A nitrogen-boron co-doped waste tea biochar adsorbent and its preparation method and application

Abstract

The present invention relates to the field of wastewater treatment, and more specifically to a nitrogen-boron co-doped waste tea biochar adsorbent, and its preparation method and application. Dihydrogen diamine and boric acid are first dissolved in deionized water to form a precursor, and then waste tea particles are added to the mixed solution. The mixed solution is freeze-dried to obtain an adsorbent powder, and then the adsorbent powder is carbonized in an inert atmosphere at high temperature to obtain a nitrogen-boron co-doped waste tea biochar adsorption material. The material has simple components, a high specific surface area and high adsorption performance, a significant adsorption effect on chloroquine phosphate and hydroxychloroquine sulfate, and an excellent adsorption effect on drugs in water bodies. The adsorbent can be reused multiple times, is low in cost, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, and in particular to a nitrogen and boron co-doped waste tea biochar adsorbent, and a preparation method and application thereof. Background Art

[0002] With the acceleration of industrialization and the rapid development of the pharmaceutical industry, wastewater generated during the production and use of various chemically synthesized drugs is increasing. This wastewater contains a certain amount of difficult-to-degrade drug residues such as antibiotics and antimalarials, such as chloroquine phosphate and hydroxychloroquine sulfate. Chloroquine phosphate, a widely used antimalarial and immunomodulatory drug, is persistent and bioaccumulative. If discharged directly into the natural environment without proper treatment, it can potentially harm ecosystems, including the increase of microbial resistance, toxic effects on aquatic organisms, and drinking water safety issues.

[0003] To address this challenge, environmental engineering research is focusing on developing efficient and environmentally friendly wastewater treatment technologies. In this context, biochar, a porous carbonaceous material derived from biomass pyrolysis, has been widely used in water treatment to remove pollutants by adsorption due to its large surface area, rich pore structure, and stable chemical properties. However, conventional biochar has limited adsorption efficiency for certain refractory drug molecules, such as chloroquine phosphate, under specific conditions.

[0004] In recent years, the modification of biochar through non-metallic element doping has become a cutting-edge research hotspot. Nitrogen-boron co-doped biochar involves physically or chemically introducing nitrogen and boron into the original biochar, significantly optimizing its physical and chemical properties. Nitrogen enriches the biochar's surface with functional groups, such as amino and amide groups, enhancing its hydrophilicity and charge adsorption properties. The addition of boron, on the other hand, can alter the carbon material's electronic structure, creating more adsorption sites and potentially enhancing the adsorption capacity and selectivity for chlorinated organic drugs like chloroquine phosphate through coordination bonds.

[0005] Therefore, as a new and highly efficient adsorbent, nitrogen-boron co-doped biochar has broad application prospects in treating chloroquine phosphate wastewater, providing important technical support for addressing the problem of refractory drug contamination. In-depth research into its preparation process, structural characteristics, and adsorption mechanism will help advance wastewater treatment technology towards greener and more efficient approaches.

[0006] The key to adsorbing chloroquine phosphate and hydroxychloroquine sulfate is to find an effective adsorbent. From an environmental perspective, it is best to use wood charcoal directly. However, this method is very inefficient. In order to improve the adsorption efficiency of the adsorbent, the biochar adsorbent material is modified and metal elements or non-metallic elements are introduced to enhance its performance. Chinese invention patent CN202210471869.9 discloses a high thermal stability carbonaceous adsorbent based on boron-nitrogen modified lignin. The adsorbent uses lignin as a carbon source, mixes lignin with boric acid and urea, and obtains a stable lignin-based BCN adsorbent after high-temperature heat treatment. It has poor adsorption effect on the aromatic rings of chloroquine phosphate and hydroxychloroquine sulfate, and its removal effect is greatly limited. Chinese invention patent CN202310259789.1 discloses a monovalent copper-doped boron-carbon-nitrogen nanofiber adsorbent, which is introduced into boron-carbon-nitrogen nanofibers to achieve a strong sulfur-copper (S-Cu) coordination effect between metal adsorption sites and thiophene sulfides, thereby obtaining higher adsorption capacity and adsorption selectivity. However, the adsorbent produced by this method has the risk of copper dissolution, new pollutants are likely to appear during the treatment process, and the cost of the adsorbent is high. Summary of the Invention

[0007] In response to the above problems, the present invention provides a nitrogen-boron co-doped waste tea biochar adsorbent and its preparation method and application. Dihydrogen diamine and boric acid are first dissolved in deionized water to form a precursor, and then waste tea particles are added to the mixed solution. The mixed solution is freeze-dried to obtain an adsorbent powder, and then the boric acid / dihydrogen diamine / waste tea particles are carbonized in an inert atmosphere at high temperature to obtain a nitrogen-boron co-doped waste tea biochar adsorbent material. The material has a simple composition, a high specific surface area and high adsorption performance, a significant adsorption effect on chloroquine phosphate and hydroxychloroquine sulfate, and an excellent adsorption effect on drugs in water bodies. The adsorbent can be reused multiple times, has low cost, and has good application prospects.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for preparing a nitrogen-boron co-doped waste tea biochar adsorbent is as follows:

[0010] S1. Using waste tea leaves as raw materials, the waste tea leaves are crushed by a crusher to obtain waste tea particles;

[0011] S2. dissolving dihydrogen diamine and boric acid in deionized water to form a mixed solution;

[0012] S3. The waste tea particles are added to the mixed solution, and the precursor powder is formed by vacuum drying after oscillation in an ultrasonic cleaner;

[0013] S4. The precursor powder is placed in a tubular furnace under an inert atmosphere and calcined at high temperature. After cleaning and drying, nitrogen and boron co-doped waste tea biochar adsorption material is obtained.

[0014] Preferably, the particle size of the waste tea particles in step S1 is 60-100 mesh.

[0015] Preferably, the amount of dihydrodiamine added in step S2 is 3-5 g, the amount of boric acid added is 3-5 g, the molar ratio of dihydrodiamine to boric acid is 1-1.2: 1, and the deionized water added is 50-100 mL. Appropriate boron doping will lead to uneven distribution of electrons on the surface of the carbon material, thereby producing more active sites, which is conducive to enhancing the adsorption performance. Appropriate nitrogen doping will produce pyrrole nitrogen, pyridinic nitrogen and graphitic nitrogen, enhancing hydrophilicity and charge adsorption properties. The addition of appropriate boron elements changes the electronic structure of the carbon material, creates more adsorption sites, and improves the adsorption capacity and selectivity of chlorine-containing organic drugs such as chloroquine phosphate through coordination bonds.

[0016] Preferably, the amount of the waste tea particles added in step S3 is 4 g, and the oscillation time is 1-2 h.

[0017] Preferably, the inert gas in step S4 is nitrogen or helium, the heating rate is 5-10°C / min, the calcination temperature is 600-800°C, and the calcination time is 2h.

[0018] The application of the nitrogen and boron co-doped waste tea biochar adsorption material obtained by the above preparation method is as follows:

[0019] Nitrogen and boron co-doped waste tea biochar adsorption material was applied to wastewater treatment.

[0020] Preferably, nitrogen and boron co-doped waste tea biochar adsorption material is put into wastewater containing chloroquine phosphate and hydroxychloroquine sulfate for selective adsorption of chloroquine phosphate and hydroxychloroquine sulfate therein.

[0021] Preferably, the nitrogen-boron co-doped waste tea biochar adsorption material is added to a wastewater solution containing chloroquine phosphate and hydroxychloroquine sulfate, stirred and allowed to stand for 12-36 hours, a stirring speed of 200-600 rpm, and a standing time of 0.5-3 hours. The nitrogen-boron co-doped waste tea biochar selectively adsorbs chloroquine phosphate and hydroxychloroquine sulfate in the wastewater, thereby effectively reducing the concentrations of chloroquine phosphate and hydroxychloroquine sulfate in the wastewater.

[0022] Preferably, the dosage of nitrogen and boron co-doped waste tea biochar adsorption material is 0.5-2 g / L, the initial concentration range of chloroquine phosphate and hydroxychloroquine sulfate is 10-400 mg / L, the pH value is 5-7, the temperature is 25-45°C, and the adsorption time is selected as 12-48h, which can maintain high adsorption efficiency and selective adsorption capacity.

[0023] Preferably, the initial concentration range of chloroquine phosphate and hydroxychloroquine sulfate is 200 mg / L, the pH value is 6, and the adsorption time is 24 h, and the adsorption effect is optimal.

[0024] Compared with the existing technology, the present invention has the following beneficial effects:

[0025] (1) The nitrogen-boron co-doped waste tea biochar obtained by the preparation method of the present invention has an ideal nitrogen and boron content, wherein the nitrogen content is 11.09% and the boron content is 13.52%. It has a blocky pore structure and a high specific surface area, which can reach up to 291.013m 2 / g, and its surface contains active adsorption sites formed by nitrogen and boron elements, which ensures its excellent adsorption performance and stability for chloroquine phosphate and hydroxychloroquine sulfate. It is specially used for the efficient adsorption and removal of chloroquine phosphate and hydroxychloroquine sulfate in water bodies.

[0026] (2) The present invention successfully loads the nitrogen element of dihydrodiamine and the boron element of boric acid onto waste tea biochar through the strong acidity of boric acid. Since biochar has a large specific surface area and many adsorption sites, it can efficiently adsorb organic matter in wastewater onto the surface of biochar, thereby increasing the adsorption capacity, which can reach up to 204.365 mg / g. In contrast, the adsorption capacity of general commercial biochar is only 53.476 mg / mg, which is 282% higher than that of the prior art.

[0027] (3) During the modification process, the adsorbent produced three nitrogen species: pyrrole nitrogen, pyridinium nitrogen, and graphite nitrogen, which enhanced the adsorption of chloroquine phosphate and hydroxychloroquine sulfate and improved the adsorption efficiency. Pyrrole nitrogen and pyridinium nitrogen are typical nitrogen-containing functional groups. They have a certain alkalinity and can form ionic bonds or hydrogen bonds with acidic molecules such as chloroquine phosphate (CQ) and hydroxychloroquine sulfate (HCQ), thereby enhancing the affinity for CQ and HCQ through charge adsorption. Graphite nitrogen is located in the graphitized structure of biochar, which may change the electronic structure of the carbon material and increase its surface charge density, thereby enhancing the adsorption performance of charged or polar pollutants such as CQ and HCQ. The pyrrole and pyridinium ring structures themselves are aromatic and can form π-π stacking with CQ and HCQ molecules. This non-covalent interaction helps to improve the binding strength during the adsorption process, especially for compounds containing aromatic structures such as CQ and HCQ.

[0028] (3) This adsorbent utilizes the weak acidity of wastewater to keep the adsorbent in the optimal working pH range. The reaction process does not require adjustment of the pH value of the wastewater. It has high adsorption efficiency for chloroquine phosphate and hydroxychloroquine sulfate wastewater, good removal effect, and low cost for wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The zeta potential diagram (1a) and adsorption curve diagram (1b) of Example 1 at different pH values ​​are shown;

[0030] Figure 2 It is the adsorption curve diagram of chloroquine phosphate and hydroxychloroquine sulfate at different initial concentrations of Example 2;

[0031] Figure 3 This is the adsorption curve of nitrogen and boron co-doped waste tea biochar adsorbent at different adsorption times in Example 3. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0033] Example 1: Study on the adsorption performance of nitrogen-boron co-doped waste tea biochar adsorbent at different initial pH values ​​of chloroquine phosphate and hydroxychloroquine sulfate

[0034] (1) Preparation of Nitrogen-Boron Co-doped Waste Tea Biochar Adsorbent: A certain amount of waste tea particles (purchased from a tea factory in Fujian, China) were ground with a crusher and passed through a 100-mesh sieve. They were washed three times with distilled water and then vacuum-dried. 3 g of DICY and 3 g of H3BO3 were weighed and dissolved in 50 mL of deionized water. The mixture was stirred magnetically for 0.5 h. After DICY and H3BO3 dissolved to form a precursor, 4 g of waste tea particles (100 mesh) were added to the mixed solution. The mixed solution was shaken using an ultrasonic cleaner for 0.5 h. After the mixed solution was vacuum-dried, it was evenly ground and placed in a quartz boat. The mixture was heated to 800 °C at a heating rate of 5 °C per minute under a nitrogen atmosphere and calcined for 2 h. The material was washed with deionized water and dried in an oven at 80 °C to obtain NB@TBC.

[0035] (2) Experimental procedure: CQ and HCQ solutions with different initial pH values ​​(2-10) were prepared, where the concentrations of CQ and HCQ were both 400 mg / L. Weigh 0.01 g of each of 9 NB@TBC materials and place them in 50 mL round-bottom flasks. Pour 10 mL of the solution containing CQ and HCQ into the flask and shake for 24 h at 298 K and 300 rpm. Adjust the pH value with NaOH and HCl, and measure the adsorption effect when the initial pH value of the solution containing CQ and HCQ is 2, 3, 4, 5, 6, 7, 8, 9, and 10. Shake horizontally at 25°C and 300 rpm for 24 h. The supernatant was extracted with a 5 mL syringe and filtered with a 0.45 μm filter membrane. After dilution of the obtained filtrate, the pollutant concentration in the filtrate was detected by UV spectrophotometer.

[0036] (3) Test results are shown in the attached Figure 1 NB@TBC( Figure 1 The pH (zero charge) in (a) is 4.91. When the pH exceeds the pH (zero charge), the negative charge on the NB@TBC surface promotes adsorption. Previous research results show that the pKa value of CQ is 8.4, indicating that CQ exists as a cation at pH < 8.4. The pKa value of HCQ is 9.7, indicating that HCQ exists as a cation at pH values ​​below 9.7.

[0037] The experimental results show that: when the pH value is 5.3-8.3 ( Figure 1 In b), the removal efficiency of CQ and HCQ is high. When the pH is 6.0, the adsorption effect of NB@TBC is the best, which is related to the electrostatic effect.

[0038] Example 2: Study on the adsorption performance of nitrogen-boron co-doped waste tea biochar adsorbent at different initial concentrations of chloroquine phosphate and hydroxychloroquine sulfate

[0039] (1) Preparation of adsorbent: A certain amount of waste tea particles (purchased from a tea factory in Fujian, China) was ground with a crusher and passed through a 100-mesh sieve, washed three times with distilled water, and then vacuum-dried; 5g of DICY and 5g of H3BO3 were weighed and dissolved in 100mL of deionized water, and stirred with a magnetic force for 2h. After DICY and H3BO3 dissolved to form a precursor, 4g of waste tea particles (100 mesh) were added to the mixed solution, and the mixed solution was shaken with an ultrasonic cleaner for 2h. After the mixed solution was vacuum-dried, it was evenly ground and placed in a quartz boat. The temperature was raised to 800℃ at a heating rate of 5℃ per minute under a nitrogen atmosphere, and calcined for 2h. The material was washed with deionized water and dried in an oven at 80℃ to obtain NB@TBC. The specific surface area of ​​the prepared NB@TBC was measured to be 291.013m 2 / g.

[0040] (2) Experimental procedure: CQ and HCQ with different initial concentrations (10-400 mg / L) were prepared separately, and the pH was adjusted to 6 with HCl. 0.01 g of each NB@TBC material was weighed and placed in a 50 mL round-bottom flask. 10 mL of CQ and HCQ solutions with different initial concentrations were poured into the flask, and the mixture was shaken and adsorbed in a shaker at 298 K and 300 rpm for 24 h.

[0041] (3) The experimental results show that when the initial concentrations of CQ and HCQ solutions are >200 mg / L (the concentrations of CQ and HCQ in the solutions are the same, both >200 mg / L), the adsorption effect of NB@TBC is the best, reaching 204.365 mg / g.

[0042] (See Appendix Figure 2 ).

[0043] The reasons are as follows: ① Saturation of adsorption sites. At high initial concentrations, the number of chloroquine phosphate molecules is sufficient to fully occupy the adsorption sites of the nitrogen-boron co-doped biochar, fully utilizing its specific surface area and pore structure, thereby achieving a high adsorption capacity. ② Reduced competition. In high-concentration solutions, competition between target pollutants is reduced, allowing more chloroquine phosphate molecules to contact the biochar surface and be adsorbed, rather than competing with each other for adsorption sites.

[0044] Example 3: Study on the adsorption performance of nitrogen-boron co-doped waste tea biochar adsorbent at different adsorption times

[0045] (1) Preparation of adsorbent: A certain amount of waste tea leaves (purchased from a tea factory in Fujian, China) were ground with a crusher and passed through a 100-mesh sieve. The mixture was washed three times with distilled water and then vacuum-dried. 4 g of DICY and 4 g of H3BO3 were weighed and dissolved in 100 mL of deionized water. The mixture was stirred magnetically for 2 h. After the DICY and H3BO3 dissolved to form a precursor, 4 g of waste tea leaves (100 mesh) were added to the mixed solution. The mixed solution was shaken in an ultrasonic cleaner for 2 h. After vacuum drying, the mixed solution was evenly ground and placed in a quartz boat. The mixture was heated to 800°C at a heating rate of 5°C per minute under a nitrogen atmosphere and calcined for 2 h. The material was washed with deionized water and dried in an oven at 80°C to obtain NB@TBC.

[0046] (2) Experimental procedure: 400 mg / L CQ and 400 mg / L HCQ were prepared respectively, and the pH was adjusted to 6 with HCl. 0.01 g of NB@TBC material was weighed and placed in a 50 mL round-bottom flask, and 10 mL of CQ and HCQ solutions were poured into the flask. The mixture was shaken and adsorbed in a shaker at 298 K and 300 rpm for 0-48 h.

[0047] A certain amount of CQ and HCQ stock solution was taken to prepare 20 mg / L CQ and HCQ working solutions (the concentration of both CQ and HCQ was 20 mg / L). 80.0 mg of NB@TBC was weighed and placed in a 2000 mL beaker. Then, 1000 mL of the working solution was weighed and mixed with 80.0 mg of NB@TBC. The mixture was stirred for a long time at 300 rpm in a magnetic stirrer, with samples taken at regular intervals while maintaining the temperature at 25°C. After the intervals, the mixed liquid was aspirated with a 5 mL syringe and filtered through 0.45 μm cellulose acid (CA) to separate the liquid from the solid. After separation, the liquid component (supernatant) was diluted with deionized water to the measurement range and placed in a glass cuvette for analysis using a UV-visible spectrophotometer. The measurement wavelengths were 342.3 nm and 343.4 nm, respectively, to improve the accuracy of CQ and HCQ detection.

[0048] Experimental results show that after 24 hours of adsorption, the adsorption efficiency of NB@TBC reached 112.356 mg / g. At high concentrations, the adsorption rate was faster and equilibrium was more easily reached. This is because more material is available for adsorption, increasing the chance of an adsorption reaction per unit time.

[0049] From the above examples 1 to 3, it can be seen that the method of the present invention is effective in removing chloroquine phosphate and hydroxychloroquine sulfate pollution in water, and the modified method has high adsorption efficiency.

[0050] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements. These changes and improvements fall within the scope of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. Application of nitrogen-boron co-doped waste tea biochar adsorbent in wastewater treatment, characterized in that: The application is for selectively adsorbing chloroquine phosphate and hydroxychloroquine sulfate in wastewater; The nitrogen and boron co-doped waste tea biochar adsorbent is prepared by the following steps: S1. Using waste tea leaves as raw materials, the waste tea leaves are crushed by a crusher to obtain waste tea particles; S2. Dissolving dicyandiamide and boric acid in deionized water to form a mixed solution; the molar ratio of dicyandiamide to boric acid is 1-1.2:1; S3. The waste tea particles are added to the mixed solution, and the precursor powder is formed by vacuum drying after oscillation in an ultrasonic cleaner; S4. The precursor powder is placed in a tubular furnace under an inert atmosphere and calcined at high temperature. After cleaning and drying, nitrogen and boron co-doped waste tea biochar adsorption material is obtained.

2. The use according to claim 1, characterized in that The particle size of the waste tea particles in step S1 is 60-100 mesh.

3. The use according to claim 1, characterized in that The amount of dicyandiamide added in step S2 is 3-5 g, the amount of boric acid added is 3-5 g, and the amount of deionized water added is 50-100 mL.

4. The use according to claim 1, characterized in that The amount of the waste tea particles added in step S3 is 4 g, and the oscillation time is 1-2 hours.

5. The use according to claim 1, characterized in that In step S4, the inert gas is nitrogen or helium, the heating rate is 5-10°C / min, the calcination temperature is 600-800°C, and the calcination time is 2-4h.

6. The use according to claim 1, characterized in that The nitrogen and boron co-doped waste tea biochar adsorption material is put into a wastewater solution containing chloroquine phosphate and hydroxychloroquine sulfate, stirred and then allowed to stand. The stirring time is 12-36 hours, the stirring speed is 200-600 rpm, and the standing time is 0.5-3 hours.

7. The use according to claim 6, characterized in that The dosage of nitrogen and boron co-doped waste tea biochar adsorption material is 0.5-2 g / L, the initial concentration ranges of chloroquine phosphate and hydroxychloroquine sulfate are 10-400 mg / L, the pH value is 5-7, the temperature is 25-45°C, and the adsorption time is 12-48h.

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