A method for using rare earth metal single-atom catalytic materials to activate bicarbonate to degrade sulfamethoxazole

Abstract

The present invention belongs to the field of environmental engineering technology, and provides a method for using a rare earth metal single-atom catalytic material to activate bicarbonate to degrade sulfamethoxazole. Using rare earth metal nitrate and modified CN as precursors, a catalytic material loaded with rare earth metal single atoms on the modified CN was synthesized by defect capture and coordination regulation strategies. By introducing rare earth metal single atoms into the modified CN with a three-dimensional porous network structure containing N defects, a stable RE-N coordination structure is formed, which not only constructs an efficient electron migration channel, promotes the rapid migration of photogenerated electrons, and reduces the photogenerated carrier recombination rate; in addition, the introduction of RE SAs structure can reconstruct the surface charge distribution of the composite material, optimize its band gap structure, and provide more adsorption and reaction active sites; RE SAs has a higher adsorption energy for bicarbonate ions, and at the same time utilizes the photogenerated charge on the substrate to activate bicarbonate, thereby reducing the reaction barrier for its conversion to carbonate free radicals.

Description

Technical Field

[0001] The present invention belongs to the field of environmental engineering technology and relates to the research on the preparation technology of graphite-phase carbon nitride photocatalytic materials loaded with rare earth metal single atoms, and in particular to the innovation of a method for using the material to activate carbonate ions under visible light conditions to generate carbonate free radicals for efficient degradation of sulfamethoxazole. Background Art

[0002] Sulfamethoxazole (SMX) is a commonly used sulfonamide antibiotic that can achieve antibacterial effects by inhibiting the synthesis of dihydropteroate synthase, which is necessary for bacterial growth. Recent studies have shown that the abuse of antibiotics is frequent. SMX has been widely detected worldwide and is an emerging persistent pollutant. SMX in the environment mainly comes from biological metabolism and sewage discharge from pharmaceutical companies and hospitals. Its half-life is more than 85-100 days and due to its biological activity, it is difficult to effectively remove it in conventional wastewater treatment plants. Residual SMX enters the environment through surface runoff or sludge, accumulates in the human body through the food chain, and leads to the production of highly resistant bacteria in the human body, which seriously threatens people's lives and safety. There is an urgent need to develop effective methods to treat SMX.

[0003] Currently, the main methods for deep removal of SMX from the environment are adsorption, biological methods, and photocatalysis. Chen et al. (Removal of sulfamethoxazole and ciprofloxacin from aqueous solutions by graphene oxide) proposed using graphene oxide (GO) to adsorb SMX through π-π interactions, achieving a removal efficiency of 98% within 12 hours and reaching adsorption equilibrium within 24 hours, with a maximum removal of 240 mg / g. While this method can easily remove SMX, its development is limited by disadvantages such as the inability to achieve complete mineralization, the easy deactivation of the adsorbent, and poor reproducibility. Liu et al. (Sulfamethoxazole degradation by Pseudomonas silesiensis F6a isolated from bioelectrochemical technology-integrated constructed wetlands) isolated Pseudomonas silesiensis F6a from a novel bioelectrochemical technology-integrated constructed wetland (BICW), which has the ability to efficiently degrade SMX. The strain was able to degrade 76.95% of SMX (10 mg / L) in 144 hours. The entire degradation process mainly relied on the unique SMX-degrading genes in F6a to destroy the CS bond, SN bond, and isoxazole ring in SMX. Biological treatment can basically remove SMX from water, but it also has disadvantages such as low degradation efficiency, long mineralization time, and large site requirements. Compared with the above two methods, photocatalytic technology, as an advanced oxidation technology, can convert solar energy into chemical energy, has the advantages of sustainability and no secondary pollution, and is considered to be an advantageous method for treating difficult-to-degrade pollutants in water. For example, Zhu et al. (2014) successfully fabricated a reduced graphene oxide-WO3 (RGO-WO3) composite material using a simple hydrothermal method as a photocatalyst, achieving a 98% SMX degradation rate within 3 hours under visible light conditions. While photocatalytic degradation can effectively remove SMX, it still suffers from low degradation efficiency, low spectral utilization, and low mineralization rate.

[0004] Therefore, the present invention uses modified graphite-phase carbon nitride as a substrate, captures rare earth metal single atoms through nitrogen defects on the substrate surface, forms a stable single-atom coordination environment through a calcination method, constructs a rapid electron migration channel (rare earth metal-nitrogen coordination bond) between the single atom and the substrate, enhances the efficiency of photogenerated carrier separation, extends the light absorption range, and improves spectral utilization; in addition, the rare earth metal single atom has a strong adsorption capacity for bicarbonate in water. With the help of photocatalysis, it can utilize photogenerated holes to catalyze the conversion of bicarbonate into carbonate free radicals, thereby achieving the purpose of directional and efficient degradation of sulfonamide pollutants in water. Summary of the Invention

[0005] The present invention provides a method for preparing a graphite-phase carbon nitride catalytic material loaded with rare earth metal single atoms, which is applied to the photoactivated bicarbonate degradation of SMX. Through defect capture and coordination regulation strategies, rare earth metal single atoms (SAs) are introduced onto the graphite-phase carbon nitride to form a stable coordination environment. This restructures the surface charge distribution of the catalytic material, provides more adsorption and reaction active sites, and constructs fast electron migration channels, thereby promoting the transfer of photogenerated electrons and improving the efficiency of photogenerated carrier separation. Under visible light conditions, the rare earth metal single atom reaction sites can also catalyze the conversion of bicarbonate into carbonate free radicals, achieving efficient and low-cost photoactivated bicarbonate degradation of SMX.

[0006] The technical solution of the present invention:

[0007] A method for using a rare earth metal single-atom catalytic material to activate bicarbonate to degrade sulfamethoxazole, comprising the following steps:

[0008] Step 1: Prepare the substrate material (modified CN) by referring to the method for preparing modified graphitic carbon nitride in the article “One-step supramolecular preorganization constructed crinkly graphitic carbon nitride nanosheets with enhanced photocatalytic activity”.

[0009] Among them, the precursor mixed solution is dried using a vacuum freeze-drying method. Compared with the traditional drying method, it can effectively inhibit the oxidative inactivation reaction of the precursor in the air. As the freeze-drying temperature decreases, the modified CN exhibits a three-dimensional network structure with more porous structures, a larger specific surface area and stronger spectral absorption ability.

[0010] Step 2: Prepare a 0.02-0.8 mmol / L anhydrous ethanol solution of rare earth metal nitrate; then disperse the modified CN powder obtained in step 1 in the anhydrous ethanol liquid of rare earth metal nitrate to prepare a dispersion with a concentration of 1-3 g / L, and ultrasonically treat for 30-60 minutes to obtain a uniform mixed liquid; dry the mixed liquid in a water bath at 80°C, and calcine the obtained mixed powder in an argon atmosphere at a temperature controlled at 250-400°C for 2-4 hours. After cooling to room temperature, take it out, wash it with deionized water three times, and dry it in an oven at 60°C to obtain a catalytic material (CRE) loaded with rare earth metal single atoms on the modified CN.

[0011] Step 3: Using the CRE material obtained in step 2 as a catalyst, deionized water, tap water, Yellow River water, and Yellow Bay seawater containing 10-40 mg / L sulfamethoxazole (SMX) were used as target water bodies, 1 mmol / L potassium bicarbonate was added, and the solution was irradiated with visible light for 60 minutes. The SMX removal rate was above 99%, and the mineralization rate was 37-58%.

[0012] The rare earth metal nitrates include erbium (III) nitrate pentahydrate (Er(NO3)3·5H2O), europium (III) nitrate hexahydrate (Eu(NO3)3·6H2O), cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O), samarium (III) nitrate hexahydrate (Sm(NO3)3·6H2O) and dysprosium (III) nitrate hexahydrate (Dy(NO3)3·6H2O), generating a series of rare earth metal single-atom loaded catalytic materials. These catalytic materials can promote the efficient separation of photogenerated carriers and reduce the reaction barrier for converting bicarbonate into carbonate free radicals.

[0013] Beneficial effects of the present invention: The present invention uses CRE single-atom catalytic materials for the first time to activate the conversion of bicarbonate ions in water into carbonate radicals under visible light conditions, thereby achieving the purpose of efficiently degrading the antibiotic SMX. The morphology of the modified CN prepared by the method in step 1 is optimized. Compared with the blocky graphite phase carbon nitride prepared by the traditional method, the modified CN prepared by this patent exhibits a three-dimensional network interpenetrating structure, which not only has a large specific surface area, but can effectively improve the mass transfer efficiency of the material. At the same time, a large number of N vacancy structures can be introduced on the surface of CN, which can enrich photogenerated electrons and effectively adjust the band gap structure, thereby enhancing the light absorption capacity of the material. In addition, the N vacancies in the modified CN can be used as sites for capturing rare earth metal single atoms. Rare earth metal nitrates are introduced into the modified CN as single-atom precursors, and CRE single-atom catalytic materials are prepared by defect capture and coordination design strategies. This method has a simple preparation process, low cost, and high product stability. It is a process method that is easy to industrialize. In the CRE structure, rare earth metal single atoms have unique f orbitals, which easily form stable coordination structures (RE-N) with nitrogen atoms containing lone pairs of electrons in CN and are evenly distributed on the CN surface in the form of isolated atoms. Due to the similarity of the extranuclear electron orbital structures of rare earth metal atoms, the coordination structures and catalytic activities of a series of single-atom catalytic materials formed by rare earth metals are similar. The formation of the RE-N coordination bond constructs an efficient electron migration channel in CE, which can enable the rapid migration of photogenerated electrons, inhibit the radiative recombination of photogenerated electrons and photogenerated holes, and effectively improve the utilization rate of photogenerated electrons; thereby achieving an improvement in the photocatalytic efficiency of the composite material. In addition, the introduction of the RE single-atom structure can reconstruct the surface charge distribution of the composite material, optimize its band gap structure, and provide more adsorption and reaction active sites; rare earth single atoms have a high adsorption energy for bicarbonate ions, that is, this site can effectively adsorb bicarbonate ions from water, and then use the photogenerated charge to activate bicarbonate, reducing the reaction barrier for its conversion to carbonate free radicals. Therefore, CRE single-atom catalytic materials can effectively improve the reaction activity of photogenerated carriers under visible light drive, and at the same time can activate bicarbonate ions in water to generate carbonate radicals with stronger degradation performance, thereby achieving efficient degradation and mineralization of SMX. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the bright field image of scanning transmission electron microscopy of CEr;

[0015] Figure 2 This is a scanning transmission electron microscope-high-angle annular dark field image of CEr (the bright spots in the image are Er atoms);

[0016] Figure 3 This is the X-ray energy spectrum element image analysis position map of the CEr sample;

[0017] Figure 4The carbon element distribution diagram of the CEr sample is analyzed by X-ray energy spectrum element image;

[0018] Figure 5 This is the nitrogen distribution diagram of the X-ray energy spectrum elemental image of the CEr sample;

[0019] Figure 6 This is the erbium element distribution map of the X-ray energy spectrum elemental image analysis of the CEr sample. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention is described in detail below in conjunction with the technical solutions and drawings.

[0021] Example 1

[0022] Preparation of CRE single-atom catalytic materials:

[0023] Disperse 3g of urea and 3g of melamine in 80ml of deionized water and stir for 6h until fully mixed. Quickly freeze the obtained mixed liquid in liquid nitrogen, put it into a freeze dryer and keep it at -50℃ vacuum drying to remove all moisture and protect the precursor from oxidation. After the solid powder is restored to room temperature after drying, it is calcined in an argon atmosphere and the temperature is controlled at 500℃ for 4h. After it is cooled to room temperature, it is taken out and washed with deionized water and ethanol three times respectively. After vacuum drying, a yellow modified CN powder is obtained. Then select -30, -40, and -60℃ freeze-drying temperatures to prepare modified CN. (Named modified CN-30, modified CN-40, modified CN-50, and modified CN-60). A series of characterizations, such as transmission electron microscopy, X-ray photoelectron spectroscopy, synchrotron radiation fine absorption spectroscopy, solid-state 13 C nuclear magnetic resonance and electron spin resonance spectroscopy were used to explore the changes in the morphology and structure of modified CN at different freeze-drying temperatures. It can be found that with the decrease of freeze-drying temperature, the agglomeration of materials in the microscopic morphology of modified CN decreases, the material tends to be more two-dimensional layered structure, the surface pore structure increases, the specific surface area increases, and the mass transfer efficiency of the material can be effectively improved. In addition, the modified CN adopts vacuum freeze-drying to eliminate the influence of oxygen in the air on the material. After calcination, the surface of the material almost does not contain oxygen elements, and a large number of N vacancy structures are generated. By comparison, it was found that, similar to the modified CN-60, the modified CN-50 has a larger specific surface area and more N vacancy structures. Because it consumes less energy, it is used as the substrate for subsequent single-atom catalytic materials.

[0024] 0.20g of modified CN-50 was dispersed into 100ml of anhydrous ethanol containing 0.3mmol / L rare earth metal nitrate (erbium, europium, cerium, samarium, dysprosium), and ultrasonicated for 30min to obtain a uniform mixed liquid. The mixed liquid was dried in a water bath at 80℃, and the obtained mixed powder was calcined in an argon atmosphere at 300℃ for 3h to obtain a series of CRE single-atom catalytic materials. Taking erbium as an example, Figure 1 and Figure 2 It can be seen that the modified CN substrate presents a three-dimensional porous structure, and the large number of scattered bright spots on its surface are single-atom Er. Figure 3-Figure 6 ), Er element is evenly distributed on the surface of modified CN substrate.

[0025] Example 2

[0026] Enhanced SMX degradation by bicarbonate activation under visible light: 0.02g of CRE single-atom catalytic material was weighed and dispersed into a photocatalytic reactor containing 100mL of 1mmol / L potassium bicarbonate and 10mg / L SMX solution. Before illumination, the reactor was stirred in the dark for 30 minutes to allow the catalyst and SMX to reach adsorption saturation. Subsequently, catalytic degradation testing under visible light was performed. The reaction was allowed to proceed for 60 minutes at room temperature. The reaction solution was sampled every 10 minutes, filtered through a 0.22μm filter, and 1mL was collected for removal efficiency testing. After 60 minutes of reaction, 10mL of the reaction solution was sampled, filtered through a 0.22μm filter, and used to test TOC removal efficiency.

[0027] The SMX concentration was measured by ultra-high performance liquid chromatography. The results showed that when the reaction proceeded for 60 minutes, the CRE series materials could achieve an SMX removal rate of more than 99%, but the catalytic material (CEr) loaded with Er single atoms had a maximum SMX mineralization rate of 58%, which was better than other catalytic materials in the series.

[0028] Performance Comparison: Using CN-50 as the control group, 0.02g of CN-50 was weighed and dispersed into a photocatalytic reactor containing 100mL of 1mmol / L potassium bicarbonate and 10mg / L SMX solution. Prior to illumination, the reactor was stirred in the dark for 30 minutes to allow the catalyst and SMX to reach adsorption saturation. Subsequently, catalytic degradation testing under visible light was performed. At room temperature, the reaction time was 60 minutes. The reaction solution was sampled every 10 minutes, filtered through a 0.22μm filter, and 1mL was collected for removal efficiency testing. After 60 minutes of reaction, 10mL of the reaction solution was sampled, filtered through a 0.22μm filter, and used to test TOC removal efficiency.

[0029] Test results showed that after 60 minutes of reaction, CN-50 had a 30% SMX removal rate and a 5% mineralization rate, significantly lower degradation performance than CRE. This suggests that the modified CN material lacks key reactive sites on its surface, making it difficult to efficiently activate bicarbonate in water and convert it into carbonate radicals. Consequently, its degradation and mineralization performance are significantly lower than those of CRE.

[0030] In addition, to further clarify the reaction mechanism, 0.02g of CN-50 and 0.001g, 0.005g, 0.01g, and 0.02g of erbium nitrate were weighed and dispersed into a photocatalytic reactor containing 100mL of 1mmol / L potassium bicarbonate and 10mg / L SMX solution. Before illumination, the reactor was placed in the dark and stirred for 30 minutes to allow the catalyst and SMX to reach adsorption saturation. Subsequently, catalytic degradation tests were performed under visible light conditions. At room temperature, the reaction time was 60 minutes, and the reaction solution was collected every 10 minutes. The removed reaction solution was filtered through a 0.22μm filter membrane and 1mL was collected for use in testing the removal rate. After 60 minutes of reaction, 10mL of the reaction solution was collected, filtered through a 0.22μm filter membrane, and used to test the TOC removal rate.

[0031] The test results show that the addition of different amounts of erbium nitrate has no significant effect on the reaction rate of CN-50 in degrading SMX, and its degradation rate is basically consistent with the degradation performance of CN-50 under conditions without the addition of erbium nitrate. This indicates that the process of activating bicarbonate requires the loading of rare earth single atoms on the surface of the modified CN substrate to form a stable coordination environment. Therefore, during the reaction process, after the rare earth single atoms adsorb bicarbonate, they can establish a stable electron migration channel under the condition of light on, allowing the electrons on the bicarbonate to migrate through the single atom site to the modified CN surface, and then react with the photogenerated holes there. The bicarbonate that loses its electrons will be converted into carbonate free radicals, which will desorb again and dissolve in water to react with SMX.

[0032] Example 3

[0033] Degradation Quenching Experiment: 0.02g of CEr single-atom catalyst was weighed and dispersed into a photocatalytic reactor containing 100mL of 1mmol / L bicarbonate and 10mg / L SMX solution. Before illumination, the reactor was stirred in the dark for 30 minutes to allow the catalyst and SMX to reach adsorption saturation. Subsequently, catalytic degradation quenching tests were conducted under visible light. 1mmol / L of p-benzoquinone, indole, tert-butyl alcohol, sodium oxalate, and potassium dichromate were added to the reactor to quench the active species superoxide radicals, carbonate radicals, hydroxyl radicals, photogenerated holes, and photogenerated electrons. The reaction was carried out at room temperature for 60 minutes, with the reaction solution sampled every 10 minutes. The sampled solution was filtered through a 0.22μm filter, and 1mL was sampled for use to measure the removal efficiency.

[0034] The SMX concentration was determined by ultra-high performance liquid chromatography. By comparing the changes in SMX removal rate, it was found that carbonate free radicals played a major role in the entire degradation system, contributing 70% to the degradation reaction, and superoxide free radicals contributed secondly, at 20%.

[0035] Example 4

[0036] SMX degradation cycle experiment: Weigh 0.10g of CEr single-atom catalyst and disperse it into a photocatalytic reactor containing 100mL1mmol / L bicarbonate ions and 10mg / L SMX solution. Before illumination, the reactor was placed in the dark and stirred for 30 minutes to allow the catalyst and SMX to reach adsorption saturation, and then a catalytic degradation cycle test was carried out under visible light conditions. After each reaction, the liquid in the reactor was filtered and washed alternately with anhydrous ethanol and deionized water three times. After drying, the above degradation experimental conditions and process were repeated. After 20 repeated uses, the degradation efficiency of the CEr single-atom catalyst for SMX remained basically unchanged, indicating that the structure and catalytic activity of the catalyst can remain stable during use.

[0037] Example 5

[0038] Sulfonamide degradation experiment: 0.10g of CEr single-atom catalyst was weighed and dispersed into a photocatalytic reactor containing 100mL of 1mmol / L bicarbonate ion and 10mg / L of a sulfonamide solution (sulfamethoxazole, sulfadimethoxine, sulfadimethoxine, sulfisoxazole, sulfaguanidine, and mafenide). Before illumination, the reactor was placed in the dark and stirred for 30 minutes to allow the catalyst and sulfonamide to reach adsorption saturation. Subsequently, catalytic degradation testing under visible light was performed. The reaction time was 60 minutes at room temperature, with the reaction solution sampled every 10 minutes. The removed solution was filtered through a 0.22μm filter membrane, and 1mL of the sample was collected for use to test the removal efficiency.

[0039] The concentration of sulfonamide pollutants was determined by ultra-high performance liquid chromatography. The results showed that when the reaction was carried out for 60 minutes, CEr could achieve a removal rate of sulfonamide pollutants of more than 90%.

Claims

1. A method for using a rare earth metal single-atom catalytic material to activate bicarbonate to degrade sulfamethoxazole, characterized in that: Here are the steps: Step 1: Prepare modified graphite phase carbon nitride CN as a substrate material; 3 g of urea and 3 g of melamine were dispersed in 80 mL of deionized water and stirred for 6 h until fully mixed. The resulting mixed liquid was quickly frozen in liquid nitrogen and placed in a freeze dryer to be vacuum dried at -50°C to remove all moisture and protect the precursor from oxidation. After the solid powder was returned to room temperature after drying, it was calcined in an argon atmosphere at 500°C for 4 h. After cooling to room temperature, it was removed and washed three times with deionized water and ethanol respectively. After vacuum drying, a yellow modified CN powder was obtained. Step 2: Prepare a 0.02-0.8 mmol / L anhydrous ethanol solution of rare earth metal nitrate; then disperse the modified CN powder obtained in step 1 in the anhydrous ethanol liquid of rare earth metal nitrate to prepare a dispersion with a concentration of 1-3 g / L, and ultrasonicate for 30-60 minutes to obtain a uniform mixed liquid; dry the mixed liquid in a water bath at 80°C, and calcine the obtained mixed powder in an argon atmosphere at a temperature of 250-400°C for 2-4 hours. After cooling to room temperature, remove the powder, rinse it with deionized water three times, and dry it in an oven at 60°C to obtain a catalytic material CRE with rare earth metal single atoms loaded on the modified CN; Step 3: Using the catalytic material CRE loaded with rare earth metal single atoms on the modified CN obtained in step 2 as a catalyst, deionized water, tap water, Yellow River water, and Yellow Bay seawater containing 10-40 mg / L sulfamethoxazole were used as target water bodies, 1 mmol / L potassium bicarbonate was added, and the solution was irradiated with visible light for 60 min.

2. The method for activating bicarbonate to degrade sulfamethoxazole using the rare earth metal single atom catalytic material according to claim 1, characterized in that: The rare earth metal nitrates include erbium (III) nitrate pentahydrate, europium (III) nitrate hexahydrate, cerium (III) nitrate hexahydrate, samarium (III) nitrate hexahydrate and dysprosium (III) nitrate hexahydrate.

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