Activated carbon aldehyde removal material, preparation method thereof and air purification device

Abstract

In order to overcome the problem that the existing amino acid modified activated carbon is difficult to balance high reaction activity, long service life and stable adsorption performance, the application provides an activated carbon aldehyde removal material and a preparation method thereof and an air purification device.The activated carbon aldehyde removal material comprises a porous activated carbon carrier and oligomeric lysine, the inner wall of the pores of the porous activated carbon carrier has a silane coupling layer, and the silane coupling layer is covalently connected with the oligomeric lysine through an amide bond.

Description

Technical Field

[0001] This invention belongs to the field of air purification materials technology, specifically relating to an activated carbon formaldehyde removal material and its preparation method, as well as an air purification device. Background Technology

[0002] Formaldehyde, a typical volatile organic pollutant in indoor air, is characterized by its long release period and significant health hazards. Long-term exposure can seriously affect human health. Therefore, efficient and continuous removal of indoor formaldehyde has become one of the core requirements in the air purification field. Activated carbon, due to its well-developed pore structure, large specific surface area, and stable chemical properties, is currently the most widely used adsorption material in air filters. It can enrich pollutants such as formaldehyde in the air through physical adsorption. However, physical adsorption is essentially a reversible process with a definite upper limit to adsorption saturation. Furthermore, it is prone to desorption when the ambient temperature rises or the pollutant concentration decreases, causing secondary pollution and making it difficult to achieve long-term stable purification effects.

[0003] To address the reversibility issue of physical adsorption, existing technologies propose combining catalytic decomposition materials with activated carbon. For example, nano-titanium dioxide is mixed and loaded with activated carbon, utilizing the photocatalytic effect of titanium dioxide to catalytically decompose adsorbed formaldehyde into carbon dioxide and water, aiming to achieve in-situ regeneration of the adsorbent. However, this type of technology relies on external ultraviolet light excitation to generate catalytic activity, but the intensity of ultraviolet light in indoor environments is extremely low, and the catalytic efficiency under visible light is very limited. At the same time, the high recombination rate of photogenerated electron-hole pairs results in insufficient actual decomposition efficiency, making it difficult to fully match the adsorption capacity of activated carbon, thus limiting the overall improvement in purification effect.

[0004] Another type of reactive activated carbon technology involves introducing substances that can chemically react with formaldehyde into activated carbon, converting formaldehyde into stable, non-toxic compounds and achieving irreversible chemical fixation. Among these, amino acids, due to their highly reactive free amino groups, can undergo nucleophilic addition reactions with formaldehyde at room temperature to generate stable hydroxymethyl derivatives. Furthermore, their high safety and readily available raw materials have made them a research hotspot in this field. Existing technologies typically prepare amino acid-loaded reactive activated carbon by impregnating activated carbon with an amino acid solution followed by direct drying. While this method is simple, it suffers from several insurmountable technical drawbacks: First, the amino acids bind to the activated carbon surface only through weak interactions such as hydrogen bonds and van der Waals forces, resulting in weak adhesion. This makes them prone to leaching and shedding during use, especially in high-humidity environments, leading to a short lifespan. Second, during drying, amino acid molecules tend to aggregate and crystallize, failing to uniformly cover the pore surface of the activated carbon. Many active sites are trapped inside the crystals and cannot contact formaldehyde. Third, the precipitated amino acid crystals clog the microporous structure of the activated carbon, significantly reducing its specific surface area and pore volume. This weakens the activated carbon's adsorption and enrichment capabilities, ultimately resulting in an actual formaldehyde purification effect far below theoretical expectations. Summary of the Invention

[0005] To address the problem that existing amino acid-modified activated carbon struggles to balance high reactivity, long service life, and stable adsorption performance, this invention provides an activated carbon material for formaldehyde removal, its preparation method, and an air purification device.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides an activated carbon formaldehyde removal material, comprising a porous activated carbon carrier and oligolysine, wherein the inner wall of the pores of the porous activated carbon carrier has a silane coupling layer, and the silane coupling layer is covalently connected to the oligolysine through amide bonds.

[0007] Optionally, the degree of polymerization of the oligolysine is 3 to 5.

[0008] Optionally, the specific surface area of ​​the porous activated carbon support is 1000~1500 m². 2 / g.

[0009] Optionally, the amino content on the surface of the activated carbon formaldehyde removal material is 1.5~2.0 mmol / g.

[0010] Furthermore, the present invention provides a method for preparing the activated carbon formaldehyde removal material as described above, comprising the following steps: Preparation of activated carbon by steam activation: Wood particles are used as raw materials, carbonized under nitrogen protection, and then activated by steam by heating and controlling the loss on ignition rate to 40%~50% to obtain crude activated carbon. Modification pretreatment: The crude activated carbon is boiled and refluxed in dilute nitric acid to complete deashing and surface hydroxylation, and then washed until neutral to obtain modified activated carbon; Surface silane amination: Prepare an ethanol solution of an amino-containing silane coupling agent and perform pre-hydrolysis. Add modified activated carbon and react in a water bath to covalently graft the amino-containing silane coupling agent onto the surface of the modified activated carbon and introduce primary amino groups. Wash and dry to obtain amination activated carbon. Grafting of oligo-lysine: Using a mixture of 2-morpholine ethanesulfonic acid buffer and ethylene glycol dimethyl ether as a solvent, oligo-lysine was added, followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt. The terminal carboxyl groups of oligo-lysine were activated under light-protected conditions. Subsequently, aminated activated carbon was added, and an amidation reaction was carried out under nitrogen protection and light-protected conditions, so that the carboxyl groups of oligo-lysine reacted with the aminated activated carbon to form amide bonds, thus obtaining activated carbon formaldehyde removal material.

[0011] Optionally, the modification pretreatment process may also include: The crude activated carbon that has undergone deashing and surface hydroxylation is transferred to an alkaline sodium borohydride solution for reduction treatment, and then washed and dried again to obtain modified activated carbon.

[0012] Optionally, in the modification pretreatment operation, the mass fraction of dilute nitric acid is 3%~6%, the boiling reflux time is 40~80 min; the concentration of sodium borohydride solution is 0.03~0.06 mol / L, the pH is adjusted to 8.0 with sodium hydroxide, and the reaction is carried out at room temperature for 20~40 min.

[0013] Optionally, in the oligolysine grafting operation, the volume ratio of 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether is (6~8):(2~4); the molar ratio of oligolysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt is 1:(1~1.3):(0.9~1.1); the terminal carboxyl group activation time is 20~40 min, the amidation reaction time is 12 h, and the reaction temperature is 20~30℃.

[0014] Optionally, during the grafting of oligo-lysine, when activating the terminal carboxyl group of oligo-lysine, the pH of the reaction system is controlled at 5-6. After adding aminated activated carbon, the pH of the system is slowly adjusted to 7.0-7.5. The reaction is carried out in the dark and protected by nitrogen gas. After the reaction is completed, the residual reactants and byproducts are washed with deionized water, dilute sodium hydroxide solution and deionized water in sequence.

[0015] In another aspect, the present invention provides an air purification device, including a purification channel, a filter module and a formaldehyde removal module, wherein the filter module and the formaldehyde removal module are sequentially arranged in the purification channel along the airflow direction, and the formaldehyde removal module is filled with activated carbon formaldehyde removal material as described above.

[0016] According to the activated carbon formaldehyde removal material provided by this invention, the porous activated carbon carrier mainly serves as an adsorption and loading framework, utilizing its well-developed pore structure to enrich formaldehyde in the air; the silane coupling layer acts as a bridging layer, stably connecting oligo-lysine to the activated carbon surface. After oligo-lysine is connected to the silane coupling layer through amide bonds, the amino groups on the molecular chain remain in a free state, allowing for nucleophilic addition reactions with formaldehyde, thereby fixing the formaldehyde into a stable hydroxymethyl derivative or methylene cross-linked structure. This structure differs from that of ordinary impregnated activated carbon loaded with amino acids. In ordinary impregnated samples, amino acids mostly exist in hydrogen bond, van der Waals force, or crystalline form, which are prone to detachment and aggregation during use, and may also clog micropores. In this solution, oligo-lysine is covalently grafted onto the silane coupling layer, resulting in a more stable bond and better uniform distribution of amino groups on the pore surface. Compared to lysine, oligo-lysine can introduce multiple active amino reaction sites, which is beneficial for increasing the amino loading on the activated carbon. At the same time, the adsorption and enrichment effect of activated carbon and the chemical reaction effect of oligo-lysine work together to continuously fix formaldehyde at room temperature. Detailed Implementation

[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0018] An embodiment of the present invention provides an activated carbon formaldehyde removal material, comprising a porous activated carbon carrier and oligolysine, wherein the inner wall of the pores of the porous activated carbon carrier has a silane coupling layer, and the silane coupling layer is covalently connected to the oligolysine through amide bonds.

[0019] In this embodiment, the porous activated carbon support primarily serves as the adsorption and loading framework, utilizing its well-developed pore structure to enrich formaldehyde in the air. The silane coupling layer acts as a bridging layer, stably connecting oligo-lysine to the activated carbon surface. After oligo-lysine is connected to the silane coupling layer via amide bonds, the amino groups on the molecular chain remain in a free state, allowing for nucleophilic addition reactions with formaldehyde, thereby fixing the formaldehyde into a stable hydroxymethyl derivative or methylene cross-linked structure. This structure differs from that of conventionally impregnated activated carbon loaded with amino acids. In conventionally impregnated samples, amino acids often exist in hydrogen bond, van der Waals force, or crystalline form, which are prone to detachment, aggregation, and potential blockage of micropores during use. In this scheme, however, oligo-lysine is covalently grafted onto the silane coupling layer, resulting in a more stable bond and better uniform distribution of amino groups on the pore surface. Furthermore, compared to lysine, oligo-lysine can introduce multiple active amino reaction sites, which is beneficial for increasing the amino loading on the activated carbon. At the same time, the adsorption and enrichment effect of activated carbon and the chemical reaction effect of oligo-lysine work together to continuously fix formaldehyde at room temperature.

[0020] In some embodiments, the degree of polymerization of the oligolysine is 3 to 5.

[0021] The degree of polymerization of oligo-L-lysine can be 3, 4, or 5. If the degree of polymerization of oligo-L-lysine is less than 3, the number of free amino groups that a single molecular chain can provide is relatively small, resulting in limited improvement in amino density and formaldehyde removal capacity. If the degree of polymerization of oligo-L-lysine is greater than 5, the molecular chain size increases significantly, making it difficult to enter the micropores of activated carbon. It may also lead to molecular chain entanglement, increasing the risk of pore blockage.

[0022] When the degree of polymerization is controlled at 3 to 5, the oligo-lysine molecules have a sufficient number of free amino groups and can better match the microporous and mesoporous structures of steam-activated activated carbon, which is conducive to the grafting reaction proceeding more uniformly on the inner surface of the pores.

[0023] In some embodiments, the specific surface area of ​​the porous activated carbon carrier is 1000~1500 m². 2 / g.

[0024] Specific surface area was tested according to GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" using a fully automated specific surface area and porosity analyzer under nitrogen adsorption conditions at 77K. The specific surface area can be 1000 m². 2 / g、1020m 2 / g、1030m 2 / g, 1050m 2 / g、1070m 2 / g、1080m 2 / g、1100m 2 / g、1120m2 / g、1150m 2 / g、1180m 2 / g、1200m 2 / g、1250m 2 / g、1300m 2 / g, 1400m 2 / g, 1450m 2 / g or 1500m 2 / g.

[0025] If the specific surface area is less than 1000 m² 2 / g, the activated carbon has insufficient pore development, resulting in weak adsorption and enrichment of formaldehyde, making it difficult to form a high substrate concentration locally, which affects the overall formaldehyde removal rate. If the specific surface area is higher than 1500m², 2 / g, the carbon wall structure is usually thin, resulting in decreased mechanical stability and making it more prone to breakage and pulverization during preparation and use; at the same time, an excessively high micropore ratio may also increase the risk of grafted molecules clogging the pores. Therefore, 1000~1500m 2 / g is more suitable for balancing adsorption capacity, loading sites, and material strength.

[0026] In some embodiments, the amino content on the surface of the activated carbon formaldehyde removal material is 1.5~2.0 mmol / g.

[0027] The surface amino content can be determined by acid-base titration: a certain amount of sample is weighed, an excess of hydrochloric acid standard solution of known concentration is added, and the sample is shaken thoroughly to allow the amino groups to combine with the hydrochloric acid. The remaining hydrochloric acid is then back-titrated with sodium hydroxide standard solution, and the surface amino content is calculated. Alternatively, the total nitrogen content can be determined by elemental analysis and then converted. Specific amino content can be 1.50 mmol / g, 1.52 mmol / g, 1.53 mmol / g, 1.55 mmol / g, 1.57 mmol / g, 1.58 mmol / g, 1.60 mmol / g, 1.65 mmol / g, 1.70 mmol / g, 1.75 mmol / g, 1.80 mmol / g, 1.85 mmol / g, 1.90 mmol / g, 1.95 mmol / g, 1.98 mmol / g, or 2.00 mmol / g.

[0028] If the amino content on the surface of the porous activated carbon carrier is below 1.5 mmol / g, there are insufficient active sites to react with formaldehyde, and the material easily reaches reaction saturation quickly. If the amino content on the surface of the activated carbon formaldehyde removal material is above 2.0 mmol / g, the grafting density is too high, and significant steric hindrance will occur between the oligo-lysine molecular chains, making it difficult for some amino groups to effectively contact formaldehyde; at the same time, excessive grafting may also clog micropores, weakening the adsorption and enrichment effect of the activated carbon itself. Controlling it at 1.5~2.0 mmol / g is more conducive to balancing reaction capacity and porosity retention.

[0029] Another embodiment of the present invention provides a method for preparing the activated carbon formaldehyde removal material as described above, comprising the following operations: Preparation of activated carbon by steam activation: Wood particles are used as raw materials, carbonized under nitrogen protection, and then activated by steam by heating and controlling the loss on ignition rate to 40%~50% to obtain crude activated carbon. Modification pretreatment: The crude activated carbon is boiled and refluxed in dilute nitric acid to complete deashing and surface hydroxylation, and then washed until neutral to obtain modified activated carbon; Surface silane amination: Prepare an ethanol solution of an amino-containing silane coupling agent and perform pre-hydrolysis. Add modified activated carbon and react in a water bath to covalently graft the amino-containing silane coupling agent onto the surface of the modified activated carbon and introduce primary amino groups. Wash and dry to obtain amination activated carbon. Grafting of oligo-lysine: Using a mixture of 2-morpholine ethanesulfonic acid buffer and ethylene glycol dimethyl ether as a solvent, oligo-lysine was added, followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt. The terminal carboxyl groups of oligo-lysine were activated under light-protected conditions. Subsequently, aminated activated carbon was added, and an amidation reaction was carried out under nitrogen protection and light-protected conditions, so that the carboxyl groups of oligo-lysine reacted with the aminated activated carbon to form amide bonds, thus obtaining activated carbon formaldehyde removal material.

[0030] Wood particles can be selected from coconut shell particles, wood chips, walnut shell particles, apricot shell particles, or jujube shell particles. Among them, coconut shell particles have lower ash content and higher hardness, making them more suitable as raw materials for activated carbon in air purification. The carbonization stage is carried out under nitrogen protection, mainly removing volatile matter and light components from the raw material to form a preliminary carbonized skeleton. In the activation stage, water vapor is introduced, and the pore structure is further developed through the reaction between carbon and water vapor. The loss on ignition rate can be controlled at 40%, 42%, 43%, 45%, 47%, 48%, or 50%. If the loss on ignition rate is too low, the pores will not develop sufficiently; if the loss on ignition rate is too high, the carbon skeleton will be over-etched, and the mechanical strength will decrease.

[0031] In the modified pretreatment, dilute nitric acid can both remove ash and introduce oxygen-containing functional groups onto the surface of activated carbon. The hydrogen ions in nitric acid can react with metal oxides, carbonates, etc. in the ash to generate soluble nitrates, which can be removed by washing. At the same time, the mild oxidation under heating conditions can introduce functional groups such as hydroxyl groups onto the surface of activated carbon, providing grafting sites for subsequent silane coupling agents.

[0032] During the surface silane amination process, the silane coupling agent is first pre-hydrolyzed in a weakly acidic ethanol solution to convert alkoxy groups into silanol groups. Pre-hydrolysis reduces self-polymerization between silane molecules and increases the proportion of monomolecular grafts. Subsequently, modified activated carbon is added, and the silanol groups undergo a dehydration reaction with the hydroxyl groups on the activated carbon surface, forming Si-OC covalent bonds, thereby introducing primary amino anchoring sites on the activated carbon surface. After the reaction, unreacted free silane is removed by washing with anhydrous ethanol, reducing pore blockage and residual side reactions.

[0033] In the grafting process of oligo-lysine, the terminal carboxyl groups of oligo-lysine are first selectively activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt, and then undergo an amidation reaction with the primary amino groups on the surface of the silane layer. This reaction pathway is beneficial for oligo-lysine to be fixed on the silane coupling layer with a single terminal carboxyl group, while the amino groups on the molecular chain remain free, thereby improving the amino group utilization efficiency.

[0034] In some embodiments, the amino-containing silane coupling agent is selected from 3-aminopropyltriethoxysilane.

[0035] In some embodiments, the modified pretreatment operation further includes: transferring the crude activated carbon that has undergone deashing and surface hydroxylation into an alkaline sodium borohydride solution for reduction treatment, and then washing and drying it again to obtain modified activated carbon.

[0036] After treatment with dilute nitric acid, a certain amount of aldehyde groups may be generated on the surface of activated carbon in addition to hydroxyl groups. These aldehyde groups can undergo Schiff base side reactions with subsequently introduced amino groups, consuming active amino sites. Sodium borohydride, under weakly alkaline conditions, can reduce some of the aldehyde groups to hydroxyl groups, thereby reducing amino deactivation caused by side reactions, while also decreasing surface oxidizability and improving amino stability. Simultaneously, the mild reduction treatment causes minimal damage to the carbon framework, which is beneficial for preserving the specific surface area and pore structure of the activated carbon.

[0037] In some embodiments, during the modification pretreatment operation, the mass fraction of dilute nitric acid is 3% to 6%, the boiling reflux time is 40 to 80 min, the concentration of sodium borohydride solution is 0.03 to 0.06 mol / L, the pH is adjusted to 8.0 with sodium hydroxide, and the reaction is carried out at room temperature for 20 to 40 min.

[0038] The mass fraction of dilute nitric acid can be 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.5%, 5.0%, 5.5%, or 6.0%. If the concentration is below 3%, the deashing and hydroxyl group introduction capabilities are insufficient; if the concentration is above 6%, the oxidation is too strong, easily generating a large number of carboxyl groups, which is detrimental to the subsequent introduction of amino groups and also easily leads to excessive etching of the pore walls, resulting in a decrease in specific surface area.

[0039] The boiling and reflux time can be 40 min, 42 min, 43 min, 45 min, 47 min, 48 min, 50 min, 52 min, 55 min, 58 min, 60 min, 65 min, 70 min, 75 min, or 80 min. If the time is less than 40 min, deashing and hydroxylation will be insufficient; if the time exceeds 80 min, the degree of carbon framework etching will increase, and the mechanical strength and specific surface area may decrease.

[0040] The concentration of sodium borohydride solution can be 0.030 mol / L, 0.032 mol / L, 0.033 mol / L, 0.035 mol / L, 0.037 mol / L, 0.038 mol / L, 0.040 mol / L, 0.042 mol / L, 0.045 mol / L, 0.048 mol / L, 0.050 mol / L, 0.052 mol / L, 0.055 mol / L, 0.058 mol / L, or 0.060 mol / L. If the concentration is below 0.03 mol / L, the reducing power is insufficient, resulting in more aldehyde groups remaining; if the concentration is above 0.06 mol / L, the reducing effect is too strong, which may destroy some hydroxyl groups and reduce silane grafting sites.

[0041] The reduction reaction time can be 20 min, 22 min, 23 min, 25 min, 27 min, 28 min, 30 min, 32 min, 35 min, 38 min, or 40 min. If the time is less than 20 min, the reduction reaction will be incomplete; if the time exceeds 40 min, the improvement in reduction effect will be limited, and it will also increase the process time and cost.

[0042] In some embodiments, during the oligolysine grafting operation, the volume ratio of 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether is (6~8):(2~4); the molar ratio of oligolysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysulfosuccinimide sodium salt is 1:(1~1.3):(0.9~1.1); the terminal carboxyl activation time is 20~40 min, the amidation reaction time is 12 h, and the reaction temperature is 20~30 °C.

[0043] The molar concentration of the 2-morpholine ethanesulfonic acid buffer is 0.1 mol / L, and the volume ratio of the 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether can be 6:4, 6.5:3.5, 7:3, 7.5:2.5, or 8:2. If the MES buffer content is less than 60%, the system's buffering capacity is insufficient, the pH is prone to fluctuation, and it affects the stability of carboxyl activation and amidation reactions. If the MES buffer content is greater than 80%, the surface tension of the solution is high, making it difficult to fully penetrate the micropores and reducing the inner surface grafting efficiency. Adding ethylene glycol dimethyl ether can reduce surface tension, improve micropore permeability, and slow down the hydrolysis of activated esters.

[0044] The molar ratio of oligolysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysulfosuccinimide sodium salt can be 1:1.0:0.9, 1:1.0:1.0, 1:1.0:1.1, 1:1.1:0.9, 1:1.1:1.0, 1:1.1:1.1, 1:1.2:0.9, 1:1.2:1.0, 1:1.2:1.1, 1:1.3:0.9, 1:1.3:1.0, 1:1.3:1.1, 1:1.05:0.95, 1:1.15:1.05, or 1:1.25:0.95. If the concentration of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is less than 1.0 times, the activation of the terminal carboxyl group of oligo-lysine is insufficient, resulting in a low grafting conversion rate. If the concentration of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is greater than 1.3 times, excess reagent may cause side reactions and increase costs. If the concentration of N-hydroxysulfosuccinimide sodium salt is less than 0.9 times, the stabilizing effect of the activation intermediate is insufficient, and hydrolysis loss increases. If the concentration of N-hydroxysulfosuccinimide sodium salt is greater than 1.1 times, excess reagent will increase the washing burden, but the performance improvement is not significant.

[0045] The activation time for the terminal carboxyl group can be 20 min, 22 min, 23 min, 25 min, 27 min, 28 min, 30 min, 32 min, 35 min, 38 min, or 40 min. If the activation time is less than 20 min, the carboxyl group will not be fully activated; if the activation time exceeds 40 min, the hydrolysis and deactivation of the activated ester will increase, which will reduce the effective grafting rate.

[0046] The reaction temperature can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃. If the temperature is below 20℃, the reaction rate is slow, and it is difficult to achieve sufficient grafting within 12 hours; if the temperature is above 30℃, the hydrolysis of the activated ester is accelerated, increasing the risk of side reactions. Controlling the amidation reaction time to 12 hours is beneficial for obtaining a higher grafting conversion rate under milder conditions.

[0047] In some embodiments, during the grafting of oligo-lysine, when activating the terminal carboxyl group of oligo-lysine, the pH of the reaction system is controlled at 5-6. After adding aminated activated carbon, the pH of the system is slowly adjusted to 7.0-7.5. The reaction is carried out in the dark and protected by nitrogen gas. After the reaction is completed, the residual reactants and byproducts are washed with deionized water, dilute sodium hydroxide solution and deionized water in sequence.

[0048] The activation stage controls the weak acidity, which ensures the activation efficiency of EDC / NHS on the terminal carboxyl groups and keeps the side chain amino groups of oligo-lysine in a protonated state, thus inhibiting intermolecular self-polymerization side reactions. The coupling stage is adjusted to a neutral to weakly basic state, which restores the primary amino groups on the silane surface to a free nucleophilic state, ensuring efficient amide bond formation. This allows oligo-lysine to be directionally coupled to the primary amino groups of the silane layer only through the terminal carboxyl groups, significantly reducing the probability of intermolecular amidation self-polymerization. Ultimately, a structure with single-end grafting and fully free side chain amino groups is achieved, balancing high active site density and structural stability.

[0049] Protecting the reaction from light reduces the light-induced decomposition of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and activated esters. Plugging with nitrogen reduces the oxidative effect of oxygen on the amino group. After the reaction, most unreacted oligolysine, activator, and water-soluble byproducts are first washed away with deionized water; then, acidic byproducts and physically adsorbed oligolysine are washed away with dilute sodium hydroxide solution; finally, the filtrate is washed with deionized water until it is nearly neutral to reduce the impact of residual impurities on material stability and performance.

[0050] Another embodiment of the present invention provides an air purification device, including a purification channel, a filter module and a formaldehyde removal module. The filter module and the formaldehyde removal module are sequentially arranged in the purification channel along the airflow direction. The formaldehyde removal module is filled with activated carbon formaldehyde removal material as described in the foregoing embodiment.

[0051] The purification flow channel guides air sequentially through each functional module. The material can be plastic or metal, depending on the device's structure. The filter module is located upstream of the airflow and primarily removes particulate matter, dust, hair, and other impurities from the air, preventing particulate matter from clogging the activated carbon pores after entering the formaldehyde removal module. The formaldehyde removal module is located downstream and filled with the aforementioned activated carbon formaldehyde removal material. When air passes through, formaldehyde is first adsorbed and enriched by the activated carbon, and then reacts chemically with the free amino groups on the surface of oligo-lysine, thus being stabilized and fixed.

[0052] This air purification device does not require an ultraviolet light source and can remove formaldehyde at room temperature. It has a relatively simple structure, is easy to maintain, and is suitable for use in indoor air purification, air conditioning filters, fresh air systems, or air purifiers.

[0053] The present invention will be further illustrated by the following examples.

[0054] Example 1 This embodiment illustrates the activated carbon formaldehyde removal material and its preparation method disclosed in this invention, including the following steps: Preparation of activated carbon by steam activation: Coconut shell granules were used as raw material and carbonized at 500℃ for 1 hour under nitrogen protection. Then, the temperature was raised to 850℃ and steam was introduced for activation. The loss on ignition was controlled at 45% to obtain crude activated carbon.

[0055] Modification pretreatment: Crude activated carbon was boiled and refluxed in 5% dilute nitric acid for 60 min to complete deashing and surface hydroxylation, and then washed until neutral. It was then transferred to a 0.05 mol / L sodium borohydride alkaline solution (pH adjusted to 8.0 with sodium hydroxide) and reacted at room temperature for 30 min for reduction treatment. After washing and drying again, modified activated carbon was obtained. The specific surface area of ​​the modified activated carbon was measured to be 1200 m² / g. 2 / g.

[0056] Surface silane amination: Prepare a 5% (w / w) ethanol solution of 3-aminopropyltriethoxysilane, add a small amount of glacial acetic acid to adjust the pH to 4.5, and pre-hydrolyze for 30 min; add modified activated carbon, and react in a 60℃ water bath for 4 h to covalently graft the silane coupling agent onto the surface of the activated carbon. After the reaction, wash three times with anhydrous ethanol and dry to obtain amination activated carbon.

[0057] Grafting of oligo-lysine: Using a 7:3 volume ratio of 0.1 mol / L 2-morpholine ethanesulfonic acid buffer and ethylene glycol dimethyl ether as a solvent, oligo-lysine with a degree of polymerization of 4 was added, followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt. The molar ratio of oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysulfosuccinimide sodium salt was 1:1.2:1.0. The pH of the system was adjusted to 5.5, and the system was activated for 30 min under light-protected conditions. Subsequently, aminated activated carbon was added, and the pH of the system was adjusted to 7. The amidation reaction was carried out for 12 h under nitrogen protection, light protection, and at 25 °C. After the reaction, the system was washed sequentially with deionized water, 0.1 mol / L dilute sodium hydroxide solution, and deionized water until neutral. The material was dried to obtain activated carbon formaldehyde removal material. The amino content on the surface of the activated carbon formaldehyde removal material was tested to be 1.8 mmol / g.

[0058] Example 2 This embodiment illustrates the activated carbon formaldehyde removal material and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The steam activation stage controlled the burn-off rate at 42%. In the modified pretreatment, the mass fraction of dilute nitric acid was 4%, and the boiling reflux time was 50 min; the concentration of sodium borohydride solution was 0.04 mol / L, and the reaction time was 25 min; the resulting modified activated carbon had a specific surface area of ​​1050 m². 2 / g; During the oligo-lysine grafting stage, the volume ratio of 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether was 6:4; the degree of polymerization of oligo-lysine was 3; the molar ratio of oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysulfosuccinimide sodium salt was 1:1.1:0.9; the terminal carboxyl group activation time was 25 min; and the reaction temperature was 22℃.

[0059] Tests showed that the amino content on the surface of the activated carbon formaldehyde removal material was 1.6 mmol / g.

[0060] Example 3 This embodiment illustrates the activated carbon formaldehyde removal material and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The steam activation stage controlled the burn-off rate at 48%. In the modified pretreatment, the mass fraction of dilute nitric acid was 6%, and the boiling reflux time was 70 min; the concentration of sodium borohydride solution was 0.06 mol / L, and the reaction time was 35 min; the resulting modified activated carbon had a specific surface area of ​​1400 m². 2 / g; During the oligo-lysine grafting stage, the volume ratio of 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether was 8:2; the degree of polymerization of oligo-lysine was 5; the molar ratio of oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and N-hydroxysulfosuccinimide sodium salt was 1:1.3:1.1; the terminal carboxyl group activation time was 35 min; and the reaction temperature was 28℃.

[0061] Tests showed that the amino content on the surface of the activated carbon formaldehyde removal material was 1.9 mmol / g.

[0062] Example 4 This embodiment illustrates the activated carbon formaldehyde removal material and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: In the modification pretreatment operation, the sodium borohydride alkaline solution reduction treatment was not performed. The modified activated carbon was obtained by boiling and refluxing with dilute nitric acid, washing until neutral, and then drying. The remaining operations and parameters were the same as in Example 1.

[0063] Comparative Example 1 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention. The modified activated carbon obtained by modification pretreatment in Example 1 is used as the test sample, without subsequent surface silane amination and oligo-lysine grafting operations.

[0064] Comparative Example 2 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention. The aminated activated carbon obtained by surface silane amination in Example 1 is used as the test sample, and no subsequent oligo-lysine grafting operation is performed.

[0065] Comparative Example 3 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention, including most of the raw materials and parameters in Example 1, with the following differences: The surface silane amination and oligo-lysine grafting were carried out simultaneously: oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt were added to the pre-hydrolyzed silane ethanol solution, mixed well, and then modified activated carbon was added. The reaction was carried out for 12 hours under the same temperature, pH, light-proof and nitrogen-protected conditions. After the reaction was completed, the sample was washed and dried to obtain the sample.

[0066] Comparative Example 4 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention, including most of the operational steps in Example 1, with the following differences: In the modified pretreatment, 5% dilute nitric acid was replaced with 5% dilute hydrochloric acid, and the remaining operations and parameters were the same as in Example 1.

[0067] Comparative Example 5 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention, including most of the operational steps in Example 1, with the following differences: In the grafting process of oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt were not added. Instead, oligo-lysine and aminated activated carbon were directly added to a mixed solvent and reacted for 12 hours under the same temperature, pH, light-proof and nitrogen-protected conditions. After the reaction was completed, the sample was washed and dried to obtain the sample.

[0068] Comparative Example 6 This comparative example is used to illustrate the activated carbon formaldehyde removal material disclosed in this invention, including most of the operating steps and parameters in Example 1, the difference being: In the oligo-lysine grafting process, oligo-lysine with a degree of polymerization of 4 was replaced with an equal amount of L-lysine monomer, while the amounts of other reagents, reaction conditions and post-treatment methods were kept the same as in Example 1.

[0069] Performance testing The activated carbon formaldehyde removal materials and comparative samples prepared above were subjected to the following performance tests: 1. Formaldehyde purification efficiency test: using a 1m... 3 The environmental testing chamber was filled with formaldehyde at an initial concentration of 1.0 mg / m³ under conditions of 25°C and 50% relative humidity. 3 ; Spread 10g of sample evenly in a petri dish and place it in the chamber. After reacting in a sealed container for 24 hours, the remaining formaldehyde concentration in the chamber is tested using the phenol reagent spectrophotometric method, and the formaldehyde purification efficiency is calculated: Purification efficiency (%) = (C0 - C1) / C0 × 100% Where C0 is the initial formaldehyde concentration and C1 is the remaining formaldehyde concentration after 24 hours.

[0070] 2. Formaldehyde saturation adsorption capacity test: A dynamic adsorption device was used at a temperature of 25℃ and an inlet formaldehyde concentration of 2.0 mg / m³. 3 Under the condition of gas flow rate of 1L / min, the formaldehyde breakthrough curve of the test sample is calculated. When the outlet concentration reaches 95% of the inlet concentration, it is considered as breakthrough saturation. The saturated adsorption capacity of formaldehyde per unit mass of sample is calculated, and the unit is mg / g.

[0071] 3. Specific surface area retention rate test: The specific surface area of ​​the finished sample was tested using the BET method, and its retention rate relative to the specific surface area of ​​the modified activated carbon was calculated. Specific surface area retention rate (%) = Specific surface area of ​​finished product / Specific surface area of ​​modified activated carbon × 100%.

[0072] The test results are entered into Table 1.

[0073] Table 1 Performance test results of each sample As can be seen from the test results of Examples 1-3, the activated carbon formaldehyde removal materials prepared within the process parameters defined in this invention all have excellent formaldehyde purification efficiency and high formaldehyde saturation adsorption capacity, while maintaining a high specific surface area retention rate. They can take into account both the physical adsorption and enrichment effect of activated carbon and the chemical fixation effect of oligo-lysine, and the overall formaldehyde removal performance is stable and excellent.

[0074] Comparing the test results of Example 1 and Example 4, it can be seen that adding sodium borohydride reduction treatment in the modification pretreatment stage can effectively improve the formaldehyde purification efficiency and saturated adsorption capacity of the material. This step can reduce the oxidized functional groups on the surface of activated carbon, reduce the protonation deactivation of subsequent grafted amino groups, and improve the effective utilization rate of active sites, which has a significant positive effect on improving the formaldehyde removal performance of the material.

[0075] Comparing the test results of Example 1 with those of Comparative Examples 1 and 2, it can be seen that the formaldehyde purification effect and adsorption capacity of activated carbon that has only undergone modification pretreatment and activated carbon that has only completed surface silane amination are far lower than those of the finished material grafted with oligo-lysine. This proves that covalent grafting oligo-lysine through the silane coupling layer is the core key to improving the formaldehyde removal performance of the material. It can introduce a large number of active amino groups that can undergo nucleophilic addition reactions with formaldehyde, thereby achieving irreversible chemical fixation of formaldehyde and significantly improving the purification capacity and adsorption capacity of the material.

[0076] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that in the process of simultaneously performing surface silane amination and oligolysine grafting, the free amino groups of the silane coupling agent will first react with the activated oligolysine in the solution to form macromolecular coupling compounds, which will lead to a decrease in both the formaldehyde removal performance and the specific surface area retention rate of the material. This indicates that the process path of performing silane grafting and oligolysine amidation in steps is more conducive to ensuring the orderliness of the reaction, reducing molecular self-aggregation and pore blockage, and balancing the grafting effect and the pore structure retention rate.

[0077] Comparing the test results of Example 1 and Comparative Example 4, it can be seen that using dilute hydrochloric acid instead of dilute nitric acid for modification pretreatment will reduce the formaldehyde purification efficiency and saturated adsorption capacity of the material. This indicates that dilute nitric acid treatment has the dual function of deashing and surface hydroxylation, which can provide sufficient covalent grafting sites for subsequent silane coupling agents, and is an important prerequisite for ensuring grafting effect and material performance.

[0078] Comparing the test results of Example 1 and Comparative Example 5, it can be seen that the formaldehyde removal performance of the material will decrease significantly when grafting reaction is carried out directly without the addition of amidation activating reagent. This indicates that the step of activating the terminal carboxyl group of oligo-lysine with carbodiimide activator and N-hydroxysulfosuccinimide sodium salt can effectively promote the formation of amide bond, improve the grafting efficiency and binding stability of oligo-lysine, and is a key process step to achieve covalent fixation of oligo-lysine.

[0079] Comparing the test results of Example 1 and Comparative Example 6, it can be seen that replacing oligo-lysine with monomeric lysine for graft modification significantly reduced the formaldehyde purification efficiency and saturated adsorption capacity of the material. This is because monomeric lysine can only graft with the silane layer through one amino group, and a single grafting site can only provide one free amino group to react with formaldehyde; while oligo-lysine, after directional grafting with a single-end carboxyl group, can retain multiple free active amino groups in the side chain, providing several times the number of reactive sites for the same number of grafting sites, significantly improving the formaldehyde chemical fixation capacity per unit mass of material.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An activated carbon formaldehyde removal material, characterized in that, It includes a porous activated carbon support and oligolysine, wherein the inner wall of the pores of the porous activated carbon support has a silane coupling layer, and the silane coupling layer is covalently connected to the oligolysine through amide bonds; The degree of polymerization of the oligo-lysine is 3 to 5; The activated carbon formaldehyde removal material has an amino content of 1.5~2.0 mmol / g on its surface.

2. The activated carbon formaldehyde removal material according to claim 1, characterized in that, The specific surface area of ​​the porous activated carbon carrier is 1000~1500 m². 2 / g.

3. The method for preparing activated carbon formaldehyde removal material according to any one of claims 1 to 2, characterized in that, Includes the following operations: Preparation of activated carbon by steam activation: Wood particles are used as raw materials, carbonized under nitrogen protection, and then activated by steam by heating and controlling the loss on ignition rate to 40%~50% to obtain crude activated carbon. Modification pretreatment: The crude activated carbon is boiled and refluxed in dilute nitric acid to complete deashing and surface hydroxylation, and then washed until neutral to obtain modified activated carbon; Surface silane amination: Prepare an ethanol solution of an amino-containing silane coupling agent and perform pre-hydrolysis. Add modified activated carbon and react in a water bath to covalently graft the amino-containing silane coupling agent onto the surface of the modified activated carbon and introduce primary amino groups. Wash and dry to obtain amination activated carbon. Grafting of oligo-lysine: Using a mixture of 2-morpholine ethanesulfonic acid buffer and ethylene glycol dimethyl ether as a solvent, oligo-lysine was added, followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt. The terminal carboxyl groups of oligo-lysine were activated under light-protected conditions. Subsequently, aminated activated carbon was added, and an amidation reaction was carried out under nitrogen protection and light-protected conditions, so that the carboxyl groups of oligo-lysine reacted with the aminated activated carbon to form amide bonds, thus obtaining activated carbon formaldehyde removal material.

4. The method for preparing activated carbon formaldehyde removal material according to claim 3, characterized in that, The modification pretreatment process also includes: The crude activated carbon that has undergone deashing and surface hydroxylation is transferred to an alkaline sodium borohydride solution for reduction treatment, and then washed and dried again to obtain modified activated carbon.

5. The method for preparing activated carbon formaldehyde removal material according to claim 4, characterized in that, In the modified pretreatment operation, the mass fraction of dilute nitric acid is 3%~6%, the boiling reflux time is 40~80min; the concentration of sodium borohydride solution is 0.03~0.06mol / L, the pH is adjusted to 8.0 with sodium hydroxide, and the reaction is carried out at room temperature for 20~40min.

6. The method for preparing activated carbon formaldehyde removal material according to claim 3, characterized in that, In the oligo-lysine grafting operation, the volume ratio of 2-morpholine ethanesulfonic acid buffer to ethylene glycol dimethyl ether was (6~8):(2~4); the molar ratio of oligo-lysine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt was 1:(1~1.3):(0.9~1.1); the terminal carboxyl group activation time was 20~40 min, the amidation reaction time was 12 h, and the reaction temperature was 20~30℃.

7. The method for preparing activated carbon formaldehyde removal material according to claim 3, characterized in that, In the grafting of oligo-lysine, when activating the terminal carboxyl group of oligo-lysine, the pH of the reaction system is controlled at 5-6. After adding aminated activated carbon, the pH of the system is slowly adjusted to 7.0-7.

5. The reaction is carried out in the dark and protected by nitrogen gas. After the reaction is completed, the residual reactants and byproducts are washed with deionized water, dilute sodium hydroxide solution and deionized water in sequence.

8. An air purification device, characterized in that, It includes a purification channel, a filter module, and a formaldehyde removal module. The filter module and the formaldehyde removal module are sequentially arranged in the purification channel along the airflow direction. The formaldehyde removal module is filled with activated carbon formaldehyde removal material as described in any one of claims 1 to 2.

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