Self-template preparation method, regeneration method and application of thermal oxidation resistant boron-nitrogen co-doped carbon catalyst

Abstract

The invention discloses a thermal oxidation resistant boron-nitrogen co-doped carbon catalyst as well as a preparation method, a regeneration method and application of a self-template of the thermal oxidation resistant boron-nitrogen co-doped carbon catalyst. The catalyst is prepared by taking traditional Chinese medicine licorice root residues as a self-template carbon skeleton precursor, mixing the self-template carbon skeleton precursor with urea and boric acid according to a mass ratio of 1: 1: 1, and performing one-step pyrolysis in an air atmosphere. According to the preparation method, licorice root residue endogenous minerals are used as a template, and a boron-nitrogen atom covalently anchored stable carbon skeleton is successfully constructed under the fluxing and lattice stabilization effects of boric acid, so that the carbon skeleton can tolerate aerobic calcination at the high temperature of 700 DEG C. The catalyst can be used for efficiently activating peroxymonosulfate, and can be used for quickly degrading and deeply mineralizing a plurality of organic pollutants such as sulfonamides, tetracyclines and phenols in a wide range of pH (Potential of Hydrogen) 111. The method realizes treatment of wastes with wastes, overcomes the technical bottleneck that the carbon-based catalyst is difficult to thermally regenerate at high temperature, has the characteristics of high activity, long service life and low cost, and has a wide application prospect in the field of advanced treatment of organic pollutants in water.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials and water treatment engineering technology, specifically a self-templating preparation method, regeneration method, and application of a heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst. Background Technology

[0002] With the rapid development of industries such as pharmaceuticals and chemicals, persistent organic pollutants (POPs), represented by sulfonamide antibiotics (such as sulfadiazine SMZ) and endocrine disruptors (such as bisphenol A BPA), continuously enter the aquatic environment. Due to their poor biodegradability, easy accumulation, and biotoxicity, they pose a serious threat to ecosystems and human health. Conventional water treatment processes are insufficient for the efficient removal and deep mineralization of these pollutants. Advanced oxidation technologies (AOPs) based on persulfate (PMS) have become one of the effective means to degrade these recalcitrant organic pollutants because they can generate strong oxidizing free radicals.

[0003] Activation of PMS typically requires a catalyst, and carbon-based catalysts have attracted much attention due to their wide availability, environmental friendliness, and lack of metal leaching risk. However, existing carbon-based catalysts face two common bottlenecks in practical applications: First, they have poor structural stability and are easily "poisoned" and deactivated during catalysis due to the adsorption of organic intermediates. Conventional solvent regeneration is incomplete, and even the most thorough high-temperature aerobic thermal regeneration (such as calcination at 700℃) can lead to the oxidation and erosion of the ordinary biochar framework, making them unusable and resulting in a short lifespan. Second, they have weak engineering applicability; powdered catalysts are easily lost and difficult to separate and recover in actual water treatment, which restricts their large-scale application.

[0004] Meanwhile, my country's traditional Chinese medicine industry generates tens of millions of tons of extraction residues such as licorice residue annually, which are currently mostly disposed of through incineration or landfill, resulting in resource waste and environmental pressure. Therefore, developing a non-metallic carbon catalyst that can utilize traditional Chinese medicine waste residue as raw material and possesses high catalytic activity, excellent structural stability, and good engineering applicability is of great significance for promoting "waste-to-waste" treatment and achieving efficient and sustainable management of recalcitrant organic pollutants. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a self-template preparation method, regeneration method and application of a heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst. Utilizing licorice residue, a traditional Chinese medicine rich in endogenous minerals, as a self-template carbon framework precursor, and through co-doping with urea and boric acid followed by one-step pyrolysis, boron and nitrogen atoms are covalently anchored in the carbon framework under the fluxing and lattice-stabilizing effects of boric acid. This successfully constructs a stable structure capable of withstanding aerobic calcination at 700℃, thereby enabling the catalyst to be completely regenerated through simple high-temperature heat treatment, significantly extending its service life.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: This invention provides a self-template preparation method for a thermally oxidizing boron-nitrogen co-doped carbon catalyst. This method innovatively utilizes licorice residue, a traditional Chinese medicine rich in endogenous minerals, as a self-template carbon framework precursor. Through the synergistic effect of boric acid and urea, a structurally stable catalyst is constructed in a one-step pyrolysis process. The method specifically includes the following steps: S1. After boiling, washing, and drying the licorice residue, pulverize it into powder. S2. Grind urea and boric acid together, then add them to the licorice residue powder obtained in S1, so that the mass ratio of licorice residue powder, urea and boric acid is 1:1:1, and mix them evenly. S3. The mixture obtained in S2 is placed in a high-temperature tube furnace and calcined at high temperature in an air atmosphere. Using the endogenous minerals in the licorice residue as a self-template, under the fluxing and lattice stabilizing effect of boric acid at high temperature, boron atoms and nitrogen atoms are covalently anchored in the carbon skeleton, thereby forming a highly stable heat-resistant oxidation-resistant bonded structure. S4. The calcined product is cooled, ground, washed, and dried to obtain the heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst.

[0007] Preferably, the high-temperature calcination in step S3 is carried out at a temperature of 600-800℃, a heating rate of 5-15℃ / min, and a holding time of 1-3 hours; more preferably, the calcination conditions are: holding at 700℃ for 2 hours and a heating rate of 10℃ / min.

[0008] This invention further provides a method for regenerating the thermally resistant boron-nitrogen co-doped carbon catalyst prepared by the aforementioned method. This catalyst, due to its unique thermally resistant structure, represents a significant breakthrough in regeneration technology. The regeneration method includes thermal regeneration or solvent regeneration. The thermal regeneration involves heat-treating the deactivated catalyst in an oxygen-containing atmosphere at 600-800°C for 1-3 hours, preferably at 700°C for 2 hours, to efficiently restore its catalytic activity.

[0009] The solvent regeneration process involves immersing the deactivated catalyst in at least one of the following solutions: acidic solution (e.g., 0.05-0.5 mol / L hydrochloric acid), alkaline solution (e.g., 0.05-0.5 mol / L sodium hydroxide solution), or organic alcohol solution (e.g., ethanol with a concentration of not less than 90%), followed by washing until neutral and drying.

[0010] Thermal regeneration is the preferred regeneration method of this invention because it is simple to operate, regenerates thoroughly, and produces no secondary waste liquid.

[0011] The present invention also provides the application of the heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst prepared by the above method in the degradation of organic pollutants in water by activated persulfate (PMS).

[0012] The catalyst can efficiently activate PMS to generate strong oxidizing free radicals, exhibiting broad-spectrum and efficient degradation and deep mineralization capabilities for a variety of typical organic pollutants, including sulfadiazine (SMZ), oxytetracycline (OTC), and bisphenol A (BPA). The recommended catalyst dosage is 0.3-0.6 g / L, and the PMS concentration is 0.1-0.5 g / L. The system maintains high reaction efficiency across a wide pH range of 1-11.

[0013] The present invention provides a self-template preparation method, regeneration method, and application of a thermally resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst. By employing this method, the following beneficial effects are achieved: (1) By using the self-template method and boron-nitrogen co-doping strategy, a stable carbon skeleton that can withstand high-temperature oxygen calcination at 700℃ was constructed, making low-cost and high-efficiency high-temperature thermal regeneration possible. After multiple regenerations, the catalyst activity can still recover more than 95%, which greatly extends the catalyst life and solves the key problem of traditional biochar being ablated during high-temperature regeneration. (2) Using licorice residue, a waste product of the Chinese medicine industry, as the main raw material not only reduces the cost of catalysts, but also provides a new way for the high-value utilization of Chinese medicine waste residue, which is in line with the concept of green circular economy. (3) The catalyst prepared has abundant pore structure and active sites, which can not only rapidly degrade pollutants, but also achieve a total organic carbon (TOC) removal rate of up to 74%, indicating that it has deep mineralization ability and can effectively avoid the accumulation of toxic intermediate products. (4) In addition to the preferred thermal regeneration, the catalyst is also compatible with various chemical solvent regeneration methods such as acid washing, alkali washing, and alcohol washing. The regeneration strategy can be flexibly selected according to the actual wastewater composition and deactivation cause, which enhances its applicability and robustness in complex water treatment environments. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 The image shows the microstructure of the thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst (LBNC) prepared in an embodiment of the present invention.

[0015] Figure 2 This diagram illustrates the environmental adaptability and application scope of an embodiment of the present invention.

[0016] Figure 3 This is a diagram showing the catalyst regeneration performance of an embodiment of the present invention. Detailed Implementation

[0017] Example 1: This embodiment details the preferred preparation process of the catalyst (LBNC) of the present invention.

[0018] Step 1 (Raw Material Pretreatment): Take 100g of waste residue from the extraction of commercially available licorice root, boil it in tap water for 2 hours to fully dissolve and remove water-soluble impurities and some ash. Then, wash repeatedly with plenty of deionized water until the pH of the washing solution is neutral. Place the washed licorice residue in a forced-air drying oven and dry it at 80℃ for 12 hours until constant weight. After removal, grind it using a pulverizer and pass it through a 100-mesh sieve to obtain uniform licorice residue powder.

[0019] Step 2 (Precursor Preparation): Accurately weigh 5.0g of the licorice residue powder obtained in Step 1, 5.0g of analytical grade urea, and 5.0g of analytical grade boric acid, and place them in an agate mortar. First, mix the urea and boric acid and grind them thoroughly for 10 minutes to allow for initial reaction and homogeneous mixing. Then, add the licorice residue powder and continue grinding for 15 minutes until the entire mixture is a uniform powder with no obvious particle texture, resulting in a precursor mixture with a mass ratio of 1:1:1. In this process, boric acid acts as a flux and dehydrating agent, helping to anchor the nitrogen source (urea) in situ onto the licorice residue framework.

[0020] Step 3 (Self-template pyrolysis carbonization): The precursor mixture obtained in Step 2 is evenly spread in a quartz boat and placed in the isothermal zone of a tube furnace. Under air atmosphere, the furnace temperature is increased from room temperature to 700℃ at a heating rate of 10℃ / min. After reaching 700℃, it is calcined at this temperature for 2 hours. During this high-temperature calcination process, the organic components in the licorice residue are carbonized, while its endogenous minerals (such as K, Ca, Mg salts, etc.) act as "self-templates" to guide the formation of porous structures; B2O3 produced by the decomposition of boric acid acts as a flux, promoting the doping and solid solution of boron and nitrogen atoms into the carbon framework, forming BC, BNC, and other heat-resistant oxidation-resistant bond structures.

[0021] Step 4 (Product Post-processing): After pyrolysis, turn off the heating power and allow the tube furnace to cool naturally to room temperature under ventilation. Remove the quartz boat to obtain a black blocky solid. Grind it again into a fine powder and wash it repeatedly with deionized water under ultrasonic assistance until the conductivity of the washing solution is basically constant to remove residual soluble salts and unreacted boron and nitrogen species from the surface. Finally, place the washed solid in a 60°C oven and dry for 12 hours to obtain the final heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst (LBNC) powder.

[0022] Figure 1(a) and (b) are SEM and TEM images of the obtained LBNC catalyst, respectively. The SEM image shows that the catalyst exhibits a rich, spherical porous structure formed by endogenous mineral templates, with well-developed pores. The TEM image further confirms that it is an amorphous carbon material, but the presence of clear layered lattice fringes indicates a certain degree of graphitization tendency and abundant edge defects, features that are beneficial to enhancing catalytic activity.

[0023] Example 2: This embodiment is used to verify the broad-spectrum efficiency of the catalyst (LBNC) of the present invention in the degradation of different types of organic pollutants by activating persulfate (PMS).

[0024] The experiments were conducted in 250 mL Erlenmeyer flasks using a batch experiment model. First, a series of simulated organic pollutant stock solutions with a concentration of 20 mg / L were prepared. The pollutants were: sulfadiazine (SMZ), oxytetracycline (OTC), 3-aminophenol (3-AP), sulfadiazine (SDZ), chlortetracycline hydrochloride (CTC), sulfamethoxazole (SMX), and bisphenol A (BPA). For each experiment, 50 mL of the target pollutant solution was placed in an Erlenmeyer flask and placed on a magnetic stirrer at a stirring speed of 300 rpm.

[0025] The specific degradation steps are as follows: (1) Add 25 mg of LBNC catalyst (addition amount 0.5 g / L) to the reaction solution and stir in the dark for 10 minutes to allow the system to reach adsorption-desorption equilibrium.

[0026] (2) Quickly add 25 mg of persulfate (PMS, analytical grade, dosage 0.5 g / L) to initiate the catalytic oxidation reaction. Record this moment as the reaction start time (t=0).

[0027] (3) At the set time intervals (e.g., 0, 10, 20, 30, 40, 50, 60 minutes), take out about 3 mL of reaction solution with a syringe and immediately filter it through a needle filter fitted with a 0.22 μm nylon membrane to separate the catalyst. Collect the filtrate in a sample vial for testing.

[0028] (4) The concentration of residual pollutants in the filtrate was determined using high-performance liquid chromatography (HPLC) or ultraviolet-visible spectrophotometry (for pollutants with characteristic absorption peaks). The degradation rate (η) was calculated using the formula: η = (C0 - C t ) / C0×100%, where C0 is the initial concentration, C t Let t be the concentration at time t.

[0029] Experimental results are as follows Figure 2As shown in (a), the removal rates of all seven pollutants tested exceeded 80% within 60 minutes. Among them, the degradation effect on SMZ was particularly outstanding, with a removal rate of 85.2% within 60 minutes, indicating that the LBNC / PMS system has excellent broad-spectrum catalytic oxidation ability and can adapt to the complex pollutant composition in actual water bodies.

[0030] Example 3: This example is used to investigate the adaptability of the LBNC / PMS catalytic system to the initial pH value of the reaction solution.

[0031] Using SMZ (20 mg / L) as the target pollutant, the dosage of both catalyst and PMS was fixed at 0.5 g / L (same as in Example 2). The initial pH of the simulated SMZ wastewater was precisely adjusted to 1.0, 3.0, 5.0, 7.0, 9.0, and 11.0, respectively, by adding 0.1 M HCl or 0.1 M NaOH solution dropwise.

[0032] Under each set initial pH condition, the degradation experimental steps in Example 2 were repeated. The concentration changes of SMZ at different reaction times were recorded.

[0033] Experimental results are as follows Figure 2 As shown in (b), the LBNC / PMS system maintained high degradation efficiency for SMZ over a wide pH range from strongly acidic (pH=1) to strongly alkaline (pH=11) for 60 minutes, with a removal rate consistently above 80%. This demonstrates that the catalytic system possesses excellent pH adaptability and environmental robustness, eliminating the need for stringent pre-adjustment of the actual wastewater pH, thus significantly reducing operating costs and treatment complexity.

[0034] Example 4: This embodiment aims to verify the core advantage of the catalyst of the present invention—that it can be regenerated and recycled multiple times through simple high-temperature aerobic heat treatment.

[0035] (1) Initial Activity Test and Catalyst Deactivation: First, following the conditions of Example 2, a degradation experiment was conducted on SMZ (20 mg / L) using fresh LBNC catalyst, completing one 60-minute catalytic cycle. After the reaction, the catalyst was recovered by vacuum filtration, washed three times with deionized water, and dried at 60°C. The recovered catalyst was then used again in the next round of the same degradation experiment. This process was repeated for four cycles. Figure 3 As shown in (a), with the increase of the number of cycles, the activity of the catalyst gradually decreases due to the adsorption of reaction intermediates on the catalyst surface and the coverage of active sites. By the fourth cycle, the SMZ removal rate had decreased significantly, indicating that the catalyst was "deactivated".

[0036] (2) Thermal regeneration operation: The catalyst that has been "deactivated" after four cycles is recovered, washed, and dried. Then, it is placed in a quartz boat in a tube furnace and heated to 700°C at 10°C / min in air atmosphere, and calcined at this temperature for 2 hours. After calcination, it is naturally cooled to room temperature to obtain the catalyst after the first thermal regeneration, labeled as Re-LBNC-1.

[0037] (3) Activity test after regeneration: Using Re-LBNC-1 as a catalyst, repeat the SMZ degradation experiment in step (1) to test its catalytic activity in the 5th cycle.

[0038] (4) Multiple thermal regeneration cycles: To examine the long-term stability of the catalyst structure, Re-LBNC-1 used in step (3) was recovered again, and the thermal regeneration process of step (2) was repeated to obtain the second regenerated catalyst Re-LBNC-2. This process can be repeated for a third regeneration (Re-LBNC-3). Activity tests were performed after each regeneration.

[0039] Experimental results are as follows Figure 3 (a) and Figure 3 As shown in (b), after the first thermal regeneration (700°C, 2 h, air), the catalyst activity was fully recovered, and the SMZ removal rate in the fifth cycle rebounded to 85.2%, matching the initial activity of the fresh catalyst. More importantly, after three consecutive high-temperature thermal regeneration cycles, the SMZ removal rate of the catalyst (Re-LBNC-3) remained stable at over 95% of its initial activity. This irrefutably demonstrates that the carbon framework constructed by boron-nitrogen co-doping in this invention possesses excellent thermal oxidation resistance, and the effectiveness and sustainability of the low-cost regeneration strategy of "high-temperature thermal regeneration" are fully verified.

[0040] Example 5: This embodiment illustrates that, in addition to thermal regeneration, the catalyst of the present invention can also be regenerated through various chemical solvent cleaning methods to address different types of deactivation causes (such as the adsorption of specific pollutants).

[0041] The LBNC catalyst sample that had been "deactivated" after four cycles in step (1) of Example 4 was divided into four portions.

[0042] First sample: serving as a control group for inactivated cells that did not regenerate.

[0043] The second part (acid washing and regeneration): The deactivated catalyst was immersed in 100 mL of 0.1 M hydrochloric acid (HCl) solution and sonicated at room temperature for 2 hours. Afterwards, it was repeatedly washed with deionized water until the pH of the filtrate was neutral, and then dried at 60 °C.

[0044] The third part (alkali washing and regeneration): The deactivated catalyst was immersed in 100 mL of 0.1 M sodium hydroxide (NaOH) solution and sonicated at room temperature for 2 hours. Afterwards, it was repeatedly washed with deionized water until the pH of the filtrate was neutral, and then dried at 60 °C.

[0045] Fourth part (alcohol washing and regeneration): The deactivated catalyst was immersed in 100 mL of 95% ethanol (C2H5OH) solution and sonicated at room temperature for 2 hours. Afterwards, it was washed several times with deionized water and dried at 60°C.

[0046] The catalysts regenerated using different solvents were then used in a new round of SMZ degradation experiments (under the same conditions as in Example 2). Their catalytic activity after regeneration was tested.

[0047] The results are as follows Figure 3 As shown in (c), compared with the deactivated control group, the catalysts treated with acid washing, alkali washing, and alcohol washing all showed significant recovery of activity, with SMZ removal rates recovering to over 80%. This indicates that the LBNC catalyst possesses good chemical stability and can withstand cleaning under different chemical environments, providing a flexible and diverse regeneration strategy for its application in the treatment of complex wastewater.

[0048] Example 6: To highlight the key role of co-doping with boric acid and urea in this invention, this example is set up as a comparative example.

[0049] Procedure: Take only 5.0 g of the licorice residue powder prepared in Example 1, without adding urea and boric acid, and place it directly in a tube furnace. Under an air atmosphere, heat to 700°C at a rate of 10°C / min and calcine at this temperature for 2 hours. After cooling, unadulterated licorice residue biochar is obtained, denoted as BC.

[0050] Thermal stability comparison test: Equal masses of LBNC (prepared in Example 1) and BC were weighed and placed in a muffle furnace, and calcined at 700°C for 2 hours in air atmosphere. They were weighed after cooling.

[0051] Results: After calcination, BC suffered a mass loss of over 70%, essentially turning into ash, and its structure was completely destroyed. In contrast, LBNC experienced a mass loss of less than 15% under the same conditions, and retained its porous structure and catalytic activity after calcination (as shown in Example 4). This comparative experiment strongly demonstrates that boron-nitrogen co-doping is the fundamental reason for endowing the carbon framework with thermal oxidation resistance and enabling high-temperature regeneration.

Claims

1. A self-template preparation method for a thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst, characterized in that: Using licorice residue containing endogenous minerals as a self-templated carbon skeleton precursor, the specific steps include: S1. After boiling, washing, and drying the licorice residue, pulverize it into powder. S2. Grind urea and boric acid together, then add them to the licorice residue powder obtained in S1, so that the mass ratio of licorice residue, urea and boric acid is 1:1:1, and mix them evenly. S3. The mixture obtained in S2 is placed in a high-temperature tube furnace and calcined at high temperature in an air atmosphere. The endogenous minerals in the licorice residue are used as self-templates to form a stable porous carbon skeleton structure under the action of boric acid flux. S4. The calcined product is cooled, ground, washed, and dried to obtain a heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst.

2. The self-templating preparation method of a thermally resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 1, characterized in that: In S3, the high-temperature calcination temperature is 600-800℃, the heating rate is 5-15℃ / min, and the holding time is 1-3 hours.

3. The self-templating preparation method of a thermally resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 2, characterized in that: The conditions for high-temperature calcination are controlled as follows: temperature 700℃, heating rate 10℃ / min, and holding time 2 hours.

4. A method for regenerating a thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst, characterized in that: The catalyst is prepared by the method according to any one of claims 1-3, and the regeneration method includes thermal regeneration or solvent regeneration. The thermal regeneration specifically refers to: The used catalyst is heat-treated at 600-800℃ for 1-3 hours in an oxygen-containing atmosphere; The solvent regeneration specifically involves: The used catalyst is immersed in at least one of an acidic solution, an alkaline solution, or an organic alcohol solution, then washed until neutral and dried.

5. The regeneration method for a thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 4, characterized in that: The conditions for thermal regeneration are as follows: in an air atmosphere, the temperature is increased to 700°C at a rate of 5-15°C / min, and held at 700°C for 2 hours.

6. The regeneration method for a thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 4, characterized in that: In the solvent regeneration process, the acidic solution is a 0.05-0.5 mol / L hydrochloric acid solution, the alkaline solution is a 0.05-0.5 mol / L sodium hydroxide solution, and the organic alcohol solution is an ethanol solution with a concentration of not less than 90%.

7. The regeneration method for a thermally resistant, oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 6, characterized in that: The acidic solution is a 0.1 mol / L hydrochloric acid solution, the alkaline solution is a 0.1 mol / L sodium hydroxide solution, and the organic alcohol solution is a 95% ethanol solution.

8. The application of the heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst prepared by the method according to any one of claims 1-3 in the activation of persulfate for the degradation of organic pollutants in water.

9. The application of the heat-resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 8, characterized in that: The organic pollutant is selected from at least one of sulfadiazine, oxytetracycline, 3-aminophenol, sulfadiazine, chlortetracycline hydrochloride, sulfamethoxazole, or bisphenol A.

10. The application of the thermally resistant oxidation-resistant boron-nitrogen co-doped carbon catalyst according to claim 8, characterized in that: When applied, the catalyst is added at a rate of 0.3-0.6 g / L, the persulfate concentration is 0.1-0.5 g / L, and the pH of the reaction system is 1-11.

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