Spatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splitting

Abstract

The electronic structures and photocatalytic properties of bismuth oxyhalide bilayers (BiOX1/BiOX2, X1 and X2 are Cl, Br, I) are studied by density functional theory. Briefly, their compositionally tunable bandgaps range from 1.85 to 3.41 eV, suitable for sun-light absorption, and all bilayers have band-alignments good for photocatalytic water-splitting. Among them, heterogeneous BiOBr/BiOI bilayer is the best as it has the smallest bandgap. More importantly, photo-excitation of BiOBr/BiOI leads to electron supply to the conduction band minimum with localized states belonging mainly to bismuth of BiOBr where the H+/H2 half-reaction of water-splitting can be sustained. Meanwhile, holes generated by such photo-excitation are mainly derived from the iodine states of BiOI in the valence band maximum; thus, the O2/H2O half-reaction of water splitting is facilitated on BiOI. Detailed band-structure analysis also indicates that this intriguing spatial separation of photo-generated electron-hole pairs and the two half-reactions of water splitting are good for a wide photo-excitation spectrum from 2–5 eV; as such, BiOBr/BiOI bilayer can be an efficient photocatalyst for water-splitting, particularly with further optimization of its optical absorptivity.

First-Principles Study of Optoelectronic Properties of the Noble Metal (Ag and Pd) Doped BiOX (X = F, Cl, Br, and I) Photocatalytic System

“…Many studies have been further attempted to reinforce the photocatalytic activity of BiOX systems, such as heterostructure designs of BiOBr/AgBr, BiOCl/BiO 3 , BiOBr/BiOI [24][25][26][27][28][29] and some specific impurity doping [30][31][32][33]. Dai et al proved that the photoluminescence, photocatalytic activity, and strong optical properties of Eu 3+ -doped BiOX (X = F, Cl, Br, and I) could be enhanced using the density functional theory (DFT) method [30].…”

Novel Three-Dimensional Flowerlike BiOBr/Bi2SiO5 p–n Heterostructured Nanocomposite for Degradation of Tetracycline: Enhanced Visible Light Photocatalytic Activity and Mechanism

“…So far, BiOBr has been widely investigated in the field of CO 2 reduction, hydrogen production, and photocatalytic degradation of organic pollutants, due to its excellent properties including narrow band gap (∼2.8 eV), chemical stability, and easy preparation. − Coupling BiOBr with wide bandgap semiconductor to construct a heterojunction photocatalyst is believed to be an effective and practicable approach for enhancing photocatalytic activity. As a p-type semiconductor, BiOBr is also selected to couple with n-type semiconductors, such as BiOBr/Bi 2 O 2 CO 3 , BiOBr/BiPO 4 , and BiOBr/ZnO, and they exhibit enhanced photocatalytic activities. − Furthermore, BiOBr and Bi 2 SiO 5 have similar crystal structure.…”

Advanced Two-Dimensional Heterojunction Photocatalysts of Stoichiometric and Non-Stoichiometric Bismuth Oxyhalides with Graphitic Carbon Nitride for Sustainable Energy and Environmental Applications

“…The approach of coupling two semiconductors to form a layered structure with an interfacial electric field is particularly promising since this enhances the possibility of satisfying the band alignment requirements for water splitting through the band structure, and subsequently boosts the separation between the photogenerated electron-hole pairs. In this context, heterolayers of BiOX 1 /BiOX 2 (with X 1 and X 2 being different halides) are plausibly superior in comparison to homogeneous BiOX bilayers owing to the possibility of heterojunction induced separation of photogenerated electron-hole pairs [241]. For instance, a ternary heterojunction between BiOI, BiOCl and g-C 3 N 4 with different weight ratios was fabricated through the precipitation technique, among which BiOI(50)-BiOCl(30)/g-C 3 N 4 (20) exhibited enhanced photodegradation of acid orange 7 (10 ppm, 97% in 140 min) under visible light irradiation in comparison to pristine and other binary/ternary heterojunction counterparts.…”