Preparation method of modified activated carbon for removing formaldehyde

Abstract

The present invention relates to the technical field of formaldehyde adsorption, and in particular to a preparation method of a modified activated carbon for removing formaldehyde, comprising: S1, performing acidification pretreatment on coconut shell charcoal, grafting polyethyleneimine onto the pretreated coconut shell charcoal to obtain activated carbon loaded with polyethyleneimine; S2, performing impregnation treatment and cyclohexanol treatment on the activated carbon loaded with polyethyleneimine to obtain functionalized activated carbon; S3, reacting magnesium-aluminum hydrotalcite with a quaternary ammonium salt solution and a sodium benzenesulfonate solution to obtain modified hydrotalcite; reacting the modified hydrotalcite with a vinyl silane coupling agent to obtain vinyl hydrotalcite; S4, reacting the vinyl hydrotalcite with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole to obtain secondary modified hydrotalcite; S5, dispersing the secondary modified hydrotalcite and the functionalized activated carbon in water, and adding glutaraldehyde to obtain modified activated carbon. The modified activated carbon prepared by the present invention realizes the selective recognition, efficient adsorption and catalytic degradation of formaldehyde.

Description

Technical Field

[0001] The present invention relates to the technical field of formaldehyde adsorption, and particularly to a preparation method of modified activated carbon for removing formaldehyde. Background Art

[0002] Formaldehyde is a highly harmful indoor air pollutant. Long-term exposure to formaldehyde can significantly increase the risk of acute or chronic toxic diseases in people, and even short-term exposure may cause respiratory problems. Formaldehyde has been classified as a Group 1 human carcinogen, and in some residential surveys, its average indoor concentration often exceeds the 8-hour reference exposure level recommended by the Environmental Protection Agency. Approximately 2.8 million people worldwide are affected by indoor pollution caused by formaldehyde each year, and people spend most of their time (about 88%) indoors. The cycle of formaldehyde release from furniture and decorative coatings is long, which poses a serious threat to human health. Currently, there are various materials for adsorbing formaldehyde on the market, including activated carbon, photocatalytic materials, diatom mud, etc., which can meet the needs of different application scenarios. Physical adsorption materials have high safety, but they also have disadvantages such as low adsorption capacity, being restricted by the environment, and high cost.

[0003] Coconut shell activated carbon has a developed microporous structure and a large specific surface area, which enables it to efficiently adsorb small molecule harmful substances such as formaldehyde. Its micropore size is relatively appropriate and can match well with formaldehyde molecules, thereby enhancing the adsorption effect on formaldehyde. At the same time, the coconut shell itself is hard and naturally environmentally friendly, and will not cause harm to the environment and human health during production and use, and the post-treatment after use is relatively simple. It is an excellent raw material for preparing activated carbon. Compared with some high-tech adsorption materials, coconut shell activated carbon has a lower cost and a higher cost performance, and can reduce the cost of treating indoor air pollution while meeting the demand for adsorbing formaldehyde. In order to further improve the efficiency of activated carbon in adsorbing formaldehyde, the activated carbon can be modified.

[0004] The existing patent CN201410713305.7 discloses a preparation method of activated carbon capable of eliminating formaldehyde. This method uses activated carbon as an adsorption material, modifies the activated carbon with a surfactant; then loads the modified activated carbon with a formaldehyde scavenger; and prepares the activated carbon capable of eliminating formaldehyde by drying the loaded activated carbon at room temperature or by freeze-drying. The activated carbon capable of eliminating formaldehyde prepared by the present invention is simple in production and use, and has obvious effects. However, in the above technical solution, only a simple combination method of surfactant modification and formaldehyde scavenger loading is used for treatment, and the degradation ability of formaldehyde is limited, resulting in the activated carbon being easily saturated, and thus it is difficult to achieve continuous and efficient removal of formaldehyde. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a modified activated carbon for removing formaldehyde, so as to solve the problem in the prior art that the formaldehyde degradation ability is limited and it is difficult to achieve continuous and efficient removal of formaldehyde.

[0006] The technical solution of the present invention is realized as follows: The present invention provides a method for preparing a modified activated carbon for removing formaldehyde, comprising the following steps:

[0007] S1. Acidify and pretreat the coconut shell charcoal, then disperse the pretreated coconut shell charcoal in deionized water, and then add polyethyleneimine and epichlorohydrin thereto, and heat and stir for reaction to obtain activated carbon loaded with polyethyleneimine;

[0008] S2. Immerse the activated carbon loaded with polyethyleneimine in a potassium permanganate solution for impregnation treatment, then disperse the impregnated activated carbon in deionized water, add a sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, and dropwise add cyclohexanol at 40 - 50 °C, and then continue to heat and react for 1 - 2 h to obtain functionalized activated carbon;

[0009] S3. Disperse magnesium aluminum hydrotalcite in water, add a quaternary ammonium salt solution and a sodium benzenesulfonate solution respectively, and stir and react at 60 - 70 °C for 16 - 20 h to obtain modified hydrotalcite; Disperse the modified hydrotalcite in a toluene solution, add a vinyl silane coupling agent for reaction, and reflux and react at 50 - 70 °C for 7 - 9 h to obtain vinyl hydrotalcite;

[0010] S4. Then disperse the vinyl hydrotalcite in ethanol, add 4 - amino - 3 - hydrazino - 5 - mercapto - 1,2,4 - triazole and benzophenone, and stir and react at 40 - 50 °C for 5 - 7 h to obtain secondary modified hydrotalcite;

[0011] S5. Disperse the secondary modified hydrotalcite and the functionalized activated carbon in water, add a sodium bicarbonate solution to adjust the pH to 7.5 - 9, add glutaraldehyde, and stir and react at 40 - 50 °C for 10 - 14 h. After the reaction is completed, filter, wash, and dry to obtain modified activated carbon.

[0012] In the present invention, the functional modification of activated carbon is achieved by grafting polyethyleneimine on the surface of activated carbon and loading manganese dioxide. The layer spacing of magnesium-aluminum hydrotalcite is increased through intercalation modification to improve its storage capacity for formaldehyde. Meanwhile, vinyl silane coupling agent is grafted on the surface and covalently bonded with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole to introduce amino, sulfur, hydrazino and imidazole groups on the surface of magnesium-aluminum hydrotalcite. Finally, the functionalized activated carbon is covalently connected with the secondary modified hydrotalcite through glutaraldehyde to form a stable composite structure. The selective recognition and directional enrichment of formaldehyde are realized through the amino, sulfur, hydrazino and imidazole groups on the surface of the modified activated carbon material, providing sufficient adsorption sites and storage space for formaldehyde. Finally, the degradation and transformation of formaldehyde are promoted by the catalytic action of manganese dioxide, thus generating a cyclic scavenging mode of recognition-adsorption-solid loading-catalytic oxidation to achieve the effect of efficiently scavenging formaldehyde.

[0013] On the basis of the above technical solutions, preferably, in step S1, the pretreatment includes: crushing and screening coconut shell charcoal to obtain granular charcoal with a mesh size of 30-60 meshes, mixing the granular charcoal with a dilute nitric acid solution, heating and reacting at 50-70 °C for 4-6 h, filtering, washing and drying to obtain pretreated coconut shell charcoal; the mass-volume ratio of the granular charcoal to the dilute nitric acid solution is 1 g:8-12 ml, and the concentration of the dilute nitric acid solution is 2-5 mol / L.

[0014] On the basis of the above technical solutions, preferably, in step S1, the mass ratio of the pretreated coconut shell charcoal, polyethyleneimine and epichlorohydrin is 6-9:4-6:2-4, and heating and stirring are carried out at 50-80 °C for 6-10 h.

[0015] The surface of coconut shell charcoal is activated through acid pretreatment to increase oxygen-containing functional groups such as surface hydroxyl groups, providing active sites for subsequent modification. At the same time, polyethyleneimine and epichlorohydrin are introduced for surface functional modification, where polyethyleneimine provides a large number of amino functional groups to form a stable functional layer. The introduction of amino groups not only improves the adsorption of formaldehyde but also provides reaction sites for subsequent reactions.

[0016] On the basis of the above technical solutions, preferably, in step S2, the mass ratio of the activated carbon loaded with polyethyleneimine to the potassium permanganate solution is 1:2.5-3.5, the concentration of the potassium permanganate solution is 0.005-0.02 mol / L, the temperature of the impregnation treatment is 30-80 °C, and the time of the impregnation treatment is 13-16 h; the mass percentage of the sodium hydroxide solution is 8-12%, and the mass ratio of the impregnated activated carbon to cyclohexanol is 1:1.5-2.

[0017] Through impregnation treatment with potassium permanganate solution, manganese oxide active centers are formed on the surface of activated carbon, and then manganese dioxide particles are generated on the surface of activated carbon to achieve the adsorption and catalytic degradation of formaldehyde, convert it into harmless carbon dioxide and water, and thus achieve the continuous removal of formaldehyde.

[0018] Based on the above technical solutions, preferably, in step S3, the mass ratio of magnesium-aluminum hydrotalcite, quaternary ammonium salt and sodium benzenesulfonate is 2-3:1-2:1-2, the concentration of the quaternary ammonium salt solution is 0.04-0.06 mol / L, and the sodium benzenesulfonate solution is 0.03-0.05 mol / L.

[0019] Based on the above technical solutions, preferably, the quaternary ammonium salt is any one of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, cetyltrimethylammonium chloride, octadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride.

[0020] Based on the above technical solutions, preferably, in step S3, the mass ratio of the modified hydrotalcite to the vinyl silane coupling agent is 1:0.5-1.0, and the vinyl silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

[0021] In step S3, the magnesium-aluminum hydrotalcite is intercalated and modified with a quaternary ammonium salt and sodium benzenesulfonate to increase its layer spacing and provide more storage space for formaldehyde; then, unsaturated double bonds are introduced on the surface of the hydrotalcite through grafting of the vinyl silane coupling agent to provide reaction sites for the introduction of subsequent functional groups.

[0022] Based on the above technical solutions, preferably, in step S4, the mass ratio of vinyl hydrotalcite, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole and benzophenone is 3-4:1-2:0.5-0.8.

[0023] In step S4, the double bond on the vinyl hydrotalcite reacts with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole to introduce sulfur atoms, amino groups and imidazole groups on the surface of the magnesium-aluminum hydrotalcite, thereby enhancing the selective recognition ability of the material for formaldehyde, achieving efficient capture of formaldehyde, preventing desorption and improving adsorption stability.

[0024] Based on the above technical solutions, preferably, in step S5, the mass ratio of the secondary modified hydrotalcite to the functionalized activated carbon is 1-1.5:1, and the addition amount of glutaraldehyde is 5-15% of the mass of the secondary modified hydrotalcite.

[0025] The present invention provides a modified activated carbon for removing formaldehyde prepared by the preparation method described in any one of the above.

[0026] The preparation method of the modified activated carbon for removing formaldehyde of the present invention has the following beneficial effects compared with the prior art:

[0027] (1) By sequentially loading a polyethyleneimine functional layer and manganese dioxide on the surface of activated carbon, and introducing a doubly modified hydrotalcite as a co-carrier, and finally forming a stable composite structure through aldehyde-amine crosslinking, the modified activated carbon is obtained. It has excellent adsorption effect when applied to formaldehyde adsorption, realizing the integration of multiple functions of selective recognition, efficient adsorption and catalytic degradation of formaldehyde; among them, the polyethyleneimine layer on the surface of activated carbon and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole grafted on the surface of hydrotalcite introduce amino groups, sulfur atoms, hydrazino groups and imidazole groups. These functional groups can realize the selective recognition and directional enrichment of formaldehyde; the intercalation-modified hydrotalcite provides a larger interlayer space for the storage of formaldehyde molecules; manganese dioxide, as a catalytic active center, can promote the oxidative degradation of formaldehyde. The functionalized activated carbon and the secondary-modified magnesium-aluminum hydrotalcite work together to achieve a cyclic scavenging mode of "recognition-adsorption-solid loading-catalytic oxidation";

[0028] (2) By first covalently grafting polyethyleneimine onto the surface of activated carbon to form a stable three-dimensional network structure. On the one hand, a large number of amino active sites are provided. The amino group can not only serve as a subsequent reaction site, but also the residual amino group can form a stable Schiff base structure with formaldehyde molecules, thus achieving efficient capture of formaldehyde; on the other hand, the polyethyleneimine layer can also provide a suitable microenvironment to promote the uniform nucleation of manganese dioxide on the surface of activated carbon; by loading manganese dioxide on the surface of activated carbon, manganese dioxide has a catalytic oxidation effect and can oxidize formaldehyde to achieve the complete removal of formaldehyde, achieving the effect of continuously adsorbing formaldehyde;

[0029] (3) By intercalation modification of magnesium-aluminum hydrotalcite with quaternary ammonium salt and sodium benzenesulfonate, its layer spacing is significantly increased, and the storage space of formaldehyde molecules is improved; then, unsaturated double bonds are introduced on the surface of hydrotalcite through vinyl silane coupling agent to provide reaction sites for subsequent functionalization; further, multiple functional groups are introduced on the surface of hydrotalcite by grafting 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole. Among them, the amino group can react with formaldehyde to form a Schiff base reaction for chemical fixation, the hydrazino group can form a stable hydrazone compound with formaldehyde, and the imidazole group enhances the affinity for formaldehyde molecules through its special electronic structure. The synergistic effect of these functional groups not only provides multiple chemisorption sites, but also realizes the selective recognition and directional enrichment of formaldehyde molecules, significantly improving the formaldehyde capture efficiency of the material; at the same time, the silylation modification of the vinyl silane coupling agent improves the organic compatibility of the hydrotalcite, providing good interfacial bonding conditions for the composite with the functionalized activated carbon. Brief Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 It is a flowchart of the preparation method of the modified activated carbon for removing formaldehyde of the present invention. Detailed implementation manners

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0033] It should be noted that in this embodiment, the magnesium-aluminum hydrotalcite is purchased from Hubei Kewode Chemical Co., Ltd., and the CAS number is 11097-59-9.

[0034] Example 1

[0035] As Figure 1 shown, this embodiment provides a preparation method of modified activated carbon for removing formaldehyde, including the following steps:

[0036] S1. Crush and screen the coconut shell charcoal to obtain granular charcoal with a mesh number of 50. Mix 10 g of the granular charcoal with 100 ml of dilute nitric acid solution (3.5 mol / L), heat and react at 60 °C for 5 h. After the reaction, filter, wash, and dry to obtain pretreated coconut shell charcoal;

[0037] Disperse 7.5 g of the pretreated coconut shell charcoal in 75 ml of deionized water, then add 5 g of polyethyleneimine and 3 g of epichlorohydrin thereto, heat and stir the reaction at 65 °C for 8 h. After the reaction, filter, wash, and dry to obtain activated carbon loaded with polyethyleneimine;

[0038] S2. Add 10 g of the activated carbon loaded with polyethyleneimine to 30 g of potassium permanganate solution (0.01 mol / L), and impregnate at 55 °C for 14.5 h; then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add 10% sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, and dropwise add 18 g of cyclohexanol at 45 °C, continue to heat and react for 1.5 h. After the reaction, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0039] S3. Disperse 25 g of magnesium aluminum hydrotalcite in 250 ml of water. Take 15 g of cetyltrimethylammonium chloride to prepare a cetyltrimethylammonium chloride solution with a concentration of 0.05 mol / L, and 15 g of sodium benzenesulfonate to prepare a sodium benzenesulfonate solution with a concentration of 0.04 mol / L. Add the quaternary ammonium salt solution and the sodium benzenesulfonate solution to the reaction solution respectively, and stir and react at 65 °C for 18 h. After the reaction is completed, filter, wash, and dry to obtain modified hydrotalcite; Disperse 10 g of the modified hydrotalcite in 150 ml of toluene solution, add 7.5 g of vinyltrimethoxysilane and react, reflux and react at 65 °C for 8 h. After the reaction is completed, filter, wash, and dry to obtain vinyl hydrotalcite;

[0040] S4. Then disperse 35 g of vinyl hydrotalcite in 350 ml of ethanol, add 7.5 g of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole and 6.5 g of diphenylacetone, and stir and react at 45 °C for 6 h. After the reaction is completed, filter, wash, and dry to obtain the secondarily modified hydrotalcite;

[0041] S5. Disperse 12.5 g of the secondarily modified hydrotalcite and 10 g of functionalized activated carbon in water, add a sodium bicarbonate solution (mass percentage is 1-2%) to adjust the pH to 7.5-9, add 1.0 g of glutaraldehyde, and stir and react at 45 °C for 12 h. After the reaction is completed, filter, wash, and dry to obtain modified activated carbon.

[0042] Example 2

[0043] This example provides a preparation method of modified activated carbon for removing formaldehyde, including the following steps:

[0044] S1. Crush and screen coconut shell charcoal to obtain granular charcoal with a mesh size of 30. Mix 10 g of the granular charcoal with 80 ml of dilute nitric acid solution (5 mol / L), heat and react at 50 °C for 6 h. After the reaction is completed, filter, wash, and dry to obtain pretreated coconut shell charcoal; Disperse 6 g of the pretreated coconut shell charcoal in 60 ml of deionized water, then add 4 g of polyethyleneimine and 2 g of epichlorohydrin thereto, and heat and stir and react at 50 °C for 10 h. After the reaction is completed, filter, wash, and dry to obtain activated carbon loaded with polyethyleneimine;

[0045] Disperse 10 g of the activated carbon loaded with polyethyleneimine in 25 g of potassium permanganate solution (0.02 mol / L), and impregnate at 30 °C for 16 h; Then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add an 8% sodium hydroxide solution to adjust the solution pH to 7.5-8.5, dropwise add 15 g of cyclohexanol at 40 °C, and continue to heat and react for 2 h. After the reaction is completed, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0046] S2. Add 10 g of the activated carbon loaded with polyethyleneimine to 25 g of potassium permanganate solution (0.02 mol / L), and carry out impregnation treatment at 30 °C for 16 h; Then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add an 8% sodium hydroxide solution to adjust the solution pH to 7.5-8.5, dropwise add 15 g of cyclohexanol at 40 °C, and continue to heat and react for 2 h. After the reaction is completed, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0047] S3. Disperse 20 g of magnesium-aluminum hydrotalcite in 200 ml of water. Take 10 g of cetyltrimethylammonium chloride and prepare a cetyltrimethylammonium chloride solution with a concentration of 0.04 mol / L, and take 10 g of sodium benzenesulfonate and prepare a sodium benzenesulfonate solution with a concentration of 0.03 mol / L. Add the quaternary ammonium salt solution and the sodium benzenesulfonate solution to the reaction solution respectively, and stir and react at 60 °C for 20 h. After the reaction is completed, filter, wash, and dry to obtain modified hydrotalcite; Disperse 10 g of the modified hydrotalcite in 150 ml of toluene solution, add 5 g of vinyltrimethoxysilane and react, reflux and react at 50 °C for 9 h. After the reaction is completed, filter, wash, and dry to obtain vinyl hydrotalcite;

[0048] S4. Then disperse 30 g of vinyl hydrotalcite in 300 ml of ethanol, add 5 g of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole and 5 g of benzophenone, and stir and react at 40 °C for 7 h. After the reaction is completed, filter, wash, and dry to obtain secondary modified hydrotalcite;

[0049] S5. Disperse 10 g of the secondary modified hydrotalcite and 10 g of functionalized activated carbon in water, add a sodium bicarbonate solution (mass percentage is 1-2%) to adjust the pH to 7.5-9, add 0.5 g of glutaraldehyde, and stir and react at 50 °C for 10 h. After the reaction is completed, filter, wash, and dry to obtain modified activated carbon.

[0050] Example 3

[0051] This example provides a preparation method of modified activated carbon for removing formaldehyde, including the following steps:

[0052] S1. Crush and screen the coconut shell charcoal to obtain granular charcoal with a mesh number of 60. Mix 10 g of the granular charcoal with 120 ml of dilute nitric acid solution (2 mol / L), and heat and react at 70 °C for 4 h. After the reaction is completed, filter, wash, and dry to obtain pretreated coconut shell charcoal;

[0053] Disperse 9 g of the pretreated coconut shell charcoal in 90 ml of deionized water, then add 6 g of polyethyleneimine and 4 g of epichlorohydrin thereto, and heat and stir and react at 80 °C for 6 h. After the reaction is completed, filter, wash, and dry to obtain activated carbon loaded with polyethyleneimine;

[0054] S2. Add 10 g of activated carbon loaded with polyethyleneimine to 35 g of potassium permanganate solution (0.005 mol / L), and carry out impregnation treatment at 80 °C for 13 h; then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add 12% sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, and dropwise add 20 g of cyclohexanol at 50 °C, continue heating and reacting for 1 h. After the reaction is completed, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0055] S3. Disperse 30 g of magnesium-aluminum hydrotalcite in 300 ml of water. Take 20 g of cetyltrimethylammonium chloride and prepare a cetyltrimethylammonium chloride solution with a concentration of 0.06 mol / L, and prepare 20 g of sodium benzenesulfonate into a sodium benzenesulfonate solution with a concentration of 0.05 mol / L. Add the quaternary ammonium salt solution and the sodium benzenesulfonate solution to the reaction solution respectively, and stir and react at 70 °C for 16 h. After the reaction is completed, filter, wash, and dry to obtain modified hydrotalcite; Disperse 10 g of the modified hydrotalcite in 150 ml of toluene solution, add 10 g of vinyltrimethoxysilane and react, reflux and react at 70 °C for 7 h. After the reaction is completed, filter, wash, and dry to obtain vinyl hydrotalcite;

[0056] S4. Then disperse 40 g of vinyl hydrotalcite in 400 ml of ethanol, add 10 g of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole and 8 g of benzophenone, and stir and react at 50 °C for 5 h. After the reaction is completed, filter, wash, and dry to obtain secondary modified hydrotalcite;

[0057] S5. Disperse 15 g of the secondary modified hydrotalcite and 10 g of the functionalized activated carbon in water, add sodium bicarbonate solution (mass percentage is 1 - 2%) to adjust the pH to 7.5 - 9, add 1.5 g of glutaraldehyde, and stir and react at 45 °C for 14 h. After the reaction is completed, filter, wash, and dry to obtain modified activated carbon.

[0058] Comparative Example 1

[0059] This comparative example provides a preparation method of modified activated carbon for removing formaldehyde, including the following steps:

[0060] S1. Crush and screen coconut shell charcoal to obtain granular charcoal with a mesh size of 50 meshes. Mix 10 g of the granular charcoal with 100 ml of dilute nitric acid solution (3.5 mol / L), heat and react at 60 °C for 5 h. After the reaction is completed, filter, wash, and dry to obtain pretreated coconut shell charcoal;

[0061] S2. Add 10 g of pretreated coconut shell charcoal to 30 g of potassium permanganate solution (0.01 mol / L), and carry out impregnation treatment at 55 °C for 14.5 h; then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add 10% sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, dropwise add 18 g of cyclohexanol at 45 °C, continue heating and reacting for 1.5 h, after the reaction is completed, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0062] S3. Disperse 10 g of magnesium-aluminum hydrotalcite in 150 ml of toluene solution, add 7.5 g of vinyltrimethoxysilane and react, reflux and react at 65 °C for 8 h, after the reaction is completed, filter, wash, and dry to obtain vinyl hydrotalcite;

[0063] S4. Disperse 12.5 g of vinyl hydrotalcite and 10 g of functionalized activated carbon in water, add sodium bicarbonate solution (mass percentage is 1 - 2%) to adjust the pH to 7.5 - 9, add 1.0 g of glutaraldehyde, stir and mix at 45 °C for 12 h, filter, wash, and dry to obtain modified activated carbon.

[0064] Comparative Example 2

[0065] This comparative example provides a preparation method of modified activated carbon for removing formaldehyde, including the following steps:

[0066] S1. Crush and screen the coconut shell charcoal to obtain granular charcoal with a mesh size of 50, mix 10 g of the granular charcoal with 100 ml of dilute nitric acid solution (3.5 mol / L), heat and react at 60 °C for 5 h, after the reaction is completed, filter, wash, and dry to obtain pretreated coconut shell charcoal;

[0067] S2. Add 10 g of pretreated coconut shell charcoal to 30 g of potassium permanganate solution (0.01 mol / L), and carry out impregnation treatment at 55 °C for 14.5 h; then take 10 g of the impregnated activated carbon and disperse it in 100 ml of deionized water, add 10% sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, dropwise add 18 g of cyclohexanol at 45 °C, continue heating and reacting for 1.5 h, after the reaction is completed, filter while it is hot, wash, and dry to obtain functionalized activated carbon;

[0068] S3 - S4 are the same as in Example 1;

[0069] S5. Disperse 12.5 g of secondary modified hydrotalcite and 10 g of functionalized activated carbon in water, add sodium bicarbonate solution (mass percentage is 1 - 2%) to adjust the pH to 7.5 - 9, add 1.0 g of glutaraldehyde, stir and mix at 45 °C for 12 h, filter, wash, and dry to obtain modified activated carbon.

[0070] Comparative Example 3

[0071] This comparative example provides a method for preparing modified activated carbon for removing formaldehyde, which includes the following steps:

[0072] S1 - S2 are the same as those in Example 1;

[0073] S3. Disperse 25 g of magnesium - aluminum hydrotalcite in 250 ml of water. Take 15 g of cetyltrimethylammonium chloride to prepare a cetyltrimethylammonium chloride solution with a concentration of 0.05 mol / L, and 15 g of sodium benzenesulfonate to prepare a sodium benzenesulfonate solution with a concentration of 0.04 mol / L. Add the quaternary ammonium salt solution and the sodium benzenesulfonate solution to the reaction solution respectively, and stir - react at 65 °C for 18 h. After the reaction, filter, wash, and dry to obtain modified hydrotalcite; Disperse 10 g of modified hydrotalcite in 150 ml of toluene solution, add 7.5 g of vinyltrimethoxysilane and react, reflux - react at 65 °C for 8 h. After the reaction, filter, wash, and dry to obtain vinyl hydrotalcite;

[0074] S4. Disperse 12.5 g of vinyl hydrotalcite and 10 g of functionalized activated carbon in water, add a sodium bicarbonate solution (mass percentage is 1 - 2%) to adjust the pH to 7.5 - 9, add 1.0 g of glutaraldehyde, stir - mix at 45 °C for 12 h, filter, wash, and dry to obtain modified activated carbon.

[0075] Comparative Example 4

[0076] This comparative example provides a method for preparing modified activated carbon for removing formaldehyde, which includes the following steps:

[0077] S1 - S2 are the same as those in Example 1;

[0078] S3. Disperse 10 g of magnesium - aluminum hydrotalcite in 150 ml of toluene solution, add 7.5 g of vinyltrimethoxysilane and react, reflux - react at 65 °C for 8 h. After the reaction, filter, wash, and dry to obtain vinyl hydrotalcite;

[0079] S4. Then disperse 35 g of vinyl hydrotalcite in 350 ml of ethanol, add 7.5 g of 4 - amino - 3 - hydrazino - 5 - mercapto - 1,2,4 - triazole and 6.5 g of diphenylacetone, stir - react at 45 °C for 6 h. After the reaction, filter, wash, and dry to obtain secondary - modified hydrotalcite;

[0080] S5. Disperse 12.5 g of secondary - modified hydrotalcite and 10 g of functionalized activated carbon in water, add a sodium bicarbonate solution (mass percentage is 1 - 2%) to adjust the pH to 7.5 - 9, add 1.0 g of glutaraldehyde, stir - react at 45 °C for 12 h. After the reaction, filter, wash, and dry to obtain modified activated carbon.

[0081] Performance detection

[0082] Take 10 g of the modified activated carbon prepared in the examples and comparative examples, and separately load them into an air purifier. The air volume of the air purifier is 10 m 3 / h, and place it in an experimental chamber of 1 m 3 . The temperature is 25 ± 2 °C, and the relative humidity is 50 ± 5%. Drop formaldehyde in the experimental chamber, and the initial formaldehyde concentration is 2.0 ± 0.2 mg / m 3 . Turn on the purifier, and sample and detect the formaldehyde concentration in the chamber at 1 h, 6 h, 12 h, 24 h, and 48 h respectively, and calculate the formaldehyde purification efficiency. The formaldehyde purification efficiency is (formaldehyde concentration before purification - formaldehyde concentration after purification) / formaldehyde concentration before purification; Persistence: Take the modified activated carbon prepared in the examples and comparative examples and place them in a sealed sample chamber. Drop formaldehyde into the sample chamber on time every day for 15 days. On the 16th day, take out the modified activated carbon and place it in an air purifier, and then place it in the experimental chamber. The environment in the experimental chamber is as described above. After 48 h, sample and detect the formaldehyde concentration in the chamber, and calculate the formaldehyde purification rate. The test results are shown in Table 1.

[0083] Table 1 Formaldehyde adsorption effect

[0084]

[0085] As can be seen from Table 1, the modified activated carbon prepared by the preparation method of the present invention has good purification rate and purification persistence for formaldehyde.

[0086] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a modified activated carbon for removing formaldehyde, characterized in that, It includes the following steps: S1. Acidify and pretreat the coconut shell charcoal, then disperse the pretreated coconut shell charcoal in deionized water, and then add polyethyleneimine and epichlorohydrin thereto, and heat and stir for reaction to obtain activated carbon loaded with polyethyleneimine; S2. Add the activated carbon loaded with polyethyleneimine into a potassium permanganate solution for impregnation treatment, then disperse the impregnated activated carbon in deionized water, add a sodium hydroxide solution to adjust the pH of the solution to 7.5 - 8.5, dropwise add cyclohexanol at 40 - 50 °C, and then continue to heat and react for 1 - 2 h to obtain functionalized activated carbon; S3. Disperse magnesium aluminum hydrotalcite in water, add a quaternary ammonium salt solution and a sodium benzenesulfonate solution respectively, and stir and react at 60 - 70 °C for 16 - 20 h to obtain modified hydrotalcite; Disperse the modified hydrotalcite in a toluene solution, add a vinyl silane coupling agent for reaction, and reflux and react at 50 - 70 °C for 7 - 9 h to obtain vinyl hydrotalcite; S4. Then disperse the vinyl hydrotalcite in ethanol, add 4 - amino - 3 - hydrazino - 5 - mercapto - 1,2,4 - triazole and benzophenone, and stir and react at 40 - 50 °C for 5 - 7 h to obtain secondary - modified hydrotalcite; S5. Disperse the secondary - modified hydrotalcite and the functionalized activated carbon in water, add a sodium bicarbonate solution to adjust the pH to 7.5 - 9, add glutaraldehyde, and stir and react at 40 - 50 °C for 10 - 14 h. After the reaction is completed, filter, wash, and dry to obtain modified activated carbon.

2. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S1, the pretreatment includes: crushing and screening the coconut shell charcoal to obtain granular charcoal with a mesh number of 30 - 60 meshes, mixing the granular charcoal with a dilute nitric acid solution, heating and reacting at 50 - 70 °C for 4 - 6 h, filtering, washing, and drying to obtain pretreated coconut shell charcoal; the mass - to - volume ratio of the granular charcoal to the dilute nitric acid solution is 1 g:8 - 12 ml, and the concentration of the dilute nitric acid solution is 2 - 5 mol / L.

3. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S1, the mass ratio of the pretreated coconut shell charcoal, polyethyleneimine, and epichlorohydrin is 6 - 9:4 - 6:2 - 4, and heat and stir at 50 - 80 °C for 6 - 10 h.

4. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S2, the mass ratio of the activated carbon loaded with polyethyleneimine to the potassium permanganate solution is 1:2.5 - 3.5, the concentration of the potassium permanganate solution is 0.005 - 0.02 mol / L, the temperature of the impregnation treatment is 30 - 80 °C, and the time of the impregnation treatment is 13 - 16 h; the mass percentage of the sodium hydroxide solution is 8 - 12%, and the mass ratio of the impregnated activated carbon to cyclohexanol is 1:1.5 - 2.

5. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S3, the mass ratio of magnesium aluminum hydrotalcite, quaternary ammonium salt, and sodium benzenesulfonate is 2 - 3:1 - 2:1 - 2, the concentration of the quaternary ammonium salt solution is 0.04 - 0.06 mol / L, and the sodium benzenesulfonate solution is 0.03 - 0.05 mol / L.

6. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: The quaternary ammonium salt is any one of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, cetyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and dodecyltrimethylammonium chloride.

7. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S3, the mass ratio of the modified hydrotalcite to the vinyl silane coupling agent is 1:0.5 - 1.0, and the vinyl silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

8. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S4, the mass ratio of the vinyl hydrotalcite, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, and benzophenone is 3 - 4:1 - 2:0.5 - 0.

8.

9. The preparation method of a modified activated carbon for removing formaldehyde according to claim 1, characterized in that: In step S5, the mass ratio of the secondary modified hydrotalcite to the functionalized activated carbon is 1 - 1.5:1, and the addition amount of glutaraldehyde is 5 - 15% of the mass of the secondary modified hydrotalcite.

10. A modified activated carbon for removing formaldehyde prepared by the preparation method according to any one of claims 1 - 9.

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