Crystal-split rod-shaped Co-Cu LDH catalyst and preparation method thereof

Abstract

Crystal-split rod-shaped Co-Cu LDH catalyst and preparation method. The crystal-split rod-shaped Co-Cu LDH catalyst has a rod-shaped structure with a length of 100-300 nm. It uses cobalt nitrate and copper nitrate as raw materials, and a mixed solution of ethylene glycol and water as a solvent. The pH value is adjusted by an alkali solution, and it is prepared by reacting at -50°C to -20°C. The preparation method is as follows: Take cobalt nitrate and copper nitrate as raw materials, use a mixed solution of ethylene glycol and water as a solvent, mix the raw materials and the solvent, adjust the pH value by an alkali solution, and react at -50°C to -20°C to obtain rod-shaped Co-Cu LDH. The preparation process of the present invention uses a co-precipitation method with synergistic control of solvent and temperature to prepare Co-Cu LDH. This method has simple steps, convenient operation, relatively low equipment cost and raw material cost, a controllable and non-toxic process, is suitable for industrial mass production, and can also be used in extremely short weather conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of metal catalysts, and particularly relates to a crystal-split rod-shaped Co-Cu LDH catalyst and a preparation method thereof. Background Art

[0002] Dye wastewater has stability, recalcitrance, and coloration, and some of it is carcinogenic. Discharging it into the environment will cause serious environmental, visual, and health problems. PPCPS in dye wastewater and water environment are two major problems in the field of water treatment. For the above two types of wastewater, traditional water treatment methods such as coagulation precipitation, adsorption, biodegradation, catalytic degradation, etc.

[0003] The heterogeneous Fenton-like reaction can degrade organic matter by generating reactive oxygen species (hydroxyl radicals, ·OH), and decompose it into small molecule substances such as CO2 and H2O. Therefore, the development of related catalysts

[0004] is of great significance. Cu and Co, as inexpensive non-precious metal catalysts, have the characteristics of high stability and can effectively activate H2O2 to generate ·OH. Therefore, it is of important scientific and practical significance to promote the rational design of high-performance Cu-Co bimetallic oxide catalysts, realize the controllable preparation of related catalysts, and clarify the structure-activity relationship between different structures and catalytic performances. Summary of the Invention

[0005] In order to overcome the above deficiencies, the present invention provides a crystal-split rod-shaped Co-Cu LDH catalyst and a preparation method thereof.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The crystal-split rod-shaped Co-Cu LDH catalyst, the crystal-split rod-shaped Co-Cu LDH catalyst is a rod-shaped structure with a length of 100-300 nm. It uses cobalt nitrate and copper nitrate as raw materials, and a mixed solution of ethylene glycol and water as a solvent, and adjusts the pH value with an alkali solution, and reacts at -50°C to -20°C to obtain.

[0008] The preparation method of the crystal-split rod-shaped Co-Cu LDH, take cobalt nitrate and copper nitrate as raw materials, and a mixed solution of ethylene glycol and water as a solvent, mix the raw materials and the solvent, adjust the pH value with an alkali solution, and react at -50°C to -20°C to obtain rod-shaped Co-Cu LDH.

[0009] Further optimization, the specific steps are as follows:

[0010] Step 1: Mix cobalt nitrate and copper nitrate in a mixed solution of ethylene glycol and water to obtain a mixed solution A;

[0011] Step 2: Prepare a mixed solution of ethylene glycol and water, and mix it with the lye to obtain a mixed solution B with a pH of 12.

[0012] Step 3: Place the mixed solution A and the mixed solution B in a low-temperature kettle respectively and maintain the temperature at -50°C to -20°C.

[0013] Step 4: Slowly drip the mixed solution A into the mixed solution B, add lye during the process, continuously stir at -50~-20°C, and perform a cleaning treatment after static aging to obtain a solid.

[0014] Step 5: Wash the solid with distilled water and ethanol respectively for multiple times, centrifuge and filter, and dry at 65°C to obtain rod-shaped Co-Cu LDH.

[0015] Further optimization: In the above Step 1, the molar ratio of cobalt nitrate to copper nitrate is 10:1 to 4:1.

[0016] Further optimization: In the above Step 2, the lye is Na2CO3 and NaOH with a molar concentration ratio of 1:2 to 2:1.

[0017] Further optimization: In the above Steps 1 and 2, the volume ratio of ethylene glycol to water is 1:9 to 9:1.

[0018] Further optimization: In the above Step 4, the aging time is 2 - 24 h.

[0019] Further optimization: In the above Step 4, the stirring time is 1 - 12 h.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The LDH prepared is different from the conventional lamellar LDH material. In this method, adding ethylene glycol changes the properties and surface tension of the solvent, thereby controlling the formation of LDH crystal nuclei and the growth of crystal grains.

[0022] 2. The freezing point of the ethylene glycol - aqueous solution is relatively low. The low-temperature condition is conducive to the splitting of crystals and inhibits the growth of crystals. The rod-shaped LDH prepared has uniform size and uniform dispersion, and at the same time avoids the common agglomeration phenomenon in the preparation process of LDH, making the product have excellent catalytic performance.

[0023] 3. Using environment-friendly potassium peroxymonosulfate or 30% H2O2 as the oxidant, without additional ultraviolet light or even visible light, the heterogeneous Fenton catalyst prepared can achieve a degradation rate of more than 99% for refractory organic compounds such as rhodamine B and metronidazole in 60 minutes at room temperature. The excellent performance and stability of this type of Fenton catalyst make it have good industrial application prospects in the field of organic pollutant remediation.

[0024] The preparation process of the present invention uses a co-precipitation method with synergistic control of solvent and temperature to prepare Co-Cu LDH. This method has simple steps, convenient operation, relatively low equipment and raw material costs, a controllable and non-toxic process, is suitable for industrial batch production, and can also be used in extremely short weather conditions. Description of the Drawings

[0025] Figure 1 is a SEM schematic diagram of sheet-like Co-Cu LDH;

[0026] Figure 2 is a SEM schematic diagram of rod-like Co-Cu LDH;

[0027] Figure 3 is a schematic diagram of the adsorption removal rate of rhodamine B by sheet-like and rod-like Co-Cu LDH;

[0028] Figure 4 is a schematic diagram of XRD of sheet-like and rod-like Co-Cu LDH. Detailed Embodiments

[0029] In order to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be described in detail below with reference to specific embodiments. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] A mixed solution of Cu(NO3)2·3H2O and Co(NO3)2·6H2O with a total metal molar amount of 7.5 mmol was dissolved in an ethylene glycol-aqueous solution with a volume ratio of 1:9 to obtain solution A, where the Co / Cu molar ratio was 7:1. Then, a solution B of NaOH and Na2CO3 with a pH of 12 (cNaOH:cNa2CO3 = 1:2) was prepared using the same ethylene glycol-aqueous solution. The stirring of solution A and solution B was controlled by a low-temperature kettle and maintained at -20°C. Then, solution A was added dropwise to solution B using a peristaltic pump. During the process, an alkaline solution was added to control the pH of solution B to remain unchanged. After stirring the solution at -20°C for 2 h, it was left to age for 1 h, washed with distilled water and ethanol, centrifuged and filtered, and the obtained solid was dried at 65°C. The obtained product was rod-like Co-Cu LDH, denoted as Co-Cu LDH-R.

[0032] Example 2

[0033] A mixed solution of Cu(NO3)2·3H2O and Co(NO3)2·6H2O with a total metal molar amount of 7.5 mmol was dissolved in an ethylene glycol - aqueous solution with a volume ratio of 55:45 to obtain solution A, where the Co / Cu molar ratio was 7:1. Then, a solution B of NaOH and Na2CO3 with pH = 12 (cNaOH:cNa2CO3 = 1:2) was prepared using the same ethylene glycol - aqueous solution. The low - temperature kettle was used to control the stirring of solution A and solution B and keep the temperature at - 40°C. Then, solution A was added dropwise to solution B using a peristaltic pump. During the process, alkali solution was added to control the pH of solution B to remain unchanged. After stirring the solution at - 40°C for 24 h, it was left to age for 8 h, and then washed, centrifuged, and filtered with distilled water and ethanol. The obtained solid was dried overnight at 65°C, and the resulting product was rod - shaped Co - Cu LDH, denoted as Co - Cu LDH - R.

[0034] Example 3

[0035] A mixed solution of Cu(NO3)2·3H2O and Co(NO3)2·6H2O with a total metal molar amount of 7.5 mmol was dissolved in an ethylene glycol - aqueous solution with a volume ratio of 9:1 to obtain solution A, where the Co / Cu molar ratio was 7:1. Then, a solution B of NaOH and Na2CO3 with pH = 12 (cNaOH:cNa2CO3 = 2:1) was prepared using the same ethylene glycol - aqueous solution. The low - temperature kettle was used to control the stirring of solution A and solution B and keep the temperature at - 50°C. Then, solution A was added dropwise to solution B using a peristaltic pump. During the process, alkali solution was added to control the pH of solution B to remain unchanged. After stirring the solution at - 50°C for 24 h, it was left to age for 12 h, and then washed, centrifuged, and filtered with distilled water and ethanol. The obtained solid was dried overnight at 65°C, and the resulting product was rod - shaped Co - Cu LDH, denoted as Co - Cu LDH - R.

[0036] Comparative example

[0037] A total of 7.5 mmol of Cu(NO3)2·3H2O and Co(NO3)2·6H2O (Co / Cu molar ratio of 7:1) were mixed and dissolved in 150.0 mL of ultrapure water. Under the condition of a stirring speed of 900 rpm, a NaOH / Na2CO3 solution was added to the solution, with the concentrations of NaOH and Na2CO3 being cNaOH = 0.4 mol / L and cNa2CO3 = 0.2 mol / L respectively, and the pH value of the solution was adjusted to about 12. Then, the solution was stirred at 40°C for 1 h, and then aged at 65°C for 24 h. Finally, the precipitate product was centrifugally washed thoroughly with ultrapure water and then dried thoroughly at 60°C to obtain different Co - Cu LDH catalysts. The structure was flaky LDH, denoted as Co - Cu LDH - P.

[0038] Using a 100 mL, 10 ppm rhodamine B (RhB) solution as the degradation target, the degradation rate of organic matter was tested. The reaction conditions for the test were as follows: the original pH value of the solution was approximately 6.1, the catalyst dosage was 10 mg, the initial reaction temperature was room temperature, approximately 25 °C. After adsorption for 1 h at a rotation speed of 500 rpm to reach adsorption-desorption equilibrium, 240 ppm H2O2 was added and the reaction continued for 30 min. As shown in the figure, the adsorption removal rate of Co-Cu LDH-R for RhB was approximately 13.3%, and the total removal rate was approximately 91.0%. The adsorption removal rate of Co-Cu LDH-P for RhB was approximately 10.0%, and the total removal rate was approximately 78.6%, proving that the performance of rod-shaped Co-Cu LDH was better than that of flake-shaped Co-Cu LDH. When the dosage of H2O2 increased to 480 ppm, the total removal rate of RhB increased to 99% under the same conditions.

[0039] It can be seen from SEM that, compared with the two, the agglomeration phenomenon of the flake-shaped Co-Cu LDH structure is more obvious. Specific surface area analysis shows that the specific surface area of Co-Cu LDH-P is approximately 60.3 m 2 / g, and the specific surface area of Co-Cu LDH-R is approximately 73.6 m 2 / g. The rod-shaped structure is slightly higher than the flake-shaped structure. This is because the low synthesis temperature accelerates crystal nucleation and splitting, reduces the crystal growth rate, weakens the tendency of nanocrystal agglomeration, induces crystal splitting, and finally the crystals that split and grow can obtain a catalyst with a high specific surface area and high catalytic activity. A higher specific surface area is conducive to the exposure of active sites and the interaction with the substrate, which promotes the reaction. From the performance comparison, it can be seen that the adsorption removal rate of rod-shaped LDH is slightly higher than that of flake-shaped LDH, which is related to the difference in specific surface area. At the same time, it can be seen from the SEM comparison that the size of rod-shaped LDH is smaller (<200 nm), and its size effect is more significant compared with flake-shaped materials. The smaller its particle size, the more active sites are exposed, and the larger the surface area, which can more effectively adsorb reactant molecules and promote the catalytic reaction. In addition, small-sized catalysts also have a higher surface energy, and the surface energy determines the interaction between the substrate and the catalyst, so the reaction rate can be increased.

[0040] It can be seen from XRD that referring to JSP, both contain the characteristic diffraction peaks of LDH (JCPDS#35-0965), and both are LDH structures, but the full width at half maximum of the two is different, which may be related to the different sizes.

[0041] The main features, usage methods, basic principles, and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have various changes and improvements according to actual situations, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A crystal-split rod-shaped Co-Cu LDH catalyst, characterized in that, The crystal-split rod-shaped Co-Cu LDH catalyst described above is a rod-shaped structure with a length of 100-300 nm. It is prepared by using cobalt nitrate and copper nitrate as raw materials, a mixed solution of ethylene glycol and water as a solvent, adjusting the pH value with an alkali solution, and reacting at -50°C to -20°C.

2. Preparation method of crystal-split rod-shaped Co-Cu LDH, characterized in that Take cobalt nitrate and copper nitrate as raw materials, use a mixed solution of ethylene glycol and water as a solvent, mix the raw materials and the solvent, adjust the pH value with an alkali solution, and react at -50°C to -20°C to obtain rod-shaped Co-Cu LDH.

3. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 2, wherein, The specific steps are as follows: Step 1: Mix cobalt nitrate and copper nitrate in a mixed solution of ethylene glycol and water to obtain a mixed solution A; Step 2: Prepare another mixed solution of ethylene glycol and water and mix it with an alkali solution to obtain a mixed solution B with a pH of 12; Step 3: Place the mixed solution A and the mixed solution B in a low-temperature kettle and maintain the temperature at -50°C to -20°C; Step 4: Drop the mixed solution A into the mixed solution B drop by drop, add the alkali solution during the process, continuously stir at -50~-20°C, perform static aging, and then carry out a cleaning treatment to obtain a solid; Step 5: Wash the solid with distilled water and ethanol several times respectively, centrifuge and filter, and dry it at 65°C to obtain rod-shaped Co-Cu LDH.

4. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 3, characterized in that, In the above Step 1, the molar ratio of cobalt nitrate to copper nitrate is 10:1 to 4:

1.

5. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 3, characterized in that, In the above Step 2, the alkali solution is NaCO3 and NaOH with a molar concentration ratio of 1:2 to 2:

1.

6. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 3, wherein, In the above Step 1 and Step 2, the volume ratio of ethylene glycol to water is 1:9 to 9:

1.

7. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 3, wherein, In the above Step 4, the aging time is 2-24 h.

8. The preparation method of the crystal-split rod-shaped Co-Cu LDH according to claim 3, wherein In the above Step 4, the stirring time is 1-12 h.

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