Direct conversion mechanism from BiOCl nanosheets to BiOF, Bi₇F₁₁O₅ and BiF₃ in the presence of a fluorine resource

Abstract

In this work, we report the facile conversion from BiOCl nanosheets to BiOF, Bi 7 F 11 O 5 and BiF 3 by a novel ion exchange approach, in which the effects of fluorine source, F/Bi molar ratio and reaction medium (ethanol/water) on the products are mainly investigated. A plausible conversion mechanism is proposed to illustrate the formation of BiOF, Bi 7 F 11 O 5 and BiF 3 . Furthermore, the photocatalytic activities of the samples are also investigated. It is amazing that under ultraviolet light irradiation (λ ≤ 420 nm), the activity of the as-formed Bi 7 F 11 O 5 /BiOCl sample is 3.28 times higher than that of BiOCl for the degradation of methyl orange (MO). It is demonstrated that the improved activity is mainly attributed to the formation of Bi 7 F 11 O 5 /BiOCl heterojunction, which has significantly improved the separation and Inspired by the results above, a simple ion exchange approach is developed to convert BiOCl to BiOF, Bi 7 F 11 O 5 and BiF 3 , in which fluoride is mainly employed as the fluorination chemical. A plausible conversion mechanism is proposed and discussed; meanwhile, we have investigated their photocatalytic activities for the degradation of MO. The results show that Bi 7 F 11 O 5 /BiOCl heterojunction shows the The simulations of energy band structures, total and a part of densities of states (T-and P-DOS) were calculated by density functional theory (DFT) as implemented in the CASTEP. The calculations were carried out using the generalized gradient approximation (GGA) level and Perdew-Burke-Ernzerh (PBE) formalism for combination of exchange and correlation function. The cut-off energy is chosen as 18 orbit contributes to both CB and VB of both BiOCl and BiOF. Hu et al. have reportedthat F 2p and O 2p oribits mainly contribute to the VB of Bi 7 F 11 O 5 , and Bi 6p oribit mainly contributes to the CB. 20 Meanwhile, the VB top of BiF 3 is mainly attributed by the F 2p orbital, and the CB bottom is mainly attributed by the Bi 6p, as well as a little of F 2p orbits (Fig. 10f). Comparing BiF 3 with BiOF, it is interesting that F 2p orbit contributes to both CB and VB of BiF 3 , which is different from BiOF. This further confirms that with the increase of fluorine, the band gaps of BiOCl, BiOF, Bi 7 F 11 O 5 and BiF 3 increase, similar to the experimental result above. Conversion mechanismIt is well known that BiOCl, BiOF have tetragonal structures and Bi 7 F 11 O 5 , BiF 3 have monoclinic, cubic structures; respectively. Due to the layer structure of BiOCl, Cl, instead of O, is easily substituted by F. Thus, BiOCl can be converted to BiOF, Bi 7 F 11 O 5 and BiF 3 . In the presence of NH 4 F at V Eth /V w =18/2, BiOCl can be facilely converted to BiOF, Bi 7 F 11 O 5 and BiF 3 . At V Eth /V w =18/2, however, we cannot achieve the complete conversion from BiOCl to phase-pure BiOF while only changing the amount of NH 4 F added. Neverheless, BiOCl can completely convert to phase-pure BiOF at low V Eth /V w ratios (0/20, 2/18, 10/10) at R F =2. According to the experiment results, the schematic ...

Ab Initio Insights into Charge Localization in Bismuth Oxyhalides BiOX (X = F, Cl, Br, I)

“…Generally, the halogens n p orbitals are located at higher energies than O 2p ones, except for X = F due to its higher electronegativity . Varying the halogen size was found to cause an upward shift of valence band maximum (VBM), in accordance with the reduced electronegativity from F to I, and a downward shift of the Bi-dominated conduction band minimum. − Consequently, the band gaps of BiOX compounds decrease from 4.01 for BiOF to 1.85 eV for BiOI (see Table ). Hence, the light absorption is extended from the ultraviolet (for BiOF and BiOCl) to the visible region (for BiOBr and BiOI) …”

Synthesis of BiF3 and BiF3-Added Plaster of Paris Composites for Photocatalytic Applications

“…In another method, by using a novel ion-exchange approach, Kan et al produced pure BiF 3 (JCPDS: 73-1988). Here, the NH 4 F solution was used for the constituent of F while BiOCl was utilized to attain the element of Bi in accordance with the molar ratio (RF = F/Bi) of 8:1 [36]. Below to the molar ratio of 8:1 (RF), the final product consisted of a small amount of Bi 7 F 11 O 5 as an impurity phase [36].…”

“…Here, the NH 4 F solution was used for the constituent of F while BiOCl was utilized to attain the element of Bi in accordance with the molar ratio (RF = F/Bi) of 8:1 [36]. Below to the molar ratio of 8:1 (RF), the final product consisted of a small amount of Bi 7 F 11 O 5 as an impurity phase [36]. Contrary to the above reported studies, in the present method, the ratio of O/F was controlled via a chemical bath of Bi 2 O 3 in a concentrated HF solution.…”

Characterisation of Defluorination Reaction and Solid Electrolyte Interphase in Fluoride-Shuttle Battery Anode MgF2

“…The band gaps of the anodes are over twice as large as typical cathode materials, for example, ~2 eV of CuF 2 21,22 and ~4 eV of BiF 3 23,24 . The large band gap of anode materials results in poor electronic conductivity, making it di cult for F ions to exchange electrons at the interfaces between a metal and a metal uoride inside active anodic materials during the (de) uorination process.…”