Composite electrode modified by polyhydroxy nitrogenous conductive MOF (Metal Organic Framework) as well as preparation method and application of composite electrode

Abstract

The invention belongs to the technical field of electrode materials, and particularly relates to a polyhydroxy nitrogenous conductive MOF modified composite electrode and a preparation method and application thereof. The preparation method of the composite electrode comprises the following steps: uniformly mixing an organic ligand, a transition metal salt and an organic solvent to prepare a mixed solution, then immersing an electrode material in the mixed solution, heating and then naturally cooling to obtain the polyhydroxy nitrogen-containing conductive MOF modified composite electrode. The HHTQ-based conductive MOF and the CDI electrode are compounded, the HHTQ-based conductive MOF and the CDI electrode have the advantages of the two kinds of materials, inherent defects of the two kinds of materials are reduced, complementation of the structure and performance is achieved, MnO2 / LDH provides nano-sheet-shaped multilevel channels, and the specific surface area is increased; the structural stability and the cycle life of the composite material are improved; the problems that an electrode for CDI lithium extraction is insufficient in cycling stability, limited in selectivity or capacity and the like are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF, its preparation method, and its application. Background Technology

[0002] With the development of the new energy industry, the demand for lithium resources has increased dramatically, and how to efficiently recover lithium ions from various lithium-containing water systems has become a research hotspot. Lithium-containing water systems include salt lake brine, geothermal water, and battery recycling waste liquid, etc., in which the lithium ion concentration is often low and coexists with high concentrations of sodium, potassium, magnesium and other ions, making selective separation and enrichment a significant challenge.

[0003] Capacitive deionization (CDI), as a green and efficient ion separation and water treatment technology, has attracted widespread attention due to its low energy consumption, simple operation, and high electrode renewability. The performance of CDI largely depends on the electrode material; among traditional CDI electrode materials, MnO... Metal oxides / hydroxides such as 2 or LDH utilize their layered / tunnel structure to resist small ions (such as Li) + While intercalation / deintercalation of MnO2 / C has inherent advantages, its low intrinsic conductivity, limited specific surface area, and susceptibility to structural collapse or dissolution during aqueous adsorption-desorption cycles result in poor cycle stability and limited adsorption capacity. To overcome the conductivity and structural stability issues of traditional electrode materials, various composite strategies have emerged in recent years, such as MnO2 / C substrates and LDH / C substrates. These composite materials have improved conductivity, stability, and the number of active sites, but current research mainly focuses on physical composites or simple coatings, resulting in weak interfacial bonding and discontinuous electron and ion transport pathways, making it difficult to achieve synergistic enhancement. Summary of the Invention

[0004] To address the aforementioned shortcomings, this invention provides a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF, its preparation method, and its application. By combining an HHTQ-based conductive MOF with a CDI electrode, the advantages of both materials can be combined while reducing their inherent defects, achieving a complementary structure and performance. MnO2 / LDH provides nanosheet-like hierarchical channels, enhancing the specific surface area; at the same time, it serves as a framework to improve the structural stability and cycle life of the composite material. This effectively solves the problems of insufficient cycle stability, selectivity, or capacity limitations of electrodes used for CDI lithium extraction.

[0005] The technical solution of the present invention: The first technical problem to be solved by the present invention is to provide a method for preparing a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, the method comprising the following steps: An organic ligand, a transition metal salt, and an organic solvent were mixed to prepare a mixed solution. The electrode material was then immersed in the mixed solution, heated, and then naturally cooled to obtain a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF. The organic ligand was 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ).

[0006] Furthermore, the electrode material is prepared using the following method: S1. The carbon fiber substrate is pretreated by immersing it in an acidic solution to obtain pretreated carbon cloth. S2. Dissolve the metal salt to prepare the precursor solution; S3. Electrochemical deposition is performed using pretreated carbon cloth and precursor solution to obtain electrode material; Furthermore, the electrode material is MnO2 or LDH.

[0007] Further, in step S1, the carbon fiber substrate is immersed in an acidic solution, washed, and vacuum dried to obtain pretreated carbon cloth.

[0008] Furthermore, in step S1, the carbon fiber substrate is raw carbon fiber cloth.

[0009] Furthermore, in step S1, the acidic solution is an acidic mixture or a potassium permanganate solution.

[0010] Furthermore, in step S1, the acidic mixture includes concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 2-4:1.

[0011] Preferably, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1.

[0012] Furthermore, in step S1, the concentration of the potassium permanganate solution is 5-20 mM.

[0013] Furthermore, in step S2, the metal salt is dissolved and the pH is adjusted to weakly acidic to obtain a precursor solution.

[0014] Furthermore, in step S2, the metal salt is a mixture of manganese salt and sodium salt or a transition metal salt.

[0015] Furthermore, in step S2, the manganese salt is manganese sulfate, manganese acetate, or manganese nitrate; and the sodium salt is sodium sulfate, sodium acetate, or sodium nitrate.

[0016] Preferably, the metal salt is manganese sulfate and sodium sulfate, with a molar ratio of 1:1.

[0017] Furthermore, in step S2, the transition metal salt is any two of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and manganese nitrate tetrahydrate.

[0018] Preferably, the transition metal salt is nickel nitrate hexahydrate and cobalt nitrate hexahydrate, with a molar ratio of 1:1.

[0019] Furthermore, in step S2, the pH is adjusted to 5.5-6.5 using sodium acetate or ammonia.

[0020] Furthermore, in step S3, Ag / AgCl is used as the reference electrode, pretreated carbon cloth is used as the working electrode, platinum sheet is used as the counter electrode, and precursor solution is used as the electrolyte. Electrochemical deposition is carried out for 300-900 s at a constant voltage of -0.8 to -1.2 V.

[0021] Furthermore, every 1 cm 2 Add 0.1-0.15 mmol of organic ligand to the electrode material.

[0022] Furthermore, the transition metal in the transition metal salt is Ni. 2+ Co 2+ Cu 2+ and Fe 2+ At least one of them.

[0023] Preferably, the transition metal salt is nickel acetate tetrahydrate.

[0024] Furthermore, the molar ratio of the transition metal salt to the organic ligand is 1.5-2:1.

[0025] Furthermore, the organic solvent is at least one of N,N-dimethylacetamide and N,N-dimethylformamide.

[0026] Further, heat at 65-85 ℃ for 12-48 h.

[0027] Furthermore, when the metal salt mentioned in step S2 is a manganese salt and a sodium salt (molar ratio 1:1), the electrode material obtained in step S3 is a MnO2 electrode, and the final composite electrode modified with a polyhydroxyl nitrogen-containing conductive MOF is an M-HHTQ / MnO2 (or M-HHTQ / MnO2 / CC) composite electrode.

[0028] When the metal salt mentioned in step S2 is two transition metal salts, the electrode material obtained in step S3 is an LDH electrode, and the final composite electrode modified by the polyhydroxyl nitrogen-containing conductive MOF is an M-HHTQ / LDH (or M-HHTQ / LDH / CC) composite electrode.

[0029] The second technical problem to be solved by the present invention is to provide a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, which is prepared by the above-mentioned method for preparing a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF.

[0030] In the composite electrode of this invention, the 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ) ligand, possessing multiple hydroxyl groups and nitrogen-containing sites, can be grown in situ on the surface of MnO2 or LDH to form a stable interface, achieving synergistic regulation of electron and ion channels. This strategy combines the reversible intercalation characteristics of MnO2 with the layered high specific surface area advantage of LDH, while significantly improving overall conductivity, ion selectivity, and structural stability. Testing showed that the fabricated electrode exhibits significant improvements in lithium-ion adsorption capacity, selectivity coefficient, and cycle life compared to single MnO2, LDH, and MOF materials.

[0031] The third technical problem to be solved by the present invention is to provide the application of the above-mentioned composite electrode modified with polyhydroxy nitrogen-containing conductive MOF in lithium extraction from lithium-containing water or capacitive deionization adsorption of lithium.

[0032] The fourth technical problem to be solved by the present invention is to provide a method for adsorbing lithium in a capacitor deionization process using a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, comprising the following steps: using the above-mentioned composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF as the cathode to fabricate a capacitor deionization device; applying a voltage between the two electrodes of the device to adsorb and enrich lithium ions; after adsorption saturation, turning off the power supply and short-circuiting or applying a reverse voltage to release the lithium ions adsorbed in the electrode into the desorption solution, thereby realizing electrode regeneration and lithium ion recovery.

[0033] Furthermore, a capacitive deionization device was fabricated using a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF as the cathode, an activated carbon sheet (AC) as the anode, and a titanium plate as the current collector. The device was connected to a peristaltic pump and a constant pressure batch circulation mode was used to conduct capacitive deionization lithium adsorption experiments on lithium-containing aqueous solutions.

[0034] Furthermore, the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF is bonded to the current collector using conductive adhesive.

[0035] Furthermore, the activated carbon sheet is made by uniformly coating a slurry composed of activated carbon, conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1 onto a current collector and then drying it.

[0036] Furthermore, the lithium-containing aqueous solution is a LiCl solution with a concentration of 1-20 mM, or a mixed solution of LiCl with any one of NaCl, KCl, MgCl2 and CaCl2.

[0037] Further, apply a voltage of 0.8-1.4 V for 10-30 minutes.

[0038] Furthermore, turn off the power and short-circuit for 5-15 minutes.

[0039] Further, apply a reverse voltage of -0.2 to -0.8 V for 5-15 minutes.

[0040] The present invention has the following beneficial effects: 1. In the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF of the present invention, the HHTQ ligand has multiple hydroxyl sites, which can form a stable coordination structure with metal ions, improving the stability and conductivity of the material; its nitrogen heterocyclic structure serves as an electron density enrichment center, generating Lewis acid-base interactions with lithium ions to enhance selectivity. By combining with traditional electrodes, the present invention achieves complementarity in structure and performance. MnO2 / LDH provides nanosheet-like hierarchical channels, enhancing the specific surface area; at the same time, it serves as a framework to improve the structural stability and cycle life of the composite material. In summary, the HHTQ composite electrode structure achieves significant improvements in capacity, stability, and selectivity, providing an effective solution for high-performance capacitor deionization lithium extraction electrode materials.

[0041] 2. The method for preparing the composite electrode modified with multi-hydroxyl nitrogen-containing conductive MOF provided by the present invention adopts a combination of electrochemical deposition and hydrothermal method. The steps are simple and the conditions are mild. The electrode loading can be precisely controlled by adjusting the electrochemical deposition time and the hydrothermal reaction time. It has good scalability and industrial application prospects.

[0042] 3. This invention significantly improves the intrinsic low conductivity of traditional electrodes by introducing M-HHTQ conductive MOF, while forming a stable heterogeneous interface structure, alleviating structural collapse during repeated adsorption-desorption processes, and improving the electrode's cycle life and regeneration capability. The resulting composite electrode modified with polyhydroxyl nitrogen-containing conductive MOF exhibits a layered / tunnel structure suitable for small-sized Li + This composite electrode exhibits preferential intercalation, and combined with the multiple coordination sites and nitrogen heterocyclic structure of the M-HHTQ conductive MOF, it enables the electrode to effectively resist Li in lithium-containing aqueous systems. + The selective adsorption coefficient is significantly higher than that of Na + K + Mg 2+ Equal coexisting ions.

[0043] 4. The composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF prepared in this invention has a rough three-dimensional framework provided by sheet-like MnO2 or LDH, while the outer layer of MOF constructs a porous conductive network. The synergistic effect of the two significantly increases the effective specific surface area and the number of active sites, thereby improving the adsorption capacity and kinetic performance of lithium ions.

[0044] 5. The composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF prepared in this invention is suitable for various lithium-containing water systems such as salt lake brine, geothermal water, and battery recycling waste liquid, providing a new solution for the green and efficient recovery of lithium resources. Attached Figure Description

[0045] Figure 1The structural formulas of the organic ligands HHTQ, HITP, and HHTP are shown. Figure 2 X-ray diffraction patterns of Ni-HHTQ / MnO2 / CC, Ni-HHTQ / CC, and MnO2 / CC; Figure 3 Scanning electron microscope (SEM) images of CC, MnO2 / CC, and Ni-HHTQ / MnO2 / CC; Figure 4 This is a real-life photo of the CDI experimental testing system during discharge testing; Figure 5 This is a comparison chart of the CDI adsorption performance of the composite electrodes obtained in Example 1 and Comparative Examples 1-6; Figure 6 The graph shows the CDI adsorption performance of the composite electrode materials obtained in Example 1 and Comparative Examples 1-6. Figure 7 This is a comparison chart of the adsorption selectivity performance of the composite electrodes obtained in Example 1 and Comparative Examples 1-6; Figure 8 This is a schematic diagram showing the adsorption capacity of the composite electrode obtained in Example 1 for different ions; Figure 9 The graphs show the CDI adsorption performance of the composite electrodes obtained in Example 2 and Comparative Examples 7-8. Figure 10 The graph shows the CDI adsorption cycle performance of the composite electrodes obtained in Example 2 and Comparative Examples 7-8. Detailed Implementation

[0046] In a first aspect, the present invention provides a method for preparing a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF, the method comprising the following steps: An organic ligand, a transition metal salt, and an organic solvent were mixed to prepare a mixed solution. The electrode material was then immersed in the mixed solution, heated, and then naturally cooled to obtain a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF. The organic ligand was 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ).

[0047] Furthermore, the electrode material is prepared using the following method: S1. The carbon fiber substrate is pretreated by immersing it in an acidic solution to obtain pretreated carbon cloth. S2. Dissolve the metal salt to prepare the precursor solution; S3. Electrochemical deposition is performed using pretreated carbon cloth and precursor solution to obtain electrode material; Furthermore, the electrode material is MnO2 or LDH.

[0048] Further, in step S1, the carbon fiber substrate is immersed in an acidic solution, washed, and vacuum dried to obtain pretreated carbon cloth.

[0049] Furthermore, in step S1, the carbon fiber substrate is raw carbon fiber cloth.

[0050] Furthermore, in step S1, the acidic solution is an acidic mixture or a potassium permanganate solution.

[0051] Further, in step S1, the acidic mixture comprises concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 2-4:1. Preferably, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1.

[0052] Furthermore, in step S1, the concentration of the potassium permanganate solution is 5-20 mM.

[0053] Furthermore, in step S2, the metal salt is dissolved and the pH is adjusted to weakly acidic to obtain a precursor solution.

[0054] Furthermore, in step S2, the metal salt is a mixture of manganese salt and sodium salt or a transition metal salt.

[0055] Further, in step S2, the manganese salt is manganese sulfate, manganese acetate, or manganese nitrate; the sodium salt is sodium sulfate, sodium acetate, or sodium nitrate. Preferably, the metal salts are manganese sulfate and sodium sulfate, with a molar ratio of 1:1.

[0056] Further, in step S2, the transition metal salt is any two of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and manganese nitrate tetrahydrate. Preferably, the transition metal salt is nickel nitrate hexahydrate and cobalt nitrate hexahydrate, with a molar ratio of 1:1.

[0057] Furthermore, in step S2, the pH is adjusted to 5.5-6.5 using sodium acetate or ammonia.

[0058] Furthermore, in step S3, Ag / AgCl is used as the reference electrode, pretreated carbon cloth is used as the working electrode, platinum sheet is used as the counter electrode, and precursor solution is used as the electrolyte. Electrochemical deposition is carried out for 300-900 s at a constant voltage of -0.8 to -1.2 V.

[0059] Furthermore, every 1 cm 2 Add 0.1-0.15 mmol of organic ligand to the electrode material.

[0060] Furthermore, the transition metal in the transition metal salt is Ni. 2+ Co 2+ Cu 2+ and Fe 2+ At least one of the following. Preferably, the transition metal salt is nickel acetate tetrahydrate.

[0061] Furthermore, the molar ratio of the transition metal salt to the organic ligand is 1.5-2:1.

[0062] Furthermore, the organic solvent is at least one of N,N-dimethylacetamide and N,N-dimethylformamide.

[0063] Further, heat at 65-85 ℃ for 12-48 h.

[0064] This invention achieves a composite electrode material with both high electronic conductivity and lithium selective adsorption capacity by first electrodepositing sheet-like MnO2 or LDH on a carbon cloth (CC) substrate, and then growing a nitrogen-containing conductive metal-organic framework in situ on its surface. The composite electrode of this invention exhibits excellent lithium-ion adsorption capacity and selectivity in lithium-containing aqueous systems, while also demonstrating good cycle stability and renewability.

[0065] Secondly, the present invention provides a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, which is prepared by the above-described method for preparing a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF.

[0066] Thirdly, the application of the composite electrode modified with the above-mentioned polyhydroxy nitrogen-containing conductive MOF is provided in lithium extraction from lithium-containing water or capacitive deionization adsorption of lithium.

[0067] On the other hand, the present invention provides the application of the above-mentioned composite electrode modified with a multi-hydroxy nitrogen-containing conductive MOF in lithium extraction from lithium-containing water or deionization of capacitors for lithium adsorption.

[0068] Specifically, the method for adsorbing lithium in a capacitor deionization process using a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF includes the following steps: fabricating a capacitor deionization device using the composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF as the cathode; applying a voltage between the two electrodes of the device to adsorb and enrich lithium ions; and after adsorption saturation, turning off the power supply and short-circuiting or applying a reverse voltage to release the lithium ions adsorbed in the electrode into the desorption solution, thereby achieving electrode regeneration and lithium ion recovery.

[0069] Furthermore, a capacitive deionization device was fabricated using a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF as the cathode, an activated carbon sheet (AC) as the anode, and a titanium plate as the current collector. The device was connected to a peristaltic pump and a constant pressure batch circulation mode was used to conduct capacitive deionization lithium adsorption experiments on lithium-containing aqueous solutions.

[0070] Furthermore, the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF is bonded to the current collector using conductive adhesive. The activated carbon sheet is made by uniformly coating the current collector with a slurry composed of activated carbon, conductive carbon black, and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1 and then drying it.

[0071] Furthermore, the lithium-containing aqueous solution is a LiCl solution with a concentration of 1-20 mM, or a mixed solution of LiCl with any one of NaCl, KCl, MgCl2 and CaCl2.

[0072] Further, apply a voltage of 0.8-1.4 V for 10-30 min; turn off the power and short-circuit for 5-15 min; apply a reverse voltage of -0.2 to -0.8 V for 5-15 min.

[0073] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0074] Example 1

[0075] A composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, the preparation method of which includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.15 M MnSO4 and 0.15 M Na2SO4 in 60 mL of deionized water, add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0, and obtain the precursor solution; S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material MnO2 / CC. S4. 1.08 mmol of 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ, structural formula as shown) Figure 1 As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of organic solvent (DMA / DMF volume ratio 1:1) and stirred for 10 min to obtain a mixed solution. Then, the electrode material MnO2 / CC was immersed in the mixed solution and heated at 65 ℃ for 24 h under sealed conditions. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain a composite electrode Ni-HHTQ / MnO2 / CC modified with polyhydroxyl nitrogen-containing conductive MOF.

[0076] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.51 mg cm⁻¹. -2 .

[0077] Example 2

[0078] A composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, the preparation method of which includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.05 M Ni(NO3)2·6H2O and 0.05 M Co(NO3)2·6H2O in 60 mL of deionized water, and add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0 to obtain the precursor solution. S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material LDH / CC. S4. 1.08 mmol of 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ, structural formula as shown) Figure 1 As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of organic solvent (DMA / DMF volume ratio 1:1) and stirred for 10 min to obtain a mixed solution. Then, the electrode material LDH / CC was immersed in the mixed solution and heated at 65 °C for 24 h under sealed conditions. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain the composite electrode HHTQ / LDH / CC modified with polyhydroxyl nitrogen-containing conductive MOF.

[0079] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.22 mg cm⁻¹. -2 .

[0080] Comparative Example 1 A method for preparing a MnO2 / CC electrode includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.15 M MnSO4 and 0.15 M Na2SO4 in 60 mL of deionized water, add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0, and obtain the precursor solution; S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 ℃ to obtain the electrode material MnO2 / CC.

[0081] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.04 mg cm⁻¹. -2 .

[0082] Comparative Example 2 A method for preparing a Ni-HHTQ / CC electrode includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. 1.08 mmol of 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline (HHTQ) organic ligand and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of organic solvent (DMA / DMF volume ratio 1:1) and stirred for 10 min to obtain a mixed solution. Then, the pretreated carbon cloth CC was immersed in the mixed solution and heated at 65 ℃ for 24 h under sealed conditions. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain the electrode material Ni-HHTQ / CC.

[0083] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 0.57 mg / cm³. -2 .

[0084] Comparative Example 3 A method for preparing a nitrogen-containing conductive Ni-HITP / CC composite electrode with selective adsorption properties includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2, add 1.08 mmol of HITP (its structural formula is shown below) Figure 1As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of DMF and stirred for 10 min to obtain a mixed solution. Then, the pretreated carbon cloth CC was immersed in the mixed solution and heated at 80 °C for 24 h under sealed conditions. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain the electrode material Ni-HITP / CC.

[0085] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 0.44 mg cm⁻¹. -2 .

[0086] Comparative Example 4 A method for preparing a nitrogen-containing conductive Ni-HITP / MnO2 / CC composite electrode with selective adsorption includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.15 M MnSO4 and 0.15 M Na2SO4 in 60 mL of deionized water, add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0, and obtain the precursor solution; S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material MnO2 / CC. S4. Add 1.08 mmol of HITP (its structural formula is shown below) Figure 1 As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of DMF and stirred for 10 min to obtain a mixed solution. Then, the electrode material MnO2 / CC was immersed in the mixed solution and heated at 80 °C for 24 h under sealed conditions. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain the electrode material Ni-HITP / MnO2 / CC.

[0087] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.43 mg cm⁻¹. -2 .

[0088] Comparative Example 5 A method for preparing a hydroxyl-containing conductive Ni-HHTP / CC composite electrode with selective adsorption includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2, add 1.08 mmol of HHTP (its structural formula is shown below) Figure 1 As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of DMF and stirred for 10 min to obtain a mixed solution. The pretreated carbon cloth CC was immersed in the mixed solution, heated at 85 °C for 24 h, removed and cooled naturally, washed with deionized water, and vacuum dried to obtain the electrode material Ni-HHTP / CC.

[0089] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 0.42 mg cm⁻¹. -2 .

[0090] Comparative Example 6 A method for preparing a hydroxyl-containing conductive Ni-HHTP / MnO2 / CC composite electrode with selective adsorption includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.15 M MnSO4 and 0.15 M Na2SO4 in 60 mL of deionized water, add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0, and obtain the precursor solution; S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material MnO2 / CC. S4. Add 1.08 mmol of HHTP (its structural formula is shown below) Figure 1 As shown, organic ligands and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O were added to 10 mL of DMF and stirred for 10 min to obtain a mixed solution. Then, the electrode material MnO2 / CC was immersed in the mixed solution and heated at 85 °C for 24 h. After removal, it was naturally cooled, washed with deionized water, and vacuum dried to obtain the electrode material Ni-HHTP / MnO2 / CC.

[0091] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.41 mg cm⁻¹.-2 .

[0092] Comparative Example 7 A method for preparing a Ni-HITP conductive MOF-modified LDH composite electrode includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.05 M Ni(NO3)2·6H2O and 0.05 M Co(NO3)2·6H2O in 60 mL of deionized water, and add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0 to obtain the precursor solution. S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material LDH / CC. S4. Add 1.08 mmol of HITP organic ligand and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O to 10 mL of organic solvent (DMA / DMF volume ratio 1:1), stir for 10 min to obtain a mixed solution; then immerse the electrode material LDH / CC in the mixed solution, heat at 65 ℃ for 24 h under sealed conditions, remove and cool naturally, wash with deionized water, and vacuum dry to obtain the electrode material HITP / LDH / CC.

[0093] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.02 mg cm⁻¹. -2 .

[0094] Comparative Example 8 A method for preparing a Ni-HHTP conductive MOF-modified LDH composite electrode includes the following steps: S1. Cut the raw carbon fiber cloth (CC) into 3 cm × 3 cm pieces, soak them in 10 mL of acidic mixed solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 20 min, take them out and wash them with a large amount of deionized water until neutral, and vacuum dry them to obtain pretreated carbon cloth. S2. Dissolve 0.05 M Ni(NO3)2·6H2O and 0.05 M cobalt nitrate hexahydrate in 60 mL of deionized water, and add 10 mM sodium acetate (NaOAc) to adjust the pH to 6.0 to obtain the precursor solution; S3. Using Ag / AgCl as the reference electrode, pretreated carbon cloth as the working electrode, and platinum sheet as the counter electrode, the electrode was immersed in the precursor solution and electrochemically deposited for 600 s at a constant voltage of -1.0 V. After removal, it was rinsed with deionized water and dried under vacuum at 60 °C to obtain the electrode material LDH / CC. S4. Add 1.08 mmol of HHTP organic ligand and 1.62 mmol of nickel acetate tetrahydrate Ni(OAc)2·4H2O to 10 mL of organic solvent (DMA / DMF volume ratio 1:1), stir for 10 min to obtain a mixed solution; then immerse the electrode material LDH / CC in the mixed solution, heat at 65 ℃ for 24 h under sealed conditions, remove and cool naturally, wash with deionized water, and vacuum dry to obtain the electrode material HHTP / LDH / CC.

[0095] The mass of the obtained composite electrode was weighed, and the mass of the blank carbon cloth was subtracted to obtain a composite material loading of approximately 1.04 mg cm⁻¹. -2 .

[0096] Experimental Example 1 The X-ray diffraction patterns of the polyhydroxyl nitrogen-containing conductive MOF-modified composite electrodes Ni-HHTQ / MnO2 / CC, Ni-HHTQ / CC, and MnO2 / CC obtained in Example 1 are shown below. Figure 2 As shown.

[0097] Depend on Figure 2 It can be seen that Ni-HHTQ / MnO2 / CC has obvious

[100] ,

[200] , and

[001] diffraction peak signals of HHTQ ligand at 6.5°, 13.2°, and 26.5°, as well as the main characteristic diffraction peaks of MnO2, indicating that the composite material was successfully prepared.

[0098] Scanning electron microscope (SEM) images of CC, MnO2 / CC, and Ni-HHTQ / MnO2 / CC in Example 1 are shown below. Figure 3 As shown.

[0099] Depend on Figure 3 It can be seen that, compared to Figure 3 a's original carbon cloth CC, Figure 3 In b, MnO2 / CC is an array of MnO2 nanosheets coated on the surface of carbon cloth fibers; Figure 3 c indicates that after the addition of HHTQ organic ligands for in-situ reaction, the material maintains the overall sheet structure, and the surface MnO2 nanosheets are coated with a layer of conductive MOF to form a thicker sheet structure, indicating that the Ni-HHTQ / MnO2 / CC composite electrode material was successfully prepared.

[0100] Experimental Example 2 Capacitive deionization adsorption test: The capacitive deionization (CDI) test device is assembled as follows: a fixing plate, a titanium plate, an ion exchange membrane, and a silicone pad are prepared, wherein the titanium plate is used as a current collector for both the cathode and anode materials; the cathode is a prepared example or comparative electrode material, and the carbon fiber cloth (3 cm × 3 cm) loaded with the material is bonded to the titanium plate with conductive adhesive; the activated carbon (AC) sheet (3 cm × 3 cm) is used as the anode. CDI experiments were conducted in a circulating system comprising a CDI element, a peristaltic pump, a power supply, a conductivity meter, and a reservoir. 40 mL of a pre-selected LiCl solution was continuously pumped into the CDI element at a flow rate of 20 mL / min, using a peristaltic pump. The operating voltage was 0.8–1.2 V, and adsorption was sustained at 25 °C. After adsorption, the power supply was disconnected or a voltage of -0.2 to -0.8 V was reversed to achieve lithium desorption. The adsorption values ​​used in the tests were calculated from the mass of the active material loaded on the carbon cloth.

[0101] Actual photos of the discharge test of the CDI experimental testing system are shown below. Figure 4 As shown. By Figure 4 It can be seen that when the adsorbed CDI module is connected to the light-emitting panel through the electrode clamp, the light-emitting panel is lit up, indicating that the electrode has the potential for energy recovery and meets the application requirements of green energy saving.

[0102] The electrode materials obtained in Examples 1-2 and Comparative Examples 1-8 were subjected to performance tests, and the results are as follows: A comparison chart of the CDI adsorption performance of the composite electrodes obtained in Example 1 (Ni-HHTQ / MnO2 / CC) and Comparative Examples 1-6 (MnO2 / CC, Ni-HHTQ / CC, Ni-HITP / CC, Ni-HITP / MnO2 / CC, Ni-HHTP / CC, Ni-HHTP / MnO2 / CC, respectively) is shown below. Figure 5 As shown.

[0103] Depend on Figure 5 It is evident that the Ni-HHTQ / MnO2 / CC of this invention exhibits the best adsorption performance. This is due to the structural support and lithium-ion channels provided by MnO2, the high conductivity and abundant nitrogen-containing coordination sites contributed by Ni-HHTQ MOF, resulting in rapid electron transport. Simultaneously, the nitrogen / hydroxyl sites can interact with Li... + Stable coordination is formed. The combination of the two creates a heterogeneous interface effect, which improves both conductivity and increases the effective specific surface area and active sites, resulting in superior adsorption kinetics and capacity. Ni-HITP / MnO2 constructed with HITP is predominantly planar conjugated, exhibiting good conductivity, but lacks polyhydroxyl sites, which affects its adsorption of Li. + The specific coordination ability of the composite electrode is not as good as that of HHTQ. The composite electrode is significantly better than that of a single MOF or a single MnO2, indicating that the composite strategy can significantly improve performance.

[0104] To verify the performance advantages of the composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF of the present invention in the capacitive deionization adsorption of lithium ions, the adsorption capacity and cycle stability of the composite electrodes obtained in Example 1 and Comparative Examples 1-6 were compared and tested. The results are as follows: Figure 6 As shown.

[0105] Depend on Figure 6 It is known that the Ni-HHTQ / MnO2 electrode of the present invention retains more than 85% of its capacity after 100 adsorption-desorption cycles, exhibiting excellent regenerability and long-term stability. This is because the combination of MOF and MnO2 not only overcomes the problem of poor intrinsic conductivity of MnO2, but also introduces additional nitrogen-containing / hydroxyl active sites, thus making it superior to the electrode materials of Comparative Examples 1-6 in terms of adsorption capacity and cycle stability.

[0106] To verify the adsorption selectivity advantage of the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF of the present invention in the process of capacitive deionization and adsorption of lithium ions, the adsorption selectivity of the composite electrodes obtained in Example 1 and Comparative Examples 1-6 in a mixed solution of 10 mM LiCl and 10 mM NaCl was compared and tested. The results are as follows: Figure 7 As shown.

[0107] Depend on Figure 7 It can be seen that the selective adsorption coefficient of the Ni-HHTQ / MnO2 electrode of the present invention for lithium ions (Li + / Na + The adsorption capacity (AUC) reached over 5.0, significantly higher than that of a single MnO2 electrode (approximately 1.8) and a single MOF electrode (approximately 4.6). This result indicates that nitrogen-containing conductive MOFs exhibit excellent selectivity. The composite electrode formed with MnO2 not only possesses high capacity but also achieves preferential separation and enrichment of lithium ions in complex multi-ion water systems, providing technical support for the efficient recovery of lithium-containing resources. In other words, the composite electrode modified with the polyhydroxyl-containing nitrogen-containing conductive MOF of this invention exhibits adsorption selectivity advantages in the capacitive deionization adsorption of lithium ions.

[0108] To verify the application effect of the composite electrode Ni-HHTQ / MnO2 modified with polyhydroxyl nitrogen-containing conductive MOF of the present invention in a real complex environment, it was used as a cathode material in a system containing Li + Na + K + Mg 2+ Ca 2+ In a mixed solution of multiple ions (8 mL of each ion was mixed with a 10 mM chloride solution to form a 40 mL solution), the adsorption capacity of different ions was tested, and the results are as follows: Figure 8 As shown.

[0109] Depend on Figure 8 It is known that the composite electrode Ni-HHTQ / MnO2 modified with a polyhydroxy nitrogen-containing conductive MOF of the present invention is effective for Li + The highest adsorption capacity was observed, reaching approximately 28.11 mg g. -1 ; and for Na + and K + The adsorption capacity was significantly low, approximately 7.34 mg g. -1 and 5.07 mg g -1 ; For divalent ions Mg 2+ and Ca 2+ Its adsorption capacity is even lower, only about 3.67 mg g. -1 and 2.58 mg g -1 .

[0110] To verify the capacitive deionization performance of the composite electrode HHTQ / LDH / CC modified with a polyhydroxy nitrogen-containing conductive MOF of the present invention, three electrode materials, HHTQ / LDH / CC (Example 2), HITP / LDH / CC (Comparative Example 7), and HHTP / LDH / CC (Comparative Example 8), were selected as representative samples. Constant voltage adsorption experiments and cycle stability tests were conducted in 10 mM LiCl solution. The results are as follows: Figure 9 As shown.

[0111] Depend on Figure 9 It can be seen that all three electrode materials exhibit a rapid lithium-ion adsorption phase in the initial stage of adsorption, followed by a plateau. The HHTQ / LDH / CC electrode reaches adsorption equilibrium in approximately 30 minutes, with an equilibrium adsorption capacity of approximately 27.77 mg g. -1 It is higher than HHTP / LDH / CC (approximately 24.63 mg g). -1 ) and HITP / LDH / CC (approximately 21.40 mg g) -1 This result indicates that the HHTQ ligand, due to its numerous hydroxyl and nitrogen heterocyclic structures, can provide more active sites that can interact with lithium ions, thereby significantly improving adsorption capacity and adsorption rate.

[0112] To verify the adsorption cycle performance of the composite electrode HHTQ / LDH / CC modified with a polyhydroxy nitrogen-containing conductive MOF of the present invention, three electrode materials, HHTQ / LDH / CC (Example 2), HITP / LDH / CC (Comparative Example 7), and HHTP / LDH / CC (Comparative Example 8), were selected. All three materials maintained high structural stability and adsorption reversibility after 100 adsorption / desorption cycles. The results are as follows: Figure 10 As shown.

[0113] Depend on Figure 10It is evident that the HHTQ / LDH / CC of this invention exhibits the best cycle retention performance, retaining over 88% of its initial adsorption capacity after 100 cycles, while HHTP / LDH / CC and HITP / LDH / CC retain approximately 83% and 79%, respectively. This demonstrates that the strong interfacial bonding between the HHTQ ligand and LDH, along with its excellent electronic conductivity, effectively alleviates structural fatigue and capacity decay of the electrode during repeated ion exchange processes.

[0114] It should be noted that while the preferred embodiments of the present invention are provided in the specification and accompanying drawings, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not intended to impose additional limitations on the content of the present invention; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of the present invention. Furthermore, the above-mentioned technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of the present invention specification. Moreover, those skilled in the art can make various improvements, substitutions, or modifications based on common technical knowledge and conventional methods without departing from the above-described technical concept of the present invention, and all such improvements, substitutions, or modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, characterized in that, The preparation method includes the following steps: An organic ligand, a transition metal salt, and an organic solvent are mixed to prepare a mixed solution. The electrode material is then immersed in the mixed solution, heated, and then naturally cooled to obtain a composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF. The organic ligand is 2,3,7,8,12,13-hexahydroxytricyclic quinoxaline.

2. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 1, characterized in that, The electrode material is prepared using the following method: S1. The carbon fiber substrate is pretreated by immersing it in an acidic solution to obtain pretreated carbon cloth. S2. Dissolve the metal salt to prepare the precursor solution; S3. Electrochemical deposition is performed using pretreated carbon cloth and precursor solution to obtain electrode material; Furthermore, the electrode material is MnO2 or LDH.

3. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 2, characterized in that, In step S1, the carbon fiber substrate is immersed in an acidic solution, washed, and vacuum dried to obtain pretreated carbon cloth. Furthermore, the carbon fiber substrate is raw carbon fiber cloth; Furthermore, the acidic solution is an acidic mixture or a potassium permanganate solution; Furthermore, the acidic mixture comprises concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of concentrated sulfuric acid to concentrated nitric acid of 2-4:1; Furthermore, the concentration of the potassium permanganate solution is 5-20 mM.

4. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 2, characterized in that, In step S2, the metal salt is dissolved and the pH is adjusted to weakly acidic to obtain the precursor solution; Furthermore, the metal salt is a mixture of manganese and sodium salts or a transition metal salt; Furthermore, the manganese salt is manganese sulfate, manganese acetate, or manganese nitrate; the sodium salt is sodium sulfate, sodium acetate, or sodium nitrate. Preferably, the metal salt is manganese sulfate and sodium sulfate; Furthermore, the transition metal salt is any two of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and manganese nitrate tetrahydrate; Preferably, the transition metal salt is nickel nitrate hexahydrate and cobalt nitrate hexahydrate; Furthermore, the pH is adjusted to 5.5-6.5 using sodium acetate or ammonia.

5. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 2, characterized in that, In step S3, Ag / AgCl is used as the reference electrode, pretreated carbon cloth is used as the working electrode, platinum sheet is used as the counter electrode, and precursor solution is used as the electrolyte. Electrochemical deposition is carried out for 300-900 s at a constant voltage of -0.8 to -1.2 V.

6. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 1, characterized in that, The transition metal in the transition metal salt is Ni. 2+ Co 2+ Cu 2+ and Fe 2+ At least one of them; Preferably, the transition metal salt is nickel acetate tetrahydrate; Furthermore, the molar ratio of the transition metal salt to the organic ligand is 1.5-2:

1.

7. The method for preparing the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF according to claim 1, characterized in that, The organic solvent is at least one of N,N-dimethylacetamide and N,N-dimethylformamide; Further, heat at 65-85 ℃ for 12-48 h.

8. A composite electrode modified with a polyhydroxy nitrogen-containing conductive MOF, characterized in that, The composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF as described in any one of claims 1-7 was prepared.

9. The application of the composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF as described in claim 8 in lithium extraction from lithium-containing water or capacitive deionization adsorption of lithium.

10. A method for adsorbing lithium in a capacitor deionization process using a composite electrode modified with a multi-hydroxyl nitrogen-containing conductive MOF, characterized in that, The process includes the following steps: using the composite electrode modified with the polyhydroxy nitrogen-containing conductive MOF as described in claim 8 as the cathode to fabricate a capacitor deionization device, and applying a voltage between the two electrodes of the device to adsorb and enrich lithium ions. After adsorption saturation, the power supply is turned off and short-circuited or a reverse voltage is applied to release the lithium ions adsorbed in the electrode into the desorption solution, thereby achieving electrode regeneration and lithium ion recovery.

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