Preparation and application of magnetic cobalt particle loaded g-C3N4 heterogeneous Fenton-like catalyst

Abstract

The invention discloses a preparation method and application of a magnetic cobalt particle loaded g-C3N4 heterogeneous Fenton-like catalyst. The preparation method comprises the following steps: firstly, synthesizing a g-C3N4 substrate through direct calcination, preparing magnetic Co particles by utilizing a hydrothermal method, and fixing the magnetic Co particles on the surface of g-C3N4 through secondary hydrothermal treatment to obtain the novel Fenton-like catalyst. The catalyst has efficient degradation capacity on various typical pollutants including sulfamethoxazole (SMZ), diclofenac sodium (DF), carbamazepine (CBZ), ciprofloxacin (CIP) and tetracycline (TC) in wastewater, is easy to recycle through magnetic force due to the excellent magnetism of the catalyst, has excellent adaptability to humic acid and anions (Cl <->, HCO3 <-> and HNO3 <->) contained in the wastewater, and can be applied to wastewater treatment. And good catalytic performance is maintained in a wide pH range (3-9). The catalyst has certain applicability in actual wastewater treatment.

Description

Technical Field

[0001] The invention relates to the application of advanced oxidation technology in sewage treatment, and in particular to a preparation method of a Fenton-like catalyst capable of effectively activating PMS to degrade pollutants. Background Art

[0002] In recent years, the development of industry has improved people's living conditions, enriched people's living materials, and greatly promoted the progress of social civilization. However, the resulting environmental problems have seriously threatened people's health. Water is a necessary resource for human life, but due to industrial, agricultural and daily discharge, water bodies have been seriously polluted. Among them, antibiotics have been widely used in animal disease prevention and control, animal husbandry and aquaculture, and human medicine. About 30%-90% of veterinary antibiotics that enter animals are excreted into the environment through urine or feces as original drugs or their metabolites, and migrate to various ecosystems, thus posing a potential threat to the ecological environment and human health.

[0003] Advanced Oxidation Process (AOP s ) is through the generation of highly oxidizing active free radicals (·OH, ·O2 - The Fenton-like oxidation technology is one of the most widely studied technologies. The traditional Fenton reaction is to use Fe 2+ It reacts with H2O2 to generate active free radicals to mineralize pollutants. However, this reaction cannot be directly applied to actual sewage treatment. Cobalt is considered to be the most promising persulfate catalyst, but pure metal catalysts are very likely to leak during operation, leading to secondary pollution. Carbon-based materials are also often used as metal-free persulfate catalysts due to their superior performance. However, carbon-based materials are relatively unstable during the activation process and have lower activity than metal catalysts, making them less used. Until the idea of ​​using metal-modified carbon-based materials as catalysts to activate persulfate was proposed, this idea not only improved the problem of low catalytic performance of carbon-based materials, but also optimized the leakage problem of metal catalysts during the catalytic process.

[0004] However, in actual processing, the reuse of catalysts is the key to measuring the efficiency of catalysts. Traditional persulfate catalysts usually need to be collected by filtration before they can be reused, but the cumbersome filtration method and low recovery rate become a problem. Based on this, the present invention provides a preparation and application of a magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton catalyst. Summary of the invention

[0005] The purpose of the present invention is to propose a preparation method of a magnetic cobalt particle-loaded g-C3N4 Fenton-like catalyst and its activation of permonosulfate (PMS) to generate free radicals to degrade antibiotic pollutants in water. First, the g-C3N4 substrate is synthesized by direct calcination, and magnetic Co particles are prepared by hydrothermal method. Then, the magnetic Co particles are fixed on the surface of g-C3N4 by secondary hydrothermal method to synthesize a new type of Fenton-like catalyst. The effect of effectively treating antibiotic pollutants in wastewater is achieved by rationally configuring the application concentration of the catalyst and permonosulfate.

[0006] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton catalyst, inducing an interfacial complexation reaction through a two-step hydrothermal method, uniformly complexing nanoscale Co particles on the surface of carbon nitride, and forming a Fenton-like catalyst with an efficient reaction mechanism.

[0007] The specific steps include: (1) Preparation of g-C3N4 substrate Urea was ground in a mortar and then heated in a muffle furnace at 550 °C for 3 h. After cooling, it was ground to obtain g-C3N4 powder; (2) Preparation of magnetic Co particle-supported g-C3N4 Fenton-type catalyst A certain amount of Co(NO3)2·6H2O was added to a methanol solution (the volume ratio of methanol to water was 1:1), and ultrasonic dispersion was performed to make it uniform. Then, it was introduced into a polytetrafluoroethylene reactor, moved into an oven and maintained at a temperature of 180°C, and the heating reaction lasted for 24 hours. After the reaction was completed, the liquid was rinsed with methanol, centrifuged, and vacuum dried to obtain a Co crystal material; the Co crystal material and carbon nitride were dispersed in a methanol solution (the volume ratio of methanol to water was 1:1) in a certain proportion, and ultrasonic dispersion was performed to make it uniform. Then, it was introduced into a polytetrafluoroethylene reactor, moved into an oven and maintained at a temperature of 180°C, and the heating reaction lasted for 24 hours. After the reaction was completed, the liquid was rinsed with methanol, centrifuged, and vacuum dried; the dried sample was crushed into powder, and then the powder was calcined at 600°C for 6 hours in a tubular furnace under N2 atmosphere. After cooling to room temperature, the solid was collected and ground into powder to finally obtain a catalyst.

[0008] Preferably, the mass ratio of the Co crystal material to the carbon nitride in step (2) is 0.5-2:1.

[0009] Preferably, the heating rate of the burning in step (2) is 2°C / min.

[0010] The magnetic cobalt particles prepared by the preparation method described above are loaded with g-C3N4 heterogeneous Fenton-like catalyst.

[0011] The application of the magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton-like catalyst in the degradation of antibiotics in water: The magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton-like catalyst degrades antibiotic pollutants by activating persulfate.

[0012] Preferably, the antibiotic pollutants include ciprofloxacin CIP, diclofenac sodium DF, sulfamethoxazole SMZ, tetracycline TC, and carbamazepine CBZ.

[0013] Preferably, the magnetic cobalt particles loaded with g-C3N4 heterogeneous Fenton-like catalyst degrades antibiotics in water and has a significant effect on the degradation of Cl - , HCO3 - , NO3 - and humic acid have anti-pollution properties.

[0014] The significant advantages of the present invention are: The present invention prepares a Fenton-like catalyst, which can efficiently activate persulfate and degrade antibiotic pollutants in a short time. In many traditional Fenton-like catalysts, active particles are often attached to the catalyst surface, which reduces the reusability of the catalyst, and traditional catalysts are usually recovered by filtration, which inevitably leads to catalyst loss during the recovery process. By introducing carbon nitride to fix the metal in the catalyst, the leakage of the metal during the catalytic process is reduced. The catalyst prepared by this method has good magnetic properties and can be easily separated from the water body by a permanent magnet for recovery.

[0015] The present invention introduces magnetic cobalt crystal particles into the surface of carbon nitride by a two-step hydrothermal method, which not only effectively fixes the magnetic cobalt crystal particles on the catalyst surface to make the catalyst magnetic, but also increases the specific surface area of ​​the catalyst to increase the active sites that can promote the reaction. Specifically, since the metal ions that are easy to leak in the catalyst are fixed by the addition of carbon nitride, and the combination of carbon nitride and cobalt particles increases the specific surface area of ​​the catalyst and promotes the activation of PMS, free radical substances are released faster, so that antibiotic pollutants are degraded faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 are the X-ray diffraction spectra of pristine g-C3N4, Co precursor, and Co@g-CN-10 Fenton-like catalysts; Figure 2 a, b, and c are scanning electron microscopy images of the original g-C3N4, Co precursor, and Co@g-CN-10 Fenton-like catalyst, respectively; Figure 3 are the BET surface area, pore volume, and average pore size distribution of the original g-C3N4 and Co@g-CN-10 Fenton-like catalysts; Figure 4is the hysteresis curve of Co@g-CN-10 Fenton-type catalyst; Figure 5 is the removal rate of SMZ by catalysts with different loading ratios; Figure 6 is the removal rate of antibiotic pollutants by Co@g-CN-10 type Fenton catalyst; Figure 7 The removal rate of sulfamethoxazole by Co@g-CN-10 type Fenton catalyst at different pH values; Figure 8 The effect of coexisting ions in water on the removal of sulfamethoxazole by Co@g-CN-10 type Fenton catalyst; Fig. 9 The removal efficiency of sulfamethoxazole after five cycle experiments of Co@g-CN-10 Fenton catalyst. Specific implementation methods In order to make the purpose, technical solution and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. The embodiments described are only some embodiments of the present invention, but not all embodiments.

[0018] A method for preparing a magnetic cobalt particle-supported g-C3N4 heterogeneous Fenton catalyst comprises the following steps: (1) Preparation of g-C3N4 substrate 20 g of urea was accurately weighed in a mortar and ground for 20 min, then heated in a muffle furnace at a heating rate of 5 °C / min and heated at 550 °C for 3 h. After cooling, the obtained yellow block g-C3N4 was completely ground into powder to obtain the original g-C3N4 powder.

[0019] (2) Preparation of g-C3N4 Fenton-type catalyst supported by magnetic Co particles Prepared by a two-step hydrothermal method of Co3(NO3)2·6H2O and carbon nitride. A certain amount of Co3(NO3)2·6H2O was added to a methanol solution (the volume ratio of methanol to water was 1:1), ultrasonicated to make it uniformly dispersed, and then introduced into a polytetrafluoroethylene reactor. In the reactor, it was moved into an oven and maintained at a temperature of 180°C, and the heating reaction lasted for 24 hours. After the reaction was completed, the liquid was washed with methanol and centrifuged 3 times, and then vacuum dried to obtain Co crystal material. Similarly, the Co crystal material obtained in the previous step was mixed with carbon nitride in a certain mass ratio (0.5:1, 1:1 and 2:1, and the obtained catalysts were named Co@g-CN-5, Co@g-CN-10 and Co@g-CN-20, respectively) and dispersed in a methanol solution (the volume ratio of methanol to water was 1:1), and ultrasonic dispersion was performed to make it uniform. Then, the mixed solution was introduced into a polytetrafluoroethylene reactor, and the reactor was moved into an oven, the temperature was maintained at 180°C, and the heating reaction lasted for 24 hours. After the reaction was completed, it was rinsed with methanol and centrifuged three times and then vacuum dried. The dried sample was crushed into powder, and then the powder was calcined at 600°C for 6 hours in a tube furnace under N2 atmosphere (heating rate was 2°C / min), and the solid was collected after cooling to room temperature, ground into powder, and finally the catalyst was obtained.

[0020] The cobalt-based catalyst prepared in step (2) is placed in a pollutant solution together with permonosulfate (PMS) to examine the adaptability of the cobalt-based catalyst to pH changes, the effect of coexisting ions in water on the removal efficiency of the catalyst, the removal rate of various pollutants and other indicators.

[0021] Example 1 The composition of several materials was investigated by X-ray diffraction spectroscopy. Figure 1 As shown in the figure, the diffraction peaks at 44.2°, 51.5° and 75.8° correspond to the (111), (200) and (220) lattice planes on Co balt, respectively (Co balt-PDF#15-0806). It can be seen that the cobalt in Co@g-CN-10 mainly exists in the form of Co balt. In addition, the characteristic peaks of carbon nitride (002) and Co balt were detected in Co@g-CN-10, indicating that the material was successfully synthesized.

[0022] Example 2 Figure 2 Figures ac show the scanning electron microscope (SEM) images of Co@g-CN-10 and their corresponding elemental surface scans. Figure 2 (a) and (b) show electron microscope images of pure carbon nitride and cobalt crystal particles. The spherical structure of the cobalt crystal particles shows a phenomenon of stacking and agglomeration, so that its surface area is not fully utilized. Figure 2In the scanning electron microscope image of Co@g-CN-10 shown in (c), it can be seen that the cobalt crystals and carbon nitride cluster together to avoid agglomeration, greatly increasing the specific surface area and increasing the area where the reaction occurs. These results show that the Co particles are successfully doped in carbon nitride and show good dispersion and structural characteristics. Figure 3 As shown in Figure 2, the BET specific surface area of ​​Co@g-CN-10 is approximately 16.9996 m 2 / g, higher than 7.1265 m 2 / g. This shows that cobalt doping brings a larger specific surface area to the catalyst, which increases the area of ​​catalytic reaction. In addition, the pore size of Co@g-CN-10 is about 6.2760 nm, which is lower than the 18.4967 nm of carbon nitride. This result also verifies the successful doping of Co. The porous structure of the catalyst contributes to the mass transfer rate and accessible diffusion, which is conducive to the efficient activation of PMS by the catalyst and the capture of pollutants. Figure 4 As shown in the figure, the hysteresis curve of Co@g-CN-10 has a magnetization saturation value of 111.96 emu / g, indicating that the material has good magnetic properties and is easy to recycle. In summary, the cobalt doping forms a mesoporous structure that provides more active sites, which is conducive to the degradation of pollutants, and has good magnetic properties, which is easy to recycle.

[0023] Example 3 Weigh 10 mg of Co@g-CN-10 Fenton-type catalyst into a beaker containing 100 ml, 40 mg / L, pH=7 pollutants, then place the beaker containing the reaction solution on a magnetic stirrer and stir at a medium speed. After adsorption equilibrium, add 20 mg of permonosulfate to the beaker, and take samples at the set reaction time intervals for subsequent analysis. The time intervals used are 1 min, 3 min, 5 min, 7 min, 9 min, and 10 min. Liquid chromatography and ultraviolet spectrophotometer are selected to measure the concentration according to the properties of the pollutants. The selected pollutants include antibiotic pollutants sulfamethoxazole (SMZ), diclofenac sodium (DF), carbamazepine (CBZ), ciprofloxacin (CIP) and tetracycline (TC). The results are shown in Figure 6 As shown in the figure, all pollutants were significantly degraded within 10 min, diclofenac sodium was completely degraded within 10 min, tetracycline was degraded by 97.8% within 10 min, and sulfamethoxazole was degraded by 99.6% within 10 min. Even for carbamazepine, which is extremely difficult to treat, the removal efficiency reached 91.3% within 10 min. These results show that Co@g-CN-10 is a promising Fenton-like catalyst for degrading organic pollutants in water.

[0024] Example 4 Weigh 10 mg of Co@g-CN-10 Fenton-like catalyst into a beaker containing 100 ml of 40 mg / L sulfamethoxazole solution, adjust the solution to different pH values ​​(3, 5, 7, 9) with H2SO4 and KOH, then place the beaker containing the reaction solution on a magnetic stirrer and stir at a medium speed. After adsorption equilibrium, add 20 mg of permonosulfate to the beaker, and take samples at set reaction time intervals for subsequent analysis. The results are shown in Figure 2. Figure 7 As shown. It can be seen that the SMZ removal efficiency of the Co@g-CN-10 catalyst exceeds 70% in a wide pH range. When the pH is 3, the SMZ removal efficiency (71%) is the lowest, because the metal ions in the catalyst are still easily leached and unstable in an acidic environment. The catalyst achieved the best performance (99.6%) at a pH of 7. These results show that the Co@g-CN-10 Fenton-like catalyst is insensitive to pH changes during the degradation of pollutants in water and degrades pollutants in a wide pH range. Subsequent experiments were carried out under optimal conditions (PMS dosage of 0.2 g / L, catalyst dosage of 0.1 g / L, and pH of 7).

[0025] Example 5 10 mg of Co@g-CN-10 Fenton catalyst was weighed into four beakers containing 100 ml of 40 mg / L sulfamethoxazole solution at pH 7. Then, different anions (Cl - , HCO3 - , HNO3 - ) and humic acid (HA) to a concentration of 5 mM, then place the beaker containing the reaction solution on a magnetic stirrer and stir at a medium speed. After adsorption equilibrium, add 20 mg of permonosulfate to the beaker and take samples at the set reaction time interval for subsequent analysis. The results are shown in Figure 8 When the Fenton catalyst system contains Cl - , HCO3 - , HNO3 - When HCO3 - , HNO3 - The presence of Cl had no significant effect on the degradation of SMZ by the catalyst. - In the presence of Cl - Consumes some free radicals to form Cl· and ClOH -·. The oxygen-containing functional groups (such as hydroxyl groups) contained in HA will be adsorbed on the catalyst surface, thereby affecting the interaction between the catalyst and PMS. In summary, the Fenton catalyst is - , HCO3 - , HNO3 - It has obvious resistance to interference from HA. Fig. 9 The degradation efficiency of SMZ by the Fenton-like catalyst was demonstrated when the experiment was run for 5 consecutive cycles. Although the removal efficiency of SMZ decreased slightly after each cycle, the efficiency remained above 88.19% after the 5th run, which shows that the catalyst has excellent reusability in practical applications.

[0026] Example 6 Weigh 10 mg of Co@g-CN-5, Co@g-CN-10, and Co@g-CN-20 Fenton catalysts into three beakers containing 100 ml, 40 mg / L, pH=7 sulfamethoxazole solution. Then place the beakers containing the reaction solutions on a magnetic stirrer and stir at a medium speed. After adsorption equilibrium, add 20 mg of permonosulfate to the beakers and take samples at the set reaction time interval for subsequent analysis. The results are shown in Figure 2. Figure 5 As shown. Figure 5 In the experiment, the removal rates of SMZ within ten minutes were 63.5%, 99.6% and 68.4%, respectively. The reason for the different removal rates is that the former may be due to the higher proportion of metals agglomerating more, thus reducing the active sites for the reaction, while the latter is due to the lower proportion of metals failing to effectively activate PMS. Therefore, Co@g-CN-10 was used in subsequent experiments and analyses.

[0027] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a magnetic cobalt particle-supported g-C3N4 heterogeneous Fenton-like catalyst, characterized in that: Through a two-step hydrothermal method to induce an interfacial complexation reaction, nanoscale Co particles are uniformly complexed on the carbon nitride surface to form a Fenton-like catalyst with an efficient reaction mechanism.

2. The method for preparing a magnetic cobalt particle-supported g-C3N4 heterogeneous Fenton-like catalyst according to claim 1, characterized in that: The following steps are involved: (1) Preparation of g-C3N4 substrate Urea was ground in a mortar and then heated in a muffle furnace at 550 °C for 3 h. After cooling, it was ground to obtain g-C3N4 powder; (2) Preparation of magnetic Co particle-supported g-C3N4 Fenton-type catalyst A certain amount of Co(NO3)2·6H2O is added to a methanol solution, ultrasonically dispersed to make it uniform, then introduced into a polytetrafluoroethylene reactor, moved into an oven to maintain the temperature at 180°C, heated to react for 24 hours, and after the reaction is completed, the liquid is rinsed with methanol, centrifuged, and then vacuum-dried to obtain a Co crystal material; the Co crystal material and carbon nitride are dispersed in a methanol solution in a certain proportion, ultrasonically dispersed to make it uniform, then introduced into a polytetrafluoroethylene reactor, moved into an oven to maintain the temperature at 180°C, heated to react for 24 hours, and after the reaction is completed, the liquid is rinsed with methanol, centrifuged, and then vacuum-dried to obtain a Co crystal material; the Co crystal material and carbon nitride are dispersed in a methanol solution in a certain proportion, ultrasonically dispersed to make it uniform, then introduced into a polytetrafluoroethylene reactor, moved into an oven to maintain the temperature at 180°C, heated to react for 24 hours, and after the reaction is completed, the solid is collected and ground into powder to finally obtain a catalyst.

3. The preparation method according to claim 2, characterized in that: In step (2), the mass ratio of the Co crystal material to the carbon nitride is 0.5-2:

1.

4. The preparation method according to claim 2, characterized in that: The volume ratio of methanol to water in the methanol solution used in step (2) is 1:

1.

5. The preparation method according to claim 2, characterized in that: The heating rate of the burning in step (2) is 2°C / min.

6. A magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton-like catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the magnetic cobalt particles loaded g-C3N4 heterogeneous Fenton-like catalyst in the degradation of antibiotics in water according to claim 6, characterized in that: The magnetic cobalt particle-loaded g-C3N4 heterogeneous Fenton-like catalyst degrades antibiotic pollutants by activating persulfate.

8. The use according to claim 7, characterized in that: The antibiotic pollutants include ciprofloxacin CIP, diclofenac sodium DF, sulfamethoxazole SMZ, tetracycline TC, and carbamazepine CBZ.

9. The use according to claim 7, characterized in that: The magnetic cobalt particles loaded g-C3N4 heterogeneous Fenton-like catalyst has a great influence on the degradation of Cl in the process of antibiotics in water. - , HCO3 - , NO3 - and humic acid have anti-pollution properties.

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