A layered metal hydroxide composite catalytic material, its preparation method and application

Abstract

The present invention discloses a layered metal hydroxide composite catalytic material, its preparation method and application. The composite catalytic material comprises a carrier carbon nanotube and a metal hydroxide loaded on the carbon nanotube, and the metal is iron, cobalt and nickel. Preparation method: (1) Dissolve nickel salt, cobalt salt, iron salt and urea in an alcohol solution, stir evenly, then add carbon nanotubes, and continue to stir evenly to obtain a mixed solution; (2) Carry out a solvothermal synthesis reaction on the mixed solution obtained in step (1), filter, wash and dry after the reaction is completed to obtain the layered metal hydroxide composite catalytic material. The carbon nanotubes are introduced into the layered metal hydroxide in this composite catalytic material, reducing the precipitation of metal ions, avoiding the aggregation of hydroxides, improving the stability and catalytic activity of the catalytic material, and being used for activating persulfate to degrade organic pollutants, realizing the efficient activation of persulfate so as to improve the degradation rate of pollutants.

Description

Technical Field

[0001] The present invention relates to a catalyst, in particular to a layered metal hydroxide composite catalytic material and a preparation method and application thereof. Background Art

[0002] Iodinated X-ray contrast media (ICMs) are a class of drugs and personal care products (PPCPs) widely used in medical examinations for organ imaging. They are a type of intravascular medication introduced in human medical diagnosis. Before undergoing an imaging test, patients are injected with approximately 200g of iodinated contrast media, which are excreted in the urine within 24 hours of entry. The high stability and persistence of ICMs make them difficult to remove in wastewater treatment plants, causing them to accumulate in the environment. Studies have shown that ICMs can induce apoptosis and oxidative stress in human neutrophils and may also cause various health problems such as headaches, nausea, urticaria, and vomiting. In addition, ICMs produce more toxic disinfection byproducts (DBPs) during the drinking water disinfection process. ICMs and these byproducts are also considered to be the main contributors to adsorbable organic iodides (AOIs) in the aquatic environment. Iohexol is currently one of the most common ICMs.

[0003] In recent years, the sulfate radical (SO4 - ) has become an emerging technology and is increasingly used in the treatment of refractory wastewater. Among them, transition metal activation technology has the characteristics of not requiring external energy input and mild reaction conditions. It is considered the most common method for activating persulfate. Its main principle is that persulfate can be activated into SO4 by electron transfer between it and transition metals. - (Reactions 1-1, 1-2), which then react with pollutants and degrade them. The activity of the metal catalyst is crucial for determining the activation rate of persulfate, and developing a low-cost, easy-to-prepare, structurally stable metal catalyst is particularly important.

[0004] S2O8 2- +M n+ →2·SO4 - + M (n+1)+ +SO4 2- (1-1)

[0005] HSO5 - + M n+ → SO4 - + M (n+1)+ +OH - (1-2)

[0006] Layered double hydroxide (LDH), also known as double metal hydroxide, is a general term for hydrotalcite and hydrotalcite-like compounds. Its layer board is composed of octahedral metal hydroxide units with positive charges, and the negatively charged anions between the layers keep it electrically neutral. The structural general formula is [M 2+ (1-x) M 3+ x (OH)2] x+ [A n- x / n ·mH2O. M 2+ and M 3+ respectively represent divalent and trivalent metal cations, A n- is the interlayer anion, x is the molar ratio of M 3+ to the total metal cations, and m is the number of water molecules. LDH has the advantages of high catalytic activity, simple synthesis method, acid-base bifunctionality, and interlayer controllability, and has been widely used in the persulfate activation system. However, there are still problems such as serious metal ion precipitation, poor stability, and low catalytic activity during the application of this material. Summary of the Invention

[0007] Object of the Invention: The first object of the present invention is to provide a layered metal hydroxide composite catalytic material with improved stability and catalytic activity; the second object of the present invention is to provide a preparation method of the layered metal hydroxide composite catalytic material; the third object of the present invention is to provide the application of the layered metal hydroxide composite catalytic material in activating persulfate to degrade organic pollutants.

[0008] Technical Solution: The layered metal hydroxide composite catalytic material of the present invention includes a carrier carbon nanotube (CNT) and a metal hydroxide loaded on the carbon nanotube, and the metal is iron, cobalt, and nickel.

[0009] Preferably, the carbon nanotube is one of carboxylated, aminated, or hydroxylated multi-walled carbon nanotubes. After acidification, some carboxyl and hydroxyl groups can be generated. Carboxylated carbon nanotubes have strong electrical conductivity and their low surface potential can effectively adsorb metal ions, which is beneficial to the synthesis of composite materials, while aminated and hydroxylated carbon nanotubes have a higher specific surface area. The three types of carbon nanotubes are all purchased from Beijing Boyu Gaoke New Materials Company

[0010] Preferably, the molar ratio of nickel, cobalt, and iron is 1:1 - 4:2.

[0011] The preparation method of the layered metal hydroxide composite catalytic material of the present invention includes the following steps:

[0012] (1) dissolving metal salts of nickel salt, cobalt salt, iron salt and urea in an alcohol solution, stirring uniformly, then adding carbon nanotubes, and continuing to stir uniformly to obtain a mixed solution;

[0013] (2) subjecting the mixed solution obtained in step (1) to a solvent thermal synthesis reaction, filtering, washing, and drying after the reaction is completed to obtain the layered metal hydroxide composite catalytic material.

[0014] Preferably, in step (1), the mass ratio of the metal salt to the carbon nanotubes is 25:1-5.

[0015] Preferably, in step (1), the nickel salt is one of nickel chloride, nickel sulfate, nickel nitrate and nickel hydroxide; the cobalt salt is one of cobalt nitrate, cobalt sulfate and cobalt chloride; and the iron salt is one of ferric chloride, ferric sulfate and ferric nitrate.

[0016] Preferably, in step (1), the alcohol solution is ethanol or methanol.

[0017] Urea is a precipitant. Urea decomposes at high temperatures to provide OH - and CO3 2- , CO3 2- As an interlayer anion, the composite material maintains electrical neutrality and enhances its stability. Insufficient urea will lead to OH - and CO3 2- The amount produced is insufficient and the layered metal hydroxide is not fully synthesized. Preferably, in step (1), the mass ratio of urea to metal salt is 1 to 4:1.

[0018] During the solvent thermal synthesis reaction, the negatively charged surface of the carboxylated, amino or hydroxylated carbon nanotubes adsorbs the metal ions in the solution, and the OH generated at high temperature - The carbon nanotubes react with the metal on the surface of the carbon nanotubes to form metal hydroxides, so that the carbon nanotubes are interspersed in the layered metal hydroxides as conductive pipes. Preferably, in step (2), the temperature of the solvent thermal synthesis reaction is 60-150°C and the reaction time is 3-12 hours.

[0019] Preferably, in step (2), the drying temperature is 30 to 120° C., and the drying time is 3 to 12 hours.

[0020] The invention relates to the application of the layered metal hydroxide composite catalytic material in the degradation of organic pollutants.

[0021] Preferably, the organic pollutant is an iodinated contrast agent.

[0022] Invention mechanism: In the present invention, carbon nanotubes, which are conductive and elastic matrices, are added to layered metal hydroxides. The highly conductive carbon nanotubes penetrate through the layered metal hydroxides as conductive channels, which can not only enhance the electrical conductivity of the particle electrode, but also optimize the arrangement of metal active sites and reduce the precipitation of metal ions due to the large specific surface area, developed pore structure and abundant functional groups of carbon nanotubes, improving the stability and catalytic activity of the catalytic material, and enabling the efficient activation of persulfate to thereby increase the degradation rate of pollutants. The good pore structure and mechanical strength of carbon nanotubes enable the uniform distribution of CoFeNi layered metal hydroxides and avoid agglomeration, which is beneficial for recycling.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The carbon nanotubes are introduced into the layered metal hydroxide in the layered metal hydroxide composite catalytic material, reducing the precipitation of metal ions, avoiding the agglomeration of hydroxides, and improving the stability and catalytic activity of the catalytic material; (2) The preparation method is simple, environmentally friendly and easy to industrialize; (3) The catalyst material is used to activate persulfate to degrade organic pollutants, achieving the efficient activation of persulfate and thus increasing the degradation rate of pollutants. Description of the drawings

[0024] Figure 1 It is the scanning electron microscope image of the catalytic material. a and b are the catalytic materials prepared in Comparative Example 1, and c and d are the catalytic materials prepared in Example 1;

[0025] Figure 2 It is the comparison chart of the effects of the catalytic materials prepared with different dosages of carbon nanotubes added in Examples 1 to 3 on activating monopersulfate to degrade pollutants;

[0026] Figure 3 It is the comparison chart of the effects of different catalytic materials on activating monopersulfate to degrade pollutants;

[0027] Figure 4 It is the catalytic activation effect diagram of different masses of catalytic materials on monopersulfate;

[0028] Figure 5 It is the catalytic activation effect diagram of the same mass of catalytic materials on different concentrations of monopersulfate. Specific embodiments

[0029] The technical solutions of the present invention will be further described below in conjunction with the embodiments.

[0030] Example 1

[0031] The layered metal hydroxide composite catalytic material of the present invention, in which the molar ratio of nickel, cobalt and iron is 1:3:2, and the carbon nanotubes are 2.56 wt% carboxylated multi-walled carbon nanotubes. Its preparation method includes the following steps:

[0032] (1) Weigh 36.35 mg (2.5 mM) of Ni(NO3)2·6H2O, 109.14 mg (7.5 mM) of Co(NO3)2·6H2O, and 101.0 mg (5.0 mM) of Fe(NO3)3·9H2O and dissolve them in 50 ml of ethanol solution. Add 0.99 g of urea and stir until completely dissolved. Then add 30 mg of 2.56 wt% carboxylated multi-walled carbon nanotubes and stir evenly for later use.

[0033] (2) Take the mixed solution from step (1) and add it to an autoclave. Carry out hydrothermal synthesis reaction at 120 °C for 12 h. After the reaction ends, take out the composite material obtained in the above process, filter it, wash it repeatedly with ethanol solution, and then put it in an oven to dry at 60 °C for 10 hours to obtain the layered metal hydroxide composite catalytic material.

[0034] Example 2

[0035] On the basis of Example 1, change the mass of 2.56 wt% carboxylated multi-walled carbon nanotubes in step (1) to 10 mg, and keep the other conditions unchanged.

[0036] Example 3

[0037] On the basis of Example 1, change the mass of 2.56 wt% carboxylated multi-walled carbon nanotubes in step (1) to 50 mg, and keep the other conditions unchanged.

[0038] Example 4

[0039] For the layered metal hydroxide composite catalytic material of the present invention, where the molar ratio of nickel, cobalt, and iron is 1:1:2, and the carbon nanotubes are 2.56 wt% aminated multi-walled carbon nanotubes, its preparation method includes the following steps:

[0040] (1) Weigh 36.35 mg (2.5 mM) of Ni(NO3)2·6H2O, 36.38 mg (2.5 mM) of Co(NO3)2·6H2O, and 101.0 mg (5.0 mM) of Fe(NO3)3·9H2O and dissolve them in 50 ml of ethanol solution. Add 0.17 g of urea and stir until completely dissolved. Then add 21 mg of 2.56 wt% aminated multi-walled carbon nanotubes and stir evenly for later use.

[0041] (2) Take the mixed solution from step (1) and add it to an autoclave. Carry out hydrothermal synthesis reaction at 60 °C for 12 h. After the reaction ends, take out the composite material obtained in the above process, filter it, wash it repeatedly with ethanol solution, and then put it in an oven to dry at 30 °C for 12 hours to obtain the layered metal hydroxide composite catalytic material.

[0042] Example 5

[0043] The layered metal hydroxide composite catalytic material of the present invention has a molar ratio of nickel, cobalt, and iron of 1:4:2, and the carbon nanotubes are 2.56 wt% hydroxylated multi-walled carbon nanotubes. Its preparation method includes the following steps:

[0044] (1) Weigh 36.35 mg (2.5 mM) of Ni(NO3)2·6H2O, 145.52 mg (10 mM) of Co(NO3)2·6H2O, and 101.0 mg (5.0 mM) of Fe(NO3)3·9H2O and dissolve them in 50 ml of ethanol solution. Add 0.57 g of urea, stir until completely dissolved, add 34 mg of 2.56 wt% hydroxylated multi-walled carbon nanotubes, and stir evenly for standby;

[0045] (2) Take the mixed solution from step (1) and add it to an autoclave. Carry out a hydrothermal synthesis reaction at 150 °C for 3 h. After the reaction is completed, take out the composite material obtained in the above process, filter it, repeatedly wash it with ethanol solution, and then put it in an oven and dry it at 120 °C for 3 hours to obtain the layered metal hydroxide composite catalytic material.

[0046] Comparative Example 1

[0047] On the basis of Example 1, do not add 2.56 wt% carboxylated multi-walled carbon nanotubes, and keep the other conditions unchanged.

[0048] Structure Characterization

[0049] Characterize the catalytic material prepared in Example 1 and the catalytic material prepared in Comparative Example 1, and the results are as Figure 1 shown. From Figure 1 (a, b), it can be seen that the single-layered metal hydroxide prepared in Comparative Example 1 is a regular sphere composed of a layered structure, with a diameter of about 4 μm. From Figure 1 (c)(d), it can be observed that the carbon nanotubes in the catalytic material prepared in Example 1 are successfully inserted into the layered metal hydroxide, and the introduction of CNTs does not destroy the layered structure of the layered metal hydroxide. The addition of carbon nanotubes increases the interlayer spacing of the layered metal hydroxide, which provides a larger specific surface area for peroxymonosulfate activation and increases the reaction active sites.

[0050] Performance Characterization

[0051] (1) The activity of the layered metal hydroxide composite catalytic material of the present invention in catalytically activating peroxymonosulfate

[0052] Test method: Configure an iopamidol simulated wastewater solution containing 10 mg / L. Take 100 mL of the simulated wastewater into the reactor. First, add 0.03 g of potassium monopersulfate powder, and then add 0.003 g of the catalytic materials prepared in Examples 1-3. The magnetic stirring speed is 650 r / min, and the reaction time is 15 min. During the reaction process, the concentration of iopamidol is analyzed by high performance liquid chromatography. The test results are as Figure 2 shown.

[0053] It can be Figure 2 seen that the degradation rates of iopamidol by the catalytic materials in Examples 1-3 activating persulfate for 15 min can reach 100%, 87.8%, and 92.9% respectively. The enhancement effect of a relatively small amount of CNT on the catalyst is not obvious, which may be because the content of carbon nanotubes is too small to penetrate widely into the layered metal hydroxide; while a higher dosage of carbon nanotubes will cover the metal catalytic centers of the layered metal hydroxide, resulting in a decrease in catalytic performance.

[0054] Using the catalytic materials prepared in Example 1 and Comparative Example 1, set up Control Group 1 to replace the catalytic material with carboxylated carbon nanotube powder of the same mass, and Control Group 2, a blank control group, without adding any persulfate-activating substances to test the degradation effect on iopamidol. The test method is the same as above. The test results are as Figure 3 shown.

[0055] It can be Figure 3 seen that the degradation rate of iopamidol by the catalytic material in Example 1 activating potassium monopersulfate for 15 min reaches 100%; the degradation rate of iopamidol by the catalytic material prepared in Comparative Example 1 activating potassium monopersulfate for 15 min is only 58.94%; the degradation rate of iopamidol by carboxylated carbon nanotube powder activating potassium monopersulfate for 15 min is only 4.46%; the degradation rate of iopamidol by activating potassium monopersulfate without adding any substances for 15 min is only 1.20%. Compared with the metal hydroxide catalytic material without carbon nanotubes in Comparative Example 1 and the pure carboxylated multi-walled carbon nanotubes in Control Group 1, the composite catalyst of layered metal hydroxide and carboxylated multi-walled carbon nanotubes prepared in the present invention has a higher removal efficiency for iopamidol wastewater by activating monopersulfate. After the composite of layered metal hydroxide and carboxylated carbon nanotubes, on the one hand, it increases the specific surface area of the material, providing more active sites for the activation of persulfate; on the other hand, the carbon nanotubes with high conductivity can improve the electron transfer performance of the composite material, which is beneficial to the activation of persulfate and thus accelerates the degradation rate of iopamidol; in addition, carboxylated carbon nanotubes as the substrate can reduce the precipitation amount of metal and thus improve the stability of the material. The composite catalyst of the present invention has good application potential in the field of treating iodinated contrast agent wastewater by activating monopersulfate.

[0056] (3) Catalytic activation effect of different masses of catalytic materials on persulfate

[0057] The degradation effect of iohexol was tested by using the catalytic material prepared in Example 1 to catalytically activate persulfate. The test method was the same as above. The added amounts of the catalyst were changed to 0.001 g, 0.002 g, 0.003 g, 0.004 g, and 0.005 g respectively. The test results are as Figure 4 shown.

[0058] It can be Figure 4 seen that when the added amount of the catalytic material was 0.001 g, the degradation rate of iohexol was 78.36% at 15 min of reaction; when the added amount of the catalytic material was 0.002 g, the degradation rate of iohexol was 90.80% at 15 min of reaction; when the added amount of the catalytic material was 0.003 g, the degradation rate of iohexol was 100% at 15 min of reaction; when the added amount of the catalytic material was 0.004 g, the degradation rate of iohexol was 100% at 10 min of reaction; when the added amount of the catalytic material was 0.005 g, the degradation rate of iohexol was 100% at 10 min of reaction. The increase in the catalyst dosage provides more reactive sites for the system, which is beneficial to the activation of persulfate to generate free radicals (such as ·SO4 - , ·OH, etc.), so the degradation rate of iohexol is increased.

[0059] (4) Catalytic activation effect of the same mass of catalytic material on different concentrations of persulfate

[0060] The degradation effect of iohexol was tested by using the catalytic material prepared in Example 1 to catalytically activate persulfate. The test method was the same as above. The initial concentrations of iohexol were changed to 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 30 mg / L. The test results are as Figure 5 shown.

[0061] It can be Figure 5 seen that when the initial concentration of iohexol was 5 mg / L, the degradation rate of iohexol could reach 100% at 12 min of reaction; when the initial concentration of iohexol was 10 mg / L, the degradation rate of iohexol could reach 100% at 15 min of reaction; when the initial concentration of iohexol was 20 mg / L, the degradation rate of iohexol could reach 93.68% at 12 min of reaction; when the initial concentration of iohexol was 30 mg / L, the degradation rate of iohexol could reach 88.99% at 30 min of reaction. As the initial concentration of iohexol increases, the amount of reactive oxygen generated in the system is not enough to react with the excess pollutants, and a large number of intermediate products generated during the reaction may compete with iohexol for free radicals. Therefore, the percentage of iohexol removed per unit time in the initial concentration decreases.

Claims

1. Application of a layered metal hydroxide composite catalytic material in activating persulfate to degrade iohexol, an iodinated contrast agent, characterized in that, The composite catalytic material includes a carrier of carbon nanotubes and a metal hydroxide loaded on the carbon nanotubes. The carbon nanotubes are inserted into the layered metal hydroxide, and the metal is iron, cobalt, and nickel; the molar ratio of nickel, cobalt, and iron is 1:1 to 4:2; the carbon nanotubes are one of carboxylated, aminated, or hydroxylated multi-walled carbon nanotubes.

2. The application according to claim 1, wherein The preparation method of the composite catalytic material includes the following steps: (1) Dissolve nickel salt, cobalt salt, iron salt, and urea in an alcohol solution, stir evenly, then add carbon nanotubes, and continue to stir evenly to obtain a mixed solution; (2) Carry out a solvothermal synthesis reaction on the mixed solution obtained in step (1). After the reaction is completed, filter, wash, and dry to obtain the layered metal hydroxide composite catalytic material.

3. The application according to claim 2, characterized in that, In step (1), the mass ratio of the metal salt to the carbon nanotubes is 25:1 to 5.

4. The application according to claim 2, characterized in that In step (2), the temperature of the solvothermal synthesis reaction is 60 to 150 °C.

5. The application according to claim 2, characterized in that, In step (1), the nickel salt is one of nickel chloride, nickel sulfate, and nickel nitrate; the cobalt salt is one of cobalt nitrate, cobalt sulfate, and cobalt chloride; the iron salt is one of iron chloride, iron sulfate, and iron nitrate.

6. The application according to claim 2, wherein In step (1), the mass ratio of urea to the metal salt is 1 to 4:1.

Images