Method for preparing flaky Ni (OH) 2-Co (OH) 2 composite nano material

Abstract

The invention relates to the technical field of nano material preparation, in particular to a method for preparing a flaky Ni (OH) 2-Co (OH) 2 composite nano material, which comprises the following steps: providing electric energy by using a direct-current power supply, using a nickel sheet as an anode, using a conical graphite rod in contact with a solution interface as a cathode, using NaCl as an electrolyte, and using Co (NO3) 2 as a cobalt source (Co < 2 + >). When enough high voltage is applied between a cathode and an anode, glow is emitted between the tip of the conical graphite rod and a surrounding solution, active species such as OH., O., H., H2O2, eaq-and the like are generated, and the species react with water to generate OH-, so that an alkali source (OH-) is provided for preparing the composite nano material; and the nickel sheet provides Ni < 2 + > through anodic oxidation in the discharging process. By regulating and controlling the discharge voltage, the release yield and speed of OH <-> and Ni < 2 + > can be accurately controlled, so that the phase, morphology and structure regulation and control of the Ni (OH) 2-Co (OH) 2 composite nano material are realized. And continuously discharging for a period of time to obtain an emerald turbid solution, centrifugally separating, washing and drying to obtain the flaky Ni (OH) 2-Co (OH) 2 composite nano material.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial preparation, and particularly to a method for preparing flaky Ni(OH)2-Co(OH)2 composite nanomaterials. Background Art

[0002] Transition metal nano-hydroxides are an important class of inorganic materials. Due to their variable valence, numerous active sites, and large specific surface area, they are widely used in fields such as catalytic hydrogen evolution, battery materials, supercapacitors, adsorption, etc. Currently, the wide application of single transition metal hydroxides is limited due to their poor stability. Recently, several transition metal hydroxides have been compounded, and through their synergistic effects, their performance has been significantly improved. For example, after compounding Ni(OH)2 and Co(OH)2, the conductivity, cycle stability, and catalytic oxidation performance are significantly enhanced. Therefore, the preparation of composite transition metal hydroxides is of great significance.

[0003] In the past 20-odd years, hydroxide composites can be prepared by methods such as co-precipitation, hydrothermal method, sol-gel method, and electrochemical deposition method, etc. However, due to their cumbersome processes, harsh conditions, and long reaction times, large-scale production is restricted; in addition, these methods strongly rely on toxic chemical reagents such as alkali sources, stabilizers, organic solvents, etc., and are prone to secondary pollution. At the same time, the one-time addition of chemical reagents in traditional preparation methods often leads to the rapid combination and rapid growth of metal ions and OH - in a high-concentration condition. This rapid nucleation and growth process easily trigger the collision and combination between microcrystals, thus forming defect structures such as twins and polycrystals, seriously damaging the long-range order and the integrity of the lattice structure. At the same time, this uncontrollable growth mechanism will further induce various structural defects, such as ion disordered filling, lattice slip, interlayer dislocation, and interlayer separation, etc., and exacerbate the problem of particle agglomeration. In order to overcome these problems, it is extremely urgent to explore a method for preparing composite double hydroxide nanomaterials with simple process, controllable morphology, and environmental friendliness.

[0004] Cathodic glow discharge electrolysis (CGDE) is a non-traditional electrolysis method, which is characterized by the plasma-liquid interaction generated between the needle-shaped electrode and the surrounding electrolyte. It uses a platinum needle and a metal sheet (rod) as the two electrodes. When a sufficiently high voltage is applied between the two electrodes, the platinum needle tip discharges, emitting a bright glow and generating plasma. In CGDE, the generated ·H, ·OH, ·O, and e aq -Highly active species that can rapidly initiate some special chemical reactions. In recent years, due to its advantages such as less use of chemical reagents and environmental friendliness, this technology has attracted extensive attention in the preparation of nanomaterials such as Mn3O4 microspheres, Fe3O4 nanoparticles, β-Ni(OH)2, and β-Co(OH)2. However, this technology uses a platinum needle as the discharge cathode, making the economic cost of preparing nanomaterials relatively high. Moreover, although a series of nanomaterials have been prepared by the CGDE technology, there is no literature report on the preparation of Ni(OH)2-Co(OH)2 composite nanomaterials by CGDE. Summary of the Invention

[0005] The object of the present invention is to provide a new method for preparing Ni(OH)2-Co(OH)2 composite nanomaterials in one step by using the glow discharge electrolysis plasma technology with a conical graphite rod as the cathode, based on the advantages of the glow discharge electrolysis plasma, aiming at the disadvantages of the existing preparation process of Ni(OH)2-Co(OH)2 composite nanomaterials, such as complex process, harsh conditions, high production cost, and secondary pollution.

[0006] In order to achieve the above object, the following technical solutions are provided:

[0007] A method for preparing flaky Ni(OH)2-Co(OH)2 composite nanomaterials, characterized by comprising the following steps:

[0008] Step 1: Use a high-voltage DC power supply to provide electrical energy, use a nickel sheet as the anode, the tip of a conical graphite rod as the cathode, use a NaCl solution as the electrolyte, add Co(NO3)2 as the cobalt source to the electrolyte, and add a resistor to the circuit to stabilize the current;

[0009] Step 2: When a sufficiently high voltage and current are applied between the anode and cathode electrodes, a bright glow is generated between the cathode conical graphite rod and the surrounding solution, forming a stable plasma, and generating active species such as OH·, O·, H·, H2O2, e aq - These active species react with water to produce OH - , thereby providing an alkali source (OH - ) for the preparation of Ni(OH)2-Co(OH)2 composite nanomaterials;

[0010] Step 3: During the discharge process, the anode nickel sheet provides Ni 2+ ions through electrochemical anodic oxidation, and a green precipitate gradually forms in the solution;

[0011] Step 4: Continuously discharge for a period of time under magnetic stirring to obtain a bright green turbid solution;

[0012] Step 5: Centrifuge the turbid liquid, wash the product successively with absolute ethanol and distilled water several times, dry it in vacuum, and grind it to obtain a bright green product, which is the Ni(OH)2-Co(OH)2 composite nanomaterial.

[0013] Preferably, in Step 1, a 1-5 kΩ resistor is added between the positive electrode of the power supply and the nickel sheet anode to stabilize the current. A 200 mL NaCl solution with a concentration of 0.5-5 g / L is used as the electrolyte, and 0.05-0.20 g of Co(NO3)2 is added as the cobalt source to the electrolyte. The distance between the two electrodes is 0.5-2.0 cm.

[0014] Preferably, in Step 1, the cathode is a graphite rod with a specification of Φ5mm×100mm, and one end of the graphite rod is ground into a cone with an angle of 20-70°.

[0015] Preferably, in Step 1, the discharge voltage provided by the high-voltage DC power supply is 580-680 V, and the discharge current is about 200-260 mA.

[0016] Preferably, in Step 1, the anode nickel sheet is processed by the following process before use: sanded and polished, then soaked in acetone for 10-15 min, and then ultrasonically washed in deionized water for 10-15 min to remove the grease on the surface.

[0017] Preferably, in Step 3, during the discharge process, the temperature of the solution is maintained at 40-90 °C, and the reaction time is 0.5-2 h.

[0018] Preferably, in Step 4, the speed of the magnetic stirring is 80-150 rpm.

[0019] Preferably, in Step 5, the rotation speed of the centrifugal separation is 8000-14000 rpm.

[0020] Preferably, in Step 5, the temperature of the vacuum drying is 50-90 °C.

[0021] A preparation device for Ni(OH)2-Co(OH)2 composite nanomaterial, comprising a reaction vessel 5 and a DC regulated power supply 1. The interior of the reaction vessel 5 contains an electrolyte solution 8. The positive electrode 2 of the DC regulated power supply 1 is connected to a loop resistor 4 and a nickel sheet anode 9 through a wire. The nickel sheet anode 9 extends into the electrolyte solution 8 inside the reaction vessel 5 from the top of the reaction vessel 5. The negative electrode 3 of the DC regulated power supply 1 is connected to a tapered graphite rod cathode 10 through a wire. The tapered graphite rod cathode 10 extends into the electrolyte solution 8 inside the reaction vessel 5 from the top of the reaction vessel 5. The DC regulated power supply 1, the loop resistor 4, the nickel sheet anode 9, the electrolyte solution 8, and the graphite rod cathode form a discharge circuit.

[0022] The outer wall of the reaction vessel 5 is of a hollow structure, and the hollow structure is filled with condensed water. A condensed water inlet 12 is provided on the bottom side wall of the hollow structure, and a condensed water outlet 13 is provided on the upper side wall of the reaction vessel 5.

[0023] A magnetic stirrer 15 is installed at the bottom of the reaction vessel 5, and the magnetic stirring bar 14 of the magnetic stirrer 15 extends into the electrolyte solution 8 inside the reaction vessel 5.

[0024] A lid 6 is provided at the top of the reaction vessel 5, and an exhaust hole 7 is provided on the lid 6.

[0025] The lid 6 is made of polytetrafluoroethylene.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The present invention proposes to use an NaCl solution as the electrolyte, a conical graphite rod in contact with the solution interface as the cathode, Co(NO3)2 as the cobalt source, the anode nickel sheet dissolution to provide the nickel source, and the cathode glow discharge electrolysis (CGDE) plasma to provide active species and an alkali source, so as to obtain a flaky Ni(OH)2-Co(OH)2 composite nanomaterial with adjustable structure and morphology in one step;

[0028] 2. Based on the principle of tip discharge, the present invention generates instant high temperature, local high pressure in the solution, accompanied by microscopic effects such as light emission, heat generation, and shock waves, and at the same time generates OH generated by cathode discharge - to provide the alkali source required for the preparation of the composite hydroxide;

[0029] 3. The present invention uses CGDE to prepare the Ni(OH)2-Co(OH)2 composite nanomaterial. The device is simple, the operation is convenient, the conditions are mild (40 - 90 °C, no other gas protection, no organic solvents, no additional alkali is required), the process is controllable (by changing parameters such as the addition amount of the cobalt source, the discharge voltage, the electrolyte concentration, etc., Ni(OH)2-Co(OH)2 composite nanosheet materials with different thicknesses can be obtained), and it is an environmentally friendly green preparation new technology;

[0030] 4. The chemical reagents used in the reaction process of the present invention are few in type and low in dosage, reducing environmental pollution; the product has high purity and is convenient for separation.

[0031] 5. In the experimental process of the present invention, an inexpensive and easily available stone grinding rod is used instead of a platinum needle as the cathode, significantly improving the economic benefit and enabling industrial production. Description of the Drawings

[0032] Figure 1It is a schematic structural diagram of the CGDE device provided by the present invention, where: 1. DC regulated power supply, 2. Positive electrode of the power supply, 3. Negative electrode of the power supply, 4. Loop resistance, 5. Reaction vessel, 6. Lid, 7. Exhaust hole, 8. Electrolyte solution, 9. Nickel sheet anode, 10. Graphite rod cathode, 11. Tip of the graphite rod, 12. Condensate inlet, 13. Condensate outlet, 14. Magnetic stirrer, 15. Magnetic stirrer;

[0033] Figure 2 It is the current-voltage characteristic curve of the CGDE for preparing Ni(OH)2-Co(OH)2 composite nanomaterials under the conditions that the discharge voltage is 650V, the electrolyte is 200 mL of 2 g / L NaCl, and the cobalt source is 0.15 g of Co(NO3)2 in the present invention;

[0034] Figure 3 It is the emission spectrum diagram of the CGDE for preparing Ni(OH)2-Co(OH)2 composite nanomaterials under the conditions that the discharge voltage is 650V, the electrolyte is 200 mL of 2 g / L NaCl, and the cobalt source is 0.15 g of Co(NO3)2 in the present invention;

[0035] Figure 4 It is the change of pH of the anode solution, cathode solution and bulk solution with the reaction time during the process of the CGDE for preparing Ni(OH)2-Co(OH)2 composite nanomaterials under the conditions that the discharge voltage is 650V, the electrolyte is 200 mL of 2 g / L NaCl, and the cobalt source is 0.15 g of Co(NO3)2 in the present invention;

[0036] Figure 5 It is the FT-IR spectra of Ni(OH)2-Co(OH)2 composite nanomaterials prepared under the conditions that the discharge voltage is 650V, the electrolyte is 200 mL of 2 g / L NaCl, and different Co(NO3)2 concentrations in the present invention, where: (a) the cobalt source is 0.05 g of Co(NO3)2; (b) the cobalt source is 0.10 g of Co(NO3)2; (c) the cobalt source is 0.15 g of Co(NO3)2; (d) the cobalt source is 0.20 g of Co(NO3)2;

[0037] Figure 6 It is the XRD patterns of Ni(OH)2-Co(OH)2 composite nanomaterials prepared under the conditions that the discharge voltage is 650V, the electrolyte is 200 mL of 2 g / L NaCl, and different Co(NO3)2 concentrations in the present invention, where: (a) the cobalt source is 0.05 g of Co(NO3)2; (b) the cobalt source is 0.10 g of Co(NO3)2; (c) the cobalt source is 0.15 g of Co(NO3)2; (d) the cobalt source is 0.20 g of Co(NO3)2;

[0038] Figure 7SEM morphologies of the Ni(OH)2-Co(OH)2 composite nanomaterials prepared in the present invention at a discharge voltage of 650 V, an electrolyte of 200 mL of 2 g / L NaCl, and different Co(NO3)2 concentrations, where: (a) the cobalt source is 0.05 g of Co(NO3)2; (b) the cobalt source is 0.10 g of Co(NO3)2; (c) the cobalt source is 0.15 g of Co(NO3)2; (d) the cobalt source is 0.20 g of Co(NO3)2;

[0039] Figure 8 TEM morphology (a), high-resolution TEM (HR-TEM) morphology (b), and selected area electron diffraction (SEAD) pattern (c) of the Ni(OH)2-Co(OH)2 composite nanomaterial prepared in the present invention at a discharge voltage of 650 V, an electrolyte of 200 mL of 2 g / L NaCl, and a cobalt source of 0.15 g of Co(NO3)2. Detailed implementation manners

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] Example 1

[0042] Using 200 mL of an NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.05 g of Co(NO3)2 as the cobalt source, a nickel sheet as the anode, and a conical stone grinding rod polished to 30° as the cathode, the distance between the two electrodes is 1.0 cm, the external circuit resistance is 2 kΩ, and a high-voltage DC power supply provides electrical energy. When a voltage of 650 V and a current of 247 mA are applied between the anode and cathode, a bright glow is generated at the tip of the cathode graphite rod, forming a stable plasma. The solution is continuously stirred at 120 rpm and the temperature is maintained at 80 °C. After discharging for 1 h, a turquoise turbid solution is obtained; the turbid solution is ultrasonically dispersed for 15 min and centrifuged at a high speed of 10,000 rpm. The product is washed successively with distilled water and absolute ethanol and vacuum dried at 60 °C to constant weight. The turquoise product obtained is the Ni(OH)2-Co(OH)2 composite nanomaterial. Its FT-IR spectrum is shown in Figure 5 a, and the XRD spectrum is shown in Figure 6 a, and the SEM is shown in Figure 7 a.

[0043] Example 2

[0044] Using 200 mL of a NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.10 g of Co(NO3)2 as the cobalt source, a nickel sheet as the anode, and a graphite rod as the cathode, the distance between the two electrodes is 1.0 cm, the external circuit resistance is 3 kΩ, and a high-voltage DC power supply provides electrical energy. A voltage of 650 V is applied between the anode and cathode to generate a bright glow at the tip of the cathode graphite rod, forming a stable plasma. The solution is continuously stirred at 120 rpm and the temperature is maintained at 80 °C. After discharging for 1 h, a turquoise turbid solution is obtained; the turbid solution is ultrasonically dispersed for 15 min and then centrifuged at 10000 rpm. The product is washed successively with distilled water and absolute ethanol, and vacuum dried at 60 °C to constant weight to obtain a turquoise product, which is the Ni(OH)2-Co(OH)2 composite nanomaterial. Its FT-IR spectrum is shown in Figure 5 b, and its XRD pattern is shown in Figure 6 b, and its SEM image is shown in Figure 7 b.

[0045] Example 3

[0046] Using 200 mL of a NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.15 g of Co(NO3)2 as the cobalt source, a nickel sheet as the anode, and a graphite rod as the cathode, the distance between the two electrodes is 1.0 cm, the external circuit resistance is 2 kΩ, and a high-voltage DC power supply provides electrical energy. A voltage of 650 V is applied between the anode and cathode to generate a bright glow at the tip of the cathode graphite rod, forming a stable plasma. The solution is continuously stirred at 120 rpm and the temperature is maintained at 80 °C. After discharging for 1 h, a turquoise turbid solution is obtained; the turbid solution is ultrasonically dispersed for 15 min and then centrifuged at 10000 rpm. The product is washed successively with distilled water and absolute ethanol, and vacuum dried at 60 °C to constant weight to obtain a turquoise product, which is the Ni(OH)2-Co(OH)2 composite nanomaterial. Its current-voltage curve is shown in Figure 2 , its emission spectrum is shown in Figure 3 , the change in solution pH is shown in Figure 4 , its FT-IR spectrum is shown in Figure 5 c, its XRD pattern is shown in Figure 6 c, its SEM image is shown in Figure 7 c, and its TEM, HR-TEM, and SEAD images are shown in Figure 8 a - c.

[0047] Example 4

[0048] Using 200 mL of an NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.20 g of Co(NO3)2 as the cobalt source, using a nickel sheet as the anode, and a polished 45° conical graphite rod as the cathode, with a distance of 1.0 cm between the two electrodes, an external circuit resistance of 2 kΩ, and a high-voltage DC power supply providing electrical energy, applying a voltage of 650 V between the anode and cathode to generate a bright glow at the tip of the cathode graphite rod, forming a stable plasma. Continuously stir the solution at 120 rpm and maintain the temperature at 80 °C, discharge for 1 h to obtain a turquoise turbid solution; ultrasonically disperse the turbid solution for 15 min, centrifuge at 10000 rpm at high speed, wash the product successively with distilled water and absolute ethanol, and vacuum dry at 60 °C to constant weight to obtain the turquoise product, which is the Ni(OH)2-Co(OH)2 composite nanomaterial. Its FT-IR spectrum is shown in Figure 5 d, and the XRD spectrum is shown in Figure 6 d, and the SEM is shown in Figure 7 d.

[0049] (I) The preparation method of the present invention:

[0050] The following is to illustrate that the method for preparing the nanomaterial Ni(OH)2-Co(OH)2 is a glow discharge process rather than an ordinary electrolysis process through the current-voltage curve ( Figure 2 ). Use the DH1722A-6 DC regulated power supply of Beijing Dahua Radio Instrument Co., Ltd. to measure the change of current at different voltages. Figure 2 Taking 2 g L -1 NaCl as the electrolyte, 0.15 g of Co(NO3)2 as the cobalt source, with a distance of 10 mm between the anode and cathode, and an external resistance of 2 kΩ, by adjusting different voltages, draw the current-voltage curve of the cathode glow discharge electrolysis plasma. From Figure 2It can be seen that the entire discharge process is divided into four segments: segment AB (0 - 450V), which is the conventional ordinary electrolysis region. As the voltage increases, the current also gradually increases, following Ohm's law and Faraday's electrolysis law; segment BC (450 - 580V), where the current-voltage curve shows a negative slope. This is because the tip surface of the graphite rod is covered by unstable vapor bubbles, and the intermittent generation and disappearance of the vapor bubbles impede the continuity of the current. Therefore, segment BC is called the unstable region; segment CD (580 - 680V), which is the glow discharge electrolysis stage. Although the voltage continues to increase, the change in current is not obvious, and the generated glow is relatively stable. So we choose to synthesize the nanomaterial Ni(OH)2-Co(OH)2 in this region. Segment DE (>680V), as the voltage increases, the glow becomes stronger, but in this stage, the cathode electrode is easily damaged due to high temperature, and the generated plasma has poor stability. When the voltage is lower than 580V, the glow is weak, the plasma has poor stability, and few highly active plasmas are generated, resulting in fewer products. Therefore, in the process of preparing the nanomaterial Ni(OH)2-Co(OH)2, in order to make the glow discharge stable, with low energy consumption and relatively high yield, the voltage range of 580 - 680V in segment CD is selected as the optimal discharge voltage range.

[0051] (2) Preparation principle of the present invention:

[0052] The principle of preparing the composite nanomaterial Ni(OH)2-Co(OH)2 is described below by analyzing the emission spectrum and the change in solution pH.

[0053] 1. Emission spectrum analysis

[0054] To explain the preparation mechanism of the Ni(OH)2-Co(OH)2 composite nanomaterial, the emission spectrum of the CGDE was measured using an optical fiber spectrometer. Figure 3 The obtained emission spectrum diagram when 0.15g of Co(NO3)2 was added to 200mL of a 2g / L NaCl solution, the distance between the anode and cathode was 10mm, the external resistance was 2kΩ, and the discharge voltage was 650V. The emission lines at wavelengths of 282.9 and 308.9nm are the transition bands of HO(A2∑ + →X2Π)((1, 0) and (0, 0)), the ionic spectral lines of OII are at 330.5 and 464.8nm, the N2 emission line is at 399.3nm, the OⅠ emission line is at 615.7nm, the H α spectral line is at 655.9nm, and the transition spectral lines of excited state O atoms can be observed at 777.8nm and 845.1nm. This is because high-energy electrons excite the vaporized water molecules to produce a large amount of HO·, H·, O·, O2 - ·. The atomic lines of Na are at 568.8, 588.7, and 819.9nm, indicating that the electrolyte contains Na+ Therefore, many chemical reactions can be initiated by cathode glow discharge electrolysis plasma.

[0055] 2. Changes in solution pH during the preparation of nanomaterial Ni(OH)2-Co(OH)2

[0056] To further understand the preparation mechanism of nanomaterial Ni(OH)2-Co(OH)2, a pH meter was used to measure the changes in pH values around the anode and cathode and in the bulk solution at different discharge times when the electrolyte was 200 mL of 2 g / L sodium chloride with 0.15 g of cobalt nitrate added. As Figure 4 shown, it can be seen that during the discharge process, the pH of the anode solution decreased slightly, indicating that a small amount of H + was generated at the anode; the pH of the cathode solution gradually increased to pH > 12, indicating that a large amount of OH - ions were generated at the cathode; the pH of the bulk solution slowly increased to around 9, indicating that the preparation of Ni(OH)2-Co(OH)2 was carried out in a weakly alkaline environment.

[0057] Based on the above analysis and experimental phenomena, the mechanism of preparing nanomaterial Ni(OH)2-Co(OH)2 by cathode glow discharge electrolysis technology is as follows:

[0058] After the reaction starts, the anode nickel sheet undergoes anodic dissolution under electrochemical action, thereby generating Ni 2+ in the solution; and migrates to the cathode under the drive of a strong electric field. At the same time, H + is generated in the anode region, and the pH value of the solution shows a downward trend.

[0059] Anode:

[0060] Ni - 2e - → Ni 2+

[0061] 2H2O - 4e - → 4H + + O2

[0062] At the plasma-liquid interface around the cathode, H2O is bombarded by high-energy electrons (e*), and then decomposes to produce various active substances, such as e aq - , H·, OH·, ·O and H2O2:

[0063] H2O + e * → e aq - + ·OH + H· + O· + H2O2

[0064] These active species undergo secondary reactions to form more stable OH - ions:

[0065] e aq - +e aq - →H2 + OH -

[0066] e aq - +·OH → OH -

[0067] e aq - +H· + H2O → H2 + OH -

[0068] The electrolyte near the cathode is alkaline, and Co 2+ and Ni 2+ in the solution migrate to the cathode under the action of the electric field and finally form Ni(OH)2 - Co(OH)2:

[0069] Ni 2+ + Co 2+ + 4OH - → Ni(OH)2 - Co(OH)2

[0070] (III) Characterization of Ni(OH)2 - Co(OH)2 Composite Nanomaterials

[0071] The characteristic peaks of the material were analyzed by Fourier transform infrared spectroscopy (FT - IR, DIGILAB FTS 3000) below. The composition and structure of the prepared samples were further determined by X - ray diffractometer (XRD, Rigaku D / max - 2400). The morphology and nanostructure of the material were observed by scanning electron microscope (SEM, JSM - 5600LV) and high - resolution transmission electron microscope (TEM, JEM - 2100plus). The composition of the material was further determined by selected area electron diffraction (SAED) pattern.

[0072] 1. FT - IR Test

[0073] Figure 5 Shows the Fourier transform infrared spectra of Co - 0.05 (a), Co - 0.10 (b), Co - 0.15 (c) and Co - 0.20 (d). The sharp and strong peak at 3646 cm -1 is the stretching vibration of hydroxide (OH - ) in brucite - like; the peaks at 3437 and 1608 cm -1 are attributed to the stretching and bending vibrations of O - H of interlayer and adsorbed water molecules respectively. The peak at 1396 cm -1 is attributed to NO3 -The N-O stretching vibration, which is attributed to the cobalt source cobalt nitrate (Co(NO3)2). 400 - 800 cm -1 The absorption peaks at are attributed to the lattice vibrations of O-M-O, M-O, and M-O-M of Ni(OH)2 and Co(OH)2. Therefore, the results of FT-IR preliminarily indicate that the obtained product is Ni(OH)2-Co(OH)2.

[0074] 2. XRD Test

[0075] Figure 6 are the X-ray diffraction (XRD) patterns of the synthesized samples under different conditions. The characteristic diffractions observed at 19.32°, 33.24°, 38.56°, 51.56°, 59.48°, 62.92°, 69.48°, and 72.62° can all correspond to the (001), (100), (101), (102), (003), (111), (103), and (112) crystal planes of Ni(OH)2 and Co(OH)2, marking the formation of the Ni(OH)2-Co(OH)2 composite nanomaterial. In addition, the diffraction peaks in the figure are significantly broadened, which is a characteristic of nanomaterials, indicating that the prepared composite material has a small size and is at the nanoscale. The broad and weak diffraction peaks presented in the spectrum intuitively reflect the amorphous characteristics of the prepared sample. It is worth noting that the diffraction peaks of different samples are found to appear at the same positions, which strongly indicates that Ni(OH)2-Co(OH)2 has the same crystal phase structure and there are no other impurity peaks, proving that the prepared Ni(OH)2-Co(OH)2 has high purity. Thus, the XRD analysis results of Ni(OH)2-Co(OH)2 are consistent with the FT-IR analysis results, proving that the product prepared by CGDE is the Ni(OH)2-Co(OH)2 composite nanomaterial.

[0076] 3. Morphology Test

[0077] The morphology of the synthesized Ni(OH)2-Co(OH)2 material was characterized by scanning electron microscopy (SEM) technology. As Figure 7 shown, the prepared Ni(OH)2-Co(OH)2 composite nanomaterials all exhibit distinct sheet-like structures, and the nanosheets are interconnected to form a 3D network structure. The thickness of the sheets is less than 20 nm, and there is no agglomeration phenomenon. To further observe the morphology of the prepared samples, the sample corresponding to Figure 7 c was analyzed by TEM, and the results are as Figure 8 shown. It can be seen that the prepared Ni(OH)2-Co(OH)2 composite nanomaterials exhibit sheet-like structures, which is consistent with the SEM analysis results. The sheet thickness was measured to be approximately 2 nm by Nano Measurer1.2.5 software. Figure 8b shows the HT-TEM morphology of the composite material. The two lattice fringes are 0.2282 nm and 0.2345 nm respectively, approximately equal to 0.23 nm, so it is attributed to the (101) crystal plane. As Figure 8 shown in c, the selected area electron diffraction (SAED) pattern of the sample shows bright rings with different intensities. From the inside to the outside, they are the (100), (102) and (111) crystal planes of Ni(OH)2-Co(OH)2. This result is consistent with the above XRD analysis result.

[0078] In summary, using NaCl as the electrolyte, Co(NO3)2 as the cobalt source, and a conical graphite rod as the cathode, the Ni(OH)2-Co(OH)2 composite nanomaterial with a thinner sheet layer and excellent morphology can be prepared by the glow discharge electrolysis plasma technology.

[0079] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A method for preparing a flaky Ni(OH)2-Co(OH)2 composite nanomaterial, characterized in that, It includes the following steps: Step 1: Use a high-voltage DC power supply to provide electrical energy. Use a nickel sheet as the anode, the tip of a conical graphite rod in contact with the solution interface as the discharge cathode, use a NaCl solution as the electrolyte, use Co(NO3)2 as the cobalt source for synthesizing Ni(OH)2-Co(OH)2, and add a resistor in the circuit to stabilize the current. Step 2: When a sufficiently high voltage and current are applied between the anode and cathode, a bright glow is generated between the cathode conical graphite rod and the surrounding solution, forming a stable plasma and generating active species such as OH·, O·, H·, H2O2, e aq - These active species react with water to produce OH - , thereby providing an alkali source (OH - ) for the preparation of Ni(OH)2-Co(OH)2; Step 3: During the discharging process, nickel ions are provided by the anodic nickel sheet through electrochemical anodic oxidation, and green precipitates gradually form in the solution; 2+ ​ Step 4: Continuously discharge for a period of time under magnetic stirring to obtain an emerald green turbid liquid. Step 5: Centrifuge the turbid liquid, wash the product successively with anhydrous ethanol and distilled water several times, dry it under vacuum, and grind it to obtain an emerald green product, which is the Ni(OH)2-Co(OH)2 composite nanomaterial.

2. The method for preparing the flaky Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, characterized in that, In Step 1, a 1-5 kΩ resistor is added between the positive pole of the power supply and the nickel sheet anode to stabilize the current. Use a 200 mL 0.5-5 g / L NaCl solution as the electrolyte, and add 0.05-0.20 g Co(NO3)2 as the cobalt source to the 200 mL NaCl electrolyte. The distance between the two electrodes is 0.5-2.0 cm.

3. The method for preparing the flaky Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, wherein, In Step 1, the cathode is a graphite rod with a specification of Φ5mm×100mm, and one end of the graphite rod is ground into a cone with an angle of 20-70°.

4. The method for preparing the flaky Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, wherein, In Step 1, the discharge voltage provided by the high-voltage DC power supply is 580-680 V, and the discharge current is about 200-260 mA.

5. The method for preparing the flaky Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, characterized in that, In Step 1, the anode nickel sheet is processed by the following process before use: sand it, polish it, soak it in acetone for 10-15 min first, and then ultrasonically wash it in deionized water for 10-15 min to remove the grease on the surface.

6. The method for preparing the sheet-like Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, wherein In Step 3, during the discharge process, the temperature of the solution is kept at 40-90 °C, and the reaction time is 0.5-2 h.

7. The method for preparing the flaky Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, characterized in that, In Step 4, the speed of the magnetic stirring is 80-150 rpm.

8. The method for preparing the sheet-like Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, wherein In Step 5, the rotation speed of the centrifugation is 8000-14000 rpm.

9. The method for preparing the sheet-like Ni(OH)2-Co(OH)2 composite nanomaterial according to claim 1, characterized in that, In Step 5, the temperature of the vacuum drying is 50-90 °C.

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