Electrochemical method for extracting boron from salt lake brine based on boron recognition functional electrode

Abstract

This invention belongs to the field of electrochemical separation, water treatment, and resource recovery technology, and discloses an electrochemical method for boron extraction from salt lake brine based on a boron recognition functional electrode. The functional electrode includes a current collector and an active layer supported on its surface. The active layer comprises a conductive porous carbon framework derived from a metal-organic framework, a polydopamine interface layer, and N-methyl-D-glucosamine boron recognition functional groups grafted onto the surface of the interface layer. This electrode can selectively adsorb boron from boron-containing water bodies under an applied positive potential, and release and regenerate boron under a negative potential and desorption system. Examples show that the adsorption capacity of this functional electrode in an alkaline system can reach 6.53 mg·g⁻¹. ‑1 The Langmuir model fitted a maximum adsorption capacity of 7.95 mg·g. ‑1 After 15 cycles, the capacity retention rate was still 83.5%, and the boron recovery rate per cycle was higher than 96.5%.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical separation, water treatment and resource recycling technology, specifically relating to a functional electrode for removing boron from boron-containing water, as well as the preparation method and application method of the functional electrode. Background Technology

[0002] Boron is widely found in brine from salt lakes, brackish water, concentrated brine from seawater desalination, and industrial wastewater from glass, ceramics, coal chemical, metallurgical, and electronics industries. Excessive boron content in water bodies can adversely affect agricultural irrigation, water resource utilization, and the ecological environment; therefore, effective treatment of boron-containing water bodies is necessary. Especially under conditions of high salinity and the coexistence of complex ions, the separation and removal of boron is challenging, requiring materials with high selectivity, stability, and regeneration performance.

[0003] Existing boron removal methods mainly include chemical precipitation, membrane separation, ion exchange, adsorption, and extraction. While these methods have a certain application basis, they still have shortcomings. Chemical precipitation consumes a large amount of reagents and easily generates secondary solid waste; membrane separation suffers from membrane fouling, high energy consumption, and insufficient adaptability to high-salt systems; traditional adsorption and ion exchange methods have drawbacks such as insufficient selectivity, slow mass transfer, and cumbersome regeneration processes.

[0004] N-methyl-D-glucosamine functional groups can complex with boron, representing an important technical route for selective boron removal. However, existing materials of this type mostly use resins or ordinary supports, which suffer from poor conductivity, insufficient interfacial bonding stability, limited mass transfer efficiency, and reliance on chemical agents for regeneration. Furthermore, their long-term performance in complex salt systems still needs improvement.

[0005] In recent years, electric field-assisted separation technology has attracted attention due to its controllable process; however, there are still few electric field-controlled functional materials for boron removal. Existing systems struggle to simultaneously achieve a conductive framework, a stable interface, and boron recognition sites, making it difficult to achieve efficient boron adsorption, reversible release, and stable recycling. Therefore, it is necessary to develop an electric field-controlled boron removal functional electrode suitable for complex boron-containing water systems. Summary of the Invention

[0006] One of the objectives of this invention is to provide a functional electrode for reversible selective boron removal controlled by an electric field, in order to solve the problems of insufficient selectivity, difficult regeneration, poor cycle stability, and insufficient process controllability of existing boron removal materials and processes in complex saline systems.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned functional electrode. The method is relatively simple, the conditions are mild, and the operability is strong, which is conducive to constructing a composite electrode structure that combines a conductive mass transfer framework, an interface stabilizing layer, and boron recognition sites.

[0008] The third objective of this invention is to provide a method for applying the above-mentioned functional electrode in the treatment of boron-containing water. By adjusting different applied potentials, the adsorption and desorption of boron can be switched, thereby reducing the consumption of reagents in the traditional chemical regeneration process and improving the recycling performance and application value of the functional electrode.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] The present invention provides a functional electrode for reversible selective removal of boron by electric field modulation. The functional electrode includes a current collector and an active layer loaded on the surface of the current collector. The active layer includes a conductive porous framework, an interfacial adhesion layer disposed on the surface of the conductive porous framework, and boron recognition functional groups grafted onto the interfacial adhesion layer.

[0011] The conductive porous framework is a conductive porous carbon material derived from a metal-organic framework, preferably a Ni-MOF-74 derived conductive porous carbon material; the interface adhesion layer is a polydopamine layer; and the boron recognition functional group is an N-methyl-D-glucosamine group.

[0012] In some preferred embodiments, the conductive porous framework has a hierarchical pore structure in which micropores and mesopores coexist, so as to improve electrolyte accessibility and mass transfer efficiency.

[0013] In some preferred embodiments, the polydopamine layer is coated on the surface of the conductive porous framework to enhance interfacial bonding stability and provide reaction sites for subsequent grafting of boron recognition functional groups.

[0014] In some preferred embodiments, the N-methyl-D-glucosamine group is fixed to the surface of the polydopamine layer by chemical grafting to endow the functional electrode with selective recognition and complexation ability for boron.

[0015] The present invention also provides a method for preparing the above-mentioned functional electrode, comprising the following steps:

[0016] Step S1: Prepare metal-organic framework precursors;

[0017] Step S2: The metal-organic framework precursor is heat-treated in an inert atmosphere to obtain a conductive porous framework material.

[0018] Step S3: Disperse the conductive porous framework material in a weakly alkaline buffer system containing dopamine, so that dopamine undergoes self-polymerization and deposition on its surface to form a polydopamine interface layer.

[0019] Step S4: The material forming the polydopamine interface layer is grafted with N-methyl-D-glucosamine to obtain a composite material with boron recognition function.

[0020] Step S5: The obtained composite material is mixed with a conductive agent and a binder to form a slurry, which is then loaded onto the surface of the current collector and dried to obtain the functional electrode.

[0021] In some preferred embodiments, the heat treatment temperature in step S2 is 500–800°C, preferably 550–700°C, and more preferably about 600°C; the heat treatment time is 1–4 h; and the inert atmosphere is one or more of nitrogen and argon.

[0022] In some preferred embodiments, the pH of the weakly alkaline buffer system in step S3 is 8.0 to 9.0, and the self-polymerization time is 2 to 12 h, preferably 4 to 8 h.

[0023] In some preferred embodiments, the pH of the grafting reaction system in step S4 is 8.5–9.5, the reaction temperature is 40–80°C, and the reaction time is 4–12 h, preferably 6–10 h.

[0024] In some preferred embodiments, the current collector in step S5 is one or more of carbon cloth, carbon paper, nickel foam, graphite paper, or stainless steel mesh.

[0025] In some preferred embodiments, the mass ratio of the composite material, conductive agent and binder in step S5 is (6-9):(0.5-2):(0.5-2), preferably 8:1:1.

[0026] The present invention also provides a method for removing boron from boron-containing water using the aforementioned functional electrode, comprising the following steps:

[0027] The functional electrode is placed in a boron-containing aqueous solution as the working electrode. A positive bias voltage is applied under alkaline conditions to enrich boron-containing species on the surface of the functional electrode and selectively complex them with the boron recognition functional groups, thereby achieving the adsorption and removal of boron.

[0028] After the adsorption has been carried out for a preset time or after the functional electrode has reached adsorption equilibrium, the functional electrode is transferred to the desorption system and a negative bias voltage or a lower potential condition is applied to cause the boron adsorbed on the surface of the functional electrode to dissociate and be released into the desorption liquid, thereby realizing the regeneration of the functional electrode.

[0029] In some preferred embodiments, the pH of the boron-containing water is 8 to 10.5, preferably 8.5 to 10.

[0030] In some preferred embodiments, the potential applied during the adsorption stage is 0.2 to 1.0 V, preferably 0.3 to 0.8 V, relative to the Ag / AgCl reference electrode.

[0031] In some preferred embodiments, the potential applied during the desorption phase is -0.8 to 0 V, preferably -0.5 to -0.1 V, relative to the Ag / AgCl reference electrode.

[0032] In some preferred embodiments, the desorption system is an acidic desorption system and may contain a polyol complexing agent; preferably, the polyol complexing agent is sorbitol.

[0033] In some preferred embodiments, the boron-containing water body is industrial wastewater, concentrated brine from seawater desalination, brackish water, high-salinity simulated wastewater, or other complex ion coexistence water systems.

[0034] In this invention, a conductive porous framework provides electron transport pathways and ion diffusion channels, a polydopamine interface layer enhances the surface stability of the material and provides functional anchoring sites, and the vicinal diol structure in N-methyl-D-glucosamine forms a reversible complex with boron species, thereby achieving selective adsorption and reversible release of boron under electric field regulation. The conductive porous framework, the polydopamine interface layer, and the boron recognition functional groups of N-methyl-D-glucosamine work together to achieve superior adsorption performance, reversible desorption performance, and cycle stability.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention constructs a synergistic functional structure consisting of a conductive porous framework, a polydopamine interface layer and an N-methyl-D-glucosamine recognition site, which takes into account electron transport, interface stability and boron selective recognition, and is beneficial to improving the overall adsorption performance of the functional electrode.

[0037] (2) The functional electrode described in this invention can enhance the adsorption process under the action of an external electric field, and realize boron release and regeneration through potential switching. Compared with traditional boron removal materials that rely solely on chemical elution, it has the advantages of better process controllability and milder regeneration conditions.

[0038] (3) The functional electrode described in this invention exhibits good adsorption performance. In an alkaline boron-containing system, the adsorption capacity can reach 6.53 mg·g at approximately 0.6 V. -1 The Langmuir model fitted a maximum adsorption capacity of 7.95 mg·g. -1 .

[0039] (4) The functional electrode described in this invention has good regeneration performance. After 15 adsorption-desorption cycles, the adsorption capacity retention rate can still reach 83.5%, and the boron recovery rate per cycle is higher than 96.5%.

[0040] (5) The functional electrode described in this invention still maintains good adsorption performance under conditions of coexisting anions and high ionic strength, and has good applicability to complex high-salt boron-containing water bodies.

[0041] (6) The preparation method described in this invention is relatively simple, the conditions are mild, and it is easy to scale up the preparation, which has good application prospects.

[0042] (7) By comparing with ordinary porous carbon supports, conventional interface connection methods, and other boron-philic groups, it can be seen that the MOF-derived conductive porous framework, polydopamine interface layer, and N-methyl-D-glucosamine recognition site used in this invention have a synergistic effect. The above-mentioned synergistic effect helps to achieve better adsorption performance, reversible desorption performance, and cycle stability, and demonstrates the comprehensive advantages of the technical solution of this invention over alternative solutions. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the preparation process of the functional electrode sample of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. It should be understood that various equivalent substitutions, simple modifications or conventional adjustments made by those skilled in the art to the present invention without departing from the spirit and substance of the present invention should fall within the scope of protection of the present invention.

[0045] Example 1

[0046] Preparation of conductive porous framework material NiMC

[0047] First, the Ni-MOF-74 precursor was prepared. 3.2713875 g of Ni(NO3)2·6H2O and 1.485975 g of 2,5-dihydroxyterephthalic acid were weighed and added to a mixed solvent prepared by N,N-dimethylformamide, anhydrous ethanol, and deionized water in a volume ratio of 1:1:1, with each solvent having a volume of 45 mL. After stirring at room temperature until fully dispersed, the resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 150 °C for 12 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the product was collected by centrifugation. The product was then washed several times sequentially with N,N-dimethylformamide, anhydrous ethanol, and deionized water, and subsequently dried under vacuum to obtain Ni-MOF-74 precursor powder.

[0048] The obtained Ni-MOF-74 precursor was placed in a quartz boat and transferred to a tube furnace. Under nitrogen protection, the temperature was increased to 600°C at a heating rate of 5°C / min and held for 2 h. Then, it was naturally cooled to room temperature, and the product was taken out to obtain the Ni-MOF-74 derived conductive porous framework material, denoted as NiMC.

[0049] Example 2

[0050] Preparation of PDA-NiMC conductive porous framework material modified with interfacial adhesion layer

[0051] 0.5 g of NiMC obtained in Example 1 was weighed and dispersed in 50 mL of 10 mM Tris-HCl buffer solution, and the pH of the system was adjusted to 8.5. 0.5 g of dopamine hydrochloride was added to the resulting dispersion, and the mixture was stirred at 60 °C for 8 h to allow dopamine to self-polymerize and deposit on the NiMC surface. After the reaction was complete, the product was collected by centrifugation and repeatedly washed with deionized water and anhydrous ethanol until the color of the supernatant showed little change. The washed product was then vacuum dried at 60 °C for 12 h to obtain a composite material with a polydopamine coating, denoted as PDA-NiMC.

[0052] Example 3

[0053] Preparation of NMDG-PDA-NiMC, a boron-recognition functional group grafted composite material

[0054] 0.5 g of the PDA-NiMC obtained in Example 2 was weighed and dispersed in a mixed solution of deionized water and anhydrous ethanol, wherein the volume of deionized water was 100 mL and the volume of anhydrous ethanol was 75 mL. 10.3 g of N-methyl-D-glucosamine was added to the above dispersion system, and the pH of the reaction system was adjusted to 8.8–9.0. The mixture was stirred at 60 °C for 8 h to immobilize N-methyl-D-glucosamine on the surface of PDA-NiMC. After the reaction, the product was collected by centrifugation and repeatedly washed with deionized water and anhydrous ethanol to remove unreacted substances. The washed product was vacuum dried at 60 °C for 12 h to obtain the N-methyl-D-glucosamine functionalized composite material, denoted as NMDG-PDA-NiMC-8 h. The preparation process of the functional electrode sample of this invention is illustrated below. Figure 1 As shown.

[0055] Example 4

[0056] Construction of functional electrodes

[0057] The NMDG-PDA-NiMC-8 h obtained in Example 3, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 8:1:1, and a homogeneous slurry was prepared using N-methylpyrrolidone as a solvent. The resulting slurry was then uniformly coated onto the surface of carbon paper, with a coating area of ​​1.5 cm².2 The active substance loading was controlled to be approximately 2 mg / cm³. 2 After coating, the electrode was vacuum dried at 60°C for 12 hours to obtain the functional electrode.

[0058] In other embodiments, the current collector can also be made of carbon cloth, nickel foam, graphite paper, or stainless steel mesh.

[0059] Example 5

[0060] Adsorption experiment of boron in boron-containing water by functional electrodes

[0061] Electrochemical adsorption experiments were conducted using a three-electrode system, in which the functional electrode obtained in Example 4 was used as the working electrode, the platinum mesh as the counter electrode, and the Ag / AgCl (saturated KCl) electrode as the reference electrode.

[0062] The adsorption solution was a 25 mL alkaline boron-containing system with an initial borate concentration of 30 mg / L and 3 mM KNO3 as a supporting electrolyte. The pH of the solution was adjusted to approximately 9.2 using KOH. The three-electrode system was placed in the adsorption solution, and adsorption was induced at room temperature by applying a potential of 0.6 V for 120 min. After adsorption, a sample was taken to determine the boron concentration in the solution, and the adsorption capacity per unit mass was calculated.

[0063] The results show that the functional electrode exhibits good boron adsorption performance under the above conditions, with an adsorption capacity of 6.53 mg·g. -1 .

[0064] Adsorption capacity is calculated using the following formula:

[0065]

[0066] in, For adsorption capacity, This is the initial concentration. This represents the concentration after adsorption. The volume of the solution. For the quality of active materials.

[0067] Example 6

[0068] Field-assisted desorption and regeneration experiments of functional electrodes

[0069] After adsorption, the functional electrode was transferred to the desorption system for boron release and regeneration. The desorption solution was prepared from 0.1 M sorbitol and 3 mM KNO3, and the pH was adjusted to approximately 2. A three-electrode system was used, with the adsorbed functional electrode as the working electrode, a platinum mesh as the counter electrode, and an Ag / AgCl (saturated KCl) electrode as the reference electrode. Desorption was performed at -0.2 V at room temperature for 30 min. After desorption, the boron concentration in the desorption solution was measured, and the boron recovery rate was calculated.

[0070] The results show that under the above conditions, boron adsorbed on the surface of the functional electrode can be effectively released, with a single desorption recovery rate of 99.53%.

[0071] Boron recovery rate is calculated using the following formula:

[0072]

[0073] in, For boron recovery rate, This represents the total amount of boron in the desorption solution. This represents the total amount of boron adsorbed during the adsorption step.

[0074] Example 7

[0075] Cyclic regeneration performance test of functional electrodes

[0076] The functional electrode obtained in Example 4 was subjected to multiple adsorption-desorption cycle tests according to the adsorption conditions described in Example 5 and the desorption conditions described in Example 6. Adsorption and desorption were performed under the same conditions in each cycle, and the adsorption capacity and boron recovery rate were measured respectively.

[0077] The results showed that after 15 adsorption-desorption cycles, the adsorption capacity retention rate of the functional electrode remained at 83.5%, and the boron recovery rate in each cycle was higher than 96.5%, indicating that the functional electrode has good cycle stability and regeneration performance. Table 1 shows the comparison results of the adsorption capacity, capacity retention rate after 15 cycles, and boron recovery rate of different electrode samples.

[0078] Example 8

[0079] Selective deboronization experiments in complex ionic systems

[0080] To evaluate the applicability of the functional electrode in complex ionic systems, a simulated boron-containing water system containing coexisting anions was prepared, including Cl-. - SO4 2- HCO3 - and HPO4 2- Electroadsorption experiments were conducted using the method described in Example 5 to investigate the boron removal performance of the functional electrode under different coexisting ion conditions.

[0081] The results show that after adding the aforementioned coexisting anions, the functional electrode still maintains good boron removal performance, with the following relative retention rates: Cl - 95.1%, SO4 2- 95.4%, HCO3 - 94.3%, HPO4 2- : 96.3%. The adsorption capacity and relative retention rate under different additional coexisting anions are shown in Table 2.

[0082] Example 9

[0083] Adsorption performance experiments of functional electrodes under different ionic strengths

[0084] To evaluate the applicability of the functional electrode under different ionic strength conditions, alkaline boron-containing systems containing different concentrations of potassium nitrate were prepared, with NO3 as the base. - Concentration changes characterize changes in the ionic strength of the system, and 3 mM NO3 is used as the metric. - The conditions were used as baseline conditions. Electroadsorption experiments were conducted using the method described in Example 5 to investigate the adsorption performance of the functional electrode for boron under different ionic strengths.

[0085] With all other conditions remaining the same, set NO3 separately. - The concentrations of 0.3 mM, 3 mM, 30 mM, and 300 mM were used to investigate the effect of ionic strength variations on the adsorption performance of the functional electrode. The results showed that the functional electrode exhibited good adsorption performance at 3 mM NO3. - Under these conditions, it exhibited the highest adsorption capacity, at 6.53 mg·g. -1 ;When NO3 - When the concentration was reduced to 0.3 mM, the adsorption capacity was 6.47 mg·g. -1 ;When NO3 - When the concentration was further increased to 30 mM and 300 mM, the adsorption capacity decreased to 5.84 mg·g⁻¹, respectively. -1 and 5.36 mg·g -1 The corresponding capacity retention rates were 89.4% and 82.2%, respectively. These results indicate that the functional electrode can maintain a high adsorption level even under high ionic strength conditions and possesses a certain degree of resistance to salt interference. The adsorption capacity and capacity retention rate under different ionic strength conditions are shown in Table 3.

[0086] Example 10

[0087] Adsorption isotherms of functional electrodes under different initial concentration conditions

[0088] To evaluate the adsorption isotherm performance of the functional electrode, alkaline boron-containing systems with different initial concentrations were prepared, and electroadsorption experiments were conducted using the method described in Example 5. The adsorption liquid volume, pH, supporting electrolyte concentration, applied potential, and adsorption time were kept consistent. The initial boron concentration was varied, and the residual boron concentration in the solution after equilibrium adsorption was measured. The adsorption capacity per unit mass was then calculated.

[0089] The experimental data were fitted using Langmuir and Freundlich models. The results showed that the adsorption process of the functional electrode better conformed to the monolayer adsorption characteristics of Langmuir, and the maximum adsorption capacity obtained by fitting was 7.95 mg·g. -1 This indicates that the functional electrode has a high boron adsorption capacity. The fitting parameters of the Langmuir model and the Freundlich model are shown in Table 4.

[0090] Example 11

[0091] Adsorption performance testing of functional electrodes under different applied potentials

[0092] To evaluate the effect of applied potential on the adsorption performance of the functional electrode, the functional electrode obtained in Example 4 was used, and adsorption experiments were conducted according to the adsorption system and test method described in Example 5, with the only difference being the applied potential applied during the adsorption stage. The applied potentials were set to 0 V, 0.2 V, 0.4 V, 0.6 V, and 0.8 V, respectively. After adsorption, samples were taken to detect the boron concentration in the solution, and the adsorption capacity per unit mass was calculated.

[0093] The results showed that the functional electrodes exhibited a certain boron removal capacity under different applied potentials, but the adsorption capacities varied significantly. The adsorption capacity at 0 V was 1.87 mg·g⁻¹. -1 The adsorption capacity at 0.2 V is 4.87 mg·g. -1 The adsorption capacity at 0.4 V is 5.27 mg·g. -1 The adsorption capacity at 0.6 V is 6.53 mg·g. -1 The adsorption capacity at 0.8 V is 6.13 mg·g. -1 .

[0094] The above results indicate that the applied potential has a significant impact on the adsorption performance of the functional electrode. Compared with the condition without applied potential, applying a positive bias voltage is beneficial for promoting the enrichment of boron-containing species at the electrode interface and enhancing the adsorption of boron by functional groups. When the applied potential is increased to a suitable range, the adsorption performance is significantly improved, with the adsorption effect being better at 0.6 V. When the potential is further increased, the adsorption capacity decreases, indicating that excessively high potentials are not conducive to maintaining the optimal adsorption state. The comparison results of the adsorption capacity of the functional electrode under different applied potential conditions are shown in Table 5.

[0095] Comparative Example 1

[0096] Fabrication and performance testing of NiMC electrodes

[0097] NiMC material was prepared according to the method in Example 1. The obtained NiMC, acetylene black and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent to make a slurry. The slurry was uniformly coated on the surface of carbon paper and dried under vacuum at 60°C for 12 h to obtain the NiMC electrode.

[0098] Adsorption experiments were conducted according to the method described in Example 5. The results showed that the electrode possesses a certain adsorption capacity for boron, with an adsorption capacity of 0.82 mg·g⁻¹. -1 This is lower than the 6.53 mg·g of the functional electrode obtained in Example 4. -1 This indicates that the electrode's adsorption capacity for boron is weak when the polydopamine interface layer and N-methyl-D-glucosamine recognition site are not introduced.

[0099] Comparative Example 2

[0100] Fabrication and performance testing of PDA-NiMC electrodes

[0101] PDA-NiMC material was prepared according to the method in Example 2. The obtained PDA-NiMC, acetylene black and polyvinylidene fluoride were mixed at a mass ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent to make a slurry. The slurry was uniformly coated on the surface of carbon paper and dried under vacuum at 60°C for 12 h to obtain the PDA-NiMC electrode.

[0102] Adsorption experiments were conducted according to the method described in Example 5. The results showed that the electrode exhibited a certain improvement compared to Comparative Example 1, with an adsorption capacity of 1.33 mg·g⁻¹. -1 However, it is still lower than the functional electrode obtained in Example 4. This indicates that although introducing a polydopamine interface layer can improve the interface properties to some extent, it is insufficient to endow the electrode with a highly efficient and selective adsorption capacity for boron.

[0103] Comparative Example 3

[0104] Performance comparison of samples with different NMDG grafting times

[0105] N-methyl-D-glucosamine functionalized composite materials with grafting times of 4 h and 12 h, respectively, were prepared according to the method of Example 3 and designated as NMDG-PDA-NiMC-4 h and NMDG-PDA-NiMC-12 h. Corresponding functional electrodes were further prepared according to the method of Example 4, and adsorption and cycling performance were tested according to the methods of Examples 5 and 7.

[0106] The results showed that different grafting times affected the overall performance of the functional electrodes. The NMDG-PDA-NiMC-4h electrode exhibited an adsorption capacity of 3.77 mg·g⁻¹. -1 The capacity retention rate after 15 cycles was 67.8%; the adsorption capacity of the NMDG-PDA-NiMC-12 h electrode was 4.73 mg·g. -1 The capacity retention rate after 15 cycles was 73.2%; while the adsorption capacity of the NMDG-PDA-NiMC-8 h electrode obtained in Example 4 was 6.53 mg·g. -1 The capacity retention rate after 15 cycles was 83.5%. As shown in Table 1, the 8-h sample exhibited better performance in terms of adsorption capacity, cycling stability, and boron recovery rate, indicating that the sample with a grafting time of 8 h had superior overall performance.

[0107] Comparative Example 4

[0108] Commercially available activated carbon powder was used to replace the Ni-MOF-74 derived conductive porous framework material in Example 1, and polydopamine coating and N-methyl-D-glucosamine grafting were performed sequentially according to the methods of Examples 2 and 3 to obtain an activated carbon-based functionalized composite material. Activated carbon-based electrodes were further prepared according to the method of Example 4.

[0109] Adsorption experiments were conducted according to the method described in Example 5. The results showed that the electrode possesses a certain adsorption capacity for boron, with an adsorption capacity of 2.68 mg·g⁻¹. -1 The desorption and cycling tests were performed according to the methods described in Examples 6 and 7. The results showed that the boron recovery rate of this electrode in a single cycle was 84.3%, and the capacity retention rate after 15 cycles was 56.4%, both lower than that of the functional electrode obtained in Example 4. This indicates that although replacing the MOF-derived conductive porous carbon framework with ordinary porous carbon materials can load functional groups, it is difficult to simultaneously maintain the framework conductivity, pore structure accessibility, and interface stability, which is not conducive to obtaining superior overall boron removal performance.

[0110] Comparative Example 5

[0111] The polydopamine coating step in Example 2 is omitted. NiMC material was prepared according to the method of Example 1, and N-methyl-D-glucosamine was grafted onto it using glutaraldehyde (GA) as a crosslinking agent to obtain a comparative composite material. Electrodes were further prepared according to the method of Example 4.

[0112] Adsorption experiments were conducted according to the method described in Example 5. The results showed that the electrode exhibited a certain boron removal capacity in the initial adsorption stage, with an adsorption capacity of 5.41 mg·g⁻¹. -1 The performance was lower than that of the functional electrode obtained in Example 4. Further desorption and cycling tests were performed according to the methods described in Examples 6 and 7. The results showed that the single-cycle boron recovery rate of this electrode was 86.7%, and the capacity retention rate after 15 cycles was 61.5%, both lower than that of the functional electrode obtained in Example 4. This indicates that the polydopamine interface layer not only acts as a connector but also enhances the interfacial stability of the conductive framework surface and provides a more favorable anchoring point for the fixation of N-methyl-D-glucosamine. Omitting the polydopamine interface layer reduces the bonding stability between the functional groups and the framework, which is detrimental to maintaining the overall performance of the electrode during repeated adsorption-desorption processes.

[0113] Comparative Example 6

[0114] In Example 3, N-methyl-D-glucosamine was replaced with D-mannitol and D-glucosamine, respectively, and the remaining steps were the same as in Examples 2 to 4, respectively, to prepare the corresponding comparative electrodes.

[0115] Adsorption experiments were conducted according to the method described in Example 5. The results showed that when D-mannitol was used as the alternative functional molecule, the electrode exhibited a certain adsorption capacity for boron, with an adsorption capacity of 2.43 mg·g⁻¹. -1 When D-glucosamine is used as the alternative functional molecule, the adsorption capacity of the electrode is 4.86 mg·g. -1 The results showed that the single-cycle boron recovery rates of the two comparative electrodes were 80.2% and 47.8%, respectively, and the capacity retention rates after 15 cycles were 51.7% and 38.6%, respectively, both lower than those of the functional electrode obtained in Example 4. This indicates that while replacing N-methyl-D-glucosamine with other boron-affinity functional molecules can impart a certain degree of affinity for boron to the electrode, its overall adsorption performance and cycle regeneration performance are still insufficient. Table 6 shows the comparison results of the adsorption capacity, capacity retention rate after 15 cycles, and boron recovery rate of the comparative electrodes with different alternative schemes.

[0116] The above embodiments are merely illustrative of preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or conventional adjustments made by those skilled in the art to the types of raw materials, process parameters, current collector forms, desorption system composition, and electrochemical operating conditions without departing from the spirit and substance of the present invention should be considered as falling within the scope of protection of the present invention.

[0117] Table 1. Comparison of adsorption performance, cycle stability and boron recovery rate of different electrode samples

[0118]

[0119] Table 2. Adsorption capacity and relative retention rate of NMDG-PDA-NiMC-8 h electrode under different additional coexisting anions.

[0120]

[0121] Table 3. Adsorption capacity and capacity retention of NMDG-PDA-NiMC-8 h electrode under different ionic strengths

[0122]

[0123] Table 4 Fitting parameters for the NMDG-PDA-NiMC-8 h electrode adsorption isotherm model

[0124]

[0125] Table 5. Comparison of adsorption performance of functional electrodes under applied potential and no applied potential conditions.

[0126]

[0127] Table 6. Comparison of adsorption performance, cycle stability, and boron recovery rate of different alternative electrodes.

[0128]

[0129] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A functional electrode for reversibly and selectively removing boron under electric field control, characterized in that, The functional electrode includes a current collector and an active layer loaded on the surface of the current collector. The active layer includes a conductive porous framework, an interface adhesion layer disposed on the surface of the conductive porous framework, and boron recognition functional groups grafted onto the interface adhesion layer. The conductive porous framework is a conductive porous carbon material derived from a metal-organic framework, the interface adhesion layer is a polydopamine layer, and the boron recognition functional group is an N-methyl-D-glucosamine group.

2. The functional electrode according to claim 1, characterized in that, The conductive porous carbon material derived from the metal-organic framework is a Ni-MOF-74 derived conductive porous carbon material.

3. The functional electrode according to claim 1, characterized in that, The conductive porous framework has a multi-level porous structure in which micropores and mesopores coexist, and the polydopamine layer is coated on the surface of the conductive porous framework.

4. The functional electrode according to any one of claims 1, characterized in that, The current collector is one or more of the following: carbon cloth, carbon paper, nickel foam, graphite paper, or stainless steel mesh.

5. A method for preparing the functional electrode according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1, Preparation of metal-organic framework precursors; S2, the metal-organic framework precursor is heat-treated under an inert atmosphere to obtain a conductive porous framework material. S3, the conductive porous framework material is dispersed in a weakly alkaline buffer system containing dopamine, so that dopamine undergoes self-polymerization and deposition on its surface to form a polydopamine interface adhesion layer. S4, the material forming the polydopamine interfacial adhesion layer is grafted with N-methyl-D-glucosamine to obtain a composite material with boron recognition function; S5, the obtained composite material is mixed with a conductive agent and a binder to form a slurry, which is then loaded onto the surface of the current collector and dried to obtain the functional electrode.

6. The preparation method according to claim 5, characterized in that, In step S2, the heat treatment temperature is 500-800℃, the heat treatment time is 1-4 h, and the inert atmosphere is one or more of nitrogen and argon.

7. The preparation method according to claim 5, characterized in that, In step S3, the pH of the weakly alkaline buffer system is 8.0–9.0, and the self-polymerization time is 2–12 h; in step S4, the pH of the grafting reaction system is 8.5–9.5, the reaction temperature is 40–80℃, and the reaction time is 4–12 h.

8. The preparation method according to claim 5, characterized in that, In step S5, the mass ratio of the composite material, conductive agent, and binder is (6-9):(0.5-2):(0.5-2).

9. A method for electrochemical boron extraction from salt lake brine using the functional electrode described in any one of claims 1 to 4, characterized in that, Includes the following steps: The functional electrode is placed in a boron-containing aqueous solution as the working electrode, and a positive bias voltage is applied under alkaline conditions to enrich boron-containing species on the surface of the functional electrode and complex them with the boron recognition functional groups, thereby achieving the adsorption and removal of boron. After the adsorption has been carried out for a preset time or after the functional electrode has reached adsorption equilibrium, the functional electrode is placed in the desorption system and a negative bias voltage or a low potential condition is applied to cause the boron adsorbed on the surface of the functional electrode to dissociate and be released into the desorption liquid, thereby realizing the regeneration of the functional electrode.

10. The method according to claim 9, characterized in that, The boron-containing aqueous solution has a pH of 8 to 10.5, and the adsorption stage is applied with a potential of 0.2 to 1.0 V relative to the Ag / AgCl reference electrode; the desorption stage is applied with a potential of -0.8 to 0 V relative to the Ag / AgCl reference electrode; the desorption system is an acidic desorption system and contains a polyol complexing agent.

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