Nanometer nickel protoxide preparation process based on coordination precursor pyrolysis

Abstract

The invention discloses a nanometer nickel protoxide preparation process based on coordination precursor pyrolysis, and belongs to the technical field of nanometer material preparation. According to the process, a gradient bond energy coordination system is constructed by compounding strong and weak coordination agents, oriented assembly is carried out by matching with an SDBS soft template, and asynchronous release of nickel ions and ordered growth of crystal nucleuses are realized through three-stage atmosphere coupling pyrolysis and water washing. The prepared nano nickel protoxide is uniform in particle size, low in agglomeration degree, few in carbon / sodium impurity residue, high in specific surface area, free of special equipment in process, simple and convenient to operate, controllable in cost and suitable for industrial batch production, and can be widely applied to the fields of energy storage, catalysis, sensing and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer material preparation, and particularly relates to a preparation process of nanometer nickel monoxide based on pyrolysis of a coordination precursor. BACKGROUND

[0002] As a typical p-type semiconductor nanometer material, nanometer nickel monoxide (NiO) has irreplaceable application value in the fields of new energy storage (lithium ion battery negative electrode, super capacitor electrode), electrocatalysis (oxygen reduction, oxygen evolution reaction), gas sensitive sensing (formaldehyde and ethanol detection) and precise catalytic carrier, etc. due to its high specific surface area, rich surface active sites and excellent electrochemical, catalytic and gas sensitive properties. It is a research hotspot and industrial core demand product in the field of inorganic functional nanometer materials. High-performance nanometer nickel monoxide has extremely strict performance requirements for "narrow particle size distribution, low agglomeration degree and high purity (no carbon / sodium impurities remaining)", for example, in the application of lithium ion battery negative electrode, uneven particle size or agglomeration will lead to poor electrolyte wettability and rapid capacity attenuation; in the field of electrocatalysis, carbon residues will cover the active sites, and alkali metal impurities will damage the crystal lattice structure, which will directly restrict the upper limit of industrial application of the product.

[0003] At present, the pyrolysis method of the coordination precursor is the mainstream technology for preparing highly dispersed nanometer nickel monoxide. Its core advantage lies in that the coordination bond between the organic ligand and the nickel ion can realize the atomic dispersion of the nickel ion and avoid the problem of rapid agglomeration of metal ions in the traditional precipitation method. However, during the industrialization amplification process, this technology route has three major core technical bottlenecks: first, it is difficult to control the particle size uniformity and dispersion. Traditional processes mostly use single ligand (such as EDTA and citric acid) or simple binary ligand physical compounding to construct the coordination system. The coordination bond energy distribution is uniform or disordered. During the pyrolysis process, a large number of nickel ions are released synchronously, leading to "explosive nucleation" and "disordered growth" of the crystal nucleus. Finally, the product has a wide particle size distribution and is prone to hard agglomeration, which greatly reduces the specific surface area; second, it is difficult to guarantee the purity of the product. On the one hand, the decomposition rate of the ligand and the oxidation rate of oxygen are difficult to match. The incomplete decomposition of the ligand at low temperature is easy to leave amorphous carbon, and the rapid decomposition of the ligand at high temperature is easy to cause local carbon deposition; on the other hand, if a coordination sodium salt is used as the raw material, the traditional water washing process lacks 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 solve the above problems, the industry has carried out a series of improvement attempts: for example, some research optimizes the coordination stability by replacing the ligand species, but it cannot break through the limitation of "single bond energy" and still cannot realize the asynchronous release of nickel ions, and the problems of uneven particle size and agglomeration have not been fundamentally improved; Some schemes use simple compounding of multiple ligands (such as mixing EDTA and citric acid), but there is no synergistic coordination between ligands, the bond energy distribution is disordered, and there is still a problem of concentrated release of nickel ions during pyrolysis; There are also studies that optimize the crystallization process by adjusting the pyrolysis temperature and holding time, and use "one-step air pyrolysis" instead of staged pyrolysis, but it cannot realize the space-time separation of "crystal nucleus formation" and "grain growth", and the decomposition and oxidation of ligands are still not synchronized, and the problems of carbon residue and agglomeration are still prominent.

[0005] However, the above existing improvement schemes have not touched the core contradiction of the coordination precursor pyrolysis method. That is, "the lack of bond energy gradient in the coordination system leads to the synchronization of nickel ion release" and "the mismatch between pyrolysis process and coordination decomposition kinetics". Single ligand replacement or simple compounding is only a parameter fine-tuning, and it does not build a controllable nickel ion release mechanism from the coordination chemical mechanism level; The one-step pyrolysis process cannot adapt to the decomposition characteristics of the coordination system, and it is difficult to balance the oxidation of ligands and the crystallization of grains. Therefore, there is an urgent need for a technical scheme that innovates the whole chain from coordination mechanism, pyrolysis process to impurity control, to break through the current industry bottleneck. SUMMARY

[0006] The purpose of the present application is to solve the problems existing in the prior art and to provide a preparation process of nano nickel protoxide based on coordination precursor pyrolysis.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: the preparation process of nano nickel protoxide based on coordination precursor pyrolysis comprises the following steps: (1) Add nickel source to deionized water, stir until dissolved, and prepare nickel salt solution; (2) Add a weak coordination agent to the nickel salt solution, stir at room temperature for 20-40 min; obtain a preliminary complex solution; (3) Add a strong coordination agent to the preliminary complex solution, stir, add ammonia water to adjust the pH of the system to 7.5-8.5, then heat to 55-65℃, stir for 2-3h, and obtain a complex solution; (4) Maintain the temperature at 55-65℃, add a directing agent to the complex solution, stir for 20-40min, then cool to 40-50℃, and ultrasonic treatment for 30-45min to obtain a gel precursor solution; (5) Vacuum dehydrate the gel precursor solution at 70-80℃ for 30-60min, then place it in a vacuum drying oven to dry to obtain a dry gel; (6) After the dry gel is crushed into powder, it is evenly laid in an alumina square case, and then is sent into a tube furnace, nitrogen is introduced, and the temperature is increased from room temperature to 250-300℃, and is kept for 30-45 min, and the first stage of temperature increase is completed; (7) After the first stage of temperature increase is completed, nitrogen / oxygen mixed gas is introduced, and the temperature is continuously increased to 380-450℃, and is kept for 60-90 min, and the second stage of temperature increase is completed; (8) After the second stage of temperature increase is completed, oxygen is introduced, and the temperature is continuously increased to 450-500℃, and is kept for 1-2 h, and the third stage of temperature increase is completed, and then the heating is stopped, and the furnace is cooled to room temperature; (9) The cooled product is ground and is washed with deionized water for 3-4 times, and after the washing is completed, the product is dried, and nano-nickelous oxide based on pyrolysis of coordination precursor is obtained.

[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 coordination agent in the preliminary complexing solution in (2) is 1:0.7-0.9.

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

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

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

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

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

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

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

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

[0019] Preferably, the temperature increase rate of the tube 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 dodecyl benzene sulfonate (SDBS) promotes the chemical design at the molecular level to the structural regulation at the mesoscopic scale. SDBS is an amphiphilic surfactant, whose hydrophilic sulfonic head group can be adsorbed on the surface of the charged nickel complex through electrostatic or polar interactions, while the hydrophobic long alkyl chain tends to aggregate with each other. Under the driving of ultrasonic energy, SDBS molecules self-assemble into ordered structures such as micelles and lamellar structures in water, which act as "soft templates" to guide and constrain the directional arrangement of the aforementioned nickel complex molecular clusters at their interfaces or interiors. This process effectively suppresses the random agglomeration of complex molecules, endowing the precursor solution (or xerogel after dehydration) with an inherent, nanoscale structural order, which is crucial for the morphology control and inhibition of hard agglomeration of the final oxide grains.

[0029] The fine design of the precursor only makes the excellent performance of the final product possible, and the key to its realization lies in the precise matching of the pyrolysis conversion process. The three-stage gradient pyrolysis program of the present invention realizes the spatial and temporal separation of the two key stages of "nucleation" and "growth".

[0030] The first stage (250-300℃, pure N2 atmosphere) is the controllable nucleation period. In this mild inert atmosphere and lower temperature, the weakest coordination bond (such as the coordination bond between aspartic acid and Ni 2+ The first stage (250-300℃, pure N2 atmosphere) is the controllable nucleation period. In this mild inert atmosphere and lower temperature, the weakest coordination bond (such as the coordination bond between aspartic acid and Ni

[0031] The second stage (380-450 DEG C, low-oxygen N2 / O2 mixed gas) is a slow-release growth and crystal phase conversion stage. After the temperature is increased, the coordination bond of the strong coordination agent (such as EDTA) begins to break, and nickel ions are continuously and slowly released, and at the same time, the trace oxygen introduced begins to play a role, which on the one hand causes mild oxidation of the decomposed organic ligand skeleton to avoid carbon deposition, and on the other hand, promotes the conversion of the intermediate such as the composite precursor nucleus formed in the first stage and the newly released nickel species to nickel oxide (NiO) crystal phase. Since the supply rate of nickel ions is controlled by the slow-release mechanism of the strong coordination bond, and a large number of crystal nuclei have been uniformly distributed, the newly formed NiO will preferentially grow on the surface of these existing crystal nuclei by epitaxy, rather than triggering new explosive nucleation. Although the SDBS template gradually decomposes during pyrolysis, the residual carbon skeleton or the pore structure formed can still play a physical isolation role during crystal growth, guiding the crystal to grow in a specific direction, thereby realizing the control of the final particle morphology.

[0032] The third stage (450-500 DEG C, pure O2 atmosphere) is a crystal lattice perfecting and purifying stage. Under the condition of oxygen enrichment and higher temperature, two main processes are carried out simultaneously: one is to completely decompose and remove any residual organic species and amorphous carbon to ensure product purity; the other is to further reorganize and perfect the crystal lattice structure of NiO crystals through Ostwald ripening effect, reduce defects, and significantly improve crystallinity. High-flow oxygen ensures that the product is completely oxidized and stoichiometric NiO. Finally, by washing with multiple steps of deionized water, and using the huge difference in solubility of sodium salts such as Na2CO3 and NaNO3, as well as sodium oxide and sodium peroxide, in water, the water-soluble impurities such as sodium ions introduced in the process can be efficiently removed, thereby obtaining a high-purity final product.

[0033] Compared with the prior art, the present application has the following beneficial effects: 1. The present application constructs a bond energy gradient system through strong and weak coordination agents. The weak coordination bond breaks at a low temperature to release nickel ions to form uniform crystal nuclei, and the strong coordination bond slowly breaks at a high temperature to continuously supply nickel ions, realizing ordered growth of crystal nuclei, and cooperating with the mesoscopic confinement effect of the SDBS soft template to double-inhibit grain fusion from the molecular and mesoscopic levels. This design makes the nano-nickel oxide particles uniformly dispersed without hard agglomeration, avoids covering of active sites, provides structural support for improving electrolyte wettability and reducing capacity attenuation in the energy storage field, and at the same time guarantees the uniformity of particle size.

[0034] 2. The present application realizes step-by-step oxidation of ligands through three-stage atmosphere coupling pyrolysis: mild decomposition of ligands in low-oxygen stage to avoid carbon deposition, and thorough removal of residual organic carbon in oxygen-rich stage; combined with water washing process controlled by conductivity difference, sodium ions are completely removed by taking advantage of the solubility difference between sodium salt and nickel protoxide. This scheme ensures that the product has no carbon residue and extremely low sodium content, meeting the stringent requirements of high-precision electronic devices and catalysis field for material purity, avoiding the destruction of lattice structure and active sites by impurities, and ensuring the stability of product performance.

[0035] 3. The present application takes into account process economy and industrial adaptability while achieving high performance, using conventional tubular furnaces, vacuum drying ovens and other equipment throughout the process, without the need for high-pressure spray drying or special atmosphere furnaces, reducing equipment investment costs; using commercially available nickel nitrate, EDTA-2Na and other conventional reagents as raw materials, which are widely available and cost controllable; three-stage gradient pyrolysis avoids energy waste caused by excessive high temperature through precise temperature control and atmosphere adjustment, while simplifying the subsequent impurity removal process. The overall process is simple to operate, short in process, and can be directly connected to existing production lines, suitable for mass production, with economic and environmental benefits.

[0036] 4. The present application builds a rich microporous structure among nano-nickel protoxide particles through the synergistic effect of SDBS soft template and gradient pyrolysis: the pores formed after SDBS micelle pyrolysis and the extremely small particle size together increase the specific surface area, making the surface active sites fully exposed. This structure not only enhances the substrate adsorption capacity of the material in catalytic reactions, but also improves the gas response rate in the field of gas sensing, while optimizing the electrolyte ion transmission channel in the energy storage electrode. In addition, uniform particle size and micropore distribution ensure batch performance consistency, providing a stable material foundation for downstream multi-field applications, and expanding the application scenarios of nano-nickel protoxide. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The transmission electron microscope (TEM) spectrum of the nano-nickel protoxide based on coordination precursor pyrolysis prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described below in conjunction with the prior known technology, obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0039] Example 1: The specific preparation process of nano-nickel protoxide based on coordination precursor pyrolysis, including 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-aspartic acid sodium to the nickel salt solution, stir at room temperature for 20 min to obtain a preliminary complex solution; (3) Add 3 mol EDTA-2Na into the preliminary complexing solution, adjust the pH of the system to 7.5 by adding ammonia water with a concentration of 25-28 wt% under stirring, then increase the temperature to 55°C, and stir for 2 h to obtain a complex solution; (4) Maintain the temperature at 55°C, add sodium dodecyl benzene sulfonate into the complex solution to make the concentration of sodium dodecyl benzene sulfonate in the system be 0.05 mol / L, stir for 20 min, then decrease the temperature to 40°C, and treat with ultrasonic waves at a power of 300 W for 30 min to obtain a gel precursor solution; (5) Dehydrate the gel precursor solution at 70°C for 30 min in vacuum, then place it in a vacuum drying oven at 80°C to obtain a dry gel; (6) Crush the dry gel into powder, uniformly lay it in an alumina square boat, then send it into a tube furnace, pass nitrogen gas at a rate of 80 ml / min, increase the temperature from room temperature to 250°C at a rate of 2-3°C / min, and keep the temperature for 30 min to complete the first stage of temperature increase; (7) After the first stage of temperature increase is completed, pass nitrogen / oxygen mixed gas (the volume fraction of oxygen is 5%) at a rate of 80 ml / min, continue to increase the temperature to 380°C at a rate of 1-2°C / min, and keep the temperature for 60 min to complete the second stage of temperature increase; (8) After the second stage of temperature increase is completed, pass oxygen gas at a rate of 150 ml / min, continue to increase the temperature to 450°C at a rate of 2-3°C / min, and keep the temperature for 1 h to complete the third stage of temperature increase, then stop heating, and cool the furnace to room temperature; (9) Grind the cooled product, wash it with deionized water for 3-4 times until the absolute difference between the conductivity of the washing liquid and the background conductivity of deionized water is ≤0.05 μS / cm, then dry it to obtain nano nickel monoxide based on the pyrolysis of a coordination precursor.

[0040] Example 2: A specific preparation process of nano nickel monoxide based on the pyrolysis of a coordination precursor, including the following steps: (1) Add 10 mol of nickel nitrate into deionized water, stir until dissolved, and prepare a nickel salt solution with a concentration of 0.5 mol / L; (2) Add 8 mol of L-aspartic acid sodium into the nickel salt solution, stir at room temperature for 30 min to obtain a preliminary complexing solution; (3) Add 4 mol of EDTA-2Na into the preliminary complexing solution, adjust the pH of the system to 8.0 by adding ammonia water with a concentration of 25-28 wt% under stirring, then increase the temperature to 60°C, and stir for 2.5 h to obtain a complex solution; (4) maintaining the temperature of 60°C, adding sodium dodecyl benzene sulfonate into the complex solution to make the concentration of sodium dodecyl benzene sulfonate in the system 0.08 mol / L, stirring for 30 min, then reducing the temperature to 45°C, and ultrasonic treating at the power of 400 W for 40 min to obtain a gel precursor solution; (5) vacuum dehydrating the gel precursor solution at 75°C for 45 min, and then drying in a vacuum drying oven at 90°C to obtain a dry gel; (6) crushing the dry gel into powder, uniformly laying the powder in an alumina square canister, then feeding into a tube furnace, feeding nitrogen at the rate of 90 ml / min, and heating from room temperature to 275°C at the heating rate of 2-3°C / min, and keeping the temperature for 40 min to complete the first stage of heating; (7) after the first stage of heating, feeding nitrogen / oxygen mixed gas (the volume fraction of oxygen is 8%) at the rate of 100 ml / min, and continuously heating to 420°C at the heating rate of 1-2°C / min, and keeping the temperature for 75 min to complete the second stage of heating; (8) after the second stage of heating, feeding oxygen at the rate of 180 ml / min, and continuously heating to 480°C at the heating rate of 2-3°C / min, and keeping the temperature for 1.5 h to complete the third stage of heating, and then stopping heating and cooling to room temperature along with the furnace; (9) grinding and dispersing the cooled product, washing with deionized water for 3-4 times until the absolute difference between the conductivity of the washing liquid and the background conductivity of the deionized water is ≤0.05 μS / cm, and then drying to obtain nano nickel monoxide based on the pyrolysis of coordination precursors, and the transmission electron microscope characterization results of the nano nickel monoxide prepared in the embodiment are shown in Figure 1 As can be seen from the figure, the obtained nano nickel monoxide particles are spherical, the morphology uniformity is excellent, and there is no irregular grain; the size of a single primary grain is concentrated in the interval of 15-25 nm; the interface between the particles is clear, and there is no obvious hard agglomeration structure, and only a small amount of soft agglomeration formed by the electrostatic force between the particles exists.

[0041] Example 3: specific preparation process of nano nickel monoxide based on the pyrolysis of coordination precursors, including the following steps: (1) adding 10 mol of nickel nitrate into deionized water, stirring to dissolve, and preparing a nickel salt solution with the concentration of 1.0 mol / L; (2) adding 9 mol of L-aspartic acid sodium into the nickel salt solution, stirring at room temperature for 40 min to obtain a preliminary complex solution; (3) adding 5 mol of EDTA-2Na into the preliminary complex solution, stirring, adding ammonia water with the concentration of 25-28 wt% to adjust the pH of the system to 8.5, then heating to 65°C, and stirring for 3 h to obtain a complex solution; (4) maintaining the temperature at 65°C, adding sodium dodecyl benzene sulfonate into the complex solution to make the concentration of sodium dodecyl benzene sulfonate in the system 0.1 mol / L, stirring for 40 min, then reducing the temperature to 50°C, and ultrasonic treating for 45 min to obtain a gel precursor solution; (5) vacuum dehydrating the gel precursor solution at 80°C for 60 min, and then placing it in a vacuum drying oven at 100°C to obtain a dry gel; (6) crushing the dry gel into powder, uniformly laying the powder in an alumina square canister, then placing it in a tube furnace, passing nitrogen at a rate of 100 ml / min, and heating from room temperature to 300°C at a heating rate of 2-3°C / min, and keeping the temperature for 45 min to complete the first stage of heating; (7) after the first stage of heating, passing nitrogen / oxygen mixed gas (the volume fraction of oxygen is 10%) at a rate of 120 ml / min, and continuing to heat to 450°C at a heating rate of 1-2°C / min, and keeping the temperature for 90 min to complete the second stage of heating; (8) after the second stage of heating, passing oxygen at a rate of 200 ml / min, and continuing to heat to 500°C at a heating rate of 2-3°C / min, and keeping the temperature for 2 h to complete the third stage of heating, and then stopping heating and cooling to room temperature with the furnace; (9) grinding and dispersing the cooled product, washing it with deionized water for 3-4 times until the absolute difference between the conductivity of the washing liquid and the background conductivity of the deionized water is ≤0.05 μS / cm, and then drying to obtain a nano nickel monoxide based on a coordination precursor pyrolysis.

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

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

[0044] Example 6: the difference between Example 6 and Example 2 is that the EDTA-2Na is replaced by sodium nitrilotriacetate.

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

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

[0047] Comparative Example 2: the difference between Comparative Example 2 and Example 2 is that no EDTA-2Na is added in step (3).

[0048] Comparative Example 3: Comparative Example 3 differs from Example 2 in that step (4) is omitted, and no sodium dodecyl benzene sulfonate is added.

[0049] Comparative Example 4: Comparative Example 4 differs from Example 2 in that steps (6)-(8) are omitted, and the xerogel obtained in step (5) is crushed, and the xerogel powder is directly placed into a tube furnace, and heated to 480°C at a heating rate of 2-3°C / min under air atmosphere, and held for 2.5h.

[0050] Comparative Example 5: Comparative Example 5 differs from Example 2 in that step (9) is omitted, and the nano-nickelous oxide based on pyrolysis of coordination precursors is obtained directly after cooling in the furnace in step (8).

[0051] Performance Test: 1. Particle size distribution and dispersibility test The nano-nickelous oxide products prepared in each of the examples and comparative examples were taken, 5mg of each sample was weighed, added into 10ml of anhydrous ethanol, and ultrasonically dispersed for 20min at a power of 300W to prepare a uniformly dispersed suspension. A dynamic light scattering particle size analyzer (DLS) was used to test the particle size distribution of the suspension at 25°C and a scattering angle of 90°, and the average particle size (D50), particle size distribution width (D90 / D10), and agglomeration index were recorded. The experimental results are shown in Table 1.

[0052] 2. Product purity test: Sodium residue test 0.5g of the nano-nickelous oxide product prepared in each of the examples and comparative examples was weighed, placed in a polytetrafluoroethylene digestion tank, and 10ml of nitric acid (superior grade) was added. After sealing, the tank was placed in a microwave digestion instrument, and digested according to the procedure of “heating to 120°C for 10min, and heating to 180°C for 20min”. After digestion was completed, the tank was cooled to room temperature, and the digestion solution was transferred to a 50ml volumetric flask, diluted to the mark with deionized water, and shaken well. An inductively coupled plasma optical emission spectrometer (ICP-OES) was used to test the concentration of sodium in the solution, and the sodium residue (ppm) in the sample was calculated according to the dilution factor. The experimental results are shown in Table 1. Carbon residue test 20mg of the nano-nickelous oxide product prepared in each of the examples and comparative examples was weighed, placed in a combustion boat of an elemental analyzer, and the carbon content was tested using an elemental analyzer (CHN mode). The test conditions were: combustion furnace temperature 950°C, reduction furnace temperature 500°C, and carrier gas high-purity helium (purity ≥99.999%). The CO2 content generated after the sample was combusted was detected automatically 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 prepared nano-nickelous oxide product of each example and comparative example was placed in a sample tube, degassed at 105°C under a vacuum degree of -0.09 MPa for 3 h to remove water and impurities adsorbed on the surface of the sample, and the N2 adsorption-desorption isotherm of the sample was tested by a specific surface area and porosity analyzer using a liquid nitrogen adsorption-desorption method, and the specific surface area (m 2 / g) of the sample was calculated according to the Brunauer-Emmett-Teller (BET) model. 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-nickelous 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 the present application “gradient coordination precursor construction + three-stage atmosphere-temperature coupled pyrolysis + water washing impurity removal”, which realizes the non-synchronous release of nickel ions through the energy gradient of strong and weak coordination agents, cooperates with the mesoscopic confinement of SDBS soft template and the crystallization regulation of segmented pyrolysis, and solves the problems of agglomeration, carbon residue, sodium residue and insufficient specific surface area in the traditional process from the root; among them, example 2 becomes the most outstanding scheme in comprehensive performance because of the optimal matching of nickel salt concentration, coordination agent ratio, pyrolysis parameters and water washing standard, and all indicators are better than other examples and all comparative examples.

[0056] The particle size distribution of example 2 is the narrowest and the agglomeration index is the lowest, which may be because in the alkaline system of pH = 8.0, the weak coordination agent L- sodium aspartate (bidentate ligand) and the strong coordination agent EDTA-2Na (hexadentate ligand) are compounded according to the molar ratio of nickel ion: strong coordination agent: weak coordination agent = 1:0.4:0.8, forming a mixed coordination molecular cluster of “weak coordination bond wrapping strong coordination bond”, and the L- sodium aspartate and Ni 2+ The formed complex has low thermal stability and preferentially breaks at 275°C under pure N2 atmosphere (reaction: , where Asp 2- is aspartate), and the slowly released Ni 2+ combines with the pyrolysis small molecules of the ligand to form uniform dispersed “nickel-carbon-oxygen-nitrogen” composite crystal nuclei; in the subsequent 420°C low oxygen (volume fraction 8%) atmosphere, the high stability chelate of EDTA-2Na and Ni 2+ gradually breaks (reaction: ), and the slowly released Ni 2+Only epitaxial growth on the surface of the existing crystal nucleus is allowed to avoid explosive nucleation; at the same time, the nano-micelles formed by SDBS as a soft template, the ordered space constructed by the hydrophobic long chains of SDBS is converted into a pore structure in pyrolysis, physically isolating the crystal grains, completely inhibiting fusion and agglomeration, and finally achieving an extremely low agglomeration index and a narrow particle size distribution.

[0057] The sodium residual amount of Example 2 is the lowest. This can be because the sodium elements in the strong complexing agent EDTA-2Na and the weak complexing agent L-sodium aspartate are combined in the form of an ionic bond, and in the pyrolysis process, the ligands are decomposed into water-soluble sodium salts (such as sodium carbonate, sodium bicarbonate) or sodium oxide, sodium peroxide, etc. In Example 2, deionized water is used for washing (until the absolute difference between the conductivity of the supernatant and the background conductivity of the deionized water is ≤0.05 μS / cm), and the solubility difference between sodium salts and sodium oxides and NiO (NiO is almost insoluble in water) is used to completely remove the sodium ions adsorbed on the surface of NiO by dissolution and the form of sodium hydroxide generated by translation with water. The sodium residual amount is far lower than that of the comparative examples.

[0058] The carbon residual amount of Example 2 is the lowest, and the key lies in the synergistic effect of step-by-step ligand decomposition and oxygen-rich crystallization. In the first stage at 275℃ under a pure N2 atmosphere, the weak complexing agent L-sodium aspartate is first decomposed into small-molecule organic compounds. Because the decomposition amount is small and dispersed, there is no carbon accumulation; in the second stage at 420℃ under a low-oxygen atmosphere, the strong complexing agent EDTA-2Na slowly decomposes, and the carbon skeleton and trace O2 undergo mild oxidation, avoiding the polymerization of the carbon skeleton to form amorphous carbon; in the third stage at 480℃ under a pure oxygen atmosphere for 1.5 h, high-concentration O2 completely oxidizes the trace amount of residual carbon, and the high-flow O2 ensures that there are no dead angles in the oxidation reaction, and finally the carbon residual amount is controlled at a very low level, which is much better than that of the comparative examples.

[0059] The specific surface area of Example 2 is the highest, which is due to the "extremely small particle size + microporous structure double contribution". The aforementioned gradient complexing and step-by-step pyrolysis mechanism allows the NiO crystal grains to maintain an extremely small size, and the specific surface area of the particles themselves is high; at the same time, the SDBS soft template is completely decomposed in pyrolysis, and the nanoscale micelle space formed by the aggregation of the hydrophobic long chains is converted into small micropores between NiO particles, greatly increasing the pore specific surface area; and the low agglomeration state ensures that the micropores are not blocked, and the active sites are fully exposed, and finally the specific surface area is significantly higher than that of other examples and comparative examples.

[0060] Comparatively, Comparative Example 1 lacks the low-temperature step-by-step decomposition of the weak complexing agent, and only EDTA-2Na and Ni 2+ forms a high-stability chelate, and in pyrolysis, the chelate bond breaks at about 420℃, and the Ni 2+The explosive release, without uniform crystal nucleus foundation, and the concentrated decomposition of ligand carbon skeleton, O2 oxidation not timely, led to the carbon residual amount significantly higher than example 2; at the same time, without the initial space barrier of weak coordination bond, the crystal grains were easy to fuse and agglomerate, and the agglomeration index and particle size distribution width were much higher than example 2; and the coarse grains and serious agglomeration led to the coverage of active sites, and the specific surface area was much lower than example 2; Comparative example 2 only relied on L-aspartic acid sodium and Ni 2+ Formed a low stable complex, completely decomposed at 250°C N2 stage, Ni 2+ Early release and no subsequent slow supply, crystal nucleus quickly merged into large particles, particle size much larger than example 2; at the same time, without the sustained dispersion effect of strong coordination agent, there was a lack of chemical barrier between particles, and the agglomeration was serious, the agglomeration index and particle size distribution width were higher than example 2; and the ligand decomposed too early, leading to the difficulty of carbon skeleton oxidation at low temperature stage, the carbon residual amount was higher than example 2; the double influence of coarsening and agglomeration made the specific surface area significantly lower than example 2; Comparative example 3, without SDBS micellar mesoscopic ordered template, the coordination complex molecules were randomly agglomerated, and the precursor formed a dense solid; in pyrolysis, oxygen could only penetrate to the surface of the particles, and the carbon produced by the decomposition of the internal ligand could not be fully oxidized (although the final carbon residual was close to example 2, but it needed to rely on longer time oxidation), and there was no pore isolation structure, the crystal grains were easy to fuse, the agglomeration index and particle size distribution width were higher than example 2; at the same time, without the microporous structure constructed by SDBS, the specific surface area was much lower than example 2 due to the densification of particles; Comparative example 4, without pure N2 low temperature nucleation stage, Ni 2+ Oxidized by air at the initial stage of temperature rise, forming unevenly distributed NiO crystal nucleus; without ligand mild decomposition in low oxygen stage, the ligand carbon skeleton was quickly carbonized and O2 could not be oxidized in time, the carbon residual amount was much higher than example 2; one-step heating led to local overheating, grain coarsening, and the agglomeration index and particle size distribution width were higher than example 2; and without the perfect process of crystallization by staged holding, the NiO crystal lattice had many defects, the active sites were covered by defects, and the specific surface area was significantly lower than example 2; Comparative example 5, without water washing to remove sodium salt and sodium oxide generated by pyrolysis, sodium ions were adsorbed on the surface of NiO, causing electrostatic attraction between particles, leading to secondary agglomeration, and the agglomeration index and particle size distribution width were higher than example 2; although the carbon residual was well controlled due to the rich oxygen crystallization, but the sodium residual amount was much higher than example 2; and the sodium salt blocked part of the micropores, and the active sites were not exposed enough, and the specific surface area was slightly lower than example 2.

[0061] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

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 complexed 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 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.

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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