Preparation and regeneration method of nitrogen-doped activated carbon and application thereof in formaldehyde adsorption

Abstract

This invention relates to the field of environmental protection materials technology, providing a method for preparing and regenerating nitrogen-doped activated carbon and its application in formaldehyde adsorption. This invention uses urea, amine compounds, and imidazolium ketones to dope activated carbon. The resulting nitrogen-doped activated carbon exhibits excellent formaldehyde adsorption performance, high formaldehyde removal rate, high clean air delivery rate (CADR), and high saturation adsorption capacity. It is low in cost, widely applicable, and can be regenerated and recycled after formaldehyde adsorption, with a high number of recycling cycles and stable adsorption performance. Example results show that the nitrogen-doped activated carbon provided by this invention achieves a 100% aldehyde removal rate within 1 hour and a CADR of up to 820 m³ / h. 3 The saturated adsorption capacity can reach 8.5 mg / g, and the formaldehyde removal rate is still above 75% within 1 hour after five adsorption-desorption cycles. The clean air delivery rate is 690 m³ / h. 3 The adsorption rate is above 6.3 mg / g / h and the saturated adsorption capacity is above 6.3 mg / g.

Description

Technical Field

[0001] This invention relates to the field of environmental protection materials technology, and in particular to a method for preparing and regenerating nitrogen-doped activated carbon and its application in formaldehyde adsorption. Background Technology

[0002] Formaldehyde (HCHO) is a colorless gas with a strong, pungent odor. Outdoor formaldehyde mainly originates from printing and dyeing materials, paints, textiles, pesticides, and adhesives; indoor formaldehyde mainly comes from decorative materials, plywood, fiberboard, particleboard, and other engineered wood products. HCHO has serious adverse effects on the human body, easily causing symptoms such as edema, eye irritation, headaches, and allergic dermatitis. HCHO also possesses strong carcinogenic, teratogenic, and photochemical reactivity; for example, it can react with nitrogen oxides (NOx). x HCHO undergoes a photochemical reaction. Therefore, in order to protect the atmospheric environment and human health, it is necessary to develop corresponding technologies to remove HCHO. Currently, the main methods used for formaldehyde pollution purification include adsorption, biological purification, photocatalytic degradation, ozone oxidation, and catalytic combustion.

[0003] Biological purification of formaldehyde waste gas refers to the use of microorganisms or plants with organic matter as a carbon source to purify formaldehyde. This technology has low operation and maintenance costs and no secondary pollution, but its biological activity is easily limited by the external environment, resulting in poor sustainability. Photocatalytic degradation mainly relies on photocatalysts. This method has a continuous effect on formaldehyde removal, does not produce secondary pollution, and has no impact on the environment or human health. However, its disadvantages include high cost and susceptibility to effects from time, light intensity, and dust concentration. Ozone oxidation utilizes the strong oxidizing properties of ozone to oxidize formaldehyde into carbon dioxide and water. This method has low purification efficiency and requires precise control of ambient temperature and humidity. Catalytic combustion is a highly efficient treatment technology, but its application is limited, and it can easily cause secondary pollution during the process.

[0004] Adsorption is the most common method for treating formaldehyde waste gas due to its low energy consumption, simple operation, and lack of environmental and application restrictions. Currently, commonly used formaldehyde adsorbents include polymer adsorbents, plant adsorbents, and porous material adsorbents. Polymer adsorbents remove formaldehyde by utilizing the chemical reaction between their functional groups and formaldehyde; plant adsorbents utilize natural plants or their extracts to adsorb formaldehyde; and porous material adsorbents utilize the porous nature of the material to adsorb formaldehyde.

[0005] While polymer adsorbents exhibit high formaldehyde removal rates and adsorption capacities, their preparation methods are complex and often involve toxic reagents, potentially causing secondary pollution. For example, US Patent No. US2017333870A1 describes a method for preparing a formaldehyde-capturing polymer. This polymer is prepared by polymerizing a diterpenoid monomer containing multiple aromatic rings to form a precursor, which is then further polymerized with a sulfonyl-containing compound. This polymer demonstrates extremely high formaldehyde capture and removal efficiency, along with a large adsorption capacity. However, the synthesis process is difficult, the polymerization reaction is hard to control, and the use of a sulfonyl-containing compound is highly toxic, easily causing secondary pollution.

[0006] Plant-based adsorbents are environmentally friendly, but they are often formulated by combining multiple plants or their extracts, resulting in complex formulations. For example, Chinese patent CN107344056A describes a method for preparing a pure natural plant-based formaldehyde removal agent. This method involves mixing, filtering, dissolving, adsorbing and precipitating tea polyphenols, aloe vera, theanine, licorice, ophiopogon japonicus, selenium, and natural antibacterial Chinese herbal medicines, followed by rotary evaporation to obtain the formaldehyde removal agent. This pure natural plant-based formaldehyde removal agent can effectively remove formaldehyde and harmful substances in the air without secondary pollution to humans or the environment. However, extracting active ingredients from natural plants results in extremely low yields, low purity, and low content, making it difficult to achieve large-scale application. Furthermore, the extraction cost is extremely high, resulting in poor economic viability.

[0007] Compared to polymer adsorbents and plant adsorbents, porous material adsorbents are inexpensive and readily available, offering significant economic advantages and being less likely to cause secondary pollution, thus exhibiting good environmental performance. However, current porous material adsorbents generally have low formaldehyde adsorption performance and removal rates, requiring complex modifications to activated carbon to improve their adsorption capacity. For example, Chinese patent CN112619607A describes a formaldehyde adsorbent composed of activated carbon, hollow nanospheres, and a formaldehyde scavenger, with manganese dioxide loaded onto the activated carbon and hollow nanospheres. This method loads manganese dioxide onto activated carbon before loading the formaldehyde scavenger, but the highest formaldehyde removal rate achieved by the resulting adsorbent is only 81.82%. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing and regenerating nitrogen-doped activated carbon and its application in formaldehyde adsorption. The nitrogen-doped activated carbon preparation method provided by the present invention is simple, has good formaldehyde adsorption performance, high formaldehyde removal rate and saturated adsorption capacity, large clean air delivery rate, and excellent circulation performance.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] A method for preparing nitrogen-doped activated carbon includes the following steps:

[0011] The activated carbon is washed with water and then dried to obtain pretreated activated carbon.

[0012] Under stirring conditions, the pretreated activated carbon is sprayed with an aqueous solution containing nitrogen dopant, and then subjected to standing and second drying in sequence to obtain nitrogen-doped activated carbon; the solute in the aqueous solution containing nitrogen dopant includes urea, amine compounds and imidazolidinone; the pH value of the aqueous solution containing nitrogen dopant is 3.5 to 5.5.

[0013] Preferably, the amine compound includes one or more of melamine, dicyandiamide, triethylenetetramine, diethylenetriamine, and trivinylamide; the mass ratio of urea, amine compound, and imidazolidinone is 0.001–12:0.18–9:3–15.

[0014] Preferably, the mass fraction of amine compounds in the nitrogen-containing dopant aqueous solution is 0.18% to 9%, the mass fraction of imidazolidinone is 3% to 15%, and the mass fraction of urea is 0.001% to 12%.

[0015] Preferably, the mass ratio of the nitrogen-containing dopant aqueous solution to the pretreated activated carbon is 1:(1-20).

[0016] Preferably, the pH adjuster used to adjust the pH value of the nitrogen-doped aqueous solution includes one or more of sodium dihydrogen phosphate, sodium bisulfite, and sodium bioxalate.

[0017] Preferably, the temperature of the first drying is 40-150°C, and the drying time is 4-48 hours; the moisture content of the pretreated activated carbon is 0.1 wt%-30 wt%.

[0018] Preferably, the activated carbon includes one or more of fruit shell activated carbon, coal-based activated carbon, and wood powder activated carbon; the mesh size of the activated carbon is 30 to 60 mesh.

[0019] Preferably, the ambient temperature during spraying is 10–50°C, the stirring speed is 60–300 rpm, and stirring continues for 0.1–5 hours after spraying; the settling time is 0.1–24 hours.

[0020] The present invention also provides nitrogen-doped activated carbon prepared by the preparation method described above, comprising activated carbon and a nitrogen-containing dopant supported on the activated carbon; the nitrogen-containing dopant includes urea, amine compounds and imidazolidinone.

[0021] The present invention also provides the application of nitrogen-doped activated carbon as described above in formaldehyde adsorption.

[0022] The present invention also provides a method for regenerating nitrogen-doped activated carbon, wherein the nitrogen-doped activated carbon after adsorbing formaldehyde is treated in a water bath at 40-95°C for 0.5-10 hours, and then dried to a moisture content of 0.1wt%-30wt%; wherein the nitrogen-doped activated carbon is the nitrogen-doped activated carbon described in the above scheme.

[0023] Beneficial effects:

[0024] This invention provides a method for preparing nitrogen-doped activated carbon. First, the method removes a large amount of dust and water-soluble impurities from the surface of the raw activated carbon through washing, preventing the dust and impurities from clogging the pore structure of the activated carbon and releasing adsorption sites on the activated carbon surface. This also facilitates the loading of dopants into the pores of the activated carbon in subsequent steps. This invention uses urea, amine compounds, and imidazolium ketones to dope the activated carbon. The activated carbon provides support for the three nitrogen-containing compounds, while increasing the contact surface between the nitrogen-containing compounds and formaldehyde, thereby increasing the mass transfer and reaction rate of formaldehyde and improving the utilization rate of the nitrogen-containing compounds. Furthermore, because nitrogen atoms have lone pairs of electrons, the electron cloud density and electronegativity around the pores of the activated carbon can be increased; while the carbonyl carbon atoms in formaldehyde are highly electron-deficient and are easily polarized into carbonyl carbocations. Therefore, by doping activated carbon with nitrogen, its electrostatic attraction to carbonyl carbocations in formaldehyde can be enhanced, promoting the addition reaction between nitrogen-containing compounds and formaldehyde to generate formic acid, thereby increasing its adsorption rate and amount of formaldehyde. In addition, the present invention uses three nitrogen-containing compounds in combination, and the synergistic effect of the three nitrogen-containing compounds greatly improves the adsorption performance of nitrogen-doped activated carbon for formaldehyde. Furthermore, since the carbonyl group in the formaldehyde molecule is a polar group, the present invention controls the pH value of the aqueous solution of nitrogen-containing dopant within the acidic range, which can enhance the polarity of activated carbon and the total amount of acidic oxygen-containing functional groups on the surface, thereby improving the adsorption capacity of activated carbon for polar formaldehyde molecules and improving the formaldehyde removal rate. Moreover, the pH value adjuster used in the present invention is a strong base weak acid salt, which will not react with the dopant, and the three nitrogen-containing compounds can exist stably without affecting the interaction between the three nitrogen-containing compounds and formaldehyde.

[0025] Furthermore, the present invention uses a spraying and stirring method to load nitrogen-containing dopants onto activated carbon. The process is simple and convenient, and does not require a high-temperature calcination process. It has low energy consumption, extremely high safety, and the spraying operation can firmly load the nitrogen-containing dopants onto the activated carbon, thereby ensuring that they are not easily detached during production and use, which is more conducive to industrial production.

[0026] This invention also provides nitrogen-doped activated carbon prepared by the preparation method described above. The nitrogen-doped activated carbon provided by this invention exhibits excellent formaldehyde adsorption performance, high formaldehyde removal rate and saturated adsorption capacity, large clean air delivery rate, excellent circulation performance, low cost, low requirements for the adsorption environment, wide applicability, and a simple preparation process that does not involve the use of hazardous chemicals or precious metal catalysts. It is safe, efficient, and has stable adsorption performance.

[0027] This invention also provides a method for regenerating nitrogen-doped activated carbon, comprising the following steps: treating the activated carbon after formaldehyde adsorption in a water bath at 40–95°C for 0.5–10 h, and then drying it to a moisture content of 0.1 wt%–30 wt%. This invention allows the nitrogen-doped activated carbon after formaldehyde adsorption to be regenerated and reused, and the regeneration method provided by this invention is simple and easy to operate.

[0028] The results of the examples show that the nitrogen-doped activated carbon provided by the present invention achieves a 100% removal efficiency of aldehydes within 1 hour, with a clean air delivery rate (CADR) of up to 820 m³ / h. 3 The saturated adsorption capacity can reach 8.5 mg / g, and the formaldehyde removal efficiency is still above 75% within 1 hour after five adsorption-desorption cycles. The clean air output is 690 m³ / h. 3 The adsorption capacity is above 6.3 mg / g per hour. Detailed Implementation

[0029] This invention provides a method for preparing nitrogen-doped activated carbon, comprising the following steps:

[0030] The activated carbon is washed with water and then dried to obtain pretreated activated carbon.

[0031] Under stirring conditions, the pretreated activated carbon is sprayed with an aqueous solution containing nitrogen dopant, and then subjected to standing and second drying in sequence to obtain nitrogen-doped activated carbon; the solute of the aqueous solution containing nitrogen dopant includes urea, amine compounds and imidazolium ketones, and the solvent is water; the pH value of the aqueous solution containing nitrogen dopant is 3.5 to 5.5.

[0032] This invention involves washing activated carbon with water followed by a first drying process to obtain pretreated activated carbon. In this invention, the activated carbon preferably includes one or more of the following: fruit shell activated carbon, coal-based activated carbon, and wood-based powdered activated carbon; the mesh size of the activated carbon is 30-60 mesh; and the specific surface area of ​​the activated carbon is preferably 700-2000 m². 2 / g, more preferably 900-1800m 2 / g, the average pore size is preferably 0.15-5nm, more preferably 1-4nm, and the total pore volume is preferably greater than 0.35cm³. 3 / g. In this invention, the water used for washing is preferably distilled water, and the number of washing cycles is preferably 1 to 20, more preferably 3 to 10; the temperature of the first drying is preferably 40 to 150°C, more preferably 60 to 120°C, and the drying time is preferably 4 to 48 hours, more preferably 8 to 36 hours; the water content of the pretreated activated carbon is preferably 0.1 wt% to 30 wt%, more preferably 0.5 wt% to 25 wt%.

[0033] After obtaining pretreated activated carbon, the present invention sprays the pretreated activated carbon with an aqueous solution containing a nitrogen dopant under stirring conditions, and then performs standing and second drying sequentially to obtain nitrogen-doped activated carbon. In the present invention, the solute of the aqueous solution containing the nitrogen dopant includes urea, amine compounds and imidazolidinone, and the solvent is water; the amine compounds include one or more of melamine, dicyandiamide, triethylenetetramine, diethylenetriamine and trivinylamide; the mass ratio of urea, amine compounds and imidazolidinone is 0.001-12:0.18-9:3-15; the mass fraction of amine compounds in the aqueous solution containing the nitrogen dopant is preferably 0.18%-9%, more preferably 0.5%-8%, the mass fraction of imidazolidinone is preferably 3%-15%, more preferably 5%-10%, and the mass fraction of urea is preferably 0.001%-12%, more preferably 0.01%-10%.

[0034] In this invention, the pH value of the nitrogen-containing dopant aqueous solution is preferably 3.5–5.5, more preferably 4–5; the pH adjuster used to adjust the pH value of the nitrogen-containing dopant aqueous solution preferably includes one or more of sodium dihydrogen phosphate, sodium bisulfite, and sodium hydrogen oxalate, more preferably sodium dihydrogen phosphate; in this invention, the above-mentioned pH adjuster is preferably used in the form of an aqueous solution, wherein the concentration of the sodium dihydrogen phosphate aqueous solution is preferably 0.01–3 mol / L, more preferably 0.5–2.5 mol / L. In a specific embodiment of this invention, it is preferable to first dissolve urea, amine compounds, and imidazolidinone in water, and then add the adjuster to adjust the pH value of the mixed solution to the above-mentioned range, thereby obtaining the nitrogen-containing dopant aqueous solution.

[0035] In this invention, the mass ratio of the nitrogen-containing dopant aqueous solution to the pretreated activated carbon is preferably 1:(1-20), more preferably 1:(1.5-10), and even more preferably 1:(2-5).

[0036] In this invention, the ambient temperature for spraying is preferably 10–50°C, more preferably 20–25°C; the stirring speed is preferably 60–300 rpm, more preferably 60–150 rpm. This invention preferably involves spraying the nitrogen-doped aqueous solution while stirring, and after spraying the nitrogen-doped aqueous solution, stirring continues for 0.1–5 hours, more preferably 0.1–3 hours. This invention sprays the nitrogen-doped aqueous solution into activated carbon under stirring conditions, resulting in a low material-to-liquid ratio, simplicity, and convenience. It also ensures sufficient loading of the nitrogen-doped agent onto the activated carbon, guaranteeing that the nitrogen-doped agent is not easily detached during production and use, and extending the service life of the nitrogen-doped activated carbon material.

[0037] After spraying, the activated carbon adsorbed with the nitrogen-containing dopant aqueous solution is subjected to a second drying process. In this invention, the settling temperature is preferably room temperature, and the settling time is preferably 0.1–24 h, more preferably 0.5–20 h, and even more preferably 4–10 h; this invention allows the nitrogen-containing dopant to be fully adsorbed and firmly loaded onto the activated carbon through settling.

[0038] In this invention, the temperature of the second drying is preferably 80-120°C, more preferably 90-110°C, and the time of the first drying is preferably 4-48 hours, more preferably 8-36 hours; after drying, it can be cooled to room temperature; the water content of the nitrogen-doped activated carbon obtained after drying is preferably 0.1wt%-30wt%, more preferably 0.5wt%-25wt%.

[0039] The present invention also provides nitrogen-doped activated carbon prepared by the preparation method described above, comprising activated carbon and a nitrogen-containing dopant supported in the activated carbon.

[0040] This invention also provides the application of the nitrogen-doped activated carbon described in the above-mentioned scheme as a formaldehyde adsorbent. This invention does not have special requirements for the method of application; any method well-known to those skilled in the art can be used. In a specific embodiment of this invention, the nitrogen-doped activated carbon prepared in this invention is made into a filter element and assembled into an air purifier for use; this invention does not have special requirements for the specific structure of the air purifier; any air purifier with a structure well-known to those skilled in the art can be used.

[0041] This invention also provides a method for regenerating nitrogen-doped activated carbon, comprising the following steps: treating the nitrogen-doped activated carbon after formaldehyde adsorption in a water bath at 40–95°C for 0.5–10 h, and then drying it to a moisture content of 0.1 wt%–30 wt%. In this invention, the drying temperature is preferably 40–120°C, the drying time is preferably 6–24 h, and the drying is preferably carried out in an oven. Specifically, the water bath treatment involves immersing the nitrogen-doped activated carbon after formaldehyde adsorption in water at the above-mentioned temperature. This invention desorbs formaldehyde adsorbed on nitrogen-doped activated carbon through water bath treatment, collects the desorbed formaldehyde for further processing, and reuses the regenerated nitrogen-doped activated carbon.

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof.

[0043] Example 1

[0044] Coal-based activated carbon with a particle size of 40 mesh (specific surface area of ​​1450 m²) was used. 2 / g, average pore size is 2.5nm, total pore volume is 0.53m³ 3 The activated carbon was washed once with distilled water and then dried in an oven at 120°C for 36 hours until the moisture content was 2%, thus obtaining pretreated activated carbon.

[0045] Urea, melamine, and imidazolidinone were dissolved in water, and the pH of the mixed solution was adjusted to 4 using 0.2 mol / L sodium dihydrogen phosphate to obtain an aqueous solution containing nitrogen dopant, wherein the mass fraction of urea was 8%, the mass fraction of melamine was 0.2%, and the mass fraction of imidazolidinone was 6%.

[0046] The nitrogen-doped activated carbon was sprayed at 25°C with a nitrogen-doped aqueous solution and pretreated activated carbon at a mass ratio of 1:2. The mixture was stirred while spraying. After spraying, the carbon was allowed to stand for 4 hours and then dried in an oven at 90°C for 10 hours until the moisture content was 4%.

[0047] The nitrogen-doped activated carbon was used to adsorb formaldehyde, and the nitrogen-doped activated carbon after adsorption saturation was regenerated and reused. The regeneration method of nitrogen-doped activated carbon is as follows: the activated carbon after adsorbing formaldehyde is treated in a water bath at 80°C for 5 hours, and then dried in an oven at 65°C for 12 hours until the moisture content is 1.5 wt%.

[0048] According to the testing requirements in GB / T 18801-2015 "Air Purifiers", the clean air delivery rate (CADR) of nitrogen-doped activated carbon was tested. 甲醛 The formaldehyde removal rate and saturated adsorption capacity were calculated. Results showed that after 1 hour of adsorption by nitrogen-doped activated carbon, the formaldehyde removal rate reached 100%, and the clean air delivery rate (CADR) was 825 m³ / h.3 The saturated adsorption capacity can reach 8.7 mg / g per hour. After five adsorption-desorption cycles, and 1 hour of adsorption after regeneration of nitrogen-doped activated carbon, the formaldehyde removal rate can still reach 80%, with a clean air delivery rate of 697 m³ / h. 3 / h, the saturated adsorption capacity can reach 6.6mg / g.

[0049] Example 2

[0050] Coconut shell activated carbon with a particle size of 50 mesh (specific surface area of ​​1750 m²) was used. 2 / g, average pore size is 3.2nm, total pore volume is 0.59m³. 3 The activated carbon was washed 13 times with distilled water and then dried in an oven at 105°C for 24 hours until the moisture content was 2%, thus obtaining pretreated activated carbon.

[0051] Urea, triethylenetetramine, and imidazolidinone were dissolved in water, and the pH of the mixed solution was adjusted to 5 using 0.2 mol / L sodium dihydrogen phosphate to obtain an aqueous solution containing nitrogen dopant, wherein the mass fraction of urea was 4%, the mass fraction of triethylenetetramine was 3%, and the mass fraction of imidazolidinone was 5%.

[0052] The nitrogen-doped activated carbon was sprayed at 25°C with a nitrogen-doped aqueous solution and pretreated activated carbon at a mass ratio of 1:1.5. The mixture was stirred while spraying. After spraying, the mixture was allowed to stand for 6 hours and then dried in an oven at 110°C for 20 hours until the moisture content was 2%.

[0053] The nitrogen-doped activated carbon was used to adsorb formaldehyde, and the nitrogen-doped activated carbon after adsorption saturation was regenerated and reused. The regeneration method of nitrogen-doped activated carbon is as follows: the activated carbon after adsorbing formaldehyde is treated in a water bath at 92°C for 8 hours, and then dried in an oven at 81°C for 15 hours until the moisture content is 3wt%.

[0054] The nitrogen-doped activated carbon obtained was tested for clean air delivery rate (CADR), formaldehyde removal rate, and saturated adsorption capacity according to the method in Example 1. The results showed that the formaldehyde removal rate was 100% after 1 hour of adsorption, and the CADR was 830 m³ / h. 3 The saturated adsorption capacity can reach 8.9 mg / g per hour. After five adsorption-desorption cycles, the regenerated nitrogen-doped activated carbon still achieves a formaldehyde removal rate of 81% after 1 hour of adsorption, with a clean air delivery rate of 700 m³ / h. 3 / h, the saturated adsorption capacity can reach 6.7mg / g.

[0055] Comparative Example 1

[0056] The other conditions were the same as in Example 2, except that urea was not added, resulting in activated carbon doped with triethylenetetramine and imidazolidinone.

[0057] Comparative Example 2

[0058] The other conditions were the same as in Example 2, except that triethylenetetramine was not added, resulting in activated carbon doped with urea and imidazolidinone.

[0059] Comparative Example 3

[0060] The other conditions were the same as in Example 2, except that imidazolidinone was not added, resulting in activated carbon doped with urea and triethylenetetramine.

[0061] Following the method in Example 1, formaldehyde adsorption tests were conducted on the doped activated carbon obtained in Example 2 and Comparative Examples 1-3. The formaldehyde removal rates at 0.5h, 1h, 1.5h, and 2h were recorded, along with the clean air delivery rate, saturated adsorption capacity, and recycling performance. The results are listed in Tables 1 and 2.

[0062] Table 1. Formaldehyde removal rate, clean air delivery rate, and saturated adsorption capacity of the nitrogen-doped activated carbon obtained in Example 2 and Comparative Examples 1-3.

[0063]

[0064] Table 2. Formaldehyde removal rate, clean air delivery rate, and saturated adsorption capacity of nitrogen-doped activated carbon obtained in Example 2 and Comparative Examples 1-3 after five adsorption-desorption cycles.

[0065]

[0066] As can be seen from the data in Tables 1-2, when one of the dopants was omitted in Comparative Examples 1-3, the formaldehyde removal rate, clean air delivery rate, and saturated adsorption capacity of the nitrogen-doped activated carbon were significantly reduced, and the recycling performance deteriorated, indicating that the three nitrogen-containing dopants had a synergistic effect.

[0067] Example 3

[0068] The other conditions are the same as in Example 1, except that the melamine is replaced with dicyandiamide.

[0069] The nitrogen-doped activated carbon obtained in Example 3 was tested for clean air delivery rate (CADR), formaldehyde removal rate, saturated adsorption capacity, and circulation performance according to the method in Example 1. The results showed that the formaldehyde removal rate reached 100% after 1 hour of adsorption, and the CADR was 828 m³ / h. 3 The saturated adsorption capacity can reach 8.7 mg / g. After five adsorption-desorption cycles, the regenerated nitrogen-doped activated carbon still achieves a formaldehyde removal rate of 77% and a clean air delivery rate of 701 m³ / h after 1 hour of adsorption. 3 / h, the saturated adsorption capacity can reach 6.4mg / g.

[0070] Example 4

[0071] The other conditions are the same as in Example 2, except that the triethylenetetramine is replaced with diethylenetriamine.

[0072] The nitrogen-doped activated carbon obtained in Example 4 was tested for clean air delivery rate (CADR), formaldehyde removal rate, saturated adsorption capacity, and circulation performance according to the method in Example 1. The results showed that the formaldehyde removal rate reached 100% after 1 hour of adsorption, and the CADR was 835 m³ / h. 3 The saturated adsorption capacity can reach 8.8 mg / g. After five adsorption-desorption cycles, the regenerated nitrogen-doped activated carbon still achieves a formaldehyde removal rate of 82% and a clean air delivery rate of 710 m³ / h after 1 hour of adsorption. 3 / h, the saturated adsorption capacity can reach 6.6mg / g.

[0073] Comparative Example 4

[0074] Other conditions are the same as in Example 1, except that the step of adjusting the pH value of the nitrogen-doped solution is omitted. Urea, melamine and imidazolidinone are dissolved in water to obtain a nitrogen-doped solution, which is then used to directly spray the pretreated activated carbon.

[0075] The nitrogen-doped activated carbon obtained in Comparative Example 4 was tested for clean air delivery rate (CADR), formaldehyde removal rate, saturated adsorption capacity, and circulation performance according to the method in Example 1. The results showed that the formaldehyde removal rate was 65% after 1 hour of adsorption, and the CADR was 550 m³ / h. 3 / h, saturated adsorption capacity 5.6mg / g, after five adsorption-desorption cycles, the regenerated nitrogen-doped activated carbon achieved a formaldehyde removal rate of 50% and a clean air delivery rate of 320m³ / h after 1 hour of adsorption. 3 The saturated adsorption capacity can reach 3.2 mg / g per hour. This result indicates that by controlling the pH of the nitrogen-doped aqueous solution within the acidic range, this invention can enhance the polarity of activated carbon and the total amount of acidic oxygen-containing functional groups on its surface, thereby improving the adsorption capacity of activated carbon for polar formaldehyde molecules.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-doped activated carbon, characterized in that, Includes the following steps: The activated carbon is washed with water and then dried to obtain pretreated activated carbon. Under stirring conditions, the pretreated activated carbon is sprayed with an aqueous solution containing a nitrogen dopant, followed by a period of settling and then drying to obtain nitrogen-doped activated carbon. The solute in the aqueous solution containing the nitrogen dopant includes urea, amine compounds, and imidazolidinone. The pH value of the aqueous solution containing the nitrogen dopant is 3.5-5.

5. The amine compounds are one or more selected from melamine, dicyandiamide, triethylenetetramine, and diethylenetriamine. The mass ratio of urea, amine compounds, and imidazolidinone is 0.001-12:0.18-9:3-15. The pH value of the nitrogen-containing dopant aqueous solution is adjusted by sodium dihydrogen phosphate; the ambient temperature during spraying is 10~50℃; the stirring speed is 60~300 rpm; stirring continues for 0.1~5 hours after spraying; and the settling time is 0.1~24 hours.

2. The preparation method according to claim 1, characterized in that, The nitrogen-doped aqueous solution contains 0.18% to 9% amine compounds, 3% to 15% imidazolidinone, and 0.001% to 12% urea by mass; the mass ratio of the nitrogen-doped aqueous solution to the pretreated activated carbon is 1:(1 to 20).

3. The preparation method according to claim 1, characterized in that, The first drying temperature is 40~150℃, and the drying time is 4~48h; the water content of the pretreated activated carbon is 0.1wt%~30wt%.

4. The preparation method according to claim 1, characterized in that, The activated carbon includes one or more of the following: fruit shell activated carbon, coal-based activated carbon, and wood powder activated carbon; the mesh size of the activated carbon is 30-60 mesh.

5. The nitrogen-doped activated carbon prepared by the preparation method according to any one of claims 1 to 4 comprises activated carbon and a nitrogen-containing dopant supported on the activated carbon; the nitrogen-containing dopant comprises urea, amine compounds and imidazolidinones.

6. The application of the nitrogen-doped activated carbon according to claim 5 in formaldehyde adsorption.

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