Microwave preparation and regeneration method and application of nitrogen-doped modified activated carbon

Abstract

The invention provides a microwave preparation and regeneration method and application of nitrogen-doped modified activated carbon, and the preparation method comprises the following steps: taking 40-60-mesh activated carbon, firstly pickling, then washing to be neutral, adding an acrylamide solution, putting into a shaking table for shaking, taking out, standing, drying, adding condensed water, and carrying out microwave heating, modification and drying to obtain microwave modified activated carbon. The regeneration method comprises the following steps: filtering and washing the nitrogen-doped activated carbon which is saturated by adsorption, drying the nitrogen-doped activated carbon in a drying oven, adding condensate water, carrying out microwave heating, cooling to room temperature, taking out the nitrogen-doped activated carbon, and washing and drying the nitrogen-doped activated carbon. When the activated carbon is applied to adsorption of norfloxacin in a water body, the optimal adsorption pH value is 11.0, the adsorption efficiency can reach 56%, and the highest adsorption efficiency of the regenerated activated carbon can reach 59%.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon preparation, and in particular relates to a microwave preparation and regeneration method of nitrogen-doped modified activated carbon and application thereof. Background Art

[0002] In recent years, environmental pollution caused by antibiotics has attracted widespread attention. As a third-generation fluoroquinolone antibiotic, norfloxacin is widely used due to its broad antibacterial spectrum and few side effects. However, due to its difficulty in degradation in the environment, quinolone antibiotics such as norfloxacin are constantly detected in surface water and wastewater. Low concentrations of norfloxacin can lead to increased bacterial resistance, and traditional treatment methods cannot completely remove norfloxacin from aqueous solutions, which may lead to drinking water pollution and endanger human health.

[0003] As a common adsorbent for treating water pollution, the adsorption effect of activated carbon is related to many factors: the properties of activated carbon itself, such as its specific surface area, pore distribution, impurity content in water, hydrophobicity, physical and chemical properties of surface functional groups, etc.; the properties of adsorbents, such as polarity, hydrophobicity, molecular diameter, etc.; the conditions of adsorption reaction, such as solution temperature, pH value and solvent polarity, etc. Among these properties, the most important factor affecting the adsorption effect is the activated carbon itself, especially the functional groups doped on its surface. These functional groups, as an active center, determine the chemical properties of activated carbon and play a very important role in improving the adsorption efficiency. Generally, more effective functional groups are doped on the surface of activated carbon through modification. The modification methods commonly used in current research include oxidation modification, acid-base modification, metal ion modification, nitrogen doping modification, etc. Among them, nitrogen doping modification can effectively control the number and type of nitrogen-containing groups in the material by selecting appropriate nitrogen sources and reaction conditions. By loading special nitrogen-containing groups, it can effectively adsorb specific types of antibiotics, improve the specific capacitance of carbon materials, and improve hydrophilicity and surface activity. There are generally two methods for nitrogen doping modification: in-situ nitrogen doping and external nitrogen source method. Compared with the in-situ nitrogen doping method, the external nitrogen source method has a higher yield and a larger specific surface area for preparing activated carbon, and has a more obvious advantage in the treatment of organic pollutants. The external nitrogen source method refers to the direct reaction of nitrogen-containing substances with activated carbon at high temperature. Nitrogen-containing substances are generally highly polar, and react more obviously in a microwave environment, and are easily loaded on activated carbon, so the microwave method is a good choice. The microwave method has a short heating time, high efficiency, and fast speed, making it easier to start or stop the reaction. Microwaves can generate a certain amount of energy by changing ion migration and dipole rotation. The continuous superposition of these energies can produce a hot spot effect and promote adsorption reactions. There are few studies on the use of microwave hot spot heating to treat activated carbon. Chinese invention patent application CN116924401A discloses a method for preparing nitrogen-doped activated carbon by microwave heating. The above preparation method takes a long time, and the products prepared by the existing method have the disadvantages of short life and low reuse rate. Therefore, it is of great value to study the method of preparing activated carbon with stable performance, high efficiency, reusability, high specific surface area, and high adsorption. Due to the limited adsorption capacity of activated carbon, it needs to be regenerated frequently. The most commonly used regeneration method in current research is pyrolysis, but this method is costly during use and will lead to the loss of activated carbon, resulting in weakened adsorption capacity of activated carbon and blocked pores of activated carbon. Summary of the invention

[0004] The technical problem solved by the present invention is that the nitrogen-doped modified activated carbon prepared by the existing method has a short lifespan, a low reuse rate, a high pyrolysis recovery cost and a poor adsorption effect.

[0005] The present invention provides a microwave preparation method for nitrogen-doped modified activated carbon, comprising the following steps: Step 1: Take 40-60 mesh activated carbon for acid washing, and then use a suction filter and distilled water to wash it to make the pH value of the activated carbon neutral. Step 2: Add the activated carbon obtained in step 1 to an acrylamide solution with a concentration of 0.6-1.4 g / L, place it on a shaker, take it out, let it stand, and dry it. Step 3: Add condensed water to the activated carbon treated with acrylamide and perform microwave heating to modify the activated carbon. The microwave heating power is 500-700W and the heating time is 2-6 minutes. Step 4: Dry the modified activated carbon to obtain microwave-modified activated carbon.

[0006] The present invention provides a microwave preparation method for nitrogen-doped modified activated carbon, comprising the following steps: Step 1: Take 40-60 mesh activated carbon for acid washing, and then use a suction filter and distilled water to wash it to make the pH value of the activated carbon neutral. Step 2: Add the activated carbon obtained in step 1 to an acrylamide solution with a concentration of 1 g / L, place it on a shaker, take it out, let it stand, and dry it. Step 3: Add condensed water to the activated carbon treated with acrylamide and perform microwave heating to modify the activated carbon. The microwave heating power is 500-650W and the heating time is 4 minutes. Step 4: Dry the modified activated carbon to obtain microwave-modified activated carbon.

[0007] Furthermore, in step 1, the activated carbon is added with an acid wash solution and placed in a shaker for shaking and washing, the acid wash solution is a 5% HCI solution, the washing temperature is 25° C., the washing time is 15 hours, and the shaking speed is 120 r / min.

[0008] Furthermore, in step 2, the shaking speed of the shaking table is 120 r / min, the temperature is 25° C., and the shaking time is 30 min.

[0009] Furthermore, in the step three, the amount of condensed water added per gram of activated carbon is 4 mL.

[0010] Furthermore, the microwave heating device in step three is a household microwave oven.

[0011] Furthermore, in step 4, the drying time is 7 hours and the drying temperature is 100°C.

[0012] The invention provides a regeneration method for nitrogen-doped modified activated carbon, comprising the following steps: filtering and washing adsorption saturated nitrogen-doped activated carbon, and then putting it into an oven for drying; adding condensed water to the dried activated carbon, and performing microwave heating, wherein the microwave heating power is 500-650W, the heating time is 2-6min, and the activated carbon is taken out after cooling to room temperature, and then washed with distilled water for 3-4 times, and then put into an oven for drying.

[0013] The invention provides application of nitrogen-doped modified activated carbon in adsorbing norfloxacin in water.

[0014] Furthermore, the pH value of the norfloxacin solution is 11.

[0015] The present invention has the following beneficial effects: the present invention modifies activated carbon by nitrogen-containing substances, loads functional groups on activated carbon by microwave method, obtains nitrogen-doped modified activated carbon, and then performs microwave regeneration treatment on activated carbon. The substance with the best nitrogen doping effect on activated carbon is acrylamide, which has a good adsorption effect of norfloxacin and a stable trend. The optimal conditions for treating activated carbon are as follows: microwave heating power is 500-650W, microwave time is 4min; the optimal adsorption pH is 11.0, and the amount of water required for the optimal microwave hotspot of 1g activated carbon is 4mL. Through infrared spectrum and liquid ultraviolet characterization, it is determined that nitrogen-doped activated carbon is loaded with acrylamide, and the adsorption efficiency can reach 56%. The activated carbon is regenerated by microwave method, and the hotspot effect can decompose the antibiotics adsorbed on the activated carbon and restore its activity. The maximum adsorption efficiency of the activated carbon after regeneration treatment can reach 59%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 , norfloxacin adsorption experimental results of each sample prepared in Comparative Examples 1, 2 and Example 1.

[0017] Figure 2 , norfloxacin adsorption experimental results of each sample prepared in Comparative Examples 2, 3, and 4.

[0018] Figure 3 FTIR analysis spectra of each sample prepared in Example 1 and Comparative Examples 1 and 2.

[0019] Figure 4 , norfloxacin adsorption experimental results of each sample prepared in Examples 1-5.

[0020] Figure 5 , norfloxacin adsorption experimental results of each sample prepared in Examples 6-9 and Example 1.

[0021] Figure 6 , norfloxacin adsorption experimental results of each sample prepared in Examples 10-14.

[0022] Figure 7, FTIR analysis spectra of each sample prepared in Examples 6 and 1.

[0023] Figure 8 , norfloxacin adsorption test results of the sample prepared in Example 1 at different solution pH values.

[0024] Fig. 9 , norfloxacin adsorption experimental results of various samples prepared by microwave regeneration. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] Example 1, a microwave preparation method for nitrogen-doped modified activated carbon, comprising the following steps, step 1, take 40-60 mesh activated carbon for acid washing, add the acid washing solution to the activated carbon and put it into a shaker for shaking washing, the acid washing solution is 5% HCI solution, the washing temperature is 25 ° C, the time is 15h, the shaking speed is 120r / min, and then use a suction filtration device and distilled water to wash, so that the pH value of the activated carbon is neutral, and the pretreated activated carbon is obtained, which is recorded as PAC. Step 2, the activated carbon obtained in step 1 is added to 1g / L acrylamide solution for immersion, step 3, the activated carbon treated with acrylamide is added with condensed water, and microwave heating is performed to modify the activated carbon, the amount of condensed water added per gram of activated carbon is 4mL, the microwave temperature is medium-high fire, and the time is 4min. Step 4, the modified activated carbon is dried, the drying time is 7h, the drying temperature is 100°C, and microwave modified activated carbon is obtained.

[0027] Comparative Example 1, muffle furnace modified activated carbon. The preparation method is to add the pretreated activated carbon PAC into 1g / L acrylamide solution for immersion, add the activated carbon treated with acrylamide into a muffle furnace for firing at a temperature of 400°C for 30 minutes to obtain muffle furnace modified activated carbon.

[0028] Comparative Example 2, pretreated activated carbon PAC.

[0029] Comparative Example 3: The difference between this example and Comparative Example 1 is that diammonium hydrogen phosphate solution is used instead of acrylamide solution to prepare muffle furnace modified activated carbon.

[0030] Comparative Example 4: This example differs from Example 1 in that diammonium hydrogen phosphate solution is used instead of acrylamide solution to prepare microwave-modified activated carbon.

[0031] Adsorption experiment 1: Comparative Examples 1, 2 and Example 1 were weighed to perform norfloxacin adsorption experiments. The results are as follows: Figure 1 As shown, comparative examples 2, 3, and 4 were weighed to perform norfloxacin adsorption experiments. The results are shown in Figure 2 shown.

[0032] The specific experimental process is as follows: weigh 10 mg of norfloxacin solution, put it into a 100 mL beaker, add 50 mL of distilled water, put it into a magnetic stirrer, heat it to 70 ° C and stir until the antibiotic is completely dissolved, then use a glass rod to transfer the antibiotic solution to a 1L volumetric flask, adjust the volume, and shake it well. Weigh 60 mg of each sample, put it into a 100 mL conical flask, add 100 mL of antibiotic solution, put it into a shaker, react at 25 ° C, 120 r / min, and use a syringe to sample 3.6 mL every 30 minutes, and take 6 times. After sampling, measure the liquid UV of the sample, record the absorbance, and calculate the adsorption efficiency.

[0033] from Figure 1 It can be seen that the concentration of norfloxacin remaining in the solution gradually decreases. The adsorption rate calculated by the adsorption formula shows that the adsorption rate of activated carbon prepared by microwave method is significantly higher than that of muffle furnace method, and the adsorption trend is very stable. This may be because the temperature of microwave effect is higher than that of muffle furnace, and the temperature is more controllable, so the activated carbon obtained by microwave method has better effect. Acrylamide modified activated carbon has the best adsorption effect, and the highest efficiency can reach 53%. Figure 2 It can be seen that the maximum adsorption efficiency of diammonium hydrogen phosphate modified activated carbon is only 42%. The reason is that the temperature is too high, which causes the diammonium hydrogen phosphate to partially decompose and is not well loaded on the activated carbon, resulting in poor adsorption effect.

[0034] The activated carbon structures of Example 1 and Comparative Examples 1 and 2 were analyzed by FTIR. The results are as follows: Figure 3 .

[0035] Depend on Figure 3 It can be seen that the characteristic peaks of the substances in Example 1 and Comparative Example 1 are basically the same, with only a slight difference in intensity. The absorption peak at 1500cm-1 may be caused by impurities in PAC, which basically disappears after pretreatment. At around 3500cm-1, the activated carbon modified by the muffle furnace method and the activated carbon modified by the microwave method have obvious primary amine absorption peaks, indicating that acrylamide has been loaded on the activated carbon.

[0036] Example 2: The difference between this example and Example 1 is that the concentration of the acrylamide solution in step 2 is 0.6 g / L.

[0037] Example 3: The difference between this example and Example 1 is that the concentration of the acrylamide solution in step 2 is 0.8 g / L.

[0038] Example 4: The difference between this example and Example 1 is that the concentration of the acrylamide solution in step 2 is 1.2 g / L.

[0039] Example 5: The difference between this example and Example 1 is that the concentration of the acrylamide solution in step 2 is 1.4 g / L.

[0040] Adsorption experiment 2: The microwave-modified activated carbons of Examples 2-5 and Example 1 were weighed to perform norfloxacin adsorption experiments. Figure 4 .

[0041] from Figure 4 It can be seen that the remaining norfloxacin concentration in the solution gradually decreases. The adsorption rate calculated by the adsorption formula shows that the adsorption rate of 0.6g / L acrylamide is 26%, the adsorption rate of 0.8g / L acrylamide is 40%, and the adsorption rate of 1.2g / L acrylamide is 38%. It can be seen that under the condition of controlling other variables the same, changing the initial acrylamide solution concentration has a greater impact on the adsorption efficiency of activated carbon. The best adsorption effect is 1.0g / L nitrogen-doped modified activated carbon, which has an adsorption efficiency of 50% for norfloxacin solution.

[0042] Example 6: The difference between this example and Example 1 is that the microwave time in step 3 is 2 minutes.

[0043] Example 7: The difference between this example and Example 1 is that the microwave time in step 3 is 3 minutes.

[0044] Example 8: The difference between this example and Example 1 is that the microwave time in step 3 is 5 minutes.

[0045] Example 9: The difference between this example and Example 1 is that the microwave time in step 3 is 6 minutes.

[0046] Example 10: The difference between this example and Example 1 is that in step 3, the microwave temperature is high and the microwave time is 2 minutes.

[0047] Example 11: The difference between this example and Example 1 is that in step 3, the microwave temperature is high and the microwave time is 3 minutes.

[0048] Example 12: The difference between this example and Example 1 is that in step 3, the microwave temperature is high and the microwave time is 4 minutes.

[0049] Example 13: The difference between this example and Example 1 is that in step 3, the microwave temperature is high and the microwave time is 5 minutes.

[0050] Example 14: The difference between this example and Example 1 is that in step 3, the microwave temperature is high and the microwave time is 6 minutes.

[0051] Adsorption experiment 3: The microwave-modified activated carbons of Examples 6-14 and Example 1 were weighed to perform norfloxacin adsorption experiments. Figure 5 and 6 .

[0052] from Figure 5 It can be seen that the remaining norfloxacin concentration in the solution is basically on a downward trend. The adsorption rate is calculated by the adsorption formula. The adsorption rate of the modified activated carbon at medium-high fire for 2 minutes is 49%, the adsorption rate of the modified activated carbon at 3 minutes is 34%, and the adsorption rate of the modified activated carbon at 4 minutes is 54%, which is the best. The adsorption rate of the modified activated carbon at 5 minutes is 48%, and the adsorption rate of the modified activated carbon at 6 minutes is 42.21%. Figure 6 It can be seen that the adsorption rate of modified activated carbon under high fire for 2 minutes is 41%, 3 minutes for 35%, 4 minutes for 42%, 5 minutes for 46%, and 6 minutes for 39%. The adsorption efficiency of activated carbon under high fire treatment is generally lower than that of activated carbon treated under medium and high fire conditions. The reason is that the temperature is too high, which causes the decomposition of the loaded acrylamide, greatly reducing its adsorption efficiency.

[0053] Depend on Figure 7 It can be seen that the characteristic peaks of the two substances are very different from those of Example 6 and Example 1 through FTIR analysis of the two nitrogen-doped modified activated carbon structures. The 3500cm-1 of the microwave-modified activated carbon is the absorption peak of acrylamide contained in the nitrogen-doped activated carbon; the primary amine absorption peak around 3500cm-1 of the modified activated carbon treated for 4 minutes disappears, indicating that acrylamide may have been decomposed, and the substance has an obvious upward absorption peak at 1650cm-1, which may be due to the reaction of acrylamide to generate acrylic acid loaded on the activated carbon.

[0054] Adsorption experiment 4: taking the sample of Example 1 to carry out norfloxacin adsorption experiment at different solution pH values, the results are as follows Figure 8 .

[0055] from Figure 8It can be seen that the concentration of norfloxacin remaining in the solution gradually decreases. The adsorption rate calculated by the adsorption formula is 40% under pH=3.0, 23% under pH=3.5, 30% under pH=4.0, 47% under pH=7.0, 56% under pH=11.0, 47% under pH=11.5, and 44% under pH=12.0. It can be seen that the adsorption efficiency of acrylamide nitrogen-doped modified activated carbon is the highest under the condition of pH=11.0 of the antibiotic solution. The efficiency of adsorption of norfloxacin under alkaline conditions is generally higher than that under acidic conditions. This is because the active center is occupied due to the salt formation of acrylamide loaded under acidic conditions, and the norfloxacin solution cannot be adsorbed. Under alkaline conditions, the adsorption efficiency can be improved due to hydrogen bonding.

[0056] In the regeneration adsorption experiment, take the samples that have been saturated with adsorption in Examples 6-9 and Example 1, filter and wash them, and then put them into an oven for drying. Add 4 mL of distilled water to 1 g of the dried activated carbon, and repeat the initial reaction temperature and time for microwave reaction again. After the activated carbon cools to room temperature, take it out, wash it with distilled water 3-4 times, and put it into an oven for drying. Use the obtained regenerated activated carbon to conduct the adsorption experiment of norfloxacin again, take samples and measure the absorbance, and calculate the adsorption efficiency. The experimental results are as follows. Fig. 9 .

[0057] from Fig. 9 It can be seen that the concentration of norfloxacin remaining in the solution gradually decreases. The adsorption rate calculated by the adsorption formula shows that the adsorption rate of the modified activated carbon is 40% after 2 minutes of medium-high fire regeneration, 59% after 3 minutes of regeneration, 47% after 4 minutes of regeneration, 38.73% after 5 minutes of regeneration, and 32% after 6 minutes of regeneration. It can be seen from the figure that the nitrogen-doped modified activated carbon after regeneration has a certain improvement in the adsorption efficiency of norfloxacin under the same initial conditions. The best regeneration condition is medium-high fire for 3 minutes, and the highest adsorption efficiency can reach 59%. Reaction again under the right temperature conditions, acrylamide is better loaded on the activated carbon, and as time goes by and the temperature rises, acrylamide decomposes, the activity disappears, and the adsorption rate decreases.

[0058] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and alterations made to the technical solutions of the present invention by those skilled in the art should all fall within the scope of protection defined by the claims of the present invention.

[0059] Other parts of the present invention not described in detail belong to the prior art and will not be described in detail here.

[0060] Although the present invention has been described in conjunction with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can implement various changes, substitutions and modifications to the subject matter listed here without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the claims.

Claims

1. A microwave preparation method for nitrogen-doped modified activated carbon, characterized in that: The following steps are included: Step 1: Take 40-60 mesh activated carbon and wash it with acid, then use a suction filter and distilled water to wash it to make the pH value of the activated carbon neutral. Step 2: Add the activated carbon obtained in step 1 to an acrylamide solution with a concentration of 0.6-1.4 g / L, place it on a shaker, take it out, let it stand, and dry it. Step 3: Add condensed water to the activated carbon treated with acrylamide and perform microwave heating to modify the activated carbon. The microwave heating power is 500-700W and the heating time is 2-6min. Step 4: Dry the modified activated carbon to obtain microwave-modified activated carbon.

2. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1, characterized in that: The following steps are included: Step 1: Take 40-60 mesh activated carbon and wash it with acid, then use a suction filter and distilled water to wash it to make the pH value of the activated carbon neutral. Step 2: Add the activated carbon obtained in step 1 to an acrylamide solution with a concentration of 1 g / L, place it on a shaker, take it out, let it stand, and dry it. Step 3: Add condensed water to the activated carbon treated with acrylamide and perform microwave heating to modify the activated carbon. The microwave heating power is 500-650W and the heating time is 4 minutes. Step 4: Dry the modified activated carbon to obtain microwave-modified activated carbon.

3. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1 or 2, characterized in that: In the step 1, the activated carbon is added with an acid wash solution and placed in a shaker for shaking and washing. The acid wash solution is a 5% HCI solution. The washing temperature is 25° C., the washing time is 15 hours, and the shaking speed is 120 r / min.

4. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1 or 2, characterized in that: In the step 2, the shaking speed of the shaking table is 120 r / min, the temperature is 25° C., and the shaking time is 30 min.

5. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1 or 2, characterized in that: In the step 3, the amount of condensed water added per gram of activated carbon is 4 mL.

6. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1 or 2, characterized in that: The microwave heating device in step 3 is a household microwave oven.

7. The microwave preparation method of nitrogen-doped modified activated carbon according to claim 1 or 2, characterized in that: The drying time in step 4 is 7 hours and the drying temperature is 100°C.

8. A method for regenerating nitrogen-doped modified activated carbon, characterized in that: The method comprises the following steps: filtering and washing the adsorption saturated nitrogen-doped activated carbon, and then drying it in an oven; adding condensed water to the dried activated carbon, and performing microwave heating, wherein the microwave heating power is 500-650W, and the heating time is 2-6 minutes; taking it out after cooling to room temperature, washing it with distilled water for 3-4 times, and drying it in an oven; the nitrogen-doped activated carbon is the nitrogen-doped activated carbon according to claim 1 or 2.

9. Use of the nitrogen-doped modified activated carbon prepared according to claim 1, 2 or 8 in adsorbing norfloxacin in water.

10. The use of nitrogen-doped modified activated carbon in adsorbing norfloxacin in water according to claim 9, characterized in that: The pH value of the norfloxacin solution is 11.

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