Iron-doped bismuth oxybromide material, preparation method thereof, membrane electrode and application thereof

Abstract

The application discloses a kind of iron-doped bismuth oxybromide materials and preparation method thereof, membrane electrode and application, belong to electrochemical ion exchange and nuclear energy wastewater treatment field, the iron-doped bismuth oxybromide material is prepared by hydrothermal method in the application, it is made into slurry with conductive carbon black, polyvinylidene fluoride, coated on stainless steel wire net to construct membrane electrode, applied to three-chamber electrically-controlled amphoteric ion selective permeation system, and steady magnetic field is applied on both sides of system, construct electromagnetic field coupling ion permeation system, the lattice distortion induced by iron doping and the spin polarization effect driven by external magnetic field are used in the application, synergistically reduce ion migration energy barrier, improve target ion permeation flux, efficient, high selectivity synchronous extraction of cesium bromide is realized, under the condition of magnetic-electric coupling, target ion permeation flux is significantly improved compared with original bismuth oxybromide material and pure electric field mode, has wide application prospect in the field of nuclear waste liquid treatment and salt lake brine resource recovery.

Description

Technical Field

[0001] This invention relates to the field of electrochemical ion exchange and nuclear wastewater treatment technology, specifically to an iron-doped bismuth oxybromine material and its preparation method, membrane electrode and application. Background Technology

[0002] Ion separation technology is a core support for membrane science, environmental engineering, and resource recycling, and is crucial in applications such as the high-value utilization of salt lake brine, radioactive wastewater treatment, and the recovery of high-value elements. The coexistence of multiple ions in actual water bodies necessitates the simultaneous separation and enrichment of paired anions and cations. However, traditional membrane separation technologies such as reverse osmosis, nanofiltration, and electrodialysis rely on static effects like pore size sieving and electrostatic repulsion. In complex, high-salinity environments, these technologies are susceptible to competition from ions, membrane fouling, and flux decay, making it difficult to achieve dynamic, reversible, and selective separation of paired ions, thus presenting inherent application bottlenecks.

[0003] Electro-controlled ion exchange (ESIX) technology leverages the electro-driven oxidation / reduction reactions of electroactive materials to achieve reversible ion insertion and release, overcoming diffusion mass transfer limitations. It boasts advantages such as high selectivity, electroregeneration, and low secondary pollution, making it a preferred alternative to traditional technologies. However, existing ESIX systems are mostly limited to single-ion separation and cannot meet the demands of simultaneous selective transport of paired ions in real-world scenarios. For example, bismuth oxybromine (BiOBr) is problematic due to its affinity for Br₂. - Its excellent selectivity makes it a typical material for anion separation. Although the electrically controlled zwitterion-selective system constructed based on it has verified the Cs... + The feasibility of simultaneous separation with Br- is limited by the low conductivity of BiOBr itself, resulting in slow charge transport and ion migration kinetics, insufficient separation flux, and the trade-off between high selectivity and high flux remains unresolved.

[0004] In recent years, numerous studies have explored the use of metal ion doping to modulate the lattice and electronic structure of BiOBr, thereby enhancing its conductivity and electroactivity. However, modification of the material itself alone is insufficient to completely eliminate the energy barrier hindering ion migration. External physical field manipulation offers a new approach to overcoming this bottleneck; for example, magnetic field effects have been proven to influence electronic spin states and accelerate interfacial mass transfer. However, current magnetic field-assisted strategies are largely limited to redox reactions such as electrocatalysis and water electrolysis. How to deeply integrate the magnetic field-induced "spin polarization effect" with the ESIX membrane separation system, and utilize electromagnetic field coupling to synergistically reduce the binding energy during ion insertion / release, remains a gap in the technological field both domestically and internationally.

[0005] In summary, existing technologies are insufficient to meet the practical requirements for efficient, synchronous, and selective separation of target cations and anions in complex ionic environments. It is necessary to develop a novel ESIX membrane separation technology that combines optimization of the material's inherent properties with synergistic control of the external field to overcome the inherent trade-off between flux and selectivity, while avoiding side reactions, reducing system energy consumption, and promoting the industrial application of electrically controlled membrane ion separation technology in the fields of resource recovery and wastewater treatment. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems of slow ion migration rate, low permeation flux, and difficulty in synchronous and efficient separation of paired ions in existing ESIX technology.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: On the one hand, the present invention provides an iron-doped bismuth oxybromine material. The material uses bismuth oxybromine as a matrix, and forms a doped structure by replacing bismuth ions in the matrix lattice with iron ions. The iron doping causes the bismuth oxybromine lattice to shrink, resulting in lattice distortion in the material, thereby improving the charge transport performance and electrochemical activity of the material. The material maintains the tetragonal crystal phase structure of bismuth oxybromine and no new phase is formed. Iron is uniformly distributed in the bismuth oxybromine lattice in ionic form, wherein the mass percentage doping amount of iron is 0.1~1.0wt%, preferably 0.5wt%.

[0008] On the other hand, the present invention provides a method for preparing the above-mentioned iron-doped bismuth oxybromine material, comprising the following steps: S1, dispersing a bismuth source and a bromine source in a solvent to obtain solution A; S2, dispersing an iron source in a solvent to obtain solution B; S3, mixing solution A and solution B and stirring to obtain mixed solution C; S4, subjecting solution C to a hydrothermal reaction; S5, collecting the precipitate after the solution C has cooled to room temperature; S6, washing and drying the precipitate collected in S5 to obtain the iron-doped bismuth oxybromine material.

[0009] Preferably, the molar ratio of the bismuth source, bromine source, and iron source is 1:1:(0.005~0.054). The bismuth source is... The bromine source is KBr, and the iron source is... The solvent is deionized water.

[0010] Preferably, in S3, the mixture is stirred and ultrasonically treated at room temperature, and the pH value is adjusted to 6-7 after stirring. In S4, the hydrothermal reaction is carried out at a temperature of 150-170°C.

[0011] In another aspect, the present invention provides a membrane electrode comprising a porous conductive substrate and an electroactive material covering the porous conductive substrate, wherein the electroactive material comprises the aforementioned iron-doped bismuth oxybromine material.

[0012] Preferably, the electroactive material comprises an iron-doped bismuth oxybromine material, conductive carbon black, and a binder in a mass ratio of 8:1:1, which are mixed and then a dispersant is added to form a slurry, which is then coated onto the porous conductive substrate.

[0013] Preferably, the adhesive is polyvinylidene fluoride, the dispersing solvent is N-methylpyrrolidone, and the porous conductive substrate is steel wire mesh.

[0014] Finally, the present invention also provides an application of a membrane electrode for regulating the migration of cesium and bromide ions under the action of magnetoelectric field coupling.

[0015] Specifically, the membrane electrode is used in an electromagnetic field-coupled ion permeation system, comprising a multi-chamber permeation tank, at least two membrane electrodes, an electric field application device, and a steady-state magnetic field generator. The multi-chamber permeation tank includes at least a feed chamber and a receiving chamber. The feed chamber contains a mixed solution containing target ions (cesium ions and bromide ions) and competing ions. The receiving chamber contains a low-concentration initial solution of cesium bromide. The membrane electrodes are positioned between the feed chamber and the receiving chamber and are connected to the electric field application device as positive and negative electrodes, respectively. The steady-state magnetic field generator is positioned on both sides of the permeation tank, providing a steady-state magnetic field parallel to the ion migration direction.

[0016] Preferably, the multi-chamber permeation tank has a three-chamber structure, including a left feed chamber, a middle receiving chamber, and a right feed chamber. Two iron-doped bismuth oxybromine membrane electrodes are respectively placed between the left feed chamber and the receiving chamber, and between the right feed chamber and the receiving chamber. The electric field application device is an electrochemical workstation, and the applied pulse potential is alternately applied at +1.0V and -1.0V, with a single pulse duration of 30~90s. Under the action of the pulsed electric field, the membrane electrodes on both sides are alternately in the oxidized state and the reduced state: the membrane electrode in the reduced state performs the cation attraction and insertion-anion repulsion and release process; the membrane electrode in the oxidized state simultaneously performs the cation repulsion and release-anion attraction and insertion process, thereby synergistically realizing the directional migration and enrichment of cations and anions. The steady-state magnetic field generating device is a permanent magnet or an electromagnetic coil with a magnetic induction intensity of 30~100mT, provided by the permanent magnet or electromagnetic coil to construct a magnetoelectric field coupled ion permeation (EMIP) system.

[0017] Under the influence of a magnetic field, the spin magnetic moments of unpaired iron ions in iron-doped bismuth oxybromine materials tend to align in an ordered manner along the magnetic field direction, forming directional magnetic dipole moments. This spin ordering alters the electron cloud distribution around the iron ions, reducing the transition state energy during the insertion and release reactions of the target ions and effectively lowering the activation energy barrier for ion migration. Simultaneously, the applied magnetic field induces micro-convection in the electrolyte solution through magnetohydrodynamic effects, reducing mass transfer resistance at the membrane electrode interface and accelerating the mass transfer rate of target ions from the solution to the membrane electrode interface. These two effects, combined with the electric field drive, synergistically enhance the directional migration rate and permeation flux of cesium and bromide ions.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention replaces bismuth ions in the bismuth oxybromine lattice with iron ions, utilizing the difference in ionic radii to induce lattice shrinkage and distortion. While maintaining the integrity of the original tetragonal bismuth oxybromine crystal structure, this effectively enhances the material's charge transport capability and electrochemical activity. Iron is uniformly distributed in the lattice as ions, without introducing new phases, resulting in a stable material structure and uniform, controllable doping effects.

[0019] 2. The electro-controlled zwitterionic selective permeation system constructed in this invention utilizes the bifunctional electrochemical response characteristics of iron-doped bismuth oxybromine material to cesium and bromide ions. Under the drive of a pulsed electric field, it realizes the alternating oxidation-reduction of the membrane electrodes on both sides, and synergistically completes the directional migration and synchronous enrichment of cations and anions, breaking through the inherent limitation of existing electro-controlled ion exchange technology that can only handle a single type of ion.

[0020] 3. This invention innovatively introduces a steady-state magnetic field into an electrically controlled ion permeation system. It utilizes the characteristic that the spin state of iron ions in iron-doped materials changes from disordered to ordered under the action of a magnetic field, forming a directional magnetic dipole moment. Combined with the auxiliary driving force of the Lorentz force experienced by the target ion during migration, it synergistically reduces the migration energy barrier during ion insertion and release from two dimensions: the intrinsic properties of the material and the dynamics of the external field. Without changing the overall structure of the system, it significantly improves the directional migration rate of ions and the permeation flux.

[0021] 4. This invention employs a hydrothermal method for one-step synthesis of iron-doped bismuth oxybromine materials. The raw materials are widely available, the preparation process is simple, and the process conditions are mild. All raw materials used are conventional chemical reagents, requiring no complex equipment or harsh environments, which facilitates large-scale production. The membrane electrode preparation also utilizes a slurry coating process, which is convenient and highly repeatable.

[0022] 5. This invention can be effectively applied to the highly selective removal of radioactive cesium from nuclear wastewater and the efficient recovery of bromine resources from salt lake brine, achieving the dual goals of environmental governance and resource utilization. It has significant practical application value and industrialization potential in the fields of nuclear wastewater treatment and salt lake resource development. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an electromagnetic field coupled ion permeation system. Figure 2 The images show the XRD patterns of BiOBr and Fe-BiOBr, where (a) is the full XRD pattern of BiOBr and Fe-BiOBr; and (b) is a magnified view of the 30°–35° region. Figure 3 The images show the SEM, TEM, and EDS spectra of BiOBr and Fe-BiOBr, where (a) and (b) are SEM images of BiOBr; (c) is an HRTEM image of BiOBr; (d) and (e) are SEM images of Fe-BiOBr; (f) is an HRTEM image of Fe-BiOBr; and (g) to (j) are EDS surface distribution diagrams of the four elements Bi, Br, O, and Fe in Fe-BiOBr, respectively. Figure 4 The figures show the performance of Fe-BiOBr film electrodes with different Fe doping ratios (0.3wt%, 0.5wt%, 0.7wt%), where (a) represents the target cation Cs. + Concentration curves of the feed solution and receiver solution over time; (b) shows the target anion Br. - (c) shows the corresponding concentration change curve; (d) shows the competing cation K. + Concentration change curves; (d) shows the competing anion SO42-. 2- Concentration change curve; Figure 5 The figures show the CV curves, EIS curves, and Fourier transform plots of the BiOBr / Pt and Fe-BiOBr / Pt membrane electrodes, where (a) is the cyclic voltammetry (CV) curve of the BiOBr / Pt and Fe-BiOBr / Pt membrane electrodes in 0.1 M CsBr solution; (b) is the electrochemical impedance spectroscopy (EIS) Nyquist plot, with the inset showing a magnified high-frequency region; (c) is the Fourier transform AC voltammetry (FT-ACV) forward scan harmonic current plot; and (d) is the FT-ACV reverse scan harmonic current plot. Figure 6 The fluxes of target ions and competing ions in the BiOBr and Fe-BiOBr membrane electrode systems are given, where (a) represents the flux of the target cation Cs in the two systems. + Concentration curves of the feed solution and receiver solution over time; (b) shows the target anion Br. - Concentration change curves; (c) shows the competing cation K + Concentration versus time curve; (d) shows the competing anion SO42-. 2- Concentration versus time curve; Figure 7 The fluxes of target ions and competing ions in the Fe-BiOBr membrane electrode system under whether an external magnetic field is applied are given, where (a) represents the fluxes of Cs under both pure electric field and magnetoelectric coupling (EMIP) conditions. + Concentration curves of Br in the feed solution and receiver solution over time; (b) shows the concentration curves of Br. - (c) shows the corresponding concentration change curve; (d) shows the competing cation K. + The concentration-time curves verify that the magnetic field has no significant effect on competing ions; (d) shows the competing anion SO42-. 2- Concentration versus time curve; Figure 8 The selectivity and stability of cations and anions in the Fe-BiOBr membrane electrode under an external magnetic field system are evaluated, where (a) represents the effect of a pure electric field on the cations (Cs) in the EMIP system. + K + Na + (a) A comparative histogram of separation coefficients; (b) A histogram of the separation coefficients for the anion (Br) - Cl - SO4 2- NO3 - (c) A comparative bar chart of separation coefficients; (d) A comparative bar chart of the stability of CsBr flux in the receiving chamber during five consecutive cyclic permeation experiments; (e) A comparative bar chart of the stability of the electrochemical active area (CV area) of the Fe-BiOBr / Pt electrode after 100 to 900 CV cycles. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in specific embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art.

[0025] The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0026] This invention provides an iron-doped bismuth oxybromine material and its preparation method, a membrane electrode made from the material, and the application of the membrane electrode in regulating the migration of cesium ions and bromide ions under the action of magnetoelectric field coupling.

[0027] The first part is an iron-doped bismuth oxybromine material. The material uses bismuth oxybromine as a matrix, and forms a doped structure by replacing bismuth ions in the matrix lattice with iron ions. The iron doping causes the bismuth oxybromine lattice to shrink, resulting in lattice distortion in the material, thereby improving the charge transport performance and electrochemical activity of the material. The material maintains the tetragonal crystal phase structure of bismuth oxybromine, and no new phase is formed. Iron is uniformly distributed in the bismuth oxybromine lattice in ionic form, wherein the mass percentage doping amount of iron is 0.1~1.0wt%, for example, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, preferably 0.5wt%.

[0028] Specifically, it is prepared through the following steps: S1, dispersing bismuth and bromine sources in a solvent to obtain solution A; S2, dispersing an iron source in a solvent to obtain solution B; S3, mixing solution A and solution B and stirring to obtain mixed solution C; S4, subjecting solution C to a hydrothermal reaction; S5, collecting the precipitate after solution C has cooled to room temperature; S6, washing and drying the precipitate collected in S5 to obtain iron-doped bismuth oxybromine material.

[0029] The bismuth source selected is bismuth pentahydrate nitrate. Potassium bromide (KBr) was chosen as the bromine source, and ferric nitrate nonahydrate was chosen as the iron source. The solvent chosen is deionized water.

[0030] Bismuth nitrate pentahydrate It possesses good water solubility and high reactivity, enabling it to rapidly release bismuth ions in aqueous solution, providing a stable and sufficient supply of bismuth. Potassium bromide (KBr) also exhibits high water solubility, ensuring the full release of bromide ions and providing a stable bromine source environment for the reaction. Ferric nitrate nonahydrate... It can efficiently release ferric ions in aqueous solution. The ferric ions replace bismuth ions in the matrix lattice to form a doped structure. The iron doping causes the bismuth oxybromine lattice to shrink, causing lattice distortion in the material, thereby improving the charge transport performance and electrochemical activity of the material. The resulting material still maintains the tetragonal crystal phase structure of bismuth oxybromine, and no new phase is generated.

[0031] The molar ratio of bismuth source, bromine source and iron source is 1:1:(0.005~0.054). For example, it can be 1:1:0.005, 1:1:0.0027, 1:1:0.054, etc., so that the mass percentage doping amount of iron is controlled within 0.1~1.0wt%.

[0032] S3 is subjected to ultrasonic treatment at room temperature for 1 hour, and the pH value is adjusted to 6-7 after stirring. This can be achieved by adding sodium hydroxide aqueous solution.

[0033] The hydrothermal reaction of S4 is carried out at a temperature of 150–170°C, preferably 160°C for 24 hours.

[0034] The second part is a membrane electrode made of iron-doped bismuth oxybromine material, which includes a porous conductive substrate and an electroactive material covering the porous conductive substrate.

[0035] The electroactive material comprises iron-doped bismuth oxybromine material (8:1:1 by mass), conductive carbon black, and a binder. After mixing, a dispersant is added to form a slurry, which is then coated onto a porous conductive substrate. The binder is preferably polyvinylidene fluoride (PVDF), the dispersant is N-methylpyrrolidone (NMP), and the porous conductive substrate is a wire mesh.

[0036] The third part describes the application of membrane electrodes made of iron-doped bismuth oxybromine material in regulating the migration of cesium and bromide ions under the action of magnetoelectric field coupling.

[0037] Specifically, an electromagnetic field-coupled ion permeation system is first constructed, including a multi-chamber permeation cell, at least two membrane electrodes, an electric field application device, and a steady-state magnetic field generator. The multi-chamber permeation cell has a three-chamber structure, including a left feed chamber, a middle receiving chamber, and a right feed chamber. Two iron-doped bismuth-oxybromine membrane electrodes are placed between the left feed chamber and the receiving chamber, and between the right feed chamber and the receiving chamber, respectively, and are connected to the electric field application device as positive and negative electrodes. The feed chamber is filled with a mixed solution containing cesium ions, bromide ions, and competing ions. The receiving chamber is filled with a low-concentration cesium bromide initial solution. The steady-state magnetic field generator is located on both sides of the permeation cell, providing a steady-state magnetic field parallel to the ion migration direction.

[0038] The electric field application device is an electrochemical workstation, with applied pulse potentials alternately ranging from +1.0V to -1.0V, and a single pulse duration of 30–90 s. Under the action of the pulsed electric field, the membrane electrodes on both sides alternately exist in oxidized and reduced states: the membrane electrode in the reduced state performs a cation attraction and insertion process followed by an anion repulsion and release process; the membrane electrode in the oxidized state simultaneously performs a cation repulsion and release process followed by an anion attraction and insertion process, thereby synergistically achieving the directional migration and enrichment of cations and anions. The steady-state magnetic field generator is a permanent magnet or electromagnetic coil, with a magnetic induction intensity of 30–100 mT, provided by the permanent magnet or electromagnetic coil to construct a magnetoelectric field coupled ion permeation (EMIP) system. Under the action of the magnetic field, the spin state of iron in the iron-doped bismuth oxybromine material changes from disordered to ordered, inducing spin polarization of the Fe-BiOBr membrane electrode, changing the interfacial electric field distribution, reducing the ion migration energy barrier, and significantly improving the directional migration rate and permeation flux of cesium ions and bromide ions.

[0039] The following will illustrate this with specific implementation examples and test cases.

[0040] Example 1 This embodiment details the preparation process and physical characterization results of the iron-doped bismuth oxybromine material (Fe-BiOBr), the core material of this invention.

[0041] Preparation steps: At room temperature, 4 mmol Disperse approximately 1.940 g of KBr and 4 mmol of KBr (approximately 0.476 g) in 30 mL of deionized water and stir thoroughly until dissolved. Separately, dissolve 0.044 g of KBr. Iron source solution was prepared by dissolving the iron in 30 mL of deionized water. The two solutions were mixed, stirred, and sonicated at room temperature for 1 h to ensure thorough and uniform dispersion of the components. Subsequently, NaOH solution was added dropwise to adjust the pH of the mixture to 6-7, during which a pale yellow precipitate appeared. The mixture was transferred to a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene (PTFE), sealed, and placed in an oven at 160°C for 24 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was centrifuged, washed three times each with deionized water and anhydrous ethanol, and then vacuum dried at 60°C for 12 h to obtain Fe-BiOBr powder.

[0042] Physical characterization results: XRD characterization of BiOBr and Fe-BiOBr was performed, and the results are as follows: Figure 2 As shown in (a) of the diagram. The diffraction peaks at 2θ of 21.7°, 25°, 31.5°, 33°, 39.3°, 44.6°, 46.1°, 50.5°, 53.2°, 56°, and 57.1° correspond to the (002), (101), (102), (003), (112), (004), (200), (104), (211), (114), and (212) crystal planes of the BiOBr standard card, respectively. This indicates that the Fe-BiOBr prepared by the hydrothermal method is a typical tetragonal phase, and no new characteristic peaks appear, indicating that the introduction of Fe did not change the basic crystal structure of BiOBr. Figure 2 The magnified view in (b) shows that the diffraction peaks shift to higher diffraction angles after Fe doping. This is due to Fe... 3+ (Ionic radius approximately 0.0645 nm) Substituted Bi 3+ After the ionic radius is approximately 0.103 nm, the surrounding lattice shrinks, causing lattice distortion, thus confirming that Fe has been successfully incorporated into the BiOBr lattice.

[0043] SEM and HRTEM characterization results are as follows: Figure 3As shown in (a), (b), (d), and (e) of the image, both BiOBr and Fe-BiOBr exhibit a nanoflower-like structure formed by stacked nanosheets, indicating that Fe doping did not alter the macroscopic morphology of BiOBr. HRTEM images of BiOBr are shown in the image. Figure 3 As shown in (c), the lattice spacing is 0.281 nm, while the lattice spacing of Fe-BiOBr is as follows: Figure 3 As shown in (f), the nm density decreased to 0.277 nm, directly confirming the Fe... 3+ Replace Bi 3+ The resulting lattice contraction. EDS elemental distribution map, as shown. Figure 3 As shown in (g)~(j), it indicates that the four elements Bi, Br, O and Fe are uniformly distributed in Fe-BiOBr, further confirming the effective preparation of the target material.

[0044] Comparative Example 1 This comparative example investigated the effect of iron doping ratio on membrane performance by varying the mass fraction (0.3, 0.5, and 0.7 wt%) of ferric nitrate nonahydrate during hydrothermal synthesis. Under optimized pulse voltage conditions (-1 / 1 V, 60 s), as... Figure 4 As shown, the membrane's permeability first increases and then decreases with increasing iron content, reaching its optimal level at an iron doping concentration of 0.5 wt%. At this point, the concentrations of cesium ions and bromide ions in the receiving chamber are respectively from... Upgraded to and The corresponding permeation flux is and Further increasing the iron doping concentration leads to a decrease in membrane performance; therefore, 0.5 wt% was determined to be the optimal iron doping ratio. Throughout all tests, the concentrations of potassium and sulfate ions remained essentially stable, confirming the excellent ion selectivity of this membrane system.

[0045] Example 2 This embodiment analyzes the influence of Fe doping on the electrochemical activity of BiOBr through systematic electrochemical performance testing.

[0046] In 0.1 M CsBr solution, with Cyclic voltammetry (CV) tests were performed on the BiOBr / Pt and Fe-BiOBr / Pt film electrodes at the specified scan rates. The results are as follows: Figure 5 As shown in (a), the CV blocking area of ​​Fe-BiOBr is much larger than that of pure BiOBr, and two pairs of clear redox peaks appear, corresponding to Cs. + and Br - The insertion and extraction processes indicate that Fe doping significantly enhances the electrochemical activity and ion storage capacity of BiOBr.

[0047] Electrochemical impedance spectroscopy (EIS) test results are as follows Figure 5 As shown in (b) in the figure, compared with BiOBr, the arc diameter in the high-frequency region of the Nyquist plot of Fe-BiOBr is significantly reduced, and the slope of the diffusion line in the low-frequency region is increased, indicating that Fe doping effectively reduces the charge transfer impedance and accelerates the interfacial ion transport dynamics.

[0048] Fourier transform alternating current-voltage (FT-ACV) test results Figure 5 Images (c) and (d) further verify the above conclusions: the peak current of Fe-BiOBr is much greater than that of pure BiOBr, indicating that charge transfer is smoother after doping; the peak located at approximately -0.3V corresponds to Cs + Embedded and Br - During the extraction process, the peak located at approximately +0.1V corresponds to Br. - Embedded and Cs + The extraction process was consistent with the results of CV and EIS analyses, jointly confirming the effect of Fe-BiOBr on Cs. + and Br - All of them exhibit good bifunctional electrochemical response characteristics.

[0049] Example 3 This embodiment illustrates a method for preparing a film electrode with Fe-BiOBr.

[0050] The Fe-BiOBr powder obtained in Example 1, conductive carbon black (CB), and polyvinylidene fluoride (PVDF) were weighed at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added and stirred thoroughly for 6-8 hours to obtain a uniform slurry. The slurry was uniformly coated on both sides of a 1000-mesh stainless steel wire mesh and then transferred to a vacuum drying oven to dry, thus obtaining the Fe-BiOBr electroactive film electrode (Fe-BiOBr / SSWM).

[0051] Example 4 This embodiment constructs an ion permeation system.

[0052] like Figure 1 As shown, a self-made three-chamber plexiglass permeation tank was used, consisting of a left feed chamber, a middle receiving chamber, and a right feed chamber. The middle receiving chamber and the two feed chambers were separated by Fe-BiOBr / SSWM membrane electrodes prepared in Example 3, with the two membrane electrodes serving as positive and negative electrodes respectively, connected to the electrochemical workstation. The feed chamber was filled with a mixed solution containing 2.5 mM MKBr and 1.25 mM MCs2SO4, which simulated the target ionized water body; the receiving chamber was filled with an initial solution of 0.075 mM MCsBr, which maintained a certain initial concentration to stabilize the electrochemical environment of the system.

[0053] Test Example 1 This test case uses the system constructed in Example 4 to verify the Fe doping effect.

[0054] A pure BiOBr / SSWM film electrode was prepared using the same fabrication process as a control. Under the conditions of -1.0V / +1.0V pulse voltage and 60s pulse width, 150 pulse experiments were performed on each.

[0055] The results are as follows Figure 6 As shown: In the pure BiOBr system, after 150 pulse cycles, the Br in the feed chamber... - and Cs + The concentrations decreased by only 0.116 and 0.116, respectively. , while in the receiving chamber Br - Increased Cs + Increased The corresponding ion fluxes are 0.450 and 0.450. The corresponding effective flux of CsBr is In the Fe-BiOBr system, Cs in the feed chamber + and Br - The concentrations decreased by 0.210 and 0.210, respectively. Meanwhile, Cs in the receiving room + Increased , Br - Increased The corresponding ion fluxes increased to 1.005 and 1.005, respectively. The effective flux of CsBr is The increase was approximately 2.57 times. In both systems, K in the raw material chamber and the receiving chamber... + and SO4 2- The concentration remained essentially unchanged, indicating that both systems exhibited good selectivity for the target ion.

[0056] Test Example 2 This test case uses the system constructed in Example 4 to verify the effect of the applied magnetic field.

[0057] Based on Example 4, a steady-state magnetic field of 70 mT was applied to both sides of the three-chamber permeation tank, provided by a permanent magnet, to construct an EMIP system, and tests were conducted under the same solution system and electric field parameters.

[0058] The results are as follows Figure 7 As shown in (a) and (b), under the control of an external magnetic field, the concentrations of Cs+ and Br- in the raw material chamber decreased respectively. and The concentrations of the two in the receiving chamber from Rise to and The corresponding ion flux reached and The corresponding effective flux of CsBr is .

[0059] This result indicates that, under the action of an applied steady-state magnetic field, Fe in Fe-BiOBr... 3+ (3d) 5 The configuration (Fe) has unpaired electrons whose spin magnetic moments tend to align in an ordered manner along the magnetic field direction, forming a directional magnetic dipole moment, which alters the Fe configuration. 3+ The distribution of the surrounding electron cloud induces spin polarization in the Fe-BiOBr membrane electrode, altering the interfacial electric field distribution, lowering the ion migration energy barrier, and enhancing the directional migration rate and permeation flux of cesium and bromide ions. Figure 7 Similarly, (c) and (d) in the diagram confirm that, under the condition of an applied magnetic field, the competing ion K... + and SO4 2- The concentration of Cs did not change significantly, indicating that the EMIP system maintained its effectiveness in improving Cs flux. + and Br - Excellent selectivity.

[0060] The data comparison of Test Example 1, Test Example 2, and the basic test (BiOBr without applied magnetic field) is shown in the table below: Table 1: Comparison of CsBr effective flux between BiOBr and Fe-BiOBr membrane electrodes

[0061] Example 5 This embodiment aims to verify the separation selectivity of the present invention under high-concentration competitive ion interference environment, as well as the stability of the system during long-term operation.

[0062] In this embodiment, the raw material chamber adopts a high-concentration multi-ion competition system, specifically composed of: KCl ( , ), KNO3 ( , ), Na2SO4 ( , )and CsBr ( , The mixed solution of the target ion has a competing ion concentration that is about 4 times that of the target ion, which fully simulates the actual complex water environment.

[0063] Selective test results: The results of cation separation are as follows Figure 8(a) shows that in the Fe-BiOBr / SSWM system where only an electric field is applied, the effect on Cs + K + and Na + The separation coefficients were 11.395, 1.271, and 1.073, respectively, Cs + Relative to K + and Na + The separation factors were 8.965 and 10.619, respectively; in the EMIP electromagnetic coupling system, for Cs + K + and Na + The separation coefficients were increased to 30.914, 2.077, and 2.759, respectively, for Cs. + Relative to K + and Na + The separation factors were 14.884 and 11.205, respectively, indicating that the applied magnetic field not only increased the flux but also further enhanced the separation of Cs. + The selectivity.

[0064] Anion separation results are as follows Figure 8 (b) shows that in the electric field system, for Br - Cl - SO4 2- and NO3 - The separation coefficients were 19.187, 1.512, 1.433, and 1.150, respectively. - The separation factors relative to the competing anions were 12.69, 13.389, and 16.684, respectively; in the EMIP system, these separation factors increased to 43.268, 4.981, 3.136, and 2.929, respectively. - The separation factors relative to competing anions were 8.687, 13.797, and 14.772, respectively, fully demonstrating that the Fe-BiOBr / SSWM membrane electrode effectively separates Cs in complex high-salt competing systems. + and Br - It has stable and excellent bidirectional selective separation performance.

[0065] Cyclic stability test: Under optimal experimental conditions, five consecutive cycles of permeation experiments were conducted on the Fe-BiOBr / SSWM membrane electrode, such as... Figure 8 As shown in (c) above. After five cycles, the CsBr flux in the receiving chamber stabilizes at [value missing] when no magnetic field is applied. When a magnetic field is applied, the CsBr flux in the receiving chamber stabilizes at [value missing]. The flux did not decrease significantly during the cycle, indicating that the membrane electrode has good stability during cyclic use.

[0066] Figure 8 (d) in the figure shows the electrochemical stability of the Fe-BiOBr / Pt electrode after 900 cyclic voltammetry tests in 0.1 M CsBr solution. The results show that the electrochemical active area of ​​Fe-BiOBr under the applied magnetic field is much larger than that without the applied magnetic field, and the electrochemical activity does not decrease significantly after 900 cycles, which further confirms the long-term operational stability of the EMIP system.

[0067] Finally, it should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. Those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents; that is, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-doped bismuth oxybromine material, characterized in that, Includes the following steps: S1. Disperse the bismuth source and bromine source in a solvent to obtain solution A; S2. Disperse the iron source in a solvent to obtain solution B; S3. Mix solution A and solution B and stir to obtain mixed solution C; S4. Perform a hydrothermal reaction on solution C; S5. Collect the precipitate after solution C has cooled to room temperature. S6. The precipitate collected in S5 is washed and dried to obtain iron-doped bismuth oxybromine material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the bismuth source, bromine source and iron source is 1:1:(0.005~0.054).

3. The preparation method according to claim 1, characterized in that, The bismuth source is The bromine source is .

4. The preparation method according to claim 1, characterized in that, The iron source is .

5. An iron-doped bismuth oxybromine material, characterized in that, The preparation is carried out by the preparation method according to any one of claims 1-4, wherein the mass percentage doping amount of iron is 0.1~1.0 wt%.

6. A membrane electrode, characterized in that, It includes a porous conductive substrate and an electroactive material covering the porous conductive substrate, wherein the electroactive material includes the iron-doped bismuth oxybromine material as described in claim 5.

7. The membrane electrode according to claim 6, characterized in that, The electroactive material comprises iron-doped bismuth oxybromine material, conductive carbon black, and binder in a mass ratio of 8:1:

1. After mixing, a dispersant is added to form a slurry, which is then coated onto the porous conductive substrate.

8. The membrane electrode according to claim 7, characterized in that, The adhesive is polyvinylidene fluoride, the dispersing solvent is N-methylpyrrolidone, and the porous conductive substrate is steel wire mesh.

9. An application of the membrane electrode according to any one of claims 6-8 in regulating the migration of cesium ions and bromide ions under the action of magnetoelectric field coupling.

10. The application according to claim 9, characterized in that, The membrane electrode is used in an electromagnetic field coupled ion permeation system, including a multi-chamber permeation cell, at least two membrane electrodes, an electric field application device, and a steady-state magnetic field generator. The multi-chamber permeation cell includes at least a feed chamber and a receiving chamber. The membrane electrodes are disposed between the feed chamber and the receiving chamber and are respectively connected to the electric field application device as positive and negative poles. The steady-state magnetic field generator is disposed on both sides of the permeation cell and provides a steady-state magnetic field parallel to the ion migration direction.

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