Nitrogen-doped porous carbon material solid adsorbent as well as preparation and application thereof

Abstract

The invention relates to a nitrogen-doped porous carbon material solid adsorbent as well as preparation and application thereof. The preparation method comprises the following specific steps: firstly, adding dopamine hydrochloride into an alkali modified ethanol solution, magnetically stirring, dropwise adding acetone, and standing for settling; then centrifugally collecting precipitates, carrying out vacuum drying, and freeze-drying to obtain PDA; mixing and grinding PDA and potassium hydroxide particles into powder, calcining at high temperature under inert gas, cooling to room temperature, and pickling; and finally, washing the product to be neutral by using deionized water, and carrying out vacuum drying to obtain the nitrogen-doped porous carbon material solid adsorbent (PDACK). The adsorbent can efficiently adsorb ciprofloxacin (CIP) in wastewater, and is large in adsorption capacity, high in speed, high in stability, convenient to recycle and high in repeated utilization rate.

Description

Technical Field

[0001] The present invention relates to a nitrogen-doped porous carbon material solid adsorbent and its preparation and application, belonging to the fields of efficient removal of ciprofloxacin (CIP) from medical wastewater and domestic wastewater, new composite materials and their preparation. Background Art

[0002] Antibiotics refer to a class of secondary metabolites produced by microorganisms that can inhibit or kill the growth of other microorganisms. These compounds are widely used in the medical, agricultural, and veterinary fields for the treatment and prevention of infections. However, antibiotics often enter water bodies through sewage discharge, causing water pollution, which has a negative impact on the growth and reproduction of aquatic organisms, may lead to the death or abnormal growth of fish and other aquatic organisms. More importantly, the residues of antibiotics may affect human health through drinking water or the food chain, increasing the dependence on antibiotic treatment and further promoting the development of drug resistance. Ciprofloxacin (CIP) is a broad-spectrum quinolone antibiotic with advantages such as low synthesis cost, significant antibacterial effect, and convenient use. As one of the commonly used antibiotics in clinical practice, ciprofloxacin plays an important role in the treatment of various bacterial infections. However, the residues of ciprofloxacin in water bodies can be absorbed by organisms, leading to the transfer of antibiotic resistance genes between organisms and the environment, thus exacerbating the problem of antibiotic resistance. Therefore, the development of treatment technologies for efficiently removing residual ciprofloxacin in water has gradually become the focus of attention.

[0003] Currently, the technologies for treating antibiotic wastewater mainly include biological methods, chemical methods, membrane separation methods, advanced oxidation technologies, and adsorption methods, etc. Biological methods use microbial metabolism to degrade antibiotics, and the degradation effect is limited by the pollutant concentration, and there are problems such as sludge bulking and high power consumption. Chemical methods such as Fenton reaction and ozone oxidation usually require complex operating conditions and high costs, and may produce harmful by-products. Membrane separation methods will cause membrane fouling and have high maintenance costs. Compared with other treatment technologies, the main advantages of the adsorption method are that the adsorbent has a wide source, simple and efficient operation, is suitable for antibiotic water bodies with different concentrations, and does not form toxic by-products. Therefore, the development and application prospects of adsorbents for efficient removal of CIP from wastewater are broad.

[0004] In recent years, carbon-based materials have shown great potential in the field of adsorption, especially in water treatment, due to their unique physical and chemical properties. The adsorption performance of carbon materials mainly depends on their surface structure, pore distribution, and functional group composition. A reasonable hierarchical pore structure (macropores, mesopores, and micropores) can significantly increase the specific surface area and active sites, while polar functional groups such as surface hydroxyl, carboxyl, and amino groups enhance the adsorption selectivity and capacity for pollutants through hydrogen bonding, electrostatic interaction, or coordination bonds. Therefore, regulating the structure and surface properties of carbon materials is a key strategy to improve their adsorption performance. Dopamine (DA) can self-polymerize to form polydopamine (PDA), which is rich in amino and hydroxyl groups on its surface and exhibits excellent adsorption ability for metal ions, dyes, and organic pollutants. The nitrogen-doped porous carbon materials (PDAC) prepared by carbonizing PDA have significant advantages compared with traditional carbon materials (such as activated carbon, graphite, and carbon black): nitrogen doping improves the conductivity and active sites, the pore structure and specific surface area can be precisely regulated by carbonization conditions, and the preparation process is simple, low-cost, and highly chemically stable. These characteristics make PDAC superior to traditional carbon materials in terms of adsorption performance, structural tunability, and economy, showing broad application prospects, but there are few related studies at present. Potassium hydroxide (KOH), as an efficient chemical activator, can significantly optimize the pore structure and surface properties of materials. KOH reacts with carbon materials at high temperatures to generate potassium metal and carbonates, while producing abundant micropores and mesopores, greatly increasing the specific surface area. In addition, the corrosiveness of KOH can etch the surface of carbon materials, expand the pore structure, and introduce more active sites, while introducing oxygen-containing functional groups (such as hydroxyl, carboxyl, etc.) on its surface, enhancing hydrophilicity and electrochemical activity, thereby improving the adsorption performance. However, the research on improving the adsorption performance of KOH-activated nitrogen-doped carbon materials is still insufficient.

[0005] In the research field of removing CIP by adsorption method, Gamze Ersan et al. prepared granular activated carbon (GAC) doped with different metals and studied its adsorption of CIP. The results showed that on the single-solute adsorption isotherm, the adsorption capacity of iron-doped activated carbon for CIP was higher than that of silver-doped activated carbon, pre-oxidized activated carbon, and undoped activated carbon. This higher absorption was attributed to the presence of Fe content (1.2%), which could strongly interact with zwitterionic CIP at neutral pH. Mohammad Rezvani-Ghalhari et al. used a green adsorbent material based on cellulose / polyvinyl alcohol (PVA) modified with mixed metal oxides (MMO) to extract CIP from water. The adsorption of CIP by this adsorbent conforms to the Freundlich isothermal adsorption model and belongs to multi-molecular layer adsorption. The optimal process conditions for adsorption are: pH = 4.5, adsorbent dosage 0.55 g·L -1 , adsorption time 83 min, and initial CIP concentration of 2 mg·L -1The adsorption capacity of the cellulose / MMO / PVA adsorbent for CIP is 19 mg·g -1 (CIP removal rate = 86.48%). Peiwen Wang et al. synthesized the SLS / PEI / GO-P adsorbent using a green method. The results showed that when the pH was 8, the temperature was 30 °C, the CIP concentration was 250 mg / L, and the adsorption time was 2 h, the maximum adsorption capacity of the adsorbent for CIP was 823.3 mg / g. And after 5 adsorption and hydrothermal regeneration cycles, the adsorption capacity of the adsorbent for CIP only decreased slightly. SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide a novel nitrogen-doped porous carbon material solid adsorbent (PDACK) for adsorbing ciprofloxacin (CIP) to improve the deficiencies of the prior art. Another object of the present invention is to provide a preparation method of the above adsorbent; still another object of the present invention is to provide the application of the above adsorbent in removing and adsorbing the typical quinolone antibiotic CIP in wastewater.

[0007] The technical solution of the present invention is as follows: A nitrogen-doped porous carbon material solid adsorbent, which is characterized in that by utilizing the self-polymerization property of polydopamine, using PDA as a carbon source, and then chemically activating with potassium hydroxide according to a certain alkali-carbon ratio to prepare a nitrogen-doped carbon material solid adsorbent with a high specific surface area, rich pore structure, and high nitrogen content; wherein the atomic ratio of the N element is 5% - 8%; the total specific surface area of the adsorbent is 1300 - 1600 m 2 ·g -1 ; the pore volume is 0.90 - 1.20 cm 3 ·g -1 ; the average pore diameter is 1.20 - 1.60 nm.

[0008] The present invention also provides a method for preparing the above nitrogen-doped porous carbon material solid adsorbent, and the specific steps are as follows:

[0009] (1) First, add a weakly alkaline solution to an ethanol solution and stir magnetically; then add dopamine hydrochloride and stir magnetically. At the end of the stirring, add acetone dropwise. After the acetone is added dropwise, let it stand for sedimentation; finally, centrifuge to collect the precipitate, vacuum dry and then freeze dry to obtain PDA;

[0010] (2) Carbonization and pore expansion: Mix PDA and potassium hydroxide particles and grind them into a powder. Then put the mixed material into a tube furnace for high-temperature calcination. After cooling to room temperature, take out the material and wash it with an acidic solution in an oscillation box. Finally, rinse it with deionized water until the pH value is 6.50 - 7.00, and vacuum dry to obtain the nitrogen-doped porous carbon material solid adsorbent PDACK.

[0011] Preferably, in step (1), the volume ratio of absolute ethanol to deionized water in the ethanol solution is 1:(4 - 9); the volume ratio of the weak alkaline solution to the ethanol solution is 1:(25 - 100); the mass ratio of dopamine hydrochloride to the volume of the ethanol solution is 20.00 - 30.00 g·L -1 ; the volume ratio of the ethanol solution to acetone is 1:(2.0 - 3.0).

[0012] Preferably, the weak alkaline solution in step (1) is ammonia water with a mass concentration of 25% - 28% or Tris buffer solution with a pH of 8.5 - 9.0; the magnetic stirring speed after dropping the weak alkaline solution into the ethanol solution is 260 - 320 rpm, and the stirring time is 20 - 30 min; the magnetic stirring speed after adding dopamine hydrochloride is 280 - 360 rpm, and the stirring time is 22 - 25 h; the static sedimentation time is 24 - 36 h; the vacuum drying temperature is 50 - 60 °C, and the vacuum drying time is 30 - 45 min.

[0013] Preferably, the high-temperature calcination temperature in step (2) is 800 - 900 °C, the calcination time is 1.5 - 2.0 h, and the heating rate is 5 - 10 °C·min -1 .

[0014] Preferably, the mass ratio of PDA to potassium hydroxide particles in step (2) is 1:(3 - 6).

[0015] Preferably, the acidic solution in step (2) is hydrochloric acid or sulfuric acid, and the concentration of the acidic solution is 1.00 - 20.00 mM; the vacuum drying temperature is 50 - 70 °C, and the vacuum drying time is 10 - 12 h.

[0016] The present invention also provides an application of the above nitrogen-doped porous carbon material solid adsorbent in adsorbing ciprofloxacin CIP in wastewater. The specific steps are as follows: adding PDACK adsorbent to the simulated CIP wastewater, placing it in a constant-temperature shaking incubator, setting the rotation speed to 150 - 250 rpm, the temperature to 20 - 30 °C, and the adsorption time to 0.5 - 1.5 h; wherein the pH of the simulated wastewater is adjusted to 2.00 - 12.00, the concentration of CIP is 5 - 35 mg·L -1 , and the mass ratio of the adsorbent dosage to the volume of the wastewater is 0.8 - 1.8 g·L -1 .

[0017] Beneficial effects:

[0018] (1) The adsorbent of the present invention has enhanced adsorption efficiency, good pH adaptability, chemical stability and renewable property, and has a good treatment effect on CIP in wastewater;

[0019] (2) The preparation process of the adsorbent of the present invention is simple, the reaction conditions are relatively low, the process is easy to control, and the product quality is stable. Detailed implementation manners

[0020] To better understand the present invention, the present invention will be further described below through embodiments. The embodiments are only used to explain the present description and will not constitute any limitation to the invention.

[0021] Example 1:

[0022] (1) Prepare a simulated wastewater containing CIP, with the concentration of CIP being 5 mg·L -1 , and the pH value being 2.00.

[0023] (2) Prepare a novel adsorbent PDACK, and the steps are as follows:

[0024] ① First, measure 20.00 mL of absolute ethanol and 80.00 mL of deionized water and pour them into a 500 mL beaker. Add 4.00 mL of 25% (mass concentration, the same as below) ammonia water to the above mixture, seal the beaker mouth with tin foil, and magnetically stir at 260 rpm for 20 min. Then add 2.00 g of dopamine hydrochloride, magnetically stir at 280 rpm for 22 h, drop in 200.00 mL of acetone, and let it stand for sedimentation for 24 h after dropping. Finally, centrifuge to collect the precipitate, vacuum dry at 50 °C for 30 min, and then freeze-dry together with the centrifuge tube to obtain PDA.

[0025] ② Carbonization and pore expansion: Mix PDA and potassium hydroxide particles in a mass ratio of 1:3 and grind them into powder. Then put the mixed material into a tube furnace and heat it to 800 °C at a rate of 5 °C·min -1 for high-temperature calcination for 1.5 h. After the tube furnace cools to room temperature, take out the material, wash it thoroughly with a hydrochloric acid solution with a concentration of 2 mM in a shaking box, and finally rinse the material after pore expansion with deionized water until the pH value of the filtrate is 7.00, and vacuum dry at 50 °C for 10 h to prepare the PDACK material. It is measured that the atomic ratio of N element in the prepared novel adsorbent PDACK is about 5%, the total specific surface area is 1328.91 m 2 ·g -1 ; the pore volume is 0.90 cm 3 ·g -1 ; the average pore diameter is 1.31 nm.

[0026] Weigh 0.08 g of the novel adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP,

[0027] place it in a constant-temperature shaking box, and reach equilibrium at 20 °C and 150 rpm in 80 min. The removal rate of CIP is 94.32%.

[0028] Example 2:

[0029] (1) Prepare the simulated wastewater containing CIP, with the concentration of CIP being 15 mg·L -1 , and the pH value being 6.00.

[0030] (2) Prepare the novel adsorbent PDACK, and the steps are as follows:

[0031] ① First, measure 12.50 mL of absolute ethanol and 87.50 mL of deionized water and pour them into a 500 mL beaker. Add 3.00 mL of Tris buffer solution (pH 9.0) to the above mixture, seal the beaker mouth with tin foil, and magnetically stir at 280 rpm for 25 min. Then add 2.50 g of dopamine hydrochloride, magnetically stir at 310 rpm for 23 h, and drop in 250.00 mL of acetone. After dropping, let it stand and settle for 28 h. Finally, centrifuge to collect the precipitate, vacuum dry at 55 °C for 35 min, and then freeze-dry together with the centrifuge tube to obtain PDA;

[0032] ② Carbonization and pore expansion: Mix PDA and potassium hydroxide particles in a mass ratio of 1:4 and grind them into a powder. Then put the mixed material into a tube furnace and heat it to 840 °C at a rate of 7 °C·min -1 for high-temperature calcination for 1.6 h. After the tube furnace cools to room temperature, take out the material, wash it thoroughly with a hydrochloric acid solution with a concentration of 8 mM in an oscillation box, and finally rinse the material after pore expansion with deionized water until the pH value of the filtrate is 6.8, and vacuum dry at 60 °C for 11 h to prepare the PDACK material. It is measured that the atomic proportion of N element in the prepared novel adsorbent PDACK is about 6%; the total specific surface area is 1468.07 m 2 ·g -1 ; the pore volume is 1.03 cm 3 ·g -1 ; the average pore diameter is 1.20 nm.

[0033] Weigh 0.12 g of the novel adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP, place it in a constant-temperature oscillation box, and reach equilibrium at 25 °C with a rotation speed of 180 rpm in 65 min. The removal rate of CIP is 96.45%.

[0034] Example 3:

[0035] (1) Prepare the simulated wastewater containing CIP, with the concentration of CIP being 25 mg·L

[0036] , and the pH value being 9.00. -1

[0037] (2) Preparation of the novel adsorbent PDACK is as follows:

[0038] ① First, measure 11.12 mL of absolute ethanol and 88.88 mL of deionized water and pour them into a 500 mL beaker. Add 2.00 mL of Tris buffer solution (pH 8.5) to the above mixture, seal the beaker mouth with tin foil, and stir magnetically at 300 rpm for 27 min. Then add 2.70 g of dopamine hydrochloride, stir magnetically at 330 rpm for 24 h, and drop in 275.00 mL of acetone. After dropping, let it stand for sedimentation for 32 h. Finally, centrifuge to collect the precipitate, vacuum dry it at 58 °C for 40 min, and then freeze-dry it together with the centrifuge tube to obtain PDA;

[0039] ② Carbonization and pore expansion: Mix PDA and potassium hydroxide particles in a mass ratio of 1:5 and grind them into a powder. Then put the mixed material into a tube furnace and heat it up to 870 °C at a rate of 8 °C·min -1 for high-temperature calcination for 1.8 h. After the tube furnace cools to room temperature, take out the material, wash it thoroughly with a hydrochloric acid solution with a concentration of 15 mM in a shaking box, and finally rinse the pore-expanded material with deionized water until the pH value of the filtrate is 6.6. Vacuum dry it at 65 °C for 11.5 h to prepare the PDACK material. It is measured that the atomic proportion of N element in the prepared novel adsorbent PDACK is about 6.5%; the total specific surface area is 1366.87 m 2 ·g -1 ; the pore volume is 0.96 cm 3 ·g -1 ; the average pore diameter is 1.43 nm.

[0040] Weigh 0.16 g of the novel adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP,

[0041] place it in a constant-temperature shaking box, and reach equilibrium at 27 °C with a rotation speed of 220 rpm in 50 min. The removal rate of CIP is 97.83%.

[0042] Example 4:

[0043] (1) Prepare simulated wastewater containing CIP with a CIP concentration of 35 mg·L -1 and a pH value of 12.00.

[0044] (2) Preparation of the novel adsorbent PDACK is as follows:

[0045] ① First, measure 10.00mL of anhydrous ethanol and 90mL of deionized water respectively and pour them into a 500mL beaker. Add 1.00mL of 28% ammonia water to the above mixture, seal the cup mouth with tin foil, and stir magnetically at 320rpm for 30min. Then add 3.00g of dopamine hydrochloride, stir magnetically at 360rpm for 25h, and drop 300.00mL of acetone. After the addition is complete, let it stand and settle for 36h. Finally, collect the precipitate by centrifugation, vacuum dry it at 60℃ for 45min, and freeze-dry it together with the centrifuge tube to obtain PDA;

[0046] ②Carbonization pore expansion: PDA and potassium hydroxide particles were mixed in a mass ratio of 1:6 and ground into powder. The mixed material was then placed in a tube furnace and heated at 10 °C min -1 The temperature was raised to 900°C for high-temperature calcination for 2.0 hours. After the tube furnace cooled to room temperature, the material was taken out and fully washed with a 20mM hydrochloric acid solution in an oscillating box. Finally, the expanded material was rinsed with deionized water until the pH value of the filtrate was 6.5. The PDACK material was prepared by vacuum drying at 70°C for 12.0 hours. The atomic proportion of N element in the prepared new adsorbent PDACK was measured to be about 8%; the total specific surface area was 1598.43m 2 ·g -1 ; pore volume is 1.20cm 3 ·g -1 ; The average pore size is 1.60nm.

[0047] Weigh 0.18 g of the novel adsorbent prepared in this example and put it into 100 mL of the CIP-containing mold prepared above.

[0048] The simulated wastewater was placed in a constant temperature oscillation box, at 30°C and 250rpm, and equilibrium was reached in 40 minutes, with a CIP removal rate of 98.30%.

Claims

1. A nitrogen-doped porous carbon material solid adsorbent, characterized in that By utilizing the self-polymerization characteristics of polydopamine, using PDA as a carbon source, and then using potassium hydroxide for chemical activation according to a certain alkali-carbon ratio, a nitrogen-doped carbon material solid adsorbent with high specific surface area, rich pore structure, and high nitrogen content was prepared; the atomic proportion of the nitrogen element was 5%-8%; the total specific surface area of ​​the adsorbent was 1300-1600m 2 ·g -1 ; The pore volume is 0.90-1.20cm 3 ·g -1 ; The average pore size is 1.20-1.60nm.

2. A method for preparing the nitrogen-doped porous carbon material solid adsorbent as claimed in claim 1, wherein the specific steps are as follows: (1) firstly add a weak alkaline solution to an ethanol solution and stir it magnetically; then add dopamine hydrochloride, add acetone dropwise after magnetic stirring, and let it stand for sedimentation after the acetone is added; finally, collect the precipitate by centrifugation, vacuum dry it and then freeze-dry it to obtain PDA; (2) Carbonization and pore expansion: PDA and potassium hydroxide particles are mixed and ground into powder, and then the mixed material is placed in a tubular furnace for high-temperature calcination. After cooling, the material is taken out and washed with an acidic solution in an oscillating box. Finally, it is rinsed with deionized water until the pH value is 6.50-7.00, and vacuum dried to obtain a nitrogen-doped porous carbon material solid adsorbent PDACK.

3. The method according to claim 2, characterized in that In step (1), the volume ratio of anhydrous ethanol to deionized water in the ethanol solution is 1:(4-9); the volume ratio of the weak alkaline solution to the ethanol solution is 1:(25-100); the mass ratio of dopamine hydrochloride to the volume ratio of the ethanol solution is 20.00-30.00 g·L -1 ; The volume ratio of ethanol solution to acetone is 1:(2.0-3.0).

4. The method according to claim 2, characterized in that The weak alkaline solution described in step (1) is ammonia water with a mass concentration of 25% to 28% or a Tris buffer solution with a pH of 8.5 to 9.0; the magnetic stirring speed after the weak alkaline solution is added dropwise to the ethanol solution is 260-320 rpm, and the stirring time is 20-30 min; the magnetic stirring speed after adding dopamine hydrochloride is 280-360 rpm, and the stirring time is 22-25 h; the static sedimentation time is 24-36 h; the vacuum drying temperature is 50-60° C., and the vacuum drying time is 30-45 min.

5. The method according to claim 2, characterized in that The high temperature calcination temperature in step (2) is 800-900°C, the calcination time is 1.5-2.0h, and the heating rate is 5-10°C·min -1 .

6. The method according to claim 2, characterized in that The mass ratio of PDA to potassium hydroxide particles described in step (2) is 1:(3-6).

7. The method according to claim 2, characterized in that The acidic solution described in step (2) is hydrochloric acid or sulfuric acid, and the concentration of the acidic solution is 1.00-20.00 mM; the vacuum drying temperature is 50-70° C., and the vacuum drying time is 10-12 h.

8. Use of the nitrogen-doped porous carbon material solid adsorbent as claimed in claim 1 for adsorbing ciprofloxacin (CIP) in wastewater.

9. The use according to claim 8, characterized in that The specific steps are as follows: add PDACK adsorbent to simulated CIP wastewater, place it in a constant temperature oscillating box, set the speed to 150-250rpm, the temperature to 20-30℃, and the adsorption time to 0.5-1.5h; wherein the pH of the simulated wastewater is adjusted to 2.00-12.00, and the concentration of CIP is 5-35mg·L -1 The volume ratio of adsorbent to wastewater is 0.8-1.8 g·L -1 .