Preparation method of NiCr-LDH nano material

Abstract

The invention relates to the technical field of nano material preparation, in particular to a preparation method of a NiCr-LDH nano material. A direct-current power supply is used for providing electric energy, a nickel sheet is used as an anode, a conical graphite rod in contact with a solution interface is used as a cathode, a NaCl solution is used as an electrolyte, and CrCl3 is used as a chromium source for preparing LDHs. When sufficiently high voltage is applied between the cathode and the anode, stable plasma is formed between the tip of the conical graphite rod of the cathode and a surrounding solution, active species such as OH., O., H., H2O2 and eaq-are generated, and the active species react with water to generate OH-, so that an alkali source (OH-) is provided for preparing LDHs; and in the discharging process, the nickel sheet is anodized to generate Ni < 2 + >. 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 NiCr-LDH nano material are realized. Discharging for a period of time to obtain a green turbid solution; and carrying out centrifugal separation, washing and drying to obtain a green product, namely the flaky NiCr-LDH nano material.

Description

Technical Field

[0001] The invention relates to the technical field of nano material preparation, in particular to a method for preparing a NiCr-LDH nano material. Background Art

[0002] Nickel-chromium double hydroxide (NiCr-LDHs), also known as nickel-chromium layered double hydroxide, is an inorganic compound with a hydrotalcite-like structure. NiCr-LDH is widely used in many fields due to its unique two-dimensional structure, good ion exchangeability, ultra-high specific surface area and multiple electron transfer characteristics. For example, in the field of electrochemical energy storage, NiCr-LDH is used as an electrode material in supercapacitors and batteries; in the field of catalysis, NiCr-LDH is used as a catalyst to catalyze hydrogen evolution, oxygen evolution and other reactions; in the field of adsorption, NiCr-LDH is used to remove heavy metal ions and organic pollutants in wastewater.

[0003] At present, the main methods for preparing LDHs include co-precipitation, hydrothermal method, calcination recovery method, etc. The essence of co-precipitation is the co-precipitation of the precursor metal salt and alkali (NaOH, NH3·H2O, urea, hexamethylenetetramine, etc.). During the reaction, the double metal ion M must be strictly controlled. 2+ / M 3+ The hydrothermal method is to use a water-alcohol mixture as a medium in a closed high-pressure reactor, and react at a high temperature (>120°C) for more than 10 hours to make the metal ions react with OH. - Combined to form a layered structure. The roasting recovery method is to add the roasting product of LDHs to a solution containing the target anion, and achieve the structural recovery of LDHs through lattice replacement of similar ions. Although the above method has been successful in the preparation of LDHs, it still has some shortcomings. The main manifestations are: harsh conditions, complex processes, and long reaction times; the above method strongly relies on toxic chemical reagents, including precursor metal salts, alkalis, stabilizers, organic solvents, etc., which are prone to secondary pollution; the one-time addition of chemical reagents in the above method leads to the reaction of metal ions with OH in the high-concentration reaction system. - Rapid combination and rapid growth lead to particle agglomeration and structural disorder. Therefore, the development of new methods for preparing nano-LDHs with simple process, controllable morphology, orderly structure and green environment has attracted wide attention from researchers.

[0004] Cathodic glow discharge electrolysis (CGDE) is a novel unconventional electrochemical process for preparing nanomaterials. As an efficient green synthesis method, it uses a platinum (Pt) needle and a metal sheet (rod) as the two electrodes. When a sufficiently high voltage is applied between the two electrodes, a bright glow continuously emits between the tip of the Pt needle and the surrounding solution, forming a plasma, and at the same time generating highly active species such as ·H, ·OH, ·O, and e aq - and other highly active species. These active species rapidly initiate some special chemical reactions at the plasma-liquid interface, such as oxidation reactions, reduction reactions, addition reactions, polymerization reactions, etc. Therefore, in recent years, CGDE technology has been widely applied in many fields such as spectral analysis, nanomaterial preparation, and wastewater degradation. However, using Pt as the discharge electrode will significantly increase the cost of generating the plasma; at the same time, there is no literature report on the preparation of NiCr-LDH nanomaterials using CGDE technology. Summary of the Invention

[0005] The object of the present invention is to provide a new method for one-step preparation of NiCr-LDH nanomaterials by using cathodic glow discharge electrolysis plasma of a conical graphite rod based on the advantages of glow discharge electrolysis plasma, aiming at the disadvantages of the existing preparation process of NiCr-LDH nanomaterials, such as complex process, strict conditions, many chemical reagents required, easy agglomeration of products, and high production cost.

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

[0007] A method for preparing NiCr-LDH 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, a NaCl solution as the electrolyte, and CrCl3 as the chromium source, and add a resistor in the circuit to stabilize the current;

[0009] Step 2: When a sufficiently high voltage is applied between the anode and the 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 - and other active species. These active species react with water to produce OH - , thus providing an alkali source (OH - ) for the preparation of LDHs;

[0010] Step 3: During the discharge process, the anode nickel sheet is gradually consumed to produce Ni 2+ , and a light green precipitate gradually appears in the solution;

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

[0012] Step 5: Centrifuge the turbid solution, wash the product successively with absolute ethanol and distilled water several times, dry it under vacuum, and grind it to obtain a green product, which is the NiCr-LDH nanomaterial.

[0013] Preferably, in Step 1, a 1-5 kΩ resistor is added between the positive electrode of the high-voltage DC 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 0.05-0.15 g of CrCl3 is added as the chromium 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 Φ5 mm×100 mm, 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 450-560 V, and the discharge current is about 70-175 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 centrifugation is 8000-14000 rpm.

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

[0021] A preparation device for NiCr-LDH nanomaterials, comprising a reaction vessel 5 and a DC regulated power supply 1. An electrolyte solution 8 is contained inside the reaction vessel 5. The positive electrode 2 of the DC regulated power supply 1 is connected to a loop resistor 4 and a nickel anode 9 through a wire. The nickel 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 conical graphite rod cathode 10 through a wire. The conical 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 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 condensed water is contained inside the hollow structure. 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 a magnetic stirrer 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 as the cathode, CrCl3 as the chromium source, Cl - as the intercalated anion for preparing LDH, and Ni 2+ dissolved and released from the anodic nickel sheet as the nickel source. By using the cathode glow discharge electrolysis (CGDE) plasma technology of conical graphite carbon, NiCr-LDH flaky nanomaterials with adjustable morphology are prepared in one step;

[0028] 2. According to the principle of tip discharge, the present invention generates instant high temperature, local high pressure and micro effects such as light emission, heat generation and shock waves in the solution. At the same time, active species such as OH·, O·, H·, H2O2, e aq - are generated. These active species react with water to generate OH - , thus providing an alkali source (OH - ) for preparing LDHs;

[0029] 3. The present invention uses CGDE to prepare NiCr-LDH nanomaterials. The device is simple, the operation is convenient, and the conditions are mild (40 - 90 °C, no need for other gas protection, no need for organic solvents). The process is controllable (by changing parameters such as the addition amount of chromium source, discharge voltage, etc., NiCr-LDH nanosheet materials with different thicknesses can be obtained). It is an environmentally friendly green preparation technology;

[0030] 4. The types of chemical reagents used in the reaction process of the present invention are few and the dosage is low, reducing environmental pollution; the product has high purity and is easy to separate.

[0031] 5. In the experimental process of the present invention, inexpensive and easily available graphite rods are used instead of platinum needles as the cathode, with significant economic benefits and can be industrially produced. Brief Description of the Drawings

[0032] Figure 1 is a schematic structural diagram of the CGDE device provided by the present invention, where: 1. DC regulated power supply, 2. Positive pole of the power supply, 3. Negative pole 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 is the current-voltage characteristic curve of the process of preparing NiCr-LDH nanomaterials by CGDE provided by the present invention, where: the discharge voltage is 500V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3;

[0034] Figure 3 is the emission spectrum diagram of the process of preparing NiCr-LDH nanomaterials by CGDE provided by the present invention, where: the discharge voltage is 500V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3;

[0035] Figure 4 is the change diagram of the solution pH with the reaction time during the process of preparing NiCr-LDH nanomaterials by CGDE provided by the present invention, where: the discharge voltage is 500V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3;

[0036] Figure 5It is the FT-IR spectrum of the NiCr-LDH nanomaterial provided by the present invention, where: (a) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.05 g of CrCl3; (b) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3; (c) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.15 g of CrCl3;

[0037] Figure 6 It is the XRD pattern of the NiCr-LDH nanomaterial provided by the present invention, where: (a) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.05 g of CrCl3; (b) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3; (c) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.15 g of CrCl3;

[0038] Figure 7 It is the SEM image of the NiCr-LDH nanomaterial provided by the present invention, where: (a) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.05 g of CrCl3; (b) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3; (c) the discharge voltage is 500 V, the electrolyte is 200 mL of 2 g / L NaCl, and the chromium source is 0.15 g of CrCl3;

[0039] Figure 8 It is the TEM morphology (a), high-resolution TEM (HR-TEM) morphology (b), and selected area electron diffraction (SEAD) pattern (c) of the NiCr-LDH nanomaterial provided by the present invention, where: the discharge voltage is 500 V, the electrolyte concentration is 2 g / L NaCl, and the chromium source is 0.10 g of CrCl3. Detailed implementation manners

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with 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 of 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 a NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.05 g of CrCl3 as the chromium source, a nickel sheet as the anode, and a conical graphite rod polished to 30° 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. When a voltage of 500 V and a current of 172 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 green turbid solution is obtained; the turbid solution is ultrasonically dispersed for 15 min and then centrifuged at 10,000 rpm. The product is washed successively with distilled water and absolute ethanol and dried in vacuo at 60 °C to constant weight to obtain a green product, which is the NiCr-LDH nanomaterial. Its FT-IR spectrum is shown in Figure 5 a, and its XRD pattern is shown in Figure 6 a, and its 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 CrCl3 as the chromium source, a nickel sheet as the anode, and a conical graphite rod polished to 60° as the cathode, with a distance of 1.0 cm between the two electrodes, an external circuit resistance of 4 kΩ, and a high-voltage DC power supply providing electrical energy. When a voltage of 500 V is 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 green turbid solution is obtained; the turbid solution is ultrasonically dispersed for 15 min and then centrifuged at 10,000 rpm. The product is washed successively with distilled water and absolute ethanol and dried in vacuo at 60 °C to constant weight to obtain a green product, which is the NiCr-LDH nanomaterial. Its current-voltage curve is shown in Figure 2 , its emission spectrum is shown in Figure 3 , the change in the solution pH is shown in Figure 4 , its FT-IR spectrum is shown in Figure 5 b, its XRD pattern is shown in Figure 6 b, its SEM is shown in Figure 7 b, and its TEM, HR-TEM, SEAD are shown in Figure 8 a - c.

[0045] Example 3

[0046] Using 200 mL of an NaCl solution with a concentration of 2 g / L as the electrolyte, adding 0.15 g of CrCl3 as the chromium source, 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 3 kΩ, and a high-voltage DC power supply providing electrical energy, a voltage of 500 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 100 rpm and the temperature is maintained at 80 °C, and the discharge is carried out for 1 h to obtain a green turbid liquid; the turbid liquid is ultrasonically dispersed for 15 min and centrifuged at a high speed of 10000 rpm, and the product is washed successively with distilled water and absolute ethanol, and vacuum dried at 60 °C to constant weight to obtain a green product, which is the NiCr-LDH nanomaterial. Its FT-IR spectrum is shown in Figure 5 c, and the XRD spectrum is shown in Figure 6 c, and the SEM is shown in Figure 7 c.

[0047] (I) The preparation method of the present invention:

[0048] The following is to illustrate that the method for preparing the nanomaterial NiCr-LDH is a glow discharge process rather than an ordinary electrolysis process by means of the current-voltage curve ( Figure 2 ). A DC regulated power supply (voltage 0 - 1000 V, current 0 - 0.5 A) is used to measure the current change at different voltages. Figure 2 Taking 200 mL of 2 g / L -1 NaCl as the electrolyte, 0.10 g of CrCl3 as the chromium source, with a distance of 10 mm between the anode and cathode and an external resistance of 2 kΩ, the current-voltage curve of the cathode glow discharge electrolytic plasma is plotted by adjusting different voltages. From Figure 2It can be seen that the entire discharge process is divided into four stages: the AB stage (0 - 340 V), which is the conventional ordinary electrolysis region. As the voltage increases, the current gradually increases, following Ohm's law and Faraday's electrolysis law; the BC stage (340 - 450 V), where the current-voltage curve shows a negative slope. This is because the tip surface of the graphite rod is surrounded by unstable vapor bubbles, which do not conduct electricity and intermittently generate and disappear, hindering the continuity of the current. Therefore, the BC stage is called the unstable region; the CD stage (450 - 560 V) is the glow discharge electrolysis stage. Although the voltage is still increasing, the current increases slowly and the generated glow is relatively stable. Therefore, we choose to synthesize NiCr-LDH nanomaterials in this region. The DE stage (>560 V), as the voltage increases, the glow becomes dazzling. At the same time, the cathode electrode is easily melted and consumed due to high temperature, and the generated plasma has poor stability. When the voltage is lower than 450 V, the glow is weak, the plasma stability is poor, and few highly active plasmas are generated, resulting in fewer products. Therefore, during the preparation of the nanomaterial NiCr-LDH, in order to make the glow discharge stable, with low energy consumption and a relatively large yield of active species, a voltage of 500 V in the CD stage is selected as the optimal discharge voltage. Figure 2 The inset shows the discharge photograph at 500 V.

[0049] (2) Preparation principle of the present invention:

[0050] The principle of preparing the nanomaterial NiCr-LDH is illustrated below by analyzing the emission spectrum and the change in solution pH.

[0051] 1. Emission spectrum analysis

[0052] To explain the preparation mechanism of NiCr-LDH nanomaterials, the emission spectrum of CGDE was measured using an optical fiber spectrometer. Figure 3 The obtained emission spectrum diagram was under the conditions that the electrolyte was 200 mL of NaCl solution with a concentration of 2 g / L, 0.10 g of CrCl3 was added as the chromium source, the distance between the anode and cathode was 10 mm, the external resistance was 2 kΩ, and the discharge voltage was 500 V. OH emission lines can be observed at 282.9 - 309.8 nm, the ionic lines of O II are at 330.5 and 464.8 nm, the emission lines of excited state OI atoms can be observed at 615.7, 777.8, and 845.1 nm, and the H α spectral line is at 655.9 nm. This is because high-energy electrons excite the vaporized water molecules to generate a large amount of HO·, H·, O·, O2 - ·. The atomic lines of Na are at 569.2, 589.2, and 819.9 nm, proving that the electrolyte contains Na +According to the emission spectrum, it was found that free radicals such as ·H, ·O, and ·OH were generated in the aqueous solution; in addition, e aq - and H2O2 were also generated during the CGDE process. Since e aq - and H· are strong reducing agents with standard potentials of -2.87 V and -2.30 V respectively, while HO˙ is a strong oxidizing agent with a standard potential of 2.85 V. Therefore, many chemical reactions can be initiated by the cathode glow discharge electrolysis plasma.

[0053] 2. Changes in the solution pH during the preparation of the nanomaterial NiCr-LDH

[0054] To further understand the preparation mechanism of the nanomaterial NiCr-LDH, a pH meter was used to measure the changes in the pH values of the solutions around the cathode and anode at different discharge times, and the results are shown in Figure 4 . From Figure 4 it can be seen that the reaction solution was acidic (pH = 4) initially due to the hydrolysis reaction of chromium ions; after the reaction started, the pH of the solution around the cathode rapidly changed from acidic to strongly basic (pH > 12); the pH of the solution around the anode nickel sheet slowly increased and was weakly acidic (4 < pH < 6); the pH of the bulk solution slowly increased from 4.0 to 7.8. This indicates that the preparation of NiCr-LDH was carried out under weakly basic conditions.

[0055] Based on the above analysis, the mechanism for the preparation of the nanomaterial NiCr-LDH by the cathode glow discharge electrolysis technique is as follows:

[0056] After the reaction starts, the anode nickel sheet dissolves under the electrochemical action to release Ni 2+ , and under the drive of the electric field, Ni 2+ migrates towards the cathode. And the generation of H + at the anode makes the solution around the anode always show weak acidity. The reactions are as follows:

[0057] Ni → Ni 2+ + 2e -

[0058] 2H2O - 4e - → 4H + + O2

[0059] At the plasma-liquid interface around the cathode, high-energy electrons (e*) react with H2O to decompose and generate e aq - , H·, OH·, ·O, OH - and various active species such as H2O2:

[0060]

[0061] Then, these active species undergo secondary reactions to generate OH near the cathode. - :

[0062]

[0063] Cr in the solution 3+ and Ni 2+ migrate towards the cathode under the action of the electric field and finally react with OH - to generate NiCr-LDH:

[0064] Ni 2+ + Cr 3+ + OH - → NiCr-LDH

[0065] (III) Characterization of NiCr-LDH Nanomaterials

[0066] The characteristic peaks of the material were analyzed by Fourier transform infrared spectroscopy (FT-IR, DIGILAB FTS 3000), and 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), and the composition of the material was further determined by selected area electron diffraction (SAED) pattern.

[0067] 1. FT-IR Test

[0068] Figure 5 The Fourier transform infrared spectra of Cr-0.05, Cr-0.10, and Cr-0.15 are shown. The peaks at 3455 and 1636 cm -1 are attributed to the stretching and bending vibrations of O-H of interlayer and adsorbed water molecules. The absorption peaks at 400 - 800 cm -1 belong to the O-M-O, M-O, and M-O-M related vibration modes of LDHs. In addition, there is no strong absorption peak (OH -1 ) generated at 3600 - 3700 cm - , which is a characteristic of hydrotalcite-like layered double hydroxides. Therefore, the results of Fourier transform infrared spectroscopy preliminarily indicate that the synthesized product may be NiCr-LDH.

[0069] 2. XRD Test

[0070] Figure 6XRD patterns of the synthesized samples under different conditions. The characteristic diffractions observed at 11.10°, 22.34°, 34.77°, 39.02°, 46.67°, and 61.01° belong to the (003), (006), (009), (015), (018), and (110) crystal planes of NiCr-LDH, respectively. The presence of (003) and (006) indicates that NiCr-LDH has a unique two-dimensional layered structure. In addition, the significant broadening of the diffraction peaks indicates that the material has a small grain size and is in the nanoscale range. It is worth noting that the diffraction peak positions and shapes of different samples show good consistency, which fully confirms that the prepared NiCr-LDH materials have the same crystal structure characteristics. There are no other impurity peaks, from which it can be inferred that the prepared NiCr-LDH has high purity. The broad and weak diffraction peaks presented in the pattern intuitively reflect the amorphous characteristics of the prepared samples. Thus, the XRD analysis results are consistent with the FT-IR analysis results, further indicating that the product prepared by CGDE is NiCr-LDH nanomaterial.

[0071] 3. Morphology test

[0072] The morphology of the synthesized NiCr-LDH material was characterized by scanning electron microscopy (SEM) technology. As Figure 7 shown in a-c, the prepared NiCr-LDH nanomaterials all exhibit distinct sheet-like structures. The nanosheets are interconnected in a three-dimensional network structure without agglomeration, and the sheet thickness is less than 20 nm. To further observe the morphology of the prepared samples, Figure 7 the sample corresponding to b was analyzed by TEM, and the results are shown in Figure 8 a. It can be seen that the prepared NiCr-LDH nanomaterials are in sheet-like structures, which is consistent with the SEM analysis results. And it was concluded by measuring with Nano Measurer 1.2.5 software that the sheet thickness of the prepared NiCr-LDH nanomaterials is about 5 nm. As Figure 8 shown in b, the selected area electron diffraction (SAED) pattern of the sample shows bright rings with different intensities, which are the (009), (015), and (110) crystal planes of NiCr-LDH from the inside to the outside in turn. This result is consistent with the XRD analysis results. Figure 8 c is the HT-TEM morphology of the obtained material. The measured lattice fringe spacings are 0.2527 and 0.2040, corresponding to the (009) and (018) crystal planes of NiCr-LDH, respectively.

[0073] Based on the above analysis, the conclusion is drawn that using NaCl as the electrolyte, CrCl3 as the chromium source, and a conical graphite rod as the cathode, the sheet-like NiCr-LDH nanomaterials with thinner sheets, excellent morphology, and no agglomeration can be prepared by the glow discharge electrolysis plasma technology.

[0074] 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 the present invention 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-limiting. 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 embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A preparation method of NiCr-LDH 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, use the tip of a conical graphite rod in contact with the solution interface as the cathode, use a NaCl solution as the electrolyte, use CrCl3 as the chromium source for synthesizing NiCr-LDH, and add a resistor in the circuit to stabilize the current; Step 2: When a sufficiently high voltage is 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 a base source (OH - ) for the preparation of LDHs; Step 3: During the discharging process, the anode nickel sheet is gradually consumed through electrochemical anodic oxidation to generate Ni 2+ , and a light green precipitate gradually forms in the solution; Step 4: Continuously discharge for a period of time under magnetic stirring to obtain a green turbid liquid; Step 5: Centrifuge the turbid liquid, wash the product successively with anhydrous ethanol and distilled water several times, dry it in vacuum, and grind it to obtain a green product, which is the flaky NiCr-LDH nanomaterial.

2. The preparation method of a NiCr-LDH nanomaterial according to claim 1, characterized in that, In Step 1, a 1-5 kΩ resistor is added between the positive pole of the high-voltage DC power supply and the nickel sheet anode to stabilize the current. Use 200 mL of a 0.5-5 g / L NaCl solution as the electrolyte, and add 0.05-0.15 g of CrCl3 as the chromium source to the electrolyte. The distance between the two electrodes is 0.5-2.0 cm.

3. The preparation method of a NiCr-LDH nanomaterial according to claim 1, characterized in that, 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 preparation method of a NiCr-LDH nanomaterial according to claim 1, characterized in that, In Step 1, the discharge voltage provided by the high-voltage DC power supply is 450-560V, and the discharge current is about 70-175 mA.

5. The preparation method of a NiCr-LDH 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, and then ultrasonically wash it in deionized water for 10-15 min to remove the grease on the surface.

6. The preparation method of a NiCr-LDH nanomaterial according to claim 1, characterized in that, 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.

7. The preparation method of a NiCr-LDH nanomaterial according to claim 1, wherein, In Step 4, the speed of the magnetic stirring is 80-150 rpm.

8. The preparation method of a NiCr-LDH nanomaterial according to claim 1, characterized in that, In Step 5, the rotation speed of the centrifugation is 8000-14000 rpm.

9. The preparation method of a NiCr-LDH nanomaterial according to claim 1, wherein, In Step 5, the temperature of the vacuum drying is 50-90 °C.

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