Preparation method of CoAl layered double hydroxide nano material

Abstract

The invention relates to the technical field of nano material preparation, in particular to a preparation method of a CoAl layered double hydroxide nano material. A high-voltage direct-current power supply is used for providing electric energy, a cobalt sheet is used as an anode, a conical graphite rod in contact with a solution interface is used as a cathode, a NaNO3 solution is used as an electrolyte, and AlCl3 is used as an aluminum source (Al < 3 + >) 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 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; in the discharging process, the anode cobalt sheet is oxidized to provide Co < 2 + >, and the electrolyte provides LDHs intercalation anions. In the discharging process, green precipitates are gradually generated in the solution, discharging is continuously carried out for a period of time, dark green turbid liquid is obtained, the turbid liquid is subjected to centrifugal separation, washing and drying, and dark green powder, namely the flaky CoAl-LDH nanometer material, is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of nano material preparation, in particular to a method for preparing a CoAl layered double hydroxide nano material. Background Art

[0002] CoAl layered double hydroxides (CoAl-LDHs) are a type of nanomaterial with a two-dimensional layered structure, and have a hydrotalcite-like or anionic clay structure. The composition ratio of divalent Co and trivalent Al ions in the layers, the type and quantity of interlayer anions are adjustable; the surface hydroxyl groups can be modified by covalent bonds, electrostatic effects, and hydrogen bonds; at the same time, due to its unique layered structure, large specific surface area, and abundant active sites, it has broad application prospects in supercapacitors, ion lithium batteries, electrocatalytic oxygen evolution reaction, wastewater treatment, biomedicine and other fields.

[0003] At present, the methods for preparing CoAl-LDHs are mainly chemical coprecipitation, hydrothermal method, solvothermal method and urea decomposition method. However, these methods require the use of alkaline sources (such as urea, sodium hydroxide), adjusting the solution pH to 8-11, high reaction temperature (over 100°C), and long reaction time (over 12h); and some also require the addition of organic solvents, which leads to a large amount of chemical drugs and easy secondary pollution; in addition, the existing methods add chemical reagents at one time, which makes it difficult to control the structure and morphology. This is because in the high-concentration reaction system, metal ions react with OH - Rapid combination and rapid growth cause collision and combination between LDHs crystallites, resulting in defect structures such as twins and polycrystalline, thus destroying the long-range effect of the LDHs structure and the order of the lattice, which in turn causes LDHs to produce more structural defects (such as ion disorder filling, lattice slip, stacking faults and interlayer separation) and particle agglomeration. Therefore, the development of new methods for preparing nano-LDHs with simple processes, controllable morphology, orderly structure and green environmental protection has attracted widespread attention from researchers.

[0004] Cathodic glow discharge electrolysis (CGDE) is an efficient green synthesis method that generates plasma in a solution. A platinum needle and a metal sheet (or a carbon rod, etc.) are used as two electrodes. When a sufficiently high voltage is applied between the two electrodes, the solution around the platinum needle is vaporized, emitting a glow and generating plasma. aq -Highly active substances (whose yields are far higher than the values expected by Faraday's law) can quickly enter the solution, thereby triggering some complex physical and chemical reactions at the plasma-liquid interface. In recent years, the CGDE technology has been widely applied in fields such as wastewater purification, surface modification, organic synthetic chemistry, spectroscopic analysis, and nanomaterial preparation. However, using Pt as the electrode material in CGDE makes its application economically costly. Additionally, there is no literature report on the preparation of CoAl-LDH nanomaterials by the CGDE technology. Summary of the Invention

[0005] The object of the present invention is to provide a new method for preparing CoAl-LDH nanomaterials by using a cathode glow discharge electrolysis plasma technology with a conical graphite rod replacing a platinum needle, based on the advantages of glow discharge electrolysis plasma, aiming at the disadvantages of the existing technology for preparing CoAl-LDH, such as harsh conditions, complex processes, long reaction time, large amount of chemical reagents used, easy agglomeration of products, easy generation of secondary pollution, and high economic cost.

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

[0007] A method for preparing CoAl layered double hydroxide nanomaterials, characterized by comprising the following steps:

[0008] Step 1: Use a high-voltage DC power supply to provide electrical energy, use a cobalt sheet as the anode, use the tip of a conical graphite rod in contact with the solution interface as the cathode, use a NaNO3 solution as the electrolyte, use AlCl3 as the aluminum source, and add a resistor in the circuit to stabilize the current;

[0009] 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 - and 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 cobalt sheet provides Co 2+ ions through electrochemical anodic oxidation, and the electrolyte provides the intercalated anions of LDHs;

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

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

[0013] Preferably, in Step 1, a 1 - 5 kΩ resistor is added between the positive electrode of the power supply and the cobalt sheet anode to stabilize the current. A 200 mL solution of 0.5 - 5 g / L NaNO3 is used as the electrolyte, and 0.05 - 0.20 g of AlCl3 is added as the aluminum source to the NaNO3 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 440 - 590 V, and the discharge current is about 80 - 180 mA.

[0016] Preferably, in Step 1, the anode cobalt 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 stirring 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 CoAl - LDH nanomaterials, as Figure 1 shown, includes a reaction vessel 5 and a DC regulated power supply 1. The inside 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 cobalt sheet anode 9 through a wire. The cobalt 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 reaction vessel 5 from the top and contacts the interface of the electrolyte solution 8. The DC regulated power supply 1, the loop resistor 4, the cobalt sheet anode 9, the electrolyte solution 8, and the graphite rod cathode 10 form a discharge circuit.

[0022] The outer wall of the reaction vessel 5 is of a hollow structure. Condensed water is contained in 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 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 a NaNO3 solution as the electrolyte, a conical graphite rod in contact with the solution interface as the discharge cathode, AlCl3 as the aluminum source, and a cathodic glow discharge electrolysis (CGDE) plasma technology in which nano-graphite sheets are produced by the dissolution of the anode cobalt sheet and the exfoliation of the cathode graphite carbon rod to obtain a CoAl-LDH sheet-like nano material 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 simultaneously generates OH - to provide the alkali source required for the preparation of double hydroxides;

[0029] 3. The present invention uses CGDE to prepare CoAl-LDH nano materials. The device is simple, the operation is convenient, the conditions are mild (40 - 90 °C, no other gas protection is required, and no organic solvents are required), the process is controllable (by changing parameters such as the addition amount of the aluminum source, the discharge voltage, and the electrolyte concentration, CoAl-LDH nano sheet materials with different thicknesses can be obtained), and it is an environmentally friendly green preparation new 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 the environmental pollution; the product purity is high and it is convenient for separation.

[0031] 5. In the experimental process of the present invention, an inexpensive and easily available graphite rod is used instead of a platinum needle as the cathode, with significant economic benefits and the possibility of 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. Cobalt 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 during the process of preparing CoAl-LDH nanomaterials by CGDE provided by the present invention, where: the discharge voltage is 550V, the electrolyte concentration is 2g / L NaNO3, and the aluminum source is 0.12g AlCl3;

[0034] Figure 3 It is the emission spectrum diagram of the CoAl-LDH nanomaterials prepared by CGDE provided by the present invention, where: the discharge voltage is 550V, the electrolyte concentration is 2g / L NaNO3, and the aluminum source is 0.12g AlCl3;

[0035] Figure 4 It is the change diagram of the solution pH with the reaction time during the process of preparing CoAl-LDH nanomaterials by CGDE provided by the present invention, where: the discharge voltage is 550V, the electrolyte concentration is 2g / L NaNO3, and the aluminum source is 0.12g of AlCl3;

[0036] Figure 5 It is the FT-IR spectrum diagram of the CoAl-LDH nanomaterials prepared by adding aluminum sources with different concentrations under the conditions of an electrolyte concentration of 2g / L NaNO3 and a voltage of 550V in the present invention, where: (a) the aluminum source is 0.08g AlCl3; (b) the aluminum source is 0.12g AlCl3; (c) the aluminum source is 0.16g AlCl3;

[0037] Figure 6 It is the XRD spectrum diagram of the CoAl-LDH nanomaterials prepared by adding aluminum sources with different concentrations under the conditions of an electrolyte concentration of 2g / L NaNO3 and a voltage of 550V in the present invention, where: (a) the aluminum source is 0.08g AlCl3; (b) the aluminum source is 0.12g AlCl3; (c) the aluminum source is 0.16g AlCl3;

[0038] Figure 7 It is the SEM morphology of the CoAl-LDH nanomaterials prepared by adding aluminum sources with different concentrations under the conditions of an electrolyte concentration of 2g / L NaNO3 and a voltage of 550V in the present invention, where: (a) the aluminum source is 0.08g AlCl3; (b) the aluminum source is 0.12g AlCl3; (c) the aluminum source is 0.16g AlCl3;

[0039] Figure 8 TEM morphology (a), high-resolution TEM (HR-TEM) morphology (b), and selected area electron diffraction (SEAD) pattern (c) of the CoAl-LDH nanomaterial provided by the present invention, where: the discharge voltage is 550 V, the electrolyte concentration is 2 g / L NaNO3, and the aluminum source is 0.12 g AlCl3. Detailed implementation mode

[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 the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] Example 1

[0042] Using 200 mL of a NaNO3 solution with a concentration of 2 g / L as the electrolyte, adding 0.08 g of AlCl3 as the aluminum source, a cobalt sheet as the anode, and a tapered graphite rod polished to 30° as the cathode, the distance between the two electrodes is 1.0 cm, and the external circuit resistance is 2 kΩ. When a voltage of 550 V and a current of 156 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 for 1 h of discharge to obtain a dark green turbid liquid; the turbid liquid 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 dark green product obtained is the CoAl-LDH nanomaterial. Its FT-IR spectrum is shown in Figure 5 a, and the XRD pattern is shown in Figure 6 a, and the SEM is shown in Figure 7 a.

[0043] Example 2

[0044] Using 200 mL of a NaNO3 solution with a concentration of 2 g / L as the electrolyte, adding 0.12 g of AlCl3 as the aluminum source, a cobalt sheet as the anode, and a graphite rod as the cathode, the distance between the two electrodes is 1.0 cm, and the external circuit resistance is 2 kΩ. A voltage of 550 V is applied between the anode and cathode to make a bright glow appear at the tip of the cathode graphite rod, forming a stable plasma. The solution is continuously stirred at 150 rpm and the temperature is maintained at 80 °C for 1 h of discharge to obtain a dark green turbid liquid; the turbid liquid is ultrasonically dispersed for 15 min and centrifuged at a high speed of 12,000 rpm. The product is washed successively with distilled water and absolute ethanol, and vacuum dried at 60 °C to constant weight. The dark green product obtained is the CoAl-LDH nanomaterial. Its current-voltage curve is shown in Figure 2, the emission spectrum is shown in Figure 3 , the change in solution pH is shown in Figure 4 , the FT-IR spectrum is shown in Figure 5 b, the XRD pattern is shown in Figure 6 b, the SEM is shown in Figure 7 b, the TEM, HR-TEM, and SEAD are shown in Figure 8 a - c.

[0045] Example 3

[0046] Using a 200 mL NaNO3 solution with a concentration of 2 g / L as the electrolyte, adding 0.16 g of AlCl3 as the aluminum source, a cobalt sheet as the anode, and a polished 45° conical 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 550 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. After discharging for 1 h, a dark green 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. The dark green product obtained is the CoAl-LDH nanomaterial. Its FT-IR pattern is shown in Figure 5 c, the XRD pattern is shown in Figure 6 c, the SEM is shown in Figure 7 c.

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

[0048] The following explains through the current-voltage curve that the method for preparing the nanomaterial CoAl-LDH is a glow discharge process rather than an ordinary electrolysis process. The DH1722A-6 DC regulated power supply is used to measure the change in current at different voltages. Figure 2 Using 2 g L -1 NaNO3 as the electrolyte, 0.12 g of AlCl3 as the aluminum source, the distance between the anode and cathode is 10 mm, and the external resistance is 2 kΩ. By adjusting different voltages, the current-voltage curve of the cathode glow discharge electrolytic plasma is plotted. From Figure 2It can be seen that the entire discharge process is divided into four segments: segment AB (0 - 360 V), 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 (360 - 440 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, 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 (440 - 590 V), which is the normal glow discharge electrolysis stage. Although the voltage continues to increase, the change in current is not obvious, and the generated glow is relatively stable. Therefore, this region is selected for synthesizing the nanomaterial CoAl-LDH. Segment DE (>590 V), 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 440 V, the glow is weak, the plasma stability is poor, few highly active plasmas are generated, and the obtained products are also fewer. Therefore, during the preparation of the nanomaterial CoAl-LDH, in order to make the glow discharge stable, the energy consumption low, and the output relatively large, the voltage range of 440 - 590 V in segment CD is selected as the optimal discharge voltage range.

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

[0050] The principle of preparing the nanomaterial CoAl-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 the CoAl-LDH nanomaterial, the emission spectrum of the CGDE was measured using an optical fiber spectrometer. Figure 3 The obtained emission spectrum diagram was when the electrolyte was a NaNO3 solution with a concentration of 2 g / L, 0.12 g of AlCl3 was added as the aluminum source, the distance between the anode and the cathode was 10 mm, the external resistance was 2 kΩ, and the discharge voltage was 550 V. OH emission lines can be observed at 283.0 nm - 309.0 nm, the spectral lines of O II are at 330.5 and 464.8 nm, the N2 emission line is at 399.3 nm, the OⅠ emission line is at 615.7 nm, the H α spectral line is at 656.0 nm, and the transition spectral lines of excited state O atoms can be observed at 777.8 nm and 845.1 nm. This is because high-energy electrons excite the vaporized water molecules to generate a large number of HO·, H·, O·, O2 - ·. The atomic lines of Na are at 569.2, 589.2, and 819.9 nm, indicating that the electrolyte contains Na + . According to the emission spectrum, it is found that free radicals such as ·H, ·O, ·OH are generated in the aqueous solution; in addition, e is also generated during the CGDE processaq - and H2O2. 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 cathode glow discharge electrolysis plasma.

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

[0054] To further study the preparation mechanism of the CoAl-LDH nanomaterial, a pH meter was used to measure the changes in the pH values around the anode and cathode and the total solution at different discharge times. The results are as Figure 4 shown. It can be seen that initially, due to the hydrolysis reaction of aluminum ions, the reaction solution is weakly acidic. As the discharge voltage increases, within 40 min, the pH of the solution around the cathode gradually increases from the initial 4.3 to 12.1, and then the pH basically remains around 12.2, indicating that OH - is generated during the cathode discharge process; the pH of the solution around the anode shows an upward trend, but basically remains at 6.2 after 40 min, indicating that a small amount of H + is generated during the discharge process. The pH of the total solution gradually increases from 4.2 to 9.8 and then basically remains at 9.8. This indicates that the preparation of CoAl-LDH is carried out in an alkaline environment.

[0055] Based on the above analysis, the mechanism of preparing the nanomaterial CoAl-LDH by cathode glow discharge electrolysis technology is as follows:

[0056] First, the anode cobalt sheet undergoes anodic dissolution under electrochemical action, thus generating Co 2+ in the solution; then Co 2+ migrates to the cathode under the drive of a strong electric field. In addition, the H + generated at the anode makes the solution around the anode acidic. The reactions are as follows:

[0057] Co → Co 2+ + 2e -

[0058] 2H2O - 4e - → 4H + + O2

[0059] In addition, 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:

[0060]

[0061] These active species undergo secondary reactions to form more structurally stable OH - ions:

[0062] e aq - +OH· → OH -

[0063] e aq - +H2O → H· + OH -

[0064] e aq - +H2O2 → OH· + OH -

[0065] Due to high-energy electron radiation and ordinary electrolysis at the cathode, OH is generated at the cathode - , resulting in an alkaline electrolyte near the cathode. Al 3+ and Co 2+ in the solution migrate towards the cathode under the action of the electric field and finally react with OH - to form flaky nano-CoAl-LDH material. The main equations are as follows:

[0066] Co 2+ +Al 3+ +OH - → CoAl-LDH

[0067] (III) Characterization of CoAl-LDH Nanomaterials

[0068] The characteristic peaks of the material are analyzed by Fourier transform infrared spectroscopy (FT-IR, DIGILAB FTS 3000), the composition and structure of the prepared samples are analyzed by X-ray diffractometer (XRD, Rigaku D / max-2400), the morphology and structure of the material are observed by scanning electron microscope (SEM, JSM-5600LV) and high-resolution transmission electron microscope (TEM, JEM-2100plus), and the composition of the material is further determined by selected area electron diffraction (SAED) pattern.

[0069] 1. FT-IR Test

[0070] Figure 5 Shows the Fourier transform infrared spectra of Al-0.08, Al-0.12, and Al-0.16. The peaks at 3455 and 1634 cm -1 are due to the O-H stretching and bending vibrations of interlayer water and surface adsorbed water molecules. The peak at 1377 cm -1The strong and sharp adsorption peak at is attributed to NO3 - 's N-O stretching vibration mode, which originates from the electrolyte sodium nitrate (NaNO3). The absorption peaks at 400 - 800 cm -1 belong to the lattice vibrations of O-M-O, M-O, and M-O-M of LDHs. Additionally, there is no strong absorption peak in the range of 3600 - 3700 cm -1 (OH - ), which is a characteristic of hydrotalcite-like layered double hydroxides. Therefore, the results of FT-IR preliminarily suggest that the prepared product may be CoAl-LDH.

[0071] 2. XRD Test

[0072] The XRD of the synthesized CoAl-LDH is as Figure 6 shown. The characteristic diffraction peaks observed at 11.60°, 23.43°, 34.58°, 39.16°, and 46.22° are attributed to the (003), (006), (012), (015), and (018) crystal planes in CoAl-LDH, which is consistent with the JCPDS card 51 - 0045 of CoAl-LDH. The doublet near 60° - 62° corresponds to the (110) and (113) crystal planes in CoAl-LDH, indicating the formation of the LDH phase. In addition, the diffraction peaks in the figure are significantly broadened, which is a characteristic of nanomaterials. This implies that the prepared CoAl-LDH is small in size and at the nanoscale. The broad and weak diffraction peaks presented in the spectrum intuitively reflect the amorphous characteristics of the prepared sample. The presence of (003) and (006) indicates that CoAl-LDH has a unique layer structure, which provides favorable conditions for the intercalation of electrolyte ions. More importantly, it is observed that the diffraction peaks of different samples appear at the same positions, which strongly indicates that CoAl-LDH has the same crystal phase structure. Additionally, in XRD, the (002) crystal plane of lamellar graphite is observed at 2θ = 26.6°, indicating that during the discharge process, a small amount of graphite is ablated and peeled off by the plasma to produce nano-graphite sheets, and the peeled nano-graphite sheets are combined with CoAl-LDH, which can just enhance the redox property, specific surface area, conductivity, and adsorption property of CoAl-LDH. During the analysis of the XRD pattern, no diffraction peaks corresponding to Al2O3, Al(OH)3, or Co(OH)2 are observed. Thus, it can be inferred that the CoAl-LDH prepared by the DGD method has high purity. In summary, the XRD analysis results of CoAl-LDH are consistent with the FT-IR analysis results, indicating that the product prepared by CGDE is CoAl-LDH with a hydrotalcite-like structure.

[0073] 3. Morphology Characterization

[0074] From Figure 7It can be seen that the CoAl-LDH prepared by this method are all nanoflowers self-assembled by interlaced nanosheets. There is no agglomeration of the nanosheets, and the thickness of the sheets is all less than 20 nm. To further observe the morphology and microstructure of the prepared samples, Figure 7 Sample b was subjected to TEM analysis, and the results are as Figure 8 shown in a. It can be seen that the prepared CoAl-LDH nanomaterial has a sheet-like structure, which is consistent with the SEM analysis results. The thickness of the nanosheets was measured to be about 5 nm using Nano Measurer 1.2.5 software ( Figure 8 inset in a). Figure 8 b shows the HT-TEM morphology of the material. The measured lattice fringe spacings are 0.3804 and 0.2601, which are consistent with the interplanar spacings of the (006) and (012) crystal planes in XRD. Figure 8 c shows the selected area electron diffraction (SAED) pattern of the sample. It can be seen that bright rings of different intensities are arranged from the inside to the outside as the (006), (012), and (110) crystal planes of CoAl-LDH. This result is consistent with the XRD analysis results.

[0075] In summary, using NaNO3 as the electrolyte, AlCl3 as the aluminum source, and a conical graphite rod as the cathode, CoAl-LDH nanomaterials with thin sheets and excellent morphology were prepared by the glow discharge electrolysis plasma technology.

[0076] 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-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 included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A preparation method of CoAl layered double hydroxide nanomaterials, characterized in that It includes the following steps: Step 1: Use a high-voltage DC power supply to provide electrical energy. Use a cobalt sheet as the anode, the tip of a conical graphite rod in contact with the solution interface as the discharge cathode, a NaNO3 solution as the electrolyte, and AlCl3 as the aluminum source for synthesizing CoAl-LDH. 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 continuously generate OH - , thereby providing an alkali source (OH - ) for the preparation of LDHs; Step 3: During the discharging process, Co ions are provided by the anodic cobalt sheet through electrochemical anodic oxidation, and the electrolyte provides the LDHs intercalated anions; 2+ ​ Step 4: Continuously discharge for a period of time under magnetic stirring to obtain a dark green turbid liquid. Step 5: Centrifuge and separate the turbid liquid, wash it several times with absolute ethanol and distilled water in sequence, dry it under vacuum and grind it to obtain a dark green product, which is the flaky CoAl-LDH nanomaterial.

2. The preparation method of a CoAl layered double hydroxide nanomaterial according to claim 1, characterized in that, In Step 1, connect a 1 - 5 kΩ resistor between the positive electrode of the power supply and the cobalt sheet anode to stabilize the current. Use a 200 mL 0.5 - 5 g / L NaNO3 solution as the electrolyte, and add 0.05 - 0.20 g AlCl3 as the aluminum source to the NaNO3 electrolyte. The distance between the two electrodes is 0.5 - 2.0 cm.

3. The preparation method of a CoAl layered double hydroxide 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 preparation method of a CoAl layered double hydroxide nanomaterial according to claim 1, wherein, In Step 1, the discharge voltage provided by the high-voltage DC power supply is 440 - 590 V, and the discharge current is about 80 - 180 mA.

5. The preparation method of a CoAl layered double hydroxide nanomaterial according to claim 1, wherein, In Step 1, the anode cobalt sheet is processed by the following process before use: polish it with sandpaper, 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 preparation method of a CoAl layered double hydroxide nanomaterial according to claim 1, wherein, 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 CoAl layered double hydroxide nanomaterial according to claim 1, characterized in that, In Step 4, the stirring speed of the magnetic stirring is 80 - 150 rpm.

8. The preparation method of a CoAl layered double hydroxide nanomaterial according to claim 1, wherein, In Step 5, the rotation speed of the centrifugal separation is 8000 - 14000 rpm.

9. The preparation method of a CoAl layered double hydroxide 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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