Piezoelectric composite catalyst, preparation method and application thereof

Abstract

The application discloses a piezoelectric composite catalyst and a preparation method and application thereof, and relates to the technical field of catalysts. The preparation method of the piezoelectric composite catalyst comprises the following steps: mixing an oxidized carbon nanotube, a cobalt source, an iron source, a barium source, a titanium source, an alkali source and a solvent to obtain a mixed solution; and performing a solvothermal reaction on the mixed solution, and then performing washing and drying to obtain the piezoelectric composite catalyst. The prepared piezoelectric composite catalyst comprises the following components in percentage by weight: 5wt.%-90wt.% of barium titanate, 5wt.%-90wt.% of cobalt tetroxide and 0.5wt.%-50wt.% of oxidized carbon nanotubes. The piezoelectric composite catalyst is prepared by using a one-pot method, and the preparation process is simple. The components in the prepared composite catalyst are uniformly mixed and closely contacted. The three components in the composite catalyst have a synergistic effect, and the piezoelectric composite catalyst has better catalytic activity and better stability when used for catalyzing piezoelectric catalytic degradation of organic pollutants in water.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically, to a piezoelectric composite catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of modern industry, the types of organic pollutants in the aquatic environment have been increasing, such as dyes, antibiotics, and endocrine disruptors. These pollutants are difficult to remove through conventional water treatment processes, posing potential threats to ecosystems and human health. While traditional physical treatment technologies such as coagulation, adsorption, and membrane filtration have shown good treatment effects on some organic pollutants, these methods can only transfer the pollutants, not transform them. Therefore, exploring efficient methods for treating organic pollutants in water has become an important research topic. Advanced oxidation technologies can achieve the oxidative degradation and even mineralization of pollutants through the formation of reactive oxygen species. Among them, persulfate advanced oxidation technology uses solid persulfate as an oxidant, which is easier to store and transport than liquid oxidants, and has been widely used in the field of organic pollutant treatment in water.

[0003] While persulfate alone can achieve the direct oxidation of some organic pollutants, it generates a significant amount of organic byproducts. To improve the degradation depth, persulfate needs to be activated to form more potent oxidizing agents such as sulfate radicals, hydroxyl radicals, and singlet oxygen. Considering the difficulty in recovering homogeneous catalysts, researchers are dedicated to developing various novel heterogeneous catalysts to promote the degradation of organic pollutants. However, catalysts often experience a decrease in activity after repeated use, primarily due to changes in their chemical structure. Since the reaction rates of high-valence metals such as Fe(III) and Co(III) with persulfate are much lower than those of their corresponding low-valence metals Fe(II) and Co(II), the proportion of highly active low-valence metals in the catalyst often decreases after the reaction, leading to a decline in catalytic activity. Furthermore, organic pollutants remaining on the catalyst surface after the reaction cover the catalytic active sites, also contributing to the decrease in catalytic activity. Simultaneously, the decrease in catalytic activity results in poor stability of the catalyst during reuse, limiting its practical application.

[0004] In recent years, piezoelectric / catalyst / persulfate systems, which incorporate piezoelectric fields into the advanced oxidation process of persulfate, have attracted considerable attention. In this reaction system, the atomic dislocations within the catalyst lattice, under external force, cause the centers of positive and negative charges to shift, creating a piezoelectric field. This leads to the separation of electrons and holes, with the separated electrons further reacting with persulfate to form various reactive oxygen species. Barium titanate is the most commonly used catalyst in piezoelectric catalysis; however, barium titanate lacks the ability to directly activate persulfate, resulting in poor degradation performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a piezoelectric composite catalyst, its preparation method and application. The piezoelectric composite catalyst prepared by the one-pot method has excellent catalytic activity and stability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A piezoelectric composite catalyst comprises the following components in weight percentages: 5 wt.% to 90 wt.% barium titanate, 5 wt.% to 90 wt.% cobalt tetraoxonide, and 0.5 wt.% to 50 wt.% carbon nanotubes.

[0008] The present invention also provides a method for preparing the piezoelectric composite catalyst as described above, comprising the following steps:

[0009] Carbon nanotubes are oxidized to obtain oxidized carbon nanotubes.

[0010] The carbon nanotubes, cobalt source, iron source, barium source, titanium source, alkali source and solvent are mixed to obtain a mixed solution;

[0011] After the mixture is subjected to a solvothermal reaction, it is washed and dried to obtain the piezoelectric composite catalyst.

[0012] The present invention also provides the application of the piezoelectric composite catalyst as described above or the piezoelectric composite catalyst prepared by any one of claims 3-8 in the piezoelectric catalytic degradation of organic pollutants in water.

[0013] Implementing the embodiments of the present invention will have the following beneficial effects:

[0014] (1) The barium titanate in the piezoelectric composite catalyst provided by the present invention has piezoelectric catalytic activity. The electrons formed by barium titanate under piezoelectric catalysis can react with persulfate to form active oxygen species with strong oxidizing ability. Cobalt tetraoxonate has metal catalytic activity and can activate persulfate to form more active oxygen species with strong oxidizing ability. Carbon nanotubes have abundant surface area and can adsorb and aggregate organic pollutants, which is conducive to the oxidation reaction between organic pollutants and active oxygen species. Therefore, the composite catalyst has better catalytic activity by synergistically working the three components of barium titanate, cobalt tetraoxonate and carbon nanotubes.

[0015] (2) The barium titanate in the piezoelectric composite catalyst provided by the present invention can reduce high-valence metals in situ through the electrons generated by the piezoelectric catalysis, promoting the metal valence cycle of cobalt tetraoxonium ferrite; the carbon oxide nanotubes in the piezoelectric composite catalyst have a high aspect ratio and good conductivity, and can serve as a bridge connecting barium titanate and cobalt tetraoxonium ferrite, facilitating electron transfer between the two and improving the efficiency of the above-mentioned in situ reduction; therefore, the composite catalyst effectively solves the problem of the decrease in activity of the catalyst in the prior art due to the reduction in the proportion of highly active low-valence metals after multiple uses by the synergistic effect of the three components of barium titanate, cobalt tetraoxonium ferrite and carbon oxide nanotubes, thus having better stability.

[0016] (3) The piezoelectric composite catalyst provided by the present invention is prepared by a one-pot method. The preparation process is simple. The components in the prepared piezoelectric composite catalyst are mixed evenly and closely connected, which is conducive to the synergistic effect between the components to improve the activity and stability of the composite catalyst.

[0017] (4) The cobalt tetraoxonide in the piezoelectric composite catalyst provided by the present invention is magnetic. After the reaction is completed, the catalyst and the reaction liquid can be separated directly by magnetic separation, which eliminates the need for centrifugation, filtration and other multi-step separation process required when using powder catalyst. Since the piezoelectric composite catalyst of the present invention is prepared by one-pot method, the components are mixed evenly and closely connected. During magnetic separation, the components can be separated together, which ensures the separation effect. Attached Figure Description

[0018] Figure 1 The image shows the X-ray diffraction pattern of the composite catalyst described in Example 1 of this invention. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0020] This invention discloses a piezoelectric composite catalyst comprising the following components in weight percentage: 5 wt.% to 90 wt.% barium titanate, 5 wt.% to 90 wt.% cobalt tetraoxonide, and 0.5 wt.% to 50 wt.% carbon nanotubes.

[0021] In one specific embodiment, the specific surface area of ​​the carbon oxide nanotubes is 60 m². 2 / g~1000m 2 / g; the diameter of carbon oxide nanotubes is 4nm~50nm.

[0022] Specifically, cobalt tetraoxonide in the composite catalyst exhibits metal catalysis, activating persulfate to form more reactive oxygen species with strong oxidizing power. Barium titanate exhibits piezoelectric catalysis; the electrons generated under piezoelectric catalysis can not only react with persulfate to form reactive oxygen species with strong oxidizing power, but also reduce high-valence metals in situ, promoting the metal valence cycle of cobalt tetraoxonide. Carbon oxide nanotubes have abundant surface area, which can adsorb and aggregate organic pollutants, facilitating the oxidation reaction between organic pollutants and reactive oxygen species. Simultaneously, due to their high aspect ratio, carbon oxide nanotubes have good conductivity, serving as a bridge connecting barium titanate and cobalt tetraoxonide, facilitating electron transfer between them and improving the efficiency of the aforementioned in-situ reduction. Therefore, the synergistic effect of the three components in the piezoelectric composite catalyst provided by this invention effectively solves the problem of decreased activity in existing catalysts after repeated use due to the reduced proportion of highly active low-valence metals, exhibiting excellent catalytic activity and stability.

[0023] Furthermore, the piezoelectric composite catalyst provided by this invention is prepared using a one-pot method, comprising the following steps:

[0024] S1. Carbon nanotubes are oxidized to obtain oxidized carbon nanotubes.

[0025] In one specific embodiment, the oxidation process in step S1 is not particularly limited and can be carried out by any oxidation method known to those skilled in the art, including but not limited to oxidation in an oxidizing atmosphere and oxidation in an oxidizing solution.

[0026] S2. Mix carbon nanotubes, cobalt source, iron source, barium source, titanium source, alkali source and solvent to obtain a mixed solution.

[0027] In one specific embodiment, the cobalt source includes one or more of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate.

[0028] In one specific embodiment, the iron source includes one or more of ferric nitrate, ferric chloride, ferrous chloride, ferric acetate, ferrous acetate, ferric sulfate, and ferrous sulfate.

[0029] In one specific embodiment, the barium source includes one or more of barium nitrate, barium chloride, barium acetate, and barium hydroxide.

[0030] In one specific embodiment, the titanium source includes one or more of titanium tetrachloride, tetrabutyl titanate, and tetraethyl titanate.

[0031] In one specific embodiment, the alkali source includes one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium acetate, and potassium acetate.

[0032] In one specific embodiment, the solvent includes one or more of water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, glycerol, and acetone.

[0033] In one specific embodiment, the molar ratio of the cobalt source (calculated as cobalt element) to the iron source (calculated as iron element) is (0.25~2):1.

[0034] In one specific embodiment, the molar ratio of barium source (based on barium element) to titanium source (based on titanium element) is (0.5-2):1.

[0035] In one specific embodiment, the molar ratio of the cobalt source (calculated as cobalt element) to the barium source (calculated as barium element) is (0.1~10):1.

[0036] In one specific embodiment, the mass ratio of the cobalt source (calculated as cobalt element) to carbon oxide nanotubes is (0.02–5):1.

[0037] In one specific embodiment, the pH of the solution is ≥7 after the addition of an alkaline source.

[0038] S3. After the mixture undergoes a solvothermal reaction, it is washed and dried to obtain a piezoelectric composite catalyst.

[0039] In one specific embodiment, the temperature of the solvothermal reaction is 120°C to 250°C; the time of the solvothermal reaction is 2h to 72h.

[0040] In one specific embodiment, the detergent used for washing includes one or more of water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, glycerol, and acetone.

[0041] In one specific embodiment, drying includes one or more of the following: natural drying, vacuum drying, freeze drying, and heat drying.

[0042] In one specific embodiment, since cobalt tetraoxonide is magnetic, the catalyst and reaction liquid can be directly separated by magnetic separation after the reaction is completed. This is simple and easy, eliminating the need for multiple separation steps such as centrifugation and filtration required when using powdered catalysts. At the same time, since the piezoelectric composite catalyst of the present invention is prepared by a one-pot method, not only is the preparation process simple, but the components in the prepared piezoelectric composite catalyst are also uniformly mixed and closely connected. During magnetic separation, the components can be separated together, resulting in good separation effect.

[0043] The present invention also discloses the application of a piezoelectric composite catalyst as described in any embodiment of the present invention or a piezoelectric composite catalyst prepared by any embodiment of the present invention in the piezoelectric catalytic degradation of organic pollutants in water.

[0044] In one specific embodiment, the application method includes: adding a piezoelectric composite catalyst and persulfate to water containing organic pollutants, and carrying out a piezoelectric catalytic degradation reaction under ultrasonic conditions.

[0045] In one specific embodiment, the temperature of the piezoelectric catalytic degradation reaction is 20°C to 40°C; the pressure of the piezoelectric catalytic degradation reaction is atmospheric pressure.

[0046] In one specific embodiment, the concentration of organic pollutants in the water is 1 mg / L to 500 mg / L, the dosage of piezoelectric composite catalyst is 0.01 g / L to 2 g / L, and the dosage of persulfate is 0.01 g / L to 5 g / L.

[0047] In one specific embodiment, the frequency of the ultrasonic condition is 20 kHz to 200 kHz; the power of the ultrasonic condition is 0 W to 1000 W.

[0048] Specifically, the piezoelectric composite catalyst with stable catalytic activity and stability used in this invention significantly improves degradation efficiency and exhibits better piezoelectric catalytic degradation activity compared to catalysts in the prior art.

[0049] The following are specific embodiments.

[0050] Example 1

[0051] The piezoelectric composite catalyst of this embodiment comprises the following components by weight percentage: 35 wt.% barium titanate, 37 wt.% cobalt tetraoxoferrate, and 28 wt.% carbon oxide nanotubes; the specific surface area of ​​the carbon oxide nanotubes is 750 m². 2 / g, with a tube diameter of 5nm.

[0052] The piezoelectric composite catalyst preparation method of this embodiment includes the following steps:

[0053] S1. Carbon nanotubes are oxidized with nitric acid to obtain oxidized carbon nanotubes.

[0054] S2. Mix the carbon oxide nanotubes, cobalt acetate, ferric acetate, barium acetate, tetraethyl titanate, sodium hydroxide, and ethylene glycol obtained in step S1 to obtain a mixed solution; the molar ratio of cobalt acetate (based on cobalt element) to ferric acetate (based on iron element) is 0.5:1, the molar ratio of barium acetate (based on barium element) to tetraethyl titanate (based on titanium element) is 1:1, the molar ratio of cobalt acetate (based on cobalt element) to barium acetate (based on barium element) is 1:1, and the mass ratio of cobalt acetate (based on cobalt element) to carbon oxide nanotubes is 0.4:1. After adding sodium hydroxide, the pH of the solution is 13.

[0055] S3. The mixture obtained in step S2 is subjected to a solvothermal reaction at a temperature of 200°C for 60 hours. The product obtained from the solvothermal reaction is washed with ethanol and water, and then vacuum dried to obtain the piezoelectric composite catalyst. The piezoelectric composite catalyst of this embodiment is characterized. Figure 1 The X-ray diffraction pattern of the composite catalyst prepared in Example 1 shows that the composite catalyst contains three components: barium titanate, cobalt tetraoxoferrate, and carbon nanotubes.

[0056] Based on this, the application of the piezoelectric composite catalyst of this embodiment in the piezoelectric catalytic degradation treatment of organic pollutants in water is specifically described as follows: 50 mg of the piezoelectric composite catalyst obtained in Example 1 and 40 mg of potassium peroxymonosulfonate are weighed and added to 100 mL of water containing 50 mg / L sulfamethoxazole. The reaction is carried out under normal pressure, 25 °C, ultrasonic frequency of 40 kHz, and ultrasonic power of 80 W. After 2 hours, the piezoelectric composite catalyst and the reaction solution are separated by magnetic separation. The piezoelectric composite catalyst can be completely separated. The reaction solution is analyzed, and the removal rate of sulfamethoxazole is 99.7%. The separated composite catalyst is reused under the same reaction conditions, and the removal rate of sulfamethoxazole is 98.5%.

[0057] Example 2

[0058] The piezoelectric composite catalyst of this embodiment comprises the following components by weight percentage: 23 wt.% barium titanate, 64 wt.% cobalt tetraoxoferrate, and 13 wt.% carbon oxide nanotubes; the specific surface area of ​​the carbon oxide nanotubes is 400 m². 2 / g, with a tube diameter of 16nm.

[0059] The piezoelectric composite catalyst preparation method of this embodiment includes the following steps:

[0060] S1. Carbon nanotubes are oxidized with nitric acid to obtain oxidized carbon nanotubes.

[0061] S2. Mix the carbon nanotubes, cobalt nitrate, ferrous sulfate, barium chloride, tetrabutyl titanate, potassium acetate, and ethanol obtained in step S1 to obtain a mixed solution. The molar ratio of cobalt nitrate (based on cobalt element) to ferrous sulfate (based on iron element) is 1:1, the molar ratio of barium chloride (based on barium element) to tetrabutyl titanate (based on titanium element) is 1.2:1, the molar ratio of cobalt nitrate (based on cobalt element) to barium chloride (based on barium element) is 3:1, and the mass ratio of cobalt nitrate (based on cobalt element) to carbon nanotubes is 1.6:1. After adding potassium acetate, the pH of the solution is 9.

[0062] S3. The mixture obtained in step S2 is subjected to a solvothermal reaction at a temperature of 170°C for 70 hours. The product obtained from the solvothermal reaction is washed with ethanol and methanol and then dried under vacuum to obtain the piezoelectric composite catalyst.

[0063] Based on this, the application of the piezoelectric composite catalyst of this embodiment in the piezoelectric catalytic degradation of organic pollutants in water is specifically described as follows: 500 mg of the piezoelectric composite catalyst obtained in Example 2 and 1000 mg of potassium peroxymonosulfonate were weighed and added to 500 mL of water containing 180 mg / L sulfamethoxazole. The reaction was carried out at normal pressure, 35 °C, ultrasonic frequency of 65 kHz, and ultrasonic power of 125 W. After 6 hours, the piezoelectric composite catalyst and the reaction solution were separated by magnetic separation. The piezoelectric composite catalyst could be completely separated. The reaction solution was analyzed, and the removal rate of sulfamethoxazole was 88.4%. The separated composite catalyst was reused under the same reaction conditions, and the removal rate of sulfamethoxazole was 87.6%.

[0064] Example 3

[0065] The piezoelectric composite catalyst of this embodiment comprises the following components by weight percentage: 59 wt.% barium titanate, 38 wt.% cobalt tetraoxoferrate, and 3 wt.% carbon oxide nanotubes; the specific surface area of ​​the carbon oxide nanotubes is 75 m². 2 / g, with a tube diameter of 42nm.

[0066] The piezoelectric composite catalyst preparation method of this embodiment includes the following steps:

[0067] S1. Carbon nanotubes are oxidized with nitric acid to obtain oxidized carbon nanotubes.

[0068] S2. Mix the carbon oxide nanotubes obtained in step S1, cobalt sulfate, ferrous acetate, barium hydroxide, titanium tetrachloride, ammonia, and glycerol to obtain a mixed solution. The molar ratio of cobalt sulfate (based on cobalt element) to ferrous acetate (based on iron element) is 0.3:1, the molar ratio of barium hydroxide (based on barium element) to titanium tetrachloride (based on titanium element) is 0.8:1, the molar ratio of cobalt sulfate (based on cobalt element) to barium hydroxide (based on barium element) is 0.6:1, and the mass ratio of cobalt sulfate (based on cobalt element) to carbon oxide nanotubes is 4:1. After adding ammonia, the pH of the solution is 14.

[0069] S3. The mixture obtained in step S2 is subjected to a solvothermal reaction at a temperature of 250°C for 7 hours. The product obtained from the solvothermal reaction is washed with acetone and methanol and then dried under vacuum to obtain the piezoelectric composite catalyst.

[0070] Based on this, the application of the piezoelectric composite catalyst of this embodiment in the piezoelectric catalytic degradation of organic pollutants in water is specifically described as follows: 1 mg of the piezoelectric composite catalyst obtained in Example 3 and 2 mg of potassium peroxymonosulfonate are weighed and added to 50 mL of water containing 2 mg / L sulfamethoxazole. The reaction is carried out under normal pressure, 20 °C, ultrasonic frequency of 140 kHz, and ultrasonic power of 40 W. After 0.5 h, the piezoelectric composite catalyst and the reaction solution are separated by magnetic separation. The piezoelectric composite catalyst can be completely separated. The reaction solution is analyzed, and the removal rate of sulfamethoxazole is 92.7%. The separated composite catalyst is reused under the same reaction conditions, and the removal rate of sulfamethoxazole is 91.0%.

[0071] Comparative Example 1

[0072] The composite catalyst in this comparative example comprises the following components by weight percentage: 48 wt.% barium titanate and 52 wt.% cobalt tetraoxonide.

[0073] The preparation method of the composite catalyst in this comparative example includes the following steps:

[0074] (1) Cobalt acetate, ferric acetate, barium acetate, tetraethyl titanate, sodium hydroxide and ethylene glycol were mixed to obtain a mixed solution. The molar ratio of cobalt acetate (calculated as cobalt element) to ferric acetate (calculated as ferric element) was 0.5:1, the molar ratio of barium acetate (calculated as barium element) to tetraethyl titanate (calculated as titanium element) was 1:1, and the molar ratio of cobalt acetate (calculated as cobalt element) to barium acetate (calculated as barium element) was 1:1. After adding sodium hydroxide, the pH of the solution was 13.

[0075] (2) The mixture obtained in step (1) is subjected to a solvothermal reaction at a temperature of 200°C for 60 hours.

[0076] (3) The product obtained in step (2) is washed with ethanol and water and dried under vacuum to obtain the composite catalyst.

[0077] Based on this, the application of the composite catalyst in the piezoelectric catalytic degradation of organic pollutants in water was investigated: 50 mg of the composite catalyst obtained in Comparative Example 1 and 40 mg of potassium peroxymonosulfonate were weighed and added to 100 mL of water containing 50 mg / L sulfamethoxazole. The reaction was carried out under normal pressure, 25 °C, ultrasonic frequency of 40 kHz, and ultrasonic power of 80 W. After 2 h, the composite catalyst and the reaction solution were separated by magnetic separation. The composite catalyst could be completely separated. The reaction solution was analyzed, and the removal rate of sulfamethoxazole was 75.2%. The separated composite catalyst was reused under the same reaction conditions, and the removal rate of sulfamethoxazole was 51.5%.

[0078] Comparing Example 1 and Comparative Example 1, it can be seen that when the composite catalyst of Comparative Example 1 does not contain carbon oxide nanotubes, the catalyst has lower activity and stability. This is because carbon oxide nanotubes have a large surface area, which can adsorb and aggregate organic pollutants, promote the oxidative degradation of organic pollutants by reactive oxygen species, and thus enhance the activity of the catalyst. At the same time, carbon oxide nanotubes have a high aspect ratio and good conductivity, which can serve as a bridge for electron transfer between barium titanate and cobalt tetraoxonium ferrite, strengthen the promoting effect of electrons formed under the piezoelectric catalysis of barium titanate on the valence state cycle of cobalt tetraoxonium ferrite, and thus improve the stability of the catalyst.

[0079] Comparative Example 2

[0080] The composite catalyst in this comparative example comprises the following components by weight percentage: 56 wt.% barium titanate and 44 wt.% carbon nanotubes.

[0081] The preparation method of the composite catalyst in this comparative example includes the following steps:

[0082] (1) Carbon nanotubes were oxidized by nitric acid to obtain oxidized carbon nanotubes;

[0083] (2) Mix the carbon nanotubes, barium acetate, tetraethyl titanate, sodium hydroxide and ethylene glycol obtained in step (1) to obtain a mixed solution. The molar ratio of barium acetate (based on barium element) to tetraethyl titanate (based on titanium element) is 1:1, and the mass ratio of barium acetate (based on cobalt element) to carbon nanotubes is 0.9:1. After adding sodium hydroxide, the pH of the solution is 13.

[0084] (3) The mixture obtained in step (2) is subjected to a solvothermal reaction at a temperature of 200°C for 60 hours.

[0085] (4) The product obtained in step (3) is washed with ethanol and water and dried under vacuum to obtain the composite catalyst.

[0086] Based on this, the application of the composite catalyst in the piezoelectric catalytic degradation of organic pollutants in water was investigated: 50 mg of the composite catalyst obtained in Comparative Example 2 and 40 mg of potassium peroxymonosulfonate were weighed and added to 100 mL of water containing 50 mg / L sulfamethoxazole. The reaction was carried out under normal pressure, 25 °C, ultrasonic frequency of 40 kHz, and ultrasonic power of 80 W for 2 h. After 2 h, the composite catalyst and the reaction solution were separated by centrifugation, and the reaction solution was analyzed. The removal rate of sulfamethoxazole was 65.2%. When the composite catalyst was reused under the same reaction conditions, the removal rate of sulfamethoxazole was 37.5%.

[0087] Comparing Example 1 and Comparative Example 2, it can be seen that when the composite catalyst of Comparative Example 2 does not contain cobalt tetraoxonide, the catalyst has lower activity and stability. This is because cobalt tetraoxonide can promote the formation of active oxygen species during the reaction through metal activation, and synergistically with the piezoelectric catalysis of barium titanate to form more active oxygen species, thereby improving the catalyst activity. At the same time, when the composite catalyst does not contain cobalt tetraoxonide, the catalyst cannot be separated from the reaction liquid by magnetic separation, and due to the insufficient formation of active oxygen species, the organic contaminants remaining on the catalyst surface after the reaction cover the catalytic active sites, resulting in a decrease in catalyst stability.

[0088] Comparative Example 3

[0089] The composite catalyst in this comparative example comprises the following components by weight percentage: 57 wt.% cobalt tetraoxonide and 43 wt.% carbon nanotubes.

[0090] The preparation method of the composite catalyst in this comparative example includes the following steps:

[0091] (1) Carbon nanotubes were oxidized by nitric acid to obtain oxidized carbon nanotubes;

[0092] (2) Mix the carbon nanotubes, cobalt acetate, iron acetate, sodium hydroxide and ethylene glycol obtained in step (1) to obtain a mixed solution. The molar ratio of cobalt acetate (calculated as cobalt element) to iron acetate (calculated as iron element) is 0.5:1, and the mass ratio of cobalt acetate (calculated as cobalt element) to carbon nanotubes is 0.4:1. After adding sodium hydroxide, the pH of the solution is 13.

[0093] (3) The mixture obtained in step (2) is subjected to a solvothermal reaction at a temperature of 200°C for a time of 60 h.

[0094] (4) The product obtained in step (3) is washed with ethanol and water and dried under vacuum to obtain the composite catalyst.

[0095] Based on this, the application of the composite catalyst in the piezoelectric catalytic degradation of organic pollutants in water was investigated: 50 mg of the composite catalyst obtained in Comparative Example 3 and 40 mg of potassium peroxymonosulfonate were weighed and added to 100 mL of water containing 50 mg / L sulfamethoxazole. The reaction was carried out under normal pressure, 25 °C, ultrasonic frequency of 40 kHz, and ultrasonic power of 80 W. After 2 h, the composite catalyst and the reaction solution were separated by magnetic separation. The composite catalyst was completely separated, and the reaction solution was analyzed. The removal rate of sulfamethoxazole was 63.8%. When the composite catalyst was reused under the same reaction conditions, the removal rate of sulfamethoxazole was 42.1%.

[0096] Comparing Example 1 and Comparative Example 3, it can be seen that when the composite catalyst of Comparative Example 3 does not contain barium titanate, the catalyst has lower activity and stability. This is because barium titanate can promote the formation of active oxygen species from persulfate through the electrons generated by piezoelectric catalysis. This, in conjunction with the metal catalysis of cobalt tetraoxonide, forms more active oxygen species, thereby improving the catalyst activity. At the same time, when the composite catalyst does not contain barium titanate, the number of active oxygen species formed is insufficient. After the reaction, the organic contaminants remaining on the catalyst surface cover the catalytic active sites, resulting in a decrease in catalyst stability.

[0097] Comparative Example 4

[0098] The composite catalyst of this comparative example comprises the following components by weight percentage: 35 wt.% barium titanate, 37 wt.% cobalt tetraoxonide, and 28 wt.% carbon nanotubes.

[0099] The preparation method of the composite catalyst in this comparative example includes the following steps:

[0100] (1) Carbon nanotubes are oxidized by nitric acid to obtain oxidized carbon nanotubes.

[0101] (2) Mix cobalt acetate, ferric acetate, sodium hydroxide and ethylene glycol. The molar ratio of cobalt acetate (calculated as cobalt element) to ferric acetate (calculated as iron element) is 0.5:1. After adding sodium hydroxide, the pH of the solution is 13.

[0102] (3) The mixture obtained in step (2) is subjected to a solvothermal reaction at a temperature of 200°C for 60 hours.

[0103] (4) The product obtained in step (3) is washed with ethanol and water and dried under vacuum to obtain cobalt tetraoxonium ferrite.

[0104] (5) Mix barium acetate, tetraethyl titanate, sodium hydroxide and ethylene glycol. The molar ratio of barium acetate (based on barium element) to tetraethyl titanate (based on titanium element) is 1:1. After adding sodium hydroxide, the pH of the solution is 13.

[0105] (6) The mixture obtained in step (5) is subjected to a solvothermal reaction at a temperature of 200°C for 60 hours.

[0106] (7) The product obtained in step (6) is washed with ethanol and water and dried under vacuum to obtain barium titanate.

[0107] (8) Mix the carbon oxide nanotubes obtained in step (1), cobalt tetraoxonide obtained in step (4), and barium titanate obtained in step (7) until the mass ratio of carbon oxide nanotubes:cobalt tetraoxonide:barium titanate is 28:37:35, and obtain a composite catalyst.

[0108] Based on this, the application of the composite catalyst in the piezoelectric catalytic degradation of organic pollutants in water was investigated: 50 mg of the composite catalyst obtained in Comparative Example 4 and 40 mg of potassium peroxymonosulfonate were weighed and added to 100 mL of water containing 50 mg / L sulfamethoxazole. The reaction was carried out under normal pressure, 25 °C, ultrasonic frequency of 40 kHz, and ultrasonic power of 80 W. After 2 h, the composite catalyst and reaction solution were separated by magnetic separation. The composite catalyst could not be completely separated, and catalyst particles remained in the reaction solution after magnetic separation. After further centrifugation, the reaction solution was analyzed, and the removal rate of sulfamethoxazole was 83.5%. When the composite catalyst was reused under the same reaction conditions, the removal rate of sulfamethoxazole was 72.4%.

[0109] Comparing Example 1 and Comparative Example 4, it is evident that the composite catalyst prepared by the one-pot method exhibits higher activity and stability. This is because the components in the composite catalyst prepared by the one-pot method are uniformly mixed and tightly bound, which facilitates synergistic effects among the components, enhancing the catalyst's activity and stability. Furthermore, the uniform and tightly bound components in the composite catalyst prepared by the one-pot method allow for efficient separation during magnetic separation, resulting in better separation efficiency. In contrast, the components in the catalyst prepared by the non-one-pot method are not tightly bound, leaving catalyst particle residues in the reaction solution after magnetic separation, requiring further centrifugation.

[0110] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a piezoelectric composite catalyst, characterized in that, Includes the following steps: Carbon nanotubes are oxidized to obtain oxidized carbon nanotubes. The carbon nanotubes, cobalt source, iron source, barium source, titanium source, alkali source and solvent are mixed to obtain a mixed solution; After the mixture is subjected to a solvothermal reaction, it is washed and dried to obtain the piezoelectric composite catalyst. The temperature of the solvothermal reaction is 120℃~250℃; the time of the solvothermal reaction is 2h~72h; The piezoelectric composite catalyst comprises the following components by weight percentage: 5 wt.%~90 wt.% barium titanate, 5 wt.%~90 wt.% cobalt tetraoxonide, and 0.5 wt.%~50 wt.% carbon oxide nanotubes; The specific surface area of ​​the carbon oxide nanotubes is 60 m². 2 / g~1000m 2 / g; The diameter of the carbon oxide nanotubes is 4 nm to 50 nm; Barium titanate has piezoelectric catalysis. The electrons formed under piezoelectric catalysis can not only react with persulfate to form reactive oxygen species with strong oxidizing power, but also reduce high-valence metals in situ and promote the metal valence cycle of cobalt tetraoxonium ferrite. Carbon oxide nanotubes can act as a bridge connecting barium titanate and cobalt tetraoxonium ferrite, facilitating electron transfer between the two. The piezoelectric composite catalyst and persulfate were added to water containing organic pollutants, and a piezoelectric catalytic degradation reaction was carried out under ultrasonic conditions; the removal rate of sulfamethoxazole was 99.7%; the separated composite catalyst was reused under the same reaction conditions, and the removal rate of sulfamethoxazole was 98.5%; after the reaction, the catalyst and reaction solution could be directly separated by magnetic separation.

2. The preparation method according to claim 1, characterized in that, The cobalt source includes one or more of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate; The iron source includes one or more of ferric nitrate, ferric chloride, ferrous chloride, ferric acetate, ferrous acetate, ferric sulfate, and ferrous sulfate. The barium source includes one or more of barium nitrate, barium chloride, barium acetate, and barium hydroxide; The titanium source includes one or more of titanium tetrachloride, tetrabutyl titanate, and tetraethyl titanate. The alkaline source includes one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium acetate, and potassium acetate. The solvent includes one or more of water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, glycerol, and acetone.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the cobalt source (calculated as cobalt element) to the iron source (calculated as iron element) is (0.25~2):1; The molar ratio of the barium source (based on barium element) to the titanium source (based on titanium element) is (0.5~2):1; The molar ratio of the cobalt source (calculated as cobalt element) to the barium source (calculated as barium element) is (0.1~10):1; The mass ratio of the cobalt source (based on cobalt element) to the carbon oxide nanotubes is (0.02~5):

1.

4. The preparation method according to claim 1, characterized in that, Add the alkaline source to adjust the pH of the solution to ≥7.

5. The preparation method according to claim 1, characterized in that, The detergent used in the washing process includes one or more of the following: water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, glycerol, and acetone. The drying process includes one or more of the following: natural drying, vacuum drying, freeze drying, and heat drying.

6. The application of a piezoelectric composite catalyst obtained by any one of claims 1-5 in the piezoelectric catalytic degradation of organic pollutants in water.

7. The application according to claim 6, characterized in that, The application method includes: The piezoelectric composite catalyst and persulfate were added to water containing organic pollutants, and a piezoelectric catalytic degradation reaction was carried out under ultrasonic conditions. The temperature of the piezoelectric catalytic degradation reaction is 20℃~40℃; the pressure of the piezoelectric catalytic degradation reaction is atmospheric pressure. The concentration of organic pollutants in the water is 1 mg / L to 500 mg / L, the dosage of the piezoelectric composite catalyst is 0.01 g / L to 2 g / L, and the dosage of persulfate is 0.01 g / L to 5 g / L. The frequency of the ultrasonic condition is 20 kHz to 200 kHz; the power of the ultrasonic condition is 0 W to 1000 W.

Images