An organic metal framework-based nano-aqueous ionic electrode and a preparation method thereof

Abstract

This invention discloses an organometallic framework-based nano-water ion electrode and its preparation method. The method includes: dispersing and mixing a transition metal salt, a nitrogen-containing heterocyclic ligand, an aromatic polycarboxylic acid ligand, a conductive nano-carbon phase, and a mixed solvent to obtain a precursor solution; subjecting it to a hydrothermal reaction, washing, and drying to obtain a conductive organometallic framework powder with hydrophilic polar channels; molding it using a blunt-tipped cylindrical mold and heat-treating it to obtain a porous conductive preform; embedding conductive metal leads at the flat bottom end and insulatingly encapsulating it to obtain the electrode. The resulting electrode is a one-piece, blunt-tipped cylindrical porous conductor with open pores and conductive pathways on the outer circumferential surface of the cylinder and the blunt-tipped arc end surface, but without metal needle tips or pinhole structures. This electrode can adsorb air moisture and form an adsorbed water film without semiconductor cooling, achieving omnidirectional, uniform, and low-ozone emission of nano-water ions.

Description

Technical Field

[0001] This invention relates to the field of air purification electrode technology, and in particular to an organometallic framework-based nano-water ion electrode and its preparation method. Background Technology

[0002] Due to their strong oxidizing activity, easy diffusion, low ozone content, and human-friendly properties, nano-water ions have been applied in air purification, health appliances, and environmental disinfection equipment. Current nano-water ion generation technologies mostly employ semiconductor cooling chips combined with metal needle tips or metal pinhole structures. Cooling causes water vapor in the air to condense on the electrode surface, and then, under a high-voltage electric field, water molecules are ionized through the needle tip effect and emitted as nano-water ions.

[0003] However, existing structures still have significant shortcomings: the semiconductor cooling chip, temperature control, and heat dissipation structure make the device complex, consume more energy, and are prone to condensation, frosting, and decreased reliability during long-term operation; the emission direction of the metal tip or pinhole electrode is concentrated, the spatial diffusion range is limited, and the ion concentration distribution is uneven; at the same time, the water absorption and storage capacity of the metal electrode surface is weak, and fluctuations in condensate volume can easily lead to unstable ionization efficiency, and may cause corrosion, dust accumulation, sparking, and increased ozone byproducts. Therefore, there is an urgent need for a nano-water ion electrode that does not require semiconductor cooling, has water absorption and retention capacity, continuous conductivity, and a porous omnidirectional emission interface. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a metal-organic framework (MOF)-based nano-water ion electrode and its preparation method. A transition metal salt, dual ligands, and conductive nano-carbon phase are in-situ composited to obtain a hydrophilic and conductive MOF powder. This powder is then molded into a blunt-tipped cylindrical porous electrode with embedded leads. This electrode eliminates the need for semiconductor cooling and metal tips, utilizing polar channels to absorb and retain water, forming a distributed ionization interface under high voltage to achieve omnidirectional emission of nano-water ions.

[0005] This invention can be achieved through the following technical solutions: A method for preparing an organometallic framework-based nano-water ion electrode, characterized by comprising the following steps: S1. A transition metal salt, a nitrogen-containing heterocyclic ligand, an aromatic polycarboxylic acid ligand, a conductive carbon nanophase, and a mixed solvent are dispersed and mixed to obtain an organometallic framework precursor solution containing a conductive carbon nanophase. S2. The organometallic framework precursor solution is subjected to hydrothermal reaction to enable the transition metal salt, nitrogen-containing heterocyclic ligand and aromatic polycarboxylic acid ligand to grow in situ on the surface of conductive nano carbon phase and between its networks. After washing and drying, conductive organometallic framework powder with hydrophilic polar channels is obtained. S3. The conductive organic metal framework powder is loaded into a cylindrical mold with a flat bottom at one end and a blunt rounded end at the other end for molding and heat treatment to obtain a blunt cylindrical porous conductive blank. S4. A conductive metal pin is embedded in the flat bottom end of a blunt cylindrical porous conductive blank, and the connection area between the conductive metal pin and the blunt cylindrical porous conductive blank is insulated and encapsulated to obtain an organometallic framework-based nano-water ion electrode. The nano-water ion organometallic framework electrode is a blunt-tipped cylindrical porous conductor integrally formed from a conductive organometallic framework material. The cylindrical outer circumferential surface and the blunt-tipped arc end surface of the blunt-tipped cylindrical porous conductor both have open orifices and conductive pathways in the pore walls, and the nano-water ion organometallic framework electrode body does not have metal needle tips or metal pinhole structures.

[0006] Preferably, the transition metal salt is one or more of nickel salt, cobalt salt, and copper salt; the nitrogen-containing heterocyclic ligand is one or more of 2-methylimidazole, imidazole, and benzimidazole; and the aromatic polycarboxylic acid ligand is one or more of terephthalic acid, 2-aminoterephthalic acid, and trimesic acid.

[0007] Preferably, based on 100 parts by mass of the transition metal salt, the amount of conductive carbon nanophase is 0.5 to 10 parts, the amount of nitrogen-containing heterocyclic ligand is 25 to 80 parts, the amount of aromatic polycarboxylic acid ligand is 30 to 100 parts, and the amount of mixed solvent is 200 to 800 parts; the conductive carbon nanophase is one or more of carbon nanotubes, graphene, and reduced graphene oxide.

[0008] Preferably, the mixed solvent is a mixture of deionized water and one of N,N-dimethylformamide, ethanol, and methanol, with a volume ratio of deionized water to the other solvent of 1:(0.5-2). In step S1, the conductive nano-carbon phase is first added to the mixed solvent and ultrasonically dispersed, and then a transition metal salt, a nitrogen-containing heterocyclic ligand, and an aromatic polycarboxylic acid ligand are added and stirred for mixing.

[0009] Preferably, the hydrothermal reaction temperature in S2 is 120–160°C, and the reaction time is 12–24 h; the washing is carried out sequentially using N,N-dimethylformamide, ethanol, and deionized water, and the drying is carried out under vacuum at 60–80°C for 6–12 h.

[0010] Preferably, in step S3, the diameter of the forming cavity of the cylindrical mold is 3-10 mm and the length is 10-50 mm; the molding pressure is 5-15 MPa and the holding time is 1-3 min; the heat treatment is annealing at 100-150℃ for 1-3 h in an air, nitrogen, or vacuum environment.

[0011] Preferably, the conductive metal pins in S4 are copper pins, nickel pins, or stainless steel pins, and the conductive metal pins are electrically connected to the blunt-headed cylindrical porous conductive blank by means of conductive adhesive connection, pressing, or insert molding.

[0012] Preferably, when the organometal framework-based nano-water ion electrode is used to generate nano-water ions, it is not necessary to lower the electrode surface below the dew point using a semiconductor cooling component.

[0013] The beneficial effects of this invention are: This invention involves in-situ composite of transition metal salts, nitrogen-containing heterocyclic ligands, aromatic polycarboxylic acid ligands, and conductive nano-carbon phases to construct an organometallic framework powder with both hydrophilic polar channels and conductive pathways in the pore walls. This powder is then molded into an integrated porous conductive electrode through blunt-tipped cylindrical molding, low-temperature heat treatment, and lead encapsulation. This allows the electrode to simultaneously possess functions such as air moisture adsorption, channel water retention, conductive transport, and distributed ionization, unlike traditional semiconductor-cooled metal tip electrodes that rely on condensation and tip discharge. The resulting electrode does not have a metal tip or pinhole structure, eliminating the need for semiconductor cooling components to lower the electrode surface below the dew point. It can stably form an adsorbed water film using hydrophilic polar channels and create multi-point ionization interfaces on the outer circumferential surface of the cylinder and the blunt-tipped arc end, achieving omnidirectional emission of nano-water ions. The electrode obtained by this invention exhibits high water absorption capacity, suitable conductivity, and a low relative standard deviation of five-point ion concentration. Its ion emission uniformity is significantly better than traditional tip structures. Simultaneously, the ozone concentration is maintained at a low level, which helps reduce the risks of ozone byproducts, ignition, and corrosion caused by localized strong discharges. This electrode has a simple structure, requires no cooling element or complex temperature control and heat dissipation structure, and has the advantages of low energy consumption, high reliability, convenient maintenance, and suitability for air purification and health home appliance applications. Detailed Implementation

[0014] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0015] Example 1: A method for preparing an organometallic framework-based nano-water ion electrode, comprising the following steps: S1. Take 100.0 g of nickel nitrate hexahydrate, 25.0 g of 2-methylimidazole, 30.0 g of terephthalic acid, 0.5 g of carbon nanotubes, and 200.0 g of mixed solvent; the mixed solvent is prepared by mixing deionized water and N,N-dimethylformamide at a volume ratio of 1:0.5; first, add the carbon nanotubes to the mixed solvent for ultrasonic dispersion, then add nickel nitrate hexahydrate, 2-methylimidazole, and terephthalic acid, and stir until uniform to obtain an organometallic framework precursor solution containing conductive nano-carbon phase; S2. The organometallic framework precursor solution obtained in step S1 is transferred to a hydrothermal reactor and hydrothermally reacted at 120°C for 24 h to allow nickel nitrate hexahydrate, 2-methylimidazole, and terephthalic acid to grow in situ on the surface of carbon nanotubes and between their networks. After the reaction is completed, the mixture is cooled, the product is collected, and washed sequentially with N,N-dimethylformamide, ethanol, and deionized water. Then, it is vacuum dried at 60°C for 12 h to obtain conductive organometallic framework powder with hydrophilic polar channels. S3. The conductive organometallic framework powder obtained in step S2 is loaded into a cylindrical mold with a flat bottom at one end and a blunt rounded end at the other end. The forming cavity of the cylindrical mold has a diameter of 3 mm and a length of 10 mm. It is molded under a pressure of 5 MPa and held under pressure for 1 min to obtain a blunt cylindrical blank. Then, the blunt cylindrical blank is placed in an air atmosphere and annealed at 100°C for 3 h to obtain a blunt cylindrical porous conductive blank. S4. A copper pin is embedded in the flat bottom end of the blunt-tipped cylindrical porous conductive blank obtained in step S3, and a conductive adhesive is used to connect the copper pin to the blunt-tipped cylindrical porous conductive blank to form an electrical connection. Then, the connection area between the conductive metal pin and the blunt-tipped cylindrical porous conductive blank is insulated and encapsulated to obtain an organometallic framework-based nano-water ion electrode. The obtained electrode is a blunt-tipped cylindrical porous conductor integrally formed from a conductive organometallic framework material. Its cylindrical outer circumferential surface and blunt arc end surface both have open orifices and conductive pathways in the hole walls, and the electrode body does not have metal needle tips or metal pinhole structures.

[0016] Example 2: A method for preparing an organometallic framework-based nano-water ion electrode, comprising the following steps: S1. Take 100.0 g of cobalt chloride hexahydrate, 52.5 g of imidazole, 65.0 g of 2-aminoterephthalic acid, 5.25 g of graphene, and 500.0 g of mixed solvent; the mixed solvent is prepared by mixing deionized water and ethanol at a volume ratio of 1:1.25; first, add graphene to the mixed solvent for ultrasonic dispersion, then add cobalt chloride hexahydrate, imidazole, and 2-aminoterephthalic acid, and stir until uniform to obtain an organometallic framework precursor solution containing conductive nano-carbon phase; S2. The organometallic framework precursor solution obtained in step S1 is transferred to a hydrothermal reactor and hydrothermally reacted at 140°C for 18 h to allow cobalt chloride hexahydrate, imidazole, and 2-aminoterephthalic acid to grow in situ on the graphene surface and between its sheet networks. After the reaction is completed, the mixture is cooled, the product is collected, and washed sequentially with N,N-dimethylformamide, ethanol, and deionized water. Then, it is vacuum dried at 70°C for 9 h to obtain conductive organometallic framework powder with hydrophilic polar channels. S3. The conductive organometallic framework powder obtained in step S2 is loaded into a cylindrical mold with a flat bottom at one end and a blunt, rounded end at the other end. The forming cavity of the cylindrical mold has a diameter of 6.5 mm and a length of 30 mm. It is molded under a pressure of 10 MPa and held under pressure for 2 min to obtain a blunt-ended cylindrical blank. Then, the blunt-ended cylindrical blank is placed in a nitrogen atmosphere and annealed at 125°C for 2 h to obtain a blunt-ended cylindrical porous conductive blank. S4. A nickel pin is embedded into the flat bottom end of the blunt-tipped cylindrical porous conductive blank obtained in step S3, and the nickel pin is electrically connected to the blunt-tipped cylindrical porous conductive blank by pressing. Then, the connection area between the conductive metal pin and the blunt-tipped cylindrical porous conductive blank is insulated and encapsulated to obtain an organometallic framework-based nano-water ion electrode. The obtained electrode is a blunt-tipped cylindrical porous conductor integrally formed from conductive organometallic framework material. Its cylindrical outer circumferential surface and blunt arc end surface both have open orifices and conductive pathways in the hole walls, and the electrode body does not have metal needle tips or metal pinhole structures.

[0017] Example 3: A method for preparing an organometallic framework-based nano-water ion electrode, comprising the following steps: S1. Take 100.0 g of copper nitrate trihydrate, 80.0 g of benzimidazole, 100.0 g of trimellitic acid, 10.0 g of reduced graphene oxide, and 800.0 g of mixed solvent; the mixed solvent is prepared by mixing deionized water and methanol at a volume ratio of 1:2; first, add the reduced graphene oxide to the mixed solvent for ultrasonic dispersion, then add copper nitrate trihydrate, benzimidazole, and trimellitic acid, and stir until uniform to obtain an organometallic framework precursor solution containing conductive nano-carbon phase; S2. The organometallic framework precursor solution obtained in step S1 is transferred to a hydrothermal reactor and hydrothermally reacted at 160°C for 12 h to allow copper nitrate trihydrate, benzimidazole, and trimesic acid to grow in situ on the surface of reduced graphene oxide and between its networks. After the reaction is completed, the mixture is cooled, the product is collected, and washed sequentially with N,N-dimethylformamide, ethanol, and deionized water. Then, it is vacuum dried at 80°C for 6 h to obtain conductive organometallic framework powder with hydrophilic polar channels. S3. The conductive organometallic framework powder obtained in step S2 is loaded into a cylindrical mold with a flat bottom at one end and a blunt, rounded end at the other end. The forming cavity of the cylindrical mold has a diameter of 10 mm and a length of 50 mm. The mold is pressed under a pressure of 15 MPa and held for 3 min to obtain a blunt-ended cylindrical blank. The blunt-ended cylindrical blank is then placed in a vacuum environment and annealed at 150°C for 1 h to obtain a blunt-ended cylindrical porous conductive blank. S4. Stainless steel pins are embedded into the flat bottom end of the blunt-tipped cylindrical porous conductive blank obtained in step S3, and the stainless steel pins are electrically connected to the blunt-tipped cylindrical porous conductive blank by insert molding. Then, the connection area between the conductive metal pins and the blunt-tipped cylindrical porous conductive blank is insulated and encapsulated to obtain an organometallic framework-based nano-water ion electrode. The obtained electrode is a blunt-tipped cylindrical porous conductor integrally formed from conductive organometallic framework material. Its cylindrical outer circumferential surface and blunt arc end surface both have open orifices and conductive pathways in the hole walls, and the electrode body does not have metal needle tips or metal pinhole structures.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that a metal needle tip is used as the discharge electrode, and condensation is formed on the surface of the metal needle tip by a semiconductor cooling chip.

[0019] The specific preparation method is as follows: S1. Take a stainless steel needle with a diameter of 0.5 mm and a length of 20 mm, process one end into a needle tip discharge terminal, and clean and dry the needle tip with ethanol before use; take a copper lead as the high voltage connection terminal. S2. Press and fix the non-discharge end of the stainless steel needle to the copper pin, and apply conductive glue to the connection to form an electrical connection between the stainless steel needle and the copper pin; control the exposed length of the discharge end of the stainless steel needle to 10 mm. S3. Attach the cold end of the thermoelectric cooler to the position of the stainless steel needle near the discharge end, and apply thermal grease to the contact surface; connect the hot end of the thermoelectric cooler to a heat sink so that the discharge end of the stainless steel needle can be cooled to below the dew point after power is applied, so that water vapor in the air condenses near the needle tip. S4. Mount the stainless steel needle, copper pin, and semiconductor cooling chip onto an insulating support, and encapsulate the copper pin connection area with insulation, while retaining the stainless steel needle tip as the discharge area, to obtain a conventional semiconductor cooling metal tip electrode.

[0020] Comparative Example 2: The difference between this comparative example and Example 1 is that the MOF electrode without the addition of conductive nano-carbon phase is not included.

[0021] The specific preparation method is as follows: S1. Take 100.0 g of nickel nitrate hexahydrate, 25.0 g of 2-methylimidazole, 30.0 g of terephthalic acid and 200.0 g of mixed solvent; the mixed solvent is prepared by mixing deionized water and N,N-dimethylformamide at a volume ratio of 1:0.5; add nickel nitrate hexahydrate, 2-methylimidazole and terephthalic acid to the mixed solvent and stir until uniform to obtain an organometallic framework precursor solution without conductive nano-carbon phase; S2. The organometallic framework precursor solution obtained in step S1 is transferred to a hydrothermal reactor and hydrothermally reacted at 120°C for 24 h to allow nickel nitrate hexahydrate, 2-methylimidazole and terephthalic acid to coordinate and grow. After the reaction is completed, the mixture is cooled, the product is collected, and washed sequentially with N,N-dimethylformamide, ethanol and deionized water. Then it is vacuum dried at 60°C for 12 h to obtain organometallic framework powder without the introduction of conductive nano-carbon phase. S3. The organometallic framework powder obtained in step S2 is loaded into a cylindrical mold with a flat bottom at one end and a blunt, rounded end at the other end. The forming cavity of the cylindrical mold has a diameter of 3 mm and a length of 10 mm. The mold is pressed under a pressure of 5 MPa and held for 1 min to obtain a blunt-ended cylindrical blank. The blunt-ended cylindrical blank is then placed in an air atmosphere and annealed at 100°C for 3 h to obtain a blunt-ended cylindrical MOF blank. S4. Insert copper leads into the flat bottom end of the blunt cylindrical MOF blank obtained in step S3, and connect the copper leads to the blunt cylindrical MOF blank using conductive adhesive; then insulate and encapsulate the connection area between the copper leads and the blunt cylindrical MOF blank to obtain a MOF electrode without the addition of conductive nano carbon phase.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that a blunt-tipped cylindrical porous conductive electrode is prepared using conductive carbon material.

[0023] The specific preparation method is as follows: S1. Take 100.0 g of conductive carbon black, 0.5 g of carbon nanotubes and 200.0 g of mixed solvent; the mixed solvent is prepared by mixing deionized water and N,N-dimethylformamide at a volume ratio of 1:0.5; first, add the carbon nanotubes to the mixed solvent for ultrasonic dispersion, then add the conductive carbon black and stir until uniform to obtain a conductive carbon material dispersion. S2. The conductive carbon material dispersion obtained in step S1 is transferred to a hydrothermal reactor and treated at 120°C for 24 h. After the treatment is completed, the mixture is cooled, the solid product is collected, and washed sequentially with N,N-dimethylformamide, ethanol and deionized water. Then, it is vacuum dried at 60°C for 12 h to obtain conductive carbon material powder. S3. The conductive carbon material powder obtained in step S2 is loaded into a cylindrical mold with a flat bottom at one end and a blunt, rounded end at the other end. The forming cavity of the cylindrical mold has a diameter of 3 mm and a length of 10 mm. The mold is pressed under a pressure of 5 MPa and held for 1 min to obtain a blunt cylindrical blank. The blunt cylindrical blank is then placed in an air atmosphere and annealed at 100°C for 3 h to obtain a conductive carbon material blunt cylindrical blank. S4. A copper pin is embedded in the flat bottom end of the conductive carbon material blunt-tipped cylindrical blank obtained in step S3, and a conductive adhesive is used to connect the copper pin to the conductive carbon material blunt-tipped cylindrical blank to form an electrical connection; then the connection area between the copper pin and the conductive carbon material blunt-tipped cylindrical blank is insulated and encapsulated to obtain a conductive carbon material blunt-tipped cylindrical electrode.

[0024] Performance testing 1. Ion Concentration and Omnidirectional Emission Test The test was conducted in a 1 m³ sealed acrylic glass test chamber. Before the test, the air circulation device was turned on for 5 minutes to stabilize the temperature and humidity inside the chamber. Then, the circulation device was turned off, and the background ion concentration C0 was recorded. The electrode to be tested was installed in the center of the test chamber with the blunt, rounded end facing upwards. The electrode was connected to a -4.0 kV DC high-voltage power supply, and the closest distance between the grounding electrode and the electrode's emitting surface was 20 mm. After running for 10 minutes, the ion concentration was measured at five test points using an air ion concentration meter: test point P1 was located 5 cm axially above the blunt, rounded end of the electrode; test points P2–P5 were located 5 cm in the front, back, left, and right radial directions on the outer circumference of the cylinder, respectively. Readings were taken continuously for 3 minutes at each test point, and the average stable reading was taken. The net ion concentration was obtained by subtracting the background ion concentration C0. Omnidirectional emission uniformity was expressed as the relative standard deviation (RSD) of the net ion concentration at the five test points. The smaller the RSD, the more uniform the omnidirectional emission of the electrode. In Comparative Example 1, the semiconductor cooling chip and metal tip high-voltage discharge were activated, and the test point arrangement was consistent with the example.

[0025] Table 1. Ion concentration and omnidirectional emission test results of Examples 1-3 and Comparative Examples 1-3

[0026] 2. Water absorption capacity test Each group of electrode samples was dried in a 60℃ vacuum drying oven for 6 h. After removal, they were cooled to room temperature in a desiccator, and their mass m0 after drying was measured. The samples were then placed in a constant temperature and humidity chamber at 25±2℃ and 80±5% relative humidity for 24 h. After removal, the non-adsorbent surface free water was quickly wiped off, and the mass m1 after moisture absorption was measured. The water absorption capacity was calculated using the formula A = (m1 - m0) / m0 × 100%, where A is the water absorption capacity in wt%. Three samples were tested in each group, and the average value was taken as the test result. Comparative Example 1 tested the natural moisture absorption mass change of its metal tip and emitter assembly without turning on the semiconductor cooling chip.

[0027] 3. Conductivity Test Each group of electrode samples was dried in a 60℃ vacuum drying oven for 2 h and then cooled to room temperature. The overall resistance of the electrodes was tested using the DC two-terminal method. A constant test current was applied between the conductive metal lead at the flat bottom end of the electrode and the surface of the blunt, rounded end, and the stable voltage value was recorded. The resistance R was then calculated. During testing, a thin layer of conductive silver paste was coated on the surface of the blunt, rounded end to ensure stable contact. The test current was selected from 0.1 to 10 mA based on the sample resistance value, and each sample was tested three times consecutively. The conductivity was calculated using the formula σ = L / (R × S), where σ is the conductivity (S / cm), L is the effective conductive length of the electrode (cm), S is the cross-sectional area of ​​the cylindrical electrode (cm²), and R is the measured resistance (Ω). The average value of three parallel samples in each group was taken as the result.

[0028] 4. Ozone Concentration Test The test was conducted in a 1 m³ sealed test chamber, identical to the ion concentration test. Before the test, the background ozone concentration O0 within the chamber was measured. The electrode to be tested was placed in the center of the test chamber, and the test was run for 30 minutes under the same voltage, grounding electrode distance, and temperature and humidity conditions as the ion concentration test. An ultraviolet absorption ozone detector was used to measure the ozone concentration at three locations: 5 cm axially above the blunt end of the electrode, 5 cm radially from the outer circumference of the cylinder, and at the center of the test chamber. Readings were taken continuously for 3 minutes at each location, and a stable average value was recorded. The ozone concentration result is expressed as the maximum value after subtracting the background ozone concentration, i.e., O = Omax - O0. The average value of three parallel samples in each group was taken as the test result. Comparative Example 1 was tested under the same conditions according to its conventional semiconductor-cooled metal tip discharge state.

[0029] Table 2. Test results of water absorption capacity, conductivity, and ozone concentration in Examples 1-3 and Comparative Examples 1-3.

[0030] As shown in Tables 1 and 2, the organometal framework-based nano-water ion electrodes obtained in Examples 1-3 all exhibited high average net ion concentration, low relative standard deviation of five-point tests, high water absorption capacity, and low ozone concentration. This indicates that the present invention forms a porous conductive MOF structure with both hydrophilic polar channels and conductive pathways in the pore walls by in-situ composite of transition metal salts, nitrogen-containing heterocyclic ligands, aromatic polycarboxylic acid ligands, and conductive nano-carbon phases. The average net ion concentrations in Examples 1-3 were 2.77 × 10⁶ ions / cm³, 3.44 × 10⁶ ions / cm³, and 3.17 × 10⁶ ions / cm³, respectively, with RSDs all below 5%, indicating that both the outer circumferential surface and the blunt arc end surface of the blunt-tipped cylinder can serve as effective emission interfaces, achieving relatively uniform omnidirectional emission. Simultaneously, the water absorption capacity reached 214.6–278.5 wt%, demonstrating that the hydrophilic polar channels can effectively adsorb and store water vapor from the air, providing a stable adsorbed water film for high-voltage ionization. The conductivity increased with increasing amounts of conductive nano-carbon phase, proving that the conductive nano-carbon phase is beneficial for constructing a continuous conductive network. The ozone concentration remained between 0.013 and 0.016 ppm, indicating that the present invention employs a blunt-tipped porous structure without metal needle tips, which avoids the increased ozone byproducts caused by localized strong discharge at traditional sharp points. The above results show that the present invention does not simply replace electrode materials, but achieves efficient, uniform, and low-ozone nano-water ion emission through the synergistic effect of water absorption and retention, conductive transport, and porous distributed ionization interface.

[0031] Compared to Example 1, Comparative Example 1, using a conventional semiconductor-cooled metal tip electrode, had an average net ion concentration of only 0.76 × 10⁶ ions / cm³, a decrease of approximately 72.6% compared to Example 1, and an RSD as high as 135.9%, indicating that its ions were mainly concentrated in the axial emission of the tip, with weak lateral emission capability, and unable to form omnidirectional uniform diffusion. Simultaneously, its water absorption capacity was only 3.8 wt%, indicating that its water source mainly relied on refrigeration and condensation rather than the material's own water absorption and retention. The ozone concentration rose to 0.043 ppm, reflecting that the strong local electric field at the tip was more likely to generate ozone byproducts. Comparative Example 2, without the addition of conductive nano-carbon phase, still retained the water absorption capacity of the MOF channels, with a water absorption capacity of 198.3 wt%, but the conductivity decreased to 4.6 × 10⁻⁻⁻⁴. 7The average net ion concentration was only 0.38 × 10⁶ ions / cm³, a decrease of approximately 86.3% compared to Example 1. This indicates that without a conductive nano-carbon phase, it is difficult to form a continuous pore wall conductive pathway, the adsorbed water film cannot be stably ionized, and the ion generation capacity is significantly limited. Comparative Example 3 used a blunt-tipped cylindrical electrode made of conductive carbon material. Although the conductivity was higher than that of Example 1, the water absorption capacity was only 36.7 wt%, and the average net ion concentration was only 0.76 × 10⁶ ions / cm³, a decrease of approximately 72.6% compared to Example 1. Moreover, the ozone concentration increased to 0.026 ppm. This indicates that the simple conductive material lacks hydrophilic polar MOF channels, making it difficult to stably adsorb and bind water molecules, and unable to form an effective adsorbed water film ionization interface.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an organometallic framework-based nano-water ion electrode, characterized in that, Includes the following steps: S1. A transition metal salt, a nitrogen-containing heterocyclic ligand, an aromatic polycarboxylic acid ligand, a conductive carbon nanophase, and a mixed solvent are dispersed and mixed to obtain an organometallic framework precursor solution containing a conductive carbon nanophase. S2. The organometallic framework precursor solution is subjected to hydrothermal reaction to enable the transition metal salt, nitrogen-containing heterocyclic ligand and aromatic polycarboxylic acid ligand to grow in situ on the surface of conductive nano carbon phase and between its networks. After washing and drying, conductive organometallic framework powder with hydrophilic polar channels is obtained. S3. The conductive organic metal framework powder is loaded into a cylindrical mold with a flat bottom at one end and a blunt rounded end at the other end for molding and heat treatment to obtain a blunt cylindrical porous conductive blank. S4. A conductive metal pin is embedded in the flat bottom end of a blunt cylindrical porous conductive blank, and the connection area between the conductive metal pin and the blunt cylindrical porous conductive blank is insulated and encapsulated to obtain an organometallic framework-based nano-water ion electrode. The nano-water ion organometallic framework electrode is a blunt-tipped cylindrical porous conductor integrally formed from a conductive organometallic framework material. The cylindrical outer circumferential surface and the blunt-tipped arc end surface of the blunt-tipped cylindrical porous conductor both have open orifices and conductive pathways in the pore walls, and the nano-water ion organometallic framework electrode body does not have metal needle tips or metal pinhole structures.

2. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, The transition metal salt is one or more of nickel salt, cobalt salt, and copper salt; the nitrogen-containing heterocyclic ligand is one or more of 2-methylimidazole, imidazole, and benzimidazole; the aromatic polycarboxylic acid ligand is one or more of terephthalic acid, 2-aminoterephthalic acid, and trimesic acid.

3. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, Based on 100 parts by mass of the transition metal salt, the amount of conductive carbon nanophase is 0.5 to 10 parts, the amount of nitrogen-containing heterocyclic ligand is 25 to 80 parts, the amount of aromatic polycarboxylic acid ligand is 30 to 100 parts, and the amount of mixed solvent is 200 to 800 parts; the conductive carbon nanophase is one or more of carbon nanotubes, graphene, and reduced graphene oxide.

4. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, The mixed solvent is a mixture of deionized water and one of N,N-dimethylformamide, ethanol, and methanol, with a volume ratio of deionized water to the other solvent of 1:(0.5-2). In step S1, the conductive nano-carbon phase is first added to the mixed solvent and ultrasonically dispersed, and then a transition metal salt, a nitrogen-containing heterocyclic ligand, and an aromatic polycarboxylic acid ligand are added and stirred and mixed.

5. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, The hydrothermal reaction in S2 is carried out at a temperature of 120–160°C for 12–24 h. The washing is performed sequentially with N,N-dimethylformamide, ethanol, and deionized water, and the drying is carried out under vacuum at 60–80°C for 6–12 h.

6. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, In S3, the diameter of the forming cavity of the cylindrical mold is 3-10 mm and the length is 10-50 mm; the molding pressure is 5-15 MPa and the holding time is 1-3 min; the heat treatment is annealing at 100-150℃ for 1-3 h in an air, nitrogen or vacuum environment.

7. The method for preparing the organometallic framework-based nano-water ion electrode according to claim 1, characterized in that, The conductive metal pins in S4 are copper pins, nickel pins, or stainless steel pins. The conductive metal pins are electrically connected to the blunt-headed cylindrical porous conductive blank by means of conductive adhesive connection, pressing, or insert molding.

8. The preparation method according to any one of claims 1-7, characterized in that, The organometal framework-based nano-water ion electrode is used to generate nano-water ions without requiring a semiconductor cooling component to lower the electrode surface below the dew point.

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