies to improve
the photocatalytic performance of BiOBr.
In recent years, domestic and foreign scientists based on the basic
principles of semiconductor photocatalysis, from three aspects of
expanding light absorption, improving carrier separation efficiency and
enhancing surface interaction to strengthen the photocatalytic
reaction[9], and among the normal modification
strategies, the construction of doping
systems[10-15] is one of the most representative
ways to enhance visible-light response and improve photocatalytic
activity of BiOBr.
TMs
doping may induce potential electron traps to prolong the lifetime of
photoexcited carriers and introduce magnetic feature, as well as change
energy band structure to increase light absorption ability and adjust
the redox potentials, thus TMs-doped BiOBr used to obtain high
photocatalytic activity[16]. For instances, Wang
et al. adopted double self-assembly method to successfully synthesize
Ti-doped BiOBr photocatalyst with more superior photocatalytic activity
than undoped BiOBr in terms of degrading RhB, attributing to the
synergetic effect of larger specific surface area, unique microspheres
structure and Ti doping[10]. Jiang et al. reported
a Ti doping and Ag decorating BiOBr microsphere with excellent
photocatalytic activity and durability[11]. For
Fe-doped BiOBr photocatalysts, Fe ions played key role for doping effect
in the self-assembly process of hollow microspheres, revealing high
photocatalytic and electrochemical
performance[13]. Recently, Guo et al. utilized
experimental and DFT methods to investigate Zn-doped BiOBr system, and
theoretical calculations reveal that there still maintain the advantages
of indirect band gap after the introduction of Zn, and Zn 3d states with
deeper energy levels could induce negligible effect on VB and CB of
Zn-doped BiOBr system[15].
Furthermore, DFT calculations were
adopted to evaluate the influence of Co doping on the electronic
structure of BiOBr by Xia et al., revealing that there is an additional
energy level introduced into the forbidden band of Co-doped BiOBr
system[17]. Based on above-mentioned results, it
could be inferred that the doping of 3d TMs should affect the electronic
and optical properties as well as macro-performances of BiOBr to a
certain extent.
However, there are few reports about exploring a series of 3d TMs doped
modulation electronic structures to influence the micro- and macro-
properties as well as both correlations and redox potentials of BiOBr.
Motivated by the previous experimental and theoretical
achievements[15-18], we investigate carefully and
systematically the electronic structure of 3d TMs-doped BiOBr using
DFT+U calculations. Given our theoretical findings, it is to clarify
that how the electronic structure influence visible light absorption and
provide possible explanations for previous experimental observations,
more importantly, also could provide significative guidance to
synthesize BiOBr-based materials with highly photocatalytic activity.