Nano-nickel oxide preparation process based on coordination precursor pyrolysis

Abstract

This invention discloses a process for preparing nano-nickel suboxide based on the pyrolysis of coordination precursors, belonging to the field of nanomaterial preparation technology. This process constructs a gradient bond energy coordination system through the combination of strong and weak ligands, and uses SDBS soft templates for directional assembly. Through a three-stage atmosphere-coupled pyrolysis and water washing, asynchronous release of nickel ions and ordered growth of crystal nuclei are achieved. The prepared nano-nickel suboxide particles have uniform size, low agglomeration, low carbon / sodium impurity residue, and high specific surface area. The process requires no special equipment, is simple to operate, and has controllable costs, making it suitable for industrial-scale mass production. It can be widely used in energy storage, catalysis, sensing, and other fields.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a nano-nickel oxide preparation process based on the pyrolysis of coordination precursors. Background Technology

[0002] As a typical p-type semiconductor nanomaterial, nano-nickel suboxide (NiO) exhibits irreplaceable application value in new energy storage (lithium-ion battery anodes, supercapacitor electrodes), electrocatalysis (oxygen reduction, oxygen evolution reaction), gas sensing (formaldehyde, ethanol detection), and precision catalytic carriers due to its high specific surface area, abundant surface active sites, and excellent electrochemical, catalytic, and gas-sensing properties. It is currently a research hotspot and a core product of industrial demand in the field of inorganic functional nanomaterials. High-performance nano-nickel suboxide, in particular, has extremely stringent requirements for "narrow particle size distribution, low agglomeration, and high purity (free from carbon / sodium and other impurities)." For example, in lithium-ion battery anode applications, uneven particle size or agglomeration can lead to poor electrolyte wettability and rapid capacity decay; in the field of electrocatalysis, carbon residues can cover active sites, and alkali metal impurities can disrupt the crystal structure, both directly limiting the upper limit of industrial application.

[0003] Currently, the coordination precursor pyrolysis method is the mainstream technical route for preparing highly dispersed nano-nickel oxide. Its core advantage lies in the fact that by forming coordination bonds with nickel ions through organic ligands, atomic-level dispersion of nickel ions can be achieved, avoiding the problem of rapid agglomeration of metal ions in traditional precipitation methods. However, this technical route has long faced three core technical bottlenecks during industrial scale-up: First, it is difficult to control the uniformity and dispersion of particle size. Traditional processes often use single ligands (such as EDTA and citric acid) or simple binary ligands to physically combine and construct coordination systems. The distribution of coordination bond energy is either uniform or disordered. During pyrolysis, a large amount of nickel ions are released simultaneously, leading to "explosive nucleation" and "disordered growth" of crystal nuclei. The final product has a wide particle size distribution and is prone to forming hard agglomerates, resulting in a significant reduction in specific surface area. Second, it is difficult to guarantee product purity. On the one hand, the pyrolysis decomposition rate of ligands and the oxygen oxidation rate are difficult to match. At low temperatures, incomplete decomposition of ligands can easily leave amorphous carbon residues, while at high temperatures, rapid decomposition of ligands can easily cause local carbon deposition. On the other hand, if coordination sodium salts are used as raw materials, traditional water washing processes lack quantitative control standards, and water-soluble impurities such as sodium ions are difficult to completely remove, which seriously affects the application of the product in the field of high-precision electronic devices.

[0004] To address these issues, the industry has undertaken a series of improvement attempts: For example, some studies have optimized coordination stability by replacing ligand types, but these have not overcome the limitations of "single bond energy" and still cannot achieve asynchronous release of nickel ions, with the problems of uneven particle size and agglomeration not fundamentally improved; some schemes use simple compounding of multiple ligands (such as a mixture of EDTA and citric acid), but there is no synergistic coordination between ligands, the bond energy distribution is disordered, and the problem of concentrated release of nickel ions still exists during pyrolysis; other studies have optimized the crystallization process by adjusting the pyrolysis temperature and holding time, using "one-step air pyrolysis" instead of segmented pyrolysis, but this cannot achieve the spatiotemporal separation of "crystal nucleation" and "grain growth," the ligand decomposition and oxidation are still asynchronous, and the problems of carbon residue and agglomeration remain prominent.

[0005] However, none of the existing improvement schemes mentioned above address the core contradictions of coordination precursor pyrolysis: the lack of bond energy gradients in the coordination system leading to synchronized nickel ion release and the mismatch between the pyrolysis process and coordination decomposition kinetics. Single ligand replacement or simple compounding only involves parameter fine-tuning and fails to construct a controllable nickel ion release mechanism at the coordination chemistry level; the one-step pyrolysis process cannot adapt to the decomposition characteristics of the coordination system, making it difficult to balance ligand oxidation and grain crystallization. Therefore, a revolutionary technical solution encompassing the entire chain from coordination mechanism and pyrolysis process to impurity control is urgently needed to overcome the current industry bottlenecks. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a nano-nickel oxide preparation process based on the pyrolysis of coordination precursors.

[0007] To achieve the above objectives, the present invention employs the following technical solution: a nano-nickel oxide preparation process based on the pyrolysis of coordination precursors, comprising the following steps: (1) Add the nickel source to deionized water and stir until dissolved to prepare a nickel salt solution; (2) Add the weak ligand to the nickel salt solution and stir at room temperature for 20-40 min to obtain a preliminary complexed solution; (3) Add the strong ligand to the preliminary complexing solution, and while stirring, add ammonia to adjust the pH of the system to 7.5-8.5. Then raise the temperature to 55-65℃ and stir the reaction for 2-3 hours to obtain the complex solution. (4) Maintain a temperature of 55-65℃, add a directing agent to the complex solution, stir for 20-40 min, then cool to 40-50℃ and sonicate for 30-45 min to obtain a gel precursor solution; (5) Dehydrate the gel precursor solution under vacuum at 70-80℃ for 30-60 min, and then dry it in a vacuum drying oven to obtain a dry gel; (6) After the dry gel is crushed into powder, it is evenly spread in the alumina boat and then sent into the tube furnace. Nitrogen gas is introduced and the temperature is raised from room temperature to 250-300℃. The temperature is held for 30-45 minutes to complete the first stage of heating. (7) After the first stage of heating is completed, nitrogen / oxygen mixture is introduced and the temperature is continued to rise to 380-450℃, and held for 60-90 minutes to complete the second stage of heating; (8) After the second stage of heating is completed, oxygen is introduced and the temperature is continued to rise to 450-500℃. The temperature is held for 1-2 hours to complete the third stage of heating. After that, heating is stopped and the furnace is cooled to room temperature. (9) Grind and break up the cooled product, wash it with deionized water 3-4 times, and dry it after washing to obtain nano-nickel oxide based on the pyrolysis of coordination precursor.

[0008] Preferably, the nickel source in (1) refers to one of nickel nitrate, nickel acetate or nickel chloride.

[0009] Preferably, the concentration of the nickel salt solution in (1) is 0.1-1.0 mol / L.

[0010] Preferably, the molar ratio of nickel ions to weak ligand in the preliminary complexing solution in (2) is 1:0.7-0.9.

[0011] Preferably, the weak ligand in (2) refers to sodium L-aspartate or malic acid.

[0012] Preferably, the molar ratio of nickel ions to strong ligands in the complex solution in (3) is 1:0.3-0.5.

[0013] Preferably, the strong ligand in (3) refers to EDTA-2Na or sodium hypotriacetate.

[0014] Preferably, the concentration of ammonia in (3) is 25-28 wt%.

[0015] Preferably, the directing agent in (4) refers to sodium dodecylbenzenesulfonate, and the concentration of sodium dodecylbenzenesulfonate in the system after its addition is 0.05-0.1 mol / L.

[0016] Preferably, the power of the ultrasonic treatment in (4) is 300-500w.

[0017] Preferably, the temperature of the vacuum drying oven in (5) is 80-100℃.

[0018] Preferably, the flow rate of nitrogen in (6) is 80-120 ml / min.

[0019] Preferably, the heating rate of the tubular furnace in (6) is 2-3℃ / min.

[0020] Preferably, the flow rate of the nitrogen / oxygen mixture in (7) is 80-120 ml / min.

[0021] Preferably, the volume fraction of oxygen in the mixed gas in (7) is 5-10%.

[0022] Preferably, the heating rate in (7) is 1-2℃ / min.

[0023] Preferably, the oxygen introduction rate in step (8) is 150-200 ml / min.

[0024] Preferably, the heating rate in (8) is 2-3℃ / min.

[0025] Preferably, the standard for completing the deionized water washing in (9) is that the absolute difference between the conductivity of the washing liquid and the background conductivity of the deionized water is ≤0.05μS / cm.

[0026] Preferably, the process mechanism of the present invention based on the pyrolysis of coordination precursor for the preparation of nano-nickel oxide is explained as follows: The preparation process of this invention first constructs a composite coordination precursor with "asynchronous decomposition" and "spatial orientation", utilizing the thermodynamic stability and kinetic differences of complexes formed between different ligands and nickel ions.

[0027] First, the combination of a strong ligand (such as EDTA-2Na) and a weak ligand (such as sodium L-aspartate) is not chosen arbitrarily. EDTA, as a hexadecantal ligand, can react with Ni... 2+ This forms chelates containing multiple five-membered rings (such as [Ni(EDTA)]). 2- Its thermodynamic stability constant is extremely high, and its coordinate bonds are strong; while sodium L-aspartate, as a bidentate ligand, interacts with Ni 2+ The resulting complexes have relatively low stability; when both coexist in alkaline aqueous solutions (pH 7.5-8.5), they do not act independently, but rather compete for Ni. 2+ The surrounding coordination sites form a dynamically balanced, mixed-coordinate "molecular cluster" or supramolecular precursor structure, in which each Ni 2+ The surrounding area contains both strong and weak coordination bonds. The fundamental purpose of this design is to facilitate the subsequent pyrolysis process of Ni. 2+ The “asynchronous release” lays the chemical foundation for this, where weak coordination bonds break preferentially at lower temperatures, while strong coordination bonds remain stable at higher temperatures.

[0028] Subsequently, the introduction of the directing agent sodium dodecylbenzenesulfonate (SDBS) elevates the molecular-level chemical design to mesoscale structural control. SDBS is an amphiphilic surfactant; its hydrophilic sulfonic acid head end can adsorb onto the surface of charged nickel complexes through electrostatic or polar interactions, while the hydrophobic long-chain alkyl groups tend to aggregate. Driven by ultrasonic energy, SDBS molecules self-assemble in water to form ordered structures such as micelles and layers. These structures act as "soft templates," guiding and constraining the aforementioned nickel complex molecular clusters to oriented at their interfaces or within their interiors. This process effectively inhibits the random aggregation of complex molecules, endowing the precursor solution (or the dehydrated dry gel) with an intrinsic, nanoscale structural order. This order is crucial, providing the initial support for morphological control of the final oxide grains and the suppression of hard aggregation.

[0029] The meticulous design of the precursor only makes the excellent performance of the final product possible; the key to turning it into reality lies in the precisely matched pyrolysis conversion process. The core of the three-stage gradient pyrolysis process of this invention is the realization of spatiotemporal separation of the two key stages of "nucleation" and "growth".

[0030] The first stage (250-300℃, pure N2 atmosphere) is the controllable nucleation period. Under this mild, inert atmosphere and relatively low temperature, the weakest coordination bonds in the precursor (such as those between aspartic acid and Ni) exhibit the worst thermal stability. 2+ The selective breaking of the coordination bonds between the nickel ions results in the slow release of these nickel ions. However, due to the lack of a strong oxidizing atmosphere, they do not directly form NiO. Instead, they tend to combine with a series of small molecular fragments (such as CO, CO2, alkenes, amines, etc.) generated by the pyrolysis reaction of organic ligand molecules in an inert atmosphere through dehydration, decarboxylation, and intramolecular recombination, as well as reducing atmospheres (such as H2, CO), to form extremely small, uniformly dispersed, and defect-rich "nickel-carbon-oxygen-nitrogen" composite precursor nuclei. The spatial confinement effect of the SDBS template ensures that the distribution of these composite precursor nuclei is highly uniform and effectively prevents their fusion. The core of this stage is to lay the foundation for the uniformity of product particle size.

[0031] The second stage (380-450℃, low-oxygen N2 / O2 mixture) is the slow-release growth and crystal phase transformation period. As the temperature rises, the coordination bonds of strong coordinating agents (such as EDTA) begin to break, and nickel ions are continuously and slowly released. At the same time, the introduced trace amounts of oxygen begin to play a role. On the one hand, it causes mild oxidation of the decomposed organic ligand skeleton, avoiding carbon deposition; on the other hand, it promotes the transformation of intermediates such as composite precursor nuclei formed in the first stage and newly released nickel species into the nickel oxide (NiO) crystal phase. Since the nickel ion supply rate is controlled by the slow-release mechanism of strong coordination bonds, and there are a large number of uniformly distributed crystal nuclei, the newly formed NiO will preferentially grow epitaxially on the surface of these existing crystal nuclei, rather than triggering new explosive nucleation. Although the SDBS template gradually decomposes during pyrolysis, its residual carbon skeleton or the formed pore structure can still play a physical isolation role in the crystal growth process, guiding the crystal to grow in a specific direction, thereby achieving the control of the final particle morphology.

[0032] The third stage (450-500℃, pure O2 atmosphere) is the lattice refinement and purification period. Under oxygen-rich conditions and higher temperatures, two main processes occur simultaneously: first, the complete decomposition and removal of any residual organic species and amorphous carbon ensures product purity; second, through the Ostwald ripening effect, the lattice structure of NiO crystals is further reorganized and improved, defects are reduced, and crystallinity is significantly increased. High-flow-rate oxygen ensures that the product is fully oxidized, stoichiometric NiO; finally, through multi-step deionized water washing, utilizing the significant difference in solubility between sodium salt byproducts such as Na2CO3 and NaNO3, as well as sodium oxide, sodium peroxide, and NiO in water, water-soluble impurities such as sodium ions introduced during the process can be efficiently removed, thereby obtaining a high-purity final product.

[0033] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs a bond energy gradient system using strong and weak coordination agents. Weak coordination bonds preferentially break at low temperatures, releasing nickel ions to form uniform crystal nuclei, while strong coordination bonds slowly break at high temperatures, continuously supplying nickel ions and achieving ordered crystal growth. Combined with the mesoscopic confinement effect of the SDBS soft template, grain fusion is inhibited at both the molecular and mesoscopic levels. This design ensures uniform dispersion of nano-nickel suboxide particles, preventing hard agglomeration and avoiding the covering of active sites. This provides structural support for improving electrolyte wettability and reducing capacity decay in energy storage applications, while simultaneously ensuring particle size uniformity.

[0034] 2. This invention achieves stepwise oxidation of ligands through a three-stage atmosphere-coupled pyrolysis: a low-oxygen stage gently decomposes the ligands to avoid carbon buildup, while an oxygen-rich stage thoroughly removes residual organic carbon; combined with a water washing process controlled by quantitative conductivity difference, the difference in solubility between sodium salt and nickel oxide completely removes sodium ions. This approach ensures that the product has no carbon residue and extremely low sodium content, meeting the stringent purity requirements of high-precision electronic devices and catalysis, preventing impurities from damaging the crystal structure and active sites, and ensuring product performance stability.

[0035] 3. This invention achieves high performance while also considering process economy and industrial adaptability. The entire process utilizes conventional tube furnaces and vacuum drying ovens, eliminating the need for high-pressure spray drying or special atmosphere furnaces, thus reducing equipment investment costs. Raw materials are selected from commercially available nickel nitrate and EDTA-2Na, ensuring wide availability and controllable costs. The three-stage gradient pyrolysis, through precise temperature control and atmosphere adjustment, avoids energy waste caused by excessively high temperatures and simplifies subsequent impurity removal processes. The overall process is simple to operate, has a short flow, can be directly integrated with existing production lines, is suitable for mass production, and offers both economic and environmental benefits.

[0036] 4. This invention utilizes the synergistic effect of SDBS soft templates and gradient pyrolysis to construct a rich microporous structure between nano-nickel oxide particles: the pores formed after the pyrolysis of SDBS micelles, along with the extremely small particle size, jointly increase the specific surface area, fully exposing the surface active sites. This structure not only enhances the substrate adsorption capacity of the material in catalytic reactions but also improves the gas response rate in gas sensing applications, while optimizing the electrolyte ion transport channels in energy storage electrodes. Furthermore, the uniform particle size and micropore distribution ensure consistent batch performance, providing a stable material basis for downstream applications in multiple fields and expanding the applicable scenarios of nano-nickel oxide. Attached Figure Description

[0037] Figure 1 This is a transmission electron microscope (TEM) image of nano-nickel oxide based on the pyrolysis of coordination precursor prepared in Example 2 of the present invention. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] Example 1: The specific preparation process of nano-nickel oxide based on coordination precursor pyrolysis includes the following steps: (1) Add 10 mol of nickel nitrate to deionized water and stir until dissolved to prepare a nickel salt solution with a concentration of 0.1 mol / L; (2) Add 7 mol of L-aspartate sodium to the nickel salt solution and stir for 20 min at room temperature to obtain a preliminary complexed solution; (3) Add 3 mol EDTA-2Na to the preliminary complexing solution, and while stirring, add ammonia water with a concentration of 25-28wt% to adjust the pH of the system to 7.5. Then raise the temperature to 55℃ and stir the reaction for 2h to obtain the complex solution. (4) Maintain the temperature at 55°C, add sodium dodecylbenzenesulfonate to the complex solution to make the concentration of sodium dodecylbenzenesulfonate in the system 0.05 mol / L, stir for 20 min, then cool down to 40°C, and sonicate at 300 W for 30 min to obtain the gel precursor solution. (5) The gel precursor solution was dehydrated under vacuum at 70°C for 30 min, and then dried in a vacuum drying oven at 80°C to obtain a dry gel. (6) After the dry gel is crushed into powder, it is evenly spread in the alumina boat and then sent into the tube furnace. Nitrogen gas is introduced at a rate of 80 ml / min, and the temperature is raised from room temperature to 250℃ at a rate of 2-3℃ / min. The temperature is held for 30 min to complete the first stage of heating. (7) After the first stage of heating is completed, nitrogen / oxygen mixture (oxygen volume fraction is 5%) is introduced at a rate of 80 ml / min, and the temperature is continued to rise to 380℃ at a rate of 1-2℃ / min. The temperature is held for 60 min to complete the second stage of heating. (8) After the second stage of heating is completed, oxygen is introduced at a rate of 150 ml / min, and the temperature is continued to rise to 450°C at a rate of 2-3°C / min. The temperature is held for 1 hour to complete the third stage of heating. After that, heating is stopped and the furnace is cooled to room temperature. (9) Grind and break up the cooled product, wash it with deionized water 3-4 times until the absolute difference between the conductivity of the washing solution and the background conductivity of the deionized water is ≤0.05μS / cm, and then dry it to obtain nano-nickel oxide based on the pyrolysis of coordination precursor.

[0040] Example 2: The specific preparation process of nano-nickel oxide based on coordination precursor pyrolysis includes the following steps: (1) Add 10 mol of nickel nitrate to deionized water and stir until dissolved to prepare a nickel salt solution with a concentration of 0.5 mol / L; (2) Add 8 mol of L-aspartate sodium to the nickel salt solution and stir for 30 min at room temperature to obtain a preliminary complexed solution; (3) Add 4 mol EDTA-2Na to the preliminary complexing solution, and while stirring, add ammonia water with a concentration of 25-28wt% to adjust the pH of the system to 8.0. Then raise the temperature to 60℃ and stir the reaction for 2.5h to obtain the complex solution. (4) Maintain the temperature at 60°C, add sodium dodecylbenzenesulfonate to the complex solution to make the concentration of sodium dodecylbenzenesulfonate in the system 0.08 mol / L, stir for 30 min, then cool down to 45°C and sonicate at 400 W for 40 min to obtain the gel precursor solution. (5) The gel precursor solution was dehydrated under vacuum at 75°C for 45 min, and then dried in a vacuum drying oven at 90°C to obtain a dry gel. (6) After the dry gel is crushed into powder, it is evenly spread in the alumina boat and then sent into the tube furnace. Nitrogen gas is introduced at a rate of 90 ml / min, and the temperature is raised from room temperature to 275℃ at a rate of 2-3℃ / min. The temperature is held for 40 min to complete the first stage of heating. (7) After the first stage of heating is completed, nitrogen / oxygen mixture (oxygen volume fraction is 8%) is introduced at a rate of 100 ml / min, and the temperature is continued to rise to 420℃ at a rate of 1-2℃ / min. The temperature is held for 75 min to complete the second stage of heating. (8) After the second stage of heating is completed, oxygen is introduced at a rate of 180 ml / min, and the temperature is continued to rise to 480℃ at a rate of 2-3℃ / min. The temperature is held for 1.5 h to complete the third stage of heating. Then the heating is stopped and the furnace is cooled to room temperature. (9) The cooled product is ground and dispersed, washed with deionized water 3-4 times until the absolute difference between the conductivity of the washing solution and the background conductivity of the deionized water is ≤0.05μS / cm, and then dried to obtain nano-nickel oxide based on the pyrolysis of the coordination precursor. The transmission electron microscopy characterization results of the nano-nickel oxide prepared in this embodiment are as follows: Figure 1 As shown in the figure, the obtained nano-nickel oxide particles are spherical with excellent morphological uniformity and no irregular grains. The size of a single primary grain is concentrated in the range of 15-25 nm. The inter-particle interfaces are clear, with no obvious hard agglomeration structure and only a very small amount of soft agglomeration formed by the electrostatic force between particles.

[0041] Example 3: The specific preparation process of nano-nickel oxide based on coordination precursor pyrolysis includes the following steps: (1) Add 10 mol of nickel nitrate to deionized water and stir until dissolved to prepare a nickel salt solution with a concentration of 1.0 mol / L; (2) Add 9 mol of L-aspartate sodium to the nickel salt solution and stir for 40 min at room temperature to obtain a preliminary complex solution; (3) Add 5 mol EDTA-2Na to the preliminary complexing solution, and while stirring, add ammonia water with a concentration of 25-28wt% to adjust the pH of the system to 8.5. Then raise the temperature to 65℃ and stir the reaction for 3h to obtain the complex solution. (4) Maintain the temperature at 65°C, add sodium dodecylbenzenesulfonate to the complex solution to make the concentration of sodium dodecylbenzenesulfonate in the system 0.1 mol / L, stir for 40 min, then cool to 50°C and sonicate for 45 min to obtain the gel precursor solution. (5) The gel precursor solution was dehydrated under vacuum at 80°C for 60 min, and then dried in a vacuum drying oven at 100°C to obtain a dry gel. (6) After the dry gel is crushed into powder, it is evenly spread in the alumina boat and then sent into the tube furnace. Nitrogen gas is introduced at a rate of 100 ml / min, and the temperature is raised from room temperature to 300℃ at a rate of 2-3℃ / min. The temperature is held for 45 min to complete the first stage of heating. (7) After the first stage of heating is completed, nitrogen / oxygen mixture (oxygen volume fraction is 10%) is introduced at a rate of 120 ml / min, and the temperature is continued to rise to 450℃ at a rate of 1-2℃ / min. The temperature is held for 90 min to complete the second stage of heating. (8) After the second stage of heating is completed, oxygen is introduced at a rate of 200 ml / min, and the temperature is continued to rise to 500℃ at a rate of 2-3℃ / min. The temperature is held for 2 hours to complete the third stage of heating. After that, heating is stopped and the furnace is cooled to room temperature. (9) Grind and break up the cooled product, wash it with deionized water 3-4 times until the absolute difference between the conductivity of the washing solution and the background conductivity of the deionized water is ≤0.05μS / cm, and then dry it to obtain nano-nickel oxide based on the pyrolysis of coordination precursor.

[0042] Example 4: The difference between Example 4 and Example 2 is that nickel nitrate is replaced with nickel acetate.

[0043] Example 5: The difference between Example 5 and Example 2 is that nickel nitrate is replaced with nickel chloride.

[0044] Example 6: The difference between Example 6 and Example 2 is that EDTA-2Na is replaced with sodium hypotriacetate.

[0045] Example 7: The difference between Example 7 and Example 2 is that L-aspartate sodium is replaced with malic acid.

[0046] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that step (2) is omitted, and EDTA-2Na is directly added to the nickel salt solution.

[0047] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that EDTA-2Na is not added in step (3).

[0048] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that step (4) is omitted and sodium dodecylbenzenesulfonate is not added.

[0049] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that steps (6)-(8) are omitted. After the dry gel obtained in step (5) is crushed, the dry gel powder is directly placed into a tube furnace and heated to 480°C at a heating rate of 2-3°C / min in an air atmosphere, and kept at the temperature for 2.5h.

[0050] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that step (9) is omitted, and in step (8), nano-nickel oxide based on the pyrolysis of coordination precursor is directly obtained after furnace cooling.

[0051] Performance testing: 1. Particle size distribution and dispersibility test Take 5 mg of the nano-nickel oxide products prepared in each example and comparative example, add them to 10 ml of anhydrous ethanol, and ultrasonically disperse them for 20 min at 300 W to prepare a uniformly dispersed suspension. Use a dynamic light scattering particle size analyzer (DLS) at 25 °C and a scattering angle of 90 ° to test the particle size distribution of the suspension. Record the average particle size (D50), particle size distribution width (D90 / D10) and agglomeration index. The experimental results are shown in Table 1.

[0052] 2. Product purity test: Sodium Residue Test Weigh 0.5 g of the nano-nickel oxide product prepared in each example and comparative example, place it in a polytetrafluoroethylene digestion vessel, add 10 ml of nitric acid (analytical grade), seal and place it in a microwave digestion apparatus, and digest according to the procedure of "heating to 120℃ and holding for 10 min → heating to 180℃ and holding for 20 min". After digestion, cool to room temperature, transfer the digestion solution to a 50 ml volumetric flask, dilute to the mark with deionized water, shake well, and use an inductively coupled plasma optical emission spectrometer (ICP-OES) to test the sodium concentration in the solution. Calculate the sodium residue (ppm) in the sample according to the dilution factor. The experimental results are shown in Table 1. Carbon residue test 20 mg of the nano-nickel oxide product prepared in each example and comparative example was weighed and placed in the combustion boat of the elemental analyzer. The carbon content was tested using the elemental analyzer (CHN mode). The test conditions were: combustion furnace temperature 950℃, reduction furnace temperature 500℃, and carrier gas was high-purity helium (purity ≥99.999%). The CO2 content generated after the sample combustion was automatically detected by the instrument, and the carbon residue (wt%) in the sample was calculated. The experimental results are shown in Table 1.

[0053] 3. Specific Surface Area Test: 0.2 g of the nano-nickel oxide products prepared in each example and comparative example were placed in sample tubes and degassed at 105℃ and a vacuum of -0.09 MPa for 3 h to remove adsorbed moisture and impurities from the sample surface. The N2 adsorption-desorption isotherm of the samples was measured using a liquid nitrogen adsorption-desorption method and a specific surface area and porosity analyzer. The specific surface area (m²) of the samples was calculated according to the Brunauer-Emmett-Teller (BET) model. 2 / g), the experimental results are shown in Table 1.

[0054] Table 1 Performance Test Results

[0055] Data Analysis: As can be seen from the performance test data in Table 1, the nano-nickel oxide prepared in all examples exhibits excellent particle size uniformity, low impurity residue, and high specific surface area, which is significantly better than the comparative examples. This is due to the core process design of this invention, which is "gradient coordination precursor construction + three-stage atmosphere-temperature coupled pyrolysis + water washing to remove impurities". The asynchronous release of nickel ions is achieved through the bond energy gradient of strong and weak coordinating agents. Combined with the mesoscopic confinement of the SDBS soft template and the crystallization control of the segmented pyrolysis, the problems of agglomeration, carbon residue, sodium residue, and insufficient specific surface area in traditional processes are solved from the root. Among them, Example 2 has the most outstanding comprehensive performance due to the optimal matching of nickel salt concentration, coordinating agent ratio, pyrolysis parameters and water washing standards. All indicators are better than other examples and all comparative examples.

[0056] Example 2 exhibited the narrowest particle size distribution and the lowest aggregation index. This is likely because, in an alkaline system at pH 8.0, the weak ligand L-aspartate sodium (bidentate ligand) and the strong ligand EDTA-2Na (hexadentate ligand) were combined in a molar ratio of nickel ions: strong ligand: weak ligand = 1:0.4:0.8, forming a mixed coordination molecular cluster where "weak coordination bonds encapsulate strong coordination bonds." The L-aspartate sodium and Ni... 2+ The resulting complex has low thermal stability and preferentially breaks down in a pure N2 atmosphere at 275℃ (reaction: Among them, Asp 2- (aspartate), slowly released Ni 2+ It combines with pyrolytic small molecules of ligands to form uniformly dispersed "nickel-carbon-oxygen-nitrogen" composite crystal nuclei; subsequently, in a low-oxygen (8% volume fraction) atmosphere at 420℃, EDTA-2Na reacts with Ni... 2+ The highly stable chelate gradually breaks down (reaction: ), slow-release Ni 2+Epitaxial growth is only performed on the surface of existing crystal nuclei to avoid explosive nucleation. At the same time, the nanomicelles formed by SDBS act as soft templates. The ordered space constructed by the aggregation of its hydrophobic long chains is transformed into a porous structure during pyrolysis, which physically isolates the grains and completely inhibits fusion and agglomeration, ultimately achieving an extremely low agglomeration index and narrow particle size distribution.

[0057] The lowest sodium residue in Example 2 is likely because the strong ligand EDTA-2Na and the sodium element in the weak ligand L-aspartate sodium are ionicly bonded. During pyrolysis, the sodium is converted into water-soluble sodium salts (such as sodium carbonate, sodium bicarbonate) or sodium oxide, sodium peroxide, etc., as the ligands decompose. In Example 2, sodium ions adsorbed on the surface of NiO are completely removed by washing with deionized water (until the absolute difference between the conductivity of the supernatant and the background conductivity of deionized water is ≤0.05μS / cm). This is achieved by utilizing the difference in solubility between sodium salts and sodium oxides and NiO (NiO is almost insoluble in water) and converting them into sodium hydroxide through dissolution and hydration. As a result, the sodium residue is much lower than that in the comparative example.

[0058] Example 2 exhibited the lowest carbon residue, primarily due to the synergistic oxidation effect of stepwise ligand decomposition and oxygen-enriched crystallization. In the first stage, under a pure N2 atmosphere at 275°C, the weak ligand, sodium L-aspartate, decomposed into small organic molecules. Because the decomposition was minimal and dispersed, no carbon accumulation occurred. In the second stage, under a low-oxygen atmosphere at 420°C, the strongly liganded EDTA-2Na slowly decomposed, its carbon skeleton undergoing gentle oxidation with trace amounts of O2, preventing the carbon skeleton from agglomerating and forming amorphous carbon. In the third stage, a 1.5-hour pure oxygen incubation at 480°C ensured that the remaining trace carbon was thoroughly oxidized by a high concentration of O2, and the high flow rate of O2 ensured that the oxidation reaction was thorough, ultimately controlling the carbon residue to an extremely low level, far superior to the comparative example.

[0059] Example 2 exhibits the highest specific surface area, attributed to the dual contribution of "extremely small particle size + microporous structure". The aforementioned gradient coordination and stepwise pyrolysis mechanism maintains the NiO grains at an extremely small size, resulting in a high base specific surface area for the particles themselves. Simultaneously, the SDBS soft template completely decomposes during pyrolysis, and the nanoscale micelle spaces formed by the aggregation of its hydrophobic long chains are transformed into small micropores between NiO particles, significantly increasing the pore specific surface area. Furthermore, the low agglomeration state ensures that the micropores are not blocked, and the active sites are fully exposed, ultimately resulting in a significantly higher specific surface area than other examples and comparative examples.

[0060] In comparison, Comparative Example 1, lacking a weak ligand to guide its low-temperature stepwise decomposition, only showed EDTA-2Na and Ni... 2+ A highly stable chelate is formed; during pyrolysis, the chelate bonds break at around 420℃. (Ni) 2+The explosive release, lacking a uniform crystal nucleus base, and due to the concentrated decomposition of the ligand carbon skeleton, the carbon residue was significantly higher than in Example 2 due to the untimely oxidation of O2; at the same time, the lack of initial spatial obstruction by weak coordination bonds made the crystals easy to fuse and agglomerate, and the agglomeration index and particle size distribution width were much higher than in Example 2; and the coarsened crystals and severe agglomeration caused the active sites to be covered, resulting in a significantly lower specific surface area than in Example 2. Comparative Example 2 depends solely on sodium L-aspartate and Ni 2+ It forms a low-stability complex and completely decomposes in the N2 stage at 250℃. Ni 2+ Premature release without subsequent sustained release caused the crystal nuclei to rapidly coalesce into large particles, with particle sizes much larger than those in Example 2. Simultaneously, the lack of a strong coordinating agent for sustained dispersion resulted in severe agglomeration due to the absence of chemical barriers between particles, leading to a higher agglomeration index and particle size distribution width compared to Example 2. Furthermore, premature ligand decomposition made it difficult for the carbon skeleton to be oxidized by O2 at low temperatures, resulting in a higher carbon residue than in Example 2. The combined effects of coarsening and agglomeration resulted in a significantly lower specific surface area compared to Example 2. In Comparative Example 3, due to the absence of the mesoscopically ordered template provided by SDBS micelles, the coordination complex molecules randomly aggregated, forming a dense solid precursor. During pyrolysis, oxygen could only penetrate to the particle surface, and the carbon generated by the decomposition of internal ligands could not be fully oxidized (although the final carbon residue was similar to that of Example 2, it required a longer oxidation time). Furthermore, the lack of a porous isolation structure made the grains prone to fusion, resulting in a higher agglomeration index and particle size distribution width compared to Example 2. At the same time, the microporous structure without SDBS resulted in a significantly lower specific surface area compared to Example 2 due to particle densification. Comparative Example 4 lacks a pure N2 low-temperature nucleation stage, Ni 2+ The NiO crystal nuclei were oxidized by air in the early stage of heating, resulting in uneven distribution of the formed NiO crystal nuclei. Without the mild decomposition of the ligands in the low-oxygen stage, the carbon skeleton of the ligands was rapidly carbonized and O2 could not be oxidized in time, resulting in a carbon residue much higher than in Example 2. The one-step heating led to local overheating, grain coarsening, and the agglomeration index and particle size distribution width were higher than in Example 2. Moreover, without the crystallization process of segmented heat preservation, there were many NiO lattice defects, the active sites were covered by defects, and the specific surface area was significantly lower than in Example 2. Comparative Example 5 did not remove the sodium salt and sodium oxide generated by pyrolysis by washing with water. Sodium ions were adsorbed on the NiO surface, which triggered electrostatic attraction between particles, resulting in secondary agglomeration. The agglomeration index and particle size distribution width were higher than those of Example 2. Although the carbon residue was well controlled by oxygen-enriched crystallization, the sodium residue was much higher than that of Example 2. In addition, sodium salt blocked some micropores, and the active sites were not exposed enough, resulting in a slightly lower specific surface area than that of Example 2.

[0061] 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 process for preparing nano-nickel oxide based on the pyrolysis of coordination precursors, characterized in that, Includes the following steps: (1) Add the nickel source to deionized water and stir until dissolved to prepare a nickel salt solution; (2) Add the weak ligand to the nickel salt solution and stir for 20-40 min at room temperature; A preliminary complexing solution was obtained; (3) Add the strong ligand to the preliminary complexing solution, and while stirring, add ammonia to adjust the pH of the system to 7.5-8.

5. Then raise the temperature to 55-65℃ and stir the reaction for 2-3 hours to obtain the complex solution. (4) Maintain a temperature of 55-65℃, add a directing agent to the complex solution, stir for 20-40 min, then cool to 40-50℃ and sonicate for 30-45 min to obtain a gel precursor solution; (5) Dehydrate the gel precursor solution under vacuum at 70-80℃ for 30-60 min, and then dry it in a vacuum drying oven to obtain dry gel; (6) After the dry gel is crushed into powder, it is evenly spread in the alumina boat and then sent into the tube furnace. Nitrogen gas is introduced and the temperature is raised from room temperature to 250-300℃. The temperature is held for 30-45 minutes to complete the first stage of heating. (7) After the first stage of heating is completed, nitrogen / oxygen mixture is introduced and the temperature is continued to rise to 380-450℃, and held for 60-90 minutes to complete the second stage of heating; (8) After the second stage of heating is completed, oxygen is introduced and the temperature is continued to rise to 450-500℃. The temperature is held for 1-2 hours to complete the third stage of heating. After that, heating is stopped and the furnace is cooled to room temperature. (9) Grind and break up the cooled product, wash it with deionized water 3-4 times, and dry it after washing to obtain nano-nickel oxide based on the pyrolysis of coordination precursor.

2. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, In (1), the nickel source refers to one of nickel nitrate, nickel acetate or nickel chloride; the concentration of the nickel salt solution is 0.1-1.0 mol / L.

3. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The molar ratio of nickel ions to weak ligand in the preliminary complexing solution in (2) is 1:0.7-0.9; the weak ligand refers to sodium L-aspartate or malic acid.

4. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, In the complex solution described in (3), the molar ratio of nickel ions to strong ligand is 1:0.3-0.5; the strong ligand refers to EDTA-2Na or sodium hypotriacetate; the concentration of ammonia is 25-28 wt%.

5. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The directing agent in (4) refers to sodium dodecylbenzenesulfonate. After its addition, the concentration of sodium dodecylbenzenesulfonate in the system is 0.05-0.1 mol / L; the power of ultrasonic treatment is 300-500 W.

6. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The temperature of the vacuum drying oven in (5) is 80-100℃.

7. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The flow rate of nitrogen in (6) is 80-120 ml / min; the heating rate of the tube furnace is 2-3 °C / min.

8. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The flow rate of the nitrogen / oxygen mixture in (7) is 80-120 ml / min; the volume fraction of oxygen in the mixture is 5-10%; and the heating rate is 1-2 °C / min.

9. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The oxygen introduction rate in (8) is 150-200 ml / min; the heating rate is 2-3 °C / min.

10. The nano-nickel oxide preparation process based on coordination precursor pyrolysis according to claim 1, characterized in that, The standard for completing the deionized water washing in (9) is that the absolute difference between the conductivity of the washing liquid and the background conductivity of the deionized water is ≤0.05μS / cm.

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