Preparation method and application of sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst

Abstract

The application relates to a preparation method and application of a sponge-loaded MOF-derived Co-doped carbon nitride nanotube catalyst, wherein the preparation method takes supramolecular self-assembly as a basic process, takes ZIF-67 as a Co source, realizes in-situ fixation of Butvar B-76 (PVB) on melamine sponge, and realizes in-situ fixation of the Co-doped carbon nitride nanotube catalyst in a melamine acid etching action and a carbonization process, so that efficient activation of PMS can remove chloroquine phosphate in water.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying a sponge-supported MOF-derived Co-doped carbon nanotube catalyst, specifically to a method for preparing and applying a sponge-supported MOF-derived Co-doped carbon nanotube catalyst suitable for the efficient activation of PMS to remove chloroquine phosphate from water, belonging to the field of composite material preparation and relating to the field of PMS catalysis. Background Technology

[0002] With the advancement of medical technology, drug use has become increasingly widespread. However, the frequent use or abuse of drugs has also brought about significant environmental problems. In particular, some difficult-to-degrade and toxic drugs, such as chloroquine phosphate (CQP), can damage aquatic ecosystems and even threaten the lives of humans and other organisms once they enter water bodies through pharmaceutical wastewater. Therefore, researching effective methods for degrading and removing CQP pollutants is crucial for protecting the aquatic environment. In recent years, Advanced Oxidation Processes (AOPs) have gradually gained widespread attention as an emerging water treatment technology. Their unique advantage lies in their ability to generate free radicals with extremely high redox potentials. These free radicals can non-selectively attack the chemical bonds in organic pollutants, thereby achieving rapid decomposition of pollutants. In AOPs, peroxymonosulfate (PMS) is particularly important due to the sulfate radicals (•SO4) it generates. − SO4 has become a research hotspot due to its higher redox potential, longer half-life, and less impact on pH. − As a strong oxidant, PMS can efficiently degrade organic pollutants, especially persistent organic pollutants that are difficult to treat using traditional methods. To fully realize the oxidation potential of PMS, effective activation is necessary. Traditional activation methods include ultraviolet irradiation, heat treatment, and heterogeneous catalysis. Among these, heterogeneous catalysis is favored due to its high efficiency, energy saving, and ease of operation. Among numerous heterogeneous catalysts, transition metal activation is the most common activation method. Cobalt (Co), in particular, as a highly efficient transition metal catalyst, has been proven to be one of the most active elements in activating PMS.

[0003] ZIF-67, containing Co, is a common MOF material with controllable pore size, large specific surface area, and low density, making it widely used in adsorption and catalysis. However, the main problems with MOF materials are the aggregation of metal ions during pyrolysis and the leaching of metals during the reaction, which weakens the activation performance of PMS and leads to the presence of toxic metal ions in aqueous solutions. Co emissions are very harmful to the environment. Therefore, to prevent the aggregation and leakage of metallic Co in the reaction system and to improve the utilization rate of catalytic sites, ZIF-67 is loaded onto a suitable support to ensure that Co can be highly dispersed in ZIF-67 beforehand. Graphitic carbon nitride (g−C3N4), a metal-free semiconductor, has become a research focus due to its unique π-conjugated electronic structure, visible light response, and chemical stability. However, the disordered stacking of traditional carbon nitride hinders the dispersion and exposure of metal-nitrogen sites, resulting in weak electron transport and severely inhibiting the non-radical activation pathway of PMS. By designing disordered morphologies into special forms, such as nanotubes (CNNT), the specific surface area and pore size can be increased, thereby achieving high dispersion of active sites and high charge transfer.

[0004] In practical industrial applications, the recovery of powdered catalysts is often a challenging problem, increasing operating costs and potentially causing environmental pollution. Therefore, developing an efficient and convenient catalyst immobilization method is crucial. Melamine sponge, as an ideal catalyst support, provides abundant adhesion sites for the catalyst due to its porous structure, ensuring that active sites are uniformly and tightly fixed on its surface. This porosity not only increases the contact area between the catalyst and contaminants, thereby improving catalytic efficiency, but also helps maintain catalyst activity and extend its service life.

[0005] By combining the advantages of ZIF-67 and CNNT, and overcoming the problems of metal species leaching, agglomeration, and difficulty in recovering powdered catalysts in MOF materials during the reaction process, we can develop a highly efficient, stable, and easily recyclable composite catalyst, providing effective technical support for the treatment of wastewater containing harmful substances such as CQP. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a preparation and application of a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst.

[0007] On one hand, the present invention provides a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst, wherein the general formula of the catalyst is Co@CNNT / Sponge.

[0008] Another objective of this invention is to provide a method for preparing the catalyst. Based on a supramolecular self-assembly method, this invention uses ZIF-67 as the Co source and cyanuric acid (CA) and melamine sponge as raw materials for carbon nitride nanotubes to prepare a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst, achieving highly efficient activated PMS removal of CQP from water.

[0009] Another object of the present invention is to provide the application of the catalyst.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] A sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst, comprising the following steps:

[0012] 1) First, the melamine sponge needs to be pre-treated. The sponge is placed in an ethanol solution and ultrasonically cleaned to remove impurities and oil from its surface. Next, it is ultrasonically cleaned again with deionized water. After cleaning, the sponge is placed in a 60°C oven overnight to ensure it is completely dry.

[0013] 2) A certain amount of PVB (Butvar B-76) was ultrasonically dispersed in an ethanol solution for 30 minutes to form a homogeneous solution. Then, ZIF-67 catalyst was added to the PVB ethanol solution (10 mL), maintaining a certain water bath temperature, and ultrasonication was continued for 30 minutes to ensure that the catalyst and immobilizer were thoroughly and uniformly mixed. Using a micropipette, the solution was added dropwise onto a single 0.2 g melamine sponge (2 cm × 2 cm × 2 cm), at a rate of 1 mL / drop for every 10 mL of the mixture. During the dropwise addition, the sponge was ensured to fully absorb the solution to avoid waste or uneven catalyst distribution. Subsequently, the catalyst-loaded sponge was placed in a 60°C oven to dry, allowing the immobilizer to fully solidify.

[0014] 3) Removal of loosely supported catalyst particles. The catalyst-loaded sponge is ultrasonically cleaned. This effectively removes catalyst particles that are not firmly attached to the sponge. After ultrasonic treatment, the sponge is rinsed thoroughly with deionized water to remove residual ethanol and loose catalyst particles. The sponge is then dried again in a 60°C oven to obtain the final sponge-supported ZIF-67 catalyst.

[0015] 4) Melamine sponge immobilized with ZIF-67 was added to deionized water, along with a certain amount of cyanuric acid. The mixture was hydrothermally stirred at a specific temperature for a certain time, and then centrifuged to obtain the catalyst precursor. This precursor was dried and then carbonized under a N2 atmosphere at a specific temperature to prepare a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst.

[0016] As a preferred embodiment of the present invention, the ZIF-67 is prepared by the following method:

[0017] Cobalt nitrate hexahydrate and PVP dissolved in methanol to form solution A. Dimethylimidazole and triethylamine dissolved in methanol to form solution B. Solution B was added to solution A under magnetic stirring and aged at room temperature for 24 hours. The product was collected by washing with methanol multiple times, centrifuging, and drying at 60°C to obtain ZIF-67.

[0018] As a preferred embodiment of the present invention, the ultrasonic cleaning in step 1) is performed 2-5 times, and the ultrasonic cleaning time is 5-10 minutes each time.

[0019] As a preferred embodiment of the present invention, in step 2), the amount of PVB added is 10-40 mg, the ultrasonic time is 30-60 min, the ethanol is anhydrous ethanol, and the amount of ZIF-67 is 0.02-0.2 g.

[0020] As a preferred embodiment of the present invention, in step 2), the mass ratio of ZIF-67 to melamine sponge is 1:1 to 1:10, and the water bath temperature is 60-80℃.

[0021] As a preferred embodiment of the present invention, the ultrasound time in step 3) is 5-10 min.

[0022] In a preferred embodiment of the present invention, in step 4), the mass ratio of cyanuric acid to melamine sponge is 1:0.5 to 1:3, the hydrothermal temperature is 60-120℃, the stirring rate is 200-800 rpm, and the hydrothermal reaction time is 60-180 min. The centrifugation speed is 5000-8000 rpm, the number of centrifugations is 1-5, and the temperature is 4-15℃.

[0023] As a preferred embodiment of the present invention, in step 4), the carbonization temperature is 300-700℃, the heating rate is 5-15℃ / min, and the carbonization time is 60-240 min.

[0024] A sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst was prepared according to the aforementioned preparation method.

[0025] The sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst and the synergistic oxidant PMS (persulfate) described in this invention are applied to the degradation of water pollutants.

[0026] The main characteristic pollutant targeted in the application for water pollutant degradation is chloroquine phosphate. The characteristic pollutant concentration in the application for antibiotic degradation in water is 5-40 mg / L.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] Using ZIF-67 as a precursor, ZIF-67 is expanded in a two-dimensional plane and interacts with melamine sponge after etching with cyanuric acid. During the carbonization process, a highly dispersed immobilized porous carbon nanotube structure of Co is synthesized in situ, which effectively prevents the leaching and aggregation of metal species during the reaction process, thereby ensuring the stability, effectiveness and recyclability of the catalyst. Attached Figure Description

[0029] Figure 1 SEM of the catalyst prepared in Example 1

[0030] A. SEM image of melamine sponge; b. SEM image of melamine sponge supported by ZIF-67; c. SEM image of Co-doped porous carbon nitride nanotubes synthesized in situ on melamine sponge; d. SEM image of ZIF-67-derived Co-doped carbon nitride nanotubes on unsupported melamine sponge.

[0031] Figure 2 The effect of different factors on the catalyst degradation effect in Example 1 (except for the factor being evaluated, other factors were controlled at a catalyst dosage of 4 g / L, a PMS dosage of 0.3 mM, a chloroquine phosphate concentration of 10 mg / L, and a temperature of 25°C).

[0032] like Figure 2 As shown in a and d, when the catalyst dosage was increased from 2 g / L to 4 g / L, the degradation efficiency of CQP increased from 55.92% to 81.80%. However, this does not mean that the more catalyst added, the better. Excessive catalyst dosage may clog the pores of the sponge support, affecting the mass transfer and diffusion of reactants, thereby reducing the reaction efficiency. When the catalyst dosage was increased from 4 g / L to 5 g / L, the degradation efficiency of CQP decreased from 81.80% to 81.03%.

[0033] like Figure 2 As shown in b and e, when the PMS dosage was increased from 0.1 mM to 0.3 mM, the degradation efficiency of CQP increased from 27.55% to 81.80%. However, when the PMS dosage was increased from 0.33 mM to 0.4 mM, the degradation efficiency of CQP decreased from 81.80% to 81.54%. This is because increasing the PMS concentration provides more oxidant, thereby enhancing the driving force of the degradation reaction. However, excessively high PMS concentrations may also have negative effects. Excessively high PMS concentrations may cause the surface of the sponge-supported catalyst to become saturated, thus limiting its contact and reaction with CQP.

[0034] like Figure 2As shown in c and f, temperature is one of the important factors affecting the chemical reaction rate and degradation efficiency. Increased temperature can accelerate intermolecular collisions and reaction kinetics, thereby increasing the reaction rate. Therefore, the degradation rate of CQP increases at higher temperatures. However, temperature can also affect the interaction between the catalyst and the sponge support, as well as the dispersion and stability of the catalyst on the sponge. If the temperature is too high, it may cause the catalyst to detach from the sponge or become deactivated.

[0035] Figure 3 Performance evaluation of the catalyst prepared in Example 1 in the presence of different inorganic anions

[0036] like Figure 3 As shown, 20 mM Cl − It improved the CQP degradation effect to a certain extent, k obs From 0.0416 min –1 Increased to 0.1301 min –1 Because of excessive Cl – Able to interact with HSO5 – SO4· – It reacts with HO· to ​​produce HClO, Cl·, HOCl· − and Cl2· − Free radicals readily react with electron-rich groups on CQP, thereby enhancing degradation. Furthermore, high concentrations of Cl... – It can produce a certain amount of Cl2, which has strong oxidizing properties, and PMS can also react directly with Cl. – The reaction generates Cl2, which directly promotes the degradation of CQP via a non-radical pathway. CO3 2− It exhibits a significant inhibitory effect on the degradation of CQP, when CO3... 2− At a concentration of 20 mM, the CQP degradation efficiency decreased from 81.80% to 51.12% (kJ / mL) within 60 min. obs From 0.0273 min –1 Reduced to 0.0114 min –1 This is because CO3 2– It can be used with SO4· – It reacts with H2O· to ​​produce CO3· – It significantly inhibits the degradation of CQP. SO4 2– and H2PO4 – The inhibitory effect on CQP degradation was not significant; even at an ion concentration of 20 mM, 76.8% and 75.1% CQP degradation rates were still achieved within 60 min. This is because SO42-... 2– Able to shorten SO4· − The path to attack CQP, H2PO4– To a certain extent, it inhibited the decomposition of PMS, thereby inhibiting the degradation of CQP. When the HA concentration was 10 mg / L, the degradation efficiency of CQP decreased from 81.8% to 53.6% within 60 min (kJ / L). obs From 0.0273 min –1 Reduced to 0.0123 min –1 This produces an inhibitory effect. This is because they can quench the oxidizing SO4· – The presence of HO· leads to a decrease in their concentration, thereby inhibiting the degradation of CQP.

[0037] Figure 4 The amount of Co metal leaching during the 21-cycle test of the catalyst in Example 1.

[0038] like Figure 4 As shown, in Example 1, the leaching concentration of Co in the catalyst during 5 cycles was 10-18 μg / L, which is much lower than the metal leaching concentration in the PMS activation process mediated by Co oxide, effectively suppressing the problem of secondary heavy metal pollution caused by the loss of active components. Detailed Implementation

[0039] The present invention will be further described in conjunction with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Example 1

[0041] The sponge was immersed in an ethanol solution and ultrasonically cleaned twice, 3 minutes each time, to remove impurities and oil from its surface. Next, it was ultrasonically cleaned twice with deionized water, 3 minutes each time. After cleaning, the sponge was placed in a 60°C oven to dry overnight, ensuring it was completely dry.

[0042] First, PVB (40 mg) was ultrasonically dispersed in anhydrous ethanol (10 mL) solution for 30 minutes to form a homogeneous solution. ZIF-67 (0.1 g) was added to the solution, and the mixture was ultrasonically dissolved in a 60°C water bath for 30 minutes. Using a micropipette, the mixture was added dropwise onto a 0.2 g melamine sponge (2 cm × 2 cm × 2 cm) at a rate of 1 mL / drop, ensuring the sponge fully absorbed the solution. After drying at 60°C for 8 hours, loosely loaded catalyst particles were removed. The catalyst-loaded sponge was then ultrasonicated for 5 minutes and rinsed thoroughly with deionized water to remove residual ethanol and loose catalyst particles. The sponge was then dried again in a 60°C oven to obtain the final sponge-supported ZIF-67 catalyst.

[0043] Melamine sponge immobilized with ZIF-67 was added to deionized water, followed by 0.2 g of cyanuric acid. The mixture was hydrothermally stirred at 60°C (300 rpm) for 120 min, then centrifuged (5000 rpm, twice, 7 min each time, 4°C) to obtain the catalyst precursor. This precursor was dried and then carbonized in a N2 atmosphere at a temperature increased to 550°C at 5°C / min for 240 min to obtain a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst.

[0044] The catalyst prepared above was used to activate PMS for the degradation of chloroquine phosphate. The reaction conditions were: catalyst dosage of 4 g / L, PMS dosage of 0.3 mM, chloroquine phosphate concentration of 10 mg / L, and temperature of 25℃. The degradation efficiency of chloroquine phosphate reached 26.58% within 60 min.

[0045] Example 2

[0046] The sponge was immersed in an ethanol solution and ultrasonically cleaned twice, 3 minutes each time, to remove impurities and oil from its surface. Next, it was ultrasonically cleaned twice with deionized water, 3 minutes each time. After cleaning, the sponge was placed in a 60°C oven to dry overnight, ensuring it was completely dry.

[0047] First, a certain amount of PVB (30 mg) was ultrasonically dispersed in anhydrous ethanol (10 mL) solution for 30 minutes to form a homogeneous solution. ZIF-67 (0.15 g) was added to the solution, and the mixture was ultrasonically dissolved in a 60℃ water bath for 30 min. Using a micropipette, the mixture was added dropwise onto a 0.2 g melamine sponge (2 cm × 2 cm × 2 cm) at a rate of 1 mL / 10 mL. During the addition process, the sponge was ensured to fully absorb the solution. After drying at 60℃ for 8 h, loosely loaded catalyst particles were removed. The catalyst-loaded sponge was ultrasonicated for 7 min, and then rinsed with deionized water to remove residual ethanol and loose catalyst particles. The sponge was then dried again in a 60℃ oven to obtain the final sponge-supported ZIF-67 catalyst.

[0048] Melamine sponge immobilized with ZIF-67 was added to deionized water, followed by 0.2 g of cyanuric acid. The mixture was hydrothermally stirred at 80°C (500 rpm) for 180 min, then centrifuged (7000 rpm, twice, 7 min each time, 10°C) to obtain the catalyst precursor. After drying, the precursor was carbonized in a N2 atmosphere at 10°C / min to 450°C for 180 min to obtain a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst.

[0049] The catalyst prepared above was used to activate PMS for the degradation of chloroquine phosphate. The reaction conditions were: catalyst dosage of 4 g / L, PMS dosage of 0.3 mM, chloroquine phosphate concentration of 10 mg / L, and temperature of 25℃. The degradation efficiency of chloroquine phosphate reached 45.75% within 60 min.

[0050] Example 3

[0051] The sponge was immersed in an ethanol solution and ultrasonically cleaned twice, 3 minutes each time, to remove impurities and oil from its surface. Next, it was ultrasonically cleaned twice with deionized water, 3 minutes each time. After cleaning, the sponge was placed in a 60°C oven to dry overnight, ensuring it was completely dry.

[0052] First, PVB (20 mg) was ultrasonically dispersed in anhydrous ethanol (10 mL) solution for 30 minutes to form a homogeneous solution. ZIF-67 (0.2 g) was added to the solution, and the mixture was ultrasonically dissolved in a 70°C water bath for 40 min. Using a micropipette, the mixture was added dropwise onto 0.2 g melamine sponges (2 cm × 2 cm × 2 cm) at a rate of 1 mL / drop of 10 mL. During the addition process, it was ensured that the sponge fully absorbed the solution to avoid waste or uneven catalyst distribution. 1 mL of the mixture was added to each 0.2 g sponge, and the sponges were dried at 60°C for 8 h to remove any loosely loaded catalyst particles.

[0053] The catalyst-loaded sponge was ultrasonicated for 10 min, then rinsed with deionized water to remove residual ethanol and loose catalyst particles. The sponge was then dried again in an oven at 60°C to obtain the final sponge-supported ZIF-67 catalyst.

[0054] Melamine sponge immobilized with ZIF-67 was added to deionized water, along with 0.2 g of cyanuric acid. The mixture was hydrothermally stirred at 90°C (700 rpm) for 120 min, then centrifuged (8000 rpm, 3 times, 7 min each time, 15°C) to obtain the catalyst precursor. After drying, the precursor was carbonized in a N2 atmosphere at a temperature increased to 600°C at 5°C / min for 120 min to obtain a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst.

[0055] The catalyst prepared above was used to activate PMS for the degradation of chloroquine phosphate. The reaction conditions were: catalyst dosage of 4 g / L, PMS dosage of 0.3 mM, chloroquine phosphate concentration of 10 mg / L, and temperature of 25℃. The degradation efficiency of chloroquine phosphate reached 58.70% within 60 min.

Claims

1. A method for preparing a sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst, characterized in that, Includes the following steps: 1) Pre-treat the melamine sponge by immersing it in anhydrous ethanol solution and cleaning it with ultrasound to remove impurities and oil from the sponge surface; then, perform the same ultrasonic cleaning with deionized water. After cleaning, place the sponge in an oven at 60°C overnight to ensure that the sponge is completely dry. 2) The immobilizing agent PVB Butvar B-76 was ultrasonically dispersed in an ethanol solution for 30 minutes to form a homogeneous solution. Then, the ZIF-67 catalyst was added to the PVB ethanol solution, and the solution was ultrasonically dispersed for another 30 minutes while maintaining a water bath temperature of 60-80°C to ensure that the catalyst and the immobilizing agent PVB were thoroughly mixed. Using a micropipette, the mixture was dropped onto a 0.2g melamine sponge at a rate of 1mL / drop of 10mL. Subsequently, the catalyst-loaded sponge was dried in a 60°C oven to allow the immobilizing agent PVB to fully solidify. The dosage of PVB in each 20mL of anhydrous ethanol solution was 10-40mg. 3) Remove loosely loaded catalyst particles. Place the catalyst-loaded sponge in an ultrasonic cleaner to effectively remove catalyst particles that are not firmly fixed to the sponge. After ultrasonic treatment, rinse the sponge with deionized water to remove residual ethanol and loose catalyst particles. Then, place the sponge in a 60°C oven to dry again to obtain the final sponge-supported ZIF-67 catalyst. 4) Melamine sponge with ZIF-67 fixed was added to deionized water and cyanuric acid was added. After hydrothermal stirring at 60-120℃ for 60-180 min, the catalyst precursor was obtained by centrifugation. After drying the precursor, it was carbonized in N2 atmosphere to prepare sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst. The stirring rate was 200-800 rpm. The mass ratio of cyanuric acid to melamine sponge was 1:0.5-3.

2. The preparation method according to claim 1, characterized in that... In step 1), the number of ultrasonic cleaning cycles should be 2-5, and the ultrasonic cleaning time for each cycle should be 5-10 minutes.

3. The preparation method according to claim 1, characterized in that... In step 2), the mass ratio of ZIF-67 to melamine sponge is 1:1-10.

4. The preparation method according to claim 1, characterized in that... The ultrasound time in step 3) is 5-10 min.

5. The preparation method according to claim 1, characterized in that... In step 4), the centrifugation speed is 5000-8000 rpm, the number of times is 1-5, and the temperature is 4-15℃.

6. The preparation method according to claim 1, characterized in that... In step 4), the carbonization temperature is 300-700℃, the heating rate is 5-15℃ / min, and the carbonization time is 60-240 min.

7. A sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst was prepared according to any one of claims 1-6.

8. The application of the sponge-supported MOF-derived Co-doped carbon nitride nanotube catalyst of claim 7 to activate PMS for the degradation of chloroquine phosphate pollutants in water, wherein the concentration of chloroquine phosphate is 5-40 mg / L.

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