A porous structure-controlled activated carbon for formaldehyde adsorption and its preparation method

Abstract

This invention belongs to the field of environmental remediation material preparation technology, and provides a porous structure-controlled activated carbon for formaldehyde adsorption and its preparation method. Eutectic microparticles are prepared by co-melting a potassium-containing activator with a nitrogen-containing precursor, which can achieve in-situ low-temperature micropore etching and nitrogen atom doping during heat treatment. Simultaneously, a microgel is prepared by complexing and self-assembling tannic acid and polyethyleneimine and mild cross-linking. This microgel acts as a soft template during the carbonization stage, constructing a continuous mesoporous network and providing abundant surface alkaline sites for the carbon skeleton. Furthermore, an inorganic nano-skeleton reinforcing agent is introduced during the forming stage, and the mechanical strength of the material is improved by microgelation treatment of the particle surface. During heat treatment, a microporous-mesoporous hierarchical pore structure is formed. Through acid washing purification and surface re-alkalization treatment, activated carbon particles with highly efficient formaldehyde capture and strong locking capabilities are obtained, showing broad application prospects in the field of indoor air purification.

Description

Technical Field

[0001] This invention belongs to the field of environmental remediation material preparation technology, and relates to a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. Background Technology

[0002] With the widespread use of modern building and interior decoration materials, formaldehyde, continuously released from boards, paints, adhesives, etc., has become one of the main pollutants affecting indoor air quality and endangering human health. Activated carbon, due to its large specific surface area and abundant pore structure, is the most widely used formaldehyde adsorbent. However, traditional activated carbon has revealed many inherent defects in practical applications. First, its adsorption process mainly relies on physical adsorption, resulting in weak adsorption force. When the ambient temperature rises or humidity changes, the adsorbed formaldehyde molecules are prone to desorption, causing secondary pollution. Second, the pore size distribution of traditional activated carbon is usually wide and disordered. A large number of mesopores or macropores, which do not contribute much to the adsorption of formaldehyde molecules, occupy the pore volume, while the micropores, especially ultramicropores, which play a decisive role, are insufficient in number and mismatched in size, resulting in a need to improve its adsorption efficiency and saturation adsorption capacity for low concentrations of formaldehyde.

[0003] To overcome these shortcomings, researchers have attempted to modify activated carbon. For example, they have loaded nitrogen-containing compounds or oxidants through impregnation to enhance formaldehyde removal through chemical adsorption or catalytic decomposition. However, impregnation often leads to uneven distribution of functional components and easily clogs existing pores, reducing the material's mass transfer performance. Furthermore, traditional activation processes are typically quite drastic, making it difficult to balance the formation of a high specific surface area with the maintenance of the material's mechanical strength. This results in a final product that is easily broken and pulverized, limiting its application in dynamic fluid environments such as fixed beds and air purifier filters. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a porous structure-controlled activated carbon for formaldehyde adsorption and its preparation method. Potassium-containing eutectic microparticles are used as micropore building agents and nitrogen sources, along with synergistic complexed microgels as mesoporous templates and surface modifiers. By granulating the aforementioned functional additives, inorganic framework reinforcing agents, and carbon precursors, followed by a unique particle surface curing treatment and programmed multi-atmosphere pyrolysis activation, a post-treatment process yields an activated carbon possessing a hierarchical pore structure, high nitrogen content, abundant alkaline sites on the surface, and excellent mechanical strength, thus meeting the needs of practical production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing porous structure-controlled activated carbon for adsorbing formaldehyde, the preparation method comprising:

[0007] S1, anhydrous potassium carbonate and urea are dissolved in deionized water, stirred and dehydrated under reduced pressure, and spray dried to obtain K2CO3-urea eutectic microparticles;

[0008] S2, tannic acid dispersed in Tris buffer, polyethyleneimine aqueous solution added to Tris buffer and sheared to form a milky white microgel emulsion, pH adjusted to 7.8-8.2 and glyoxal aqueous solution added to obtain complexed microgel powder;

[0009] S3, coconut shell powder, sucrose, complexed microgel powder and K2CO3-urea eutectic microparticles are dry mixed, deionized water is added to the target slurry viscosity, then silica sol is added in two batches, and deionized water is added to the final viscosity to obtain wet particles. The surface of the wet particles is microgelled by spraying with glacial acetic acid solution, and then graded and dried to obtain green granules. The green granules are then subjected to a carbonization-activation process to obtain the finished product precursor.

[0010] S4. The precursor of the finished product is added to hydrochloric acid solution for acid washing, then impregnated with ammonium bicarbonate solution, and then annealed for a short time to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0011] Specifically, it includes:

[0012] S1, dissolve anhydrous potassium carbonate and urea in deionized water, under nitrogen atmosphere, stir at a constant temperature at the first temperature and dehydrate under reduced pressure until a uniform high-viscosity eutectic slurry is formed, and spray dry to obtain K2CO3-urea eutectic microparticles.

[0013] S2, tannic acid was dispersed in Tris buffer, and polyethyleneimine aqueous solution was added to Tris buffer at a second temperature and sheared to form a milky white microgel emulsion. The pH was adjusted to 7.8-8.2 and glyoxal aqueous solution was added for cross-linking. After centrifugation, washing, and freeze drying, complexed microgel powder was obtained.

[0014] S3, coconut shell powder, sucrose, complexed microgel powder and K2CO3-urea eutectic microparticles are dry mixed, deionized water is added to the target slurry viscosity, then silica sol is added in two batches, and deionized water is added to the final viscosity. Wet granules are obtained by granulation / extrusion. The surface of the wet granules is microgelled by spraying with glacial acetic acid solution, and then graded and dried to obtain green granules. The green granules are subjected to carbonization-activation process to obtain the finished product precursor.

[0015] S4. The product precursor is added to hydrochloric acid solution, stirred and acid-washed at room temperature to remove soluble metal salts and dried. Then it is impregnated with ammonium bicarbonate solution and dried to complete the re-alkalization. Then it is annealed for a short time to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0016] In the preparation of K2CO3-urea eutectic microparticles, anhydrous potassium carbonate and urea are dissolved in water and heated, utilizing the ability of urea molecules to form stable supramolecular structures through hydrogen bonds and ion-dipole interactions with carbonate and potassium ions. During decompression dehydration, the system becomes supersaturated and undergoes eutectic-quasi-eutectic solidification.

[0017] In the preparation of the complexed microgel powder, tannic acid contains a large number of pyrogallol groups in its molecular structure, while polyethyleneimine is a branched polymer containing a large number of primary, secondary, and tertiary amines. Under alkaline Tris buffer conditions, the phenolic hydroxyl groups of tannic acid are partially deprotonated, exhibiting negative charge; simultaneously, the amino groups of polyethyleneimine are partially protonated, exhibiting positive charge. The partial deprotonation of tannic acid and the protonation of the amino groups of polyethyleneimine jointly drive multi-point hydrogen bonding / ion-pairing, forming micelles-microgels, resulting in core-shell colloidal particles. The subsequently added glyoxal, as a bifunctional crosslinking agent, reacts with the primary and secondary amine groups of polyethyleneimine to form imine / hemiacetal crosslinks, thereby chemically fixing the three-dimensional network structure of the microgel and enhancing its structural stability.

[0018] In step S3, spraying with glacial acetic acid triggers a rapid sol-gel transition of the surface silica nanoparticles by lowering the pH value of the particles, forming a Si-O-Si network gel layer, i.e., outer microgelation, which imparts the mechanical strength required for the green carbon particles during drying and initial heat treatment. In the programmed carbonization-activation steps, the low-temperature pre-carbonization platform in stage one causes the organic precursors (coconut shell powder, sucrose, complexed microgels) to undergo dehydration, chain scission, and condensation, forming a preliminary amorphous carbon framework. Simultaneously, K2CO3-urea eutectic particles melt and penetrate into the carbon matrix, and nitrogen-containing substances such as ammonia and isocyanate produced by urea decomposition begin to react with the carbon framework, achieving preliminary nitrogen doping. Entering stage two, the atmosphere is switched to a N2 / CO2 mixed atmosphere and the temperature is increased. On the one hand, CO2, as a mild gas-phase activator, etches pores into the carbon framework through the carbon vaporization reaction (C + CO2 → 2CO), a reaction that tends to form micropores. On the other hand, K₂CO₃ undergoes a complex chemical reaction with carbon at high temperatures. Potassium metal vapor (K₂CO₃ + 2C → 2K + 3CO) embeds into the graphite-like layers of carbon, widening the interlayer spacing. The subsequent departure of the potassium vapor leaves behind numerous ultrapores and micropores. The carbon structure formed after the carbonization of the complexed microgel is relatively loose, acting as a soft template effect to construct mesoporous channels. Further decomposition products of urea continue to undergo nitrogen doping.

[0019] In the final processing step, hydrochloric acid washing aims to remove acid-soluble potassium salts formed during activation through acid-base neutralization and ion exchange, thus clearing blocked pores while retaining the acid-insoluble silica framework. The re-alkalization treatment utilizes the thermal instability of ammonium bicarbonate; after impregnation and drying, the ammonium bicarbonate decomposes into ammonia and carbon dioxide, introducing or restoring weakly basic oxygen-containing functional groups to the carbon material surface. Low-temperature ammonia annealing utilizes the decomposition of ammonia at high temperatures to generate active nitrogen species, enhancing the surface alkalinity / amine-like sites and thus optimizing the material's chemical affinity for acidic formaldehyde molecules.

[0020] As a preferred technical solution of the present invention, in S1, the mass ratio of anhydrous potassium carbonate, urea and deionized water is (30-33):(54-60):(100-120), for example, it can be (30, 30.3, 30.6, 30.9, 31.2, 31.5, 31.8, 32.1, 32.4, 32.7 or 33):(54, 54.6, 55.2, 55.8, 56.4, 57, 57.6, 58.2, 58.8, 59.4 or 60):(100, 102, 104, 106, 108, 110, 112, 114, 116, 118 or 120), but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] In some alternative embodiments, the first temperature is 80-90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the isothermal stirring time is 1.5-2 hours, for example, it can be 1.5 hours, 1.55 hours, 1.6 hours, 1.65 hours, 1.7 hours, 1.75 hours, 1.8 hours, 1.85 hours, 1.9 hours, 1.95 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the D50 of the K2CO3-urea eutectic microparticles is 2-10 μm, for example, it can be 2.0 μm, 2.8 μm, 3.6 μm, 4.4 μm, 5.2 μm, 6.0 μm, 6.8 μm, 7.6 μm, 8.4 μm, 9.2 μm or 10.0 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] As a preferred embodiment of the present invention, in S2, the mass-to-volume ratio of tannic acid, Tris buffer solution, polyethyleneimine aqueous solution, and glyoxal aqueous solution is (10-12) g: 1000 mL: 1000 mL: (0.5-1) g. For example, it can be (10.0, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8, or 12.0) g: 1000 mL: 1000 mL: (0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0) g, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the concentration of the polyethyleneimine aqueous solution is 20 mg / mL.

[0026] In some optional embodiments, the number-average molecular weight of the polyethyleneimine is 10,000.

[0027] In some optional embodiments, the concentration of the glyoxal aqueous solution is 35-40 wt.%; for example, it can be 35 wt.%, 35.5 wt.%, 36 wt.%, 36.5 wt.%, 37 wt.%, 37.5 wt.%, 38 wt.%, 38.5 wt.%, 39 wt.%, 39.5 wt.% or 40 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the crosslinking time is 30-40 min, for example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] As a preferred embodiment of the present invention, in S3, the mass ratio of coconut shell powder, sucrose, complexed microgel powder, K2CO3-urea eutectic microparticles, and silica sol is 100:(10-12):(15-18):(25-30):(13-14), for example, it can be 100:(10, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8 or 12):(15, 15.3, 15.6, ... 15.9, 16.2, 16.5, 16.8, 17.1, 17.4, 17.7 or 18: (25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5 or 30): (13, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9 or 14), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0030] In some optional embodiments, the target slurry viscosity is 3000-4000 mPa·s at 25°C, for example, it can be 3000 mPa·s, 3100 mPa·s, 3200 mPa·s, 3300 mPa·s, 3400 mPa·s, 3500 mPa·s, 3600 mPa·s, 3700 mPa·s, 3800 mPa·s, 3900 mPa·s or 4000 mPa·s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the mass fraction of the silica sol is 30-35 wt.%; for example, it can be 30 wt.%, 30.5 wt.%, 31 wt.%, 31.5 wt.%, 32 wt.%, 32.5 wt.%, 33 wt.%, 33.5 wt.%, 34 wt.%, 34.5 wt.%, or 35 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the final viscosity is 4500-6500 mPa·s at 25°C, for example, it can be 4500 mPa·s, 4700 mPa·s, 4900 mPa·s, 5100 mPa·s, 5300 mPa·s, 5500 mPa·s, 5700 mPa·s, 5900 mPa·s, 6100 mPa·s, 6300 mPa·s or 6500 mPa·s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some alternative embodiments, the D50 of the wet particles is 0.75-0.85 mm, for example, it can be 0.75 mm, 0.76 mm, 0.77 mm, 0.78 mm, 0.79 mm, 0.8 mm, 0.81 mm, 0.82 mm, 0.83 mm, 0.84 mm or 0.85 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the mass fraction of the glacial acetic acid solution is 0.2-0.5 wt.%; for example, it can be 0.2 wt.%, 0.23 wt.%, 0.26 wt.%, 0.29 wt.%, 0.32 wt.%, 0.35 wt.%, 0.38 wt.%, 0.41 wt.%, 0.44 wt.%, 0.47 wt.% or 0.5 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] In some alternative embodiments, the spraying time is 20-40 seconds, for example, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds, 30 seconds, 32 seconds, 34 seconds, 36 seconds, 38 seconds, or 40 seconds, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the graded drying is performed sequentially at 45°C for 2 hours, at 80°C for 2 hours, and at 120°C for 2 hours.

[0037] In some optional embodiments, the carbonization-activation procedure is as follows: Under a nitrogen atmosphere, the temperature is raised to 200-210°C and held for 0.5 h, then raised to 520-540°C and held for 0.5 h. Subsequently, a mixed gas is switched, with a N2 to CO2 volume ratio of 1:1 and a total flow rate of 1.5 L / min, raising the temperature to 790-800°C and holding for 40 min. The temperature is then switched back to nitrogen and allowed to cool naturally to ≤150°C before being removed from the furnace. Alternatively, the procedure could be: Under a nitrogen atmosphere, the temperature is raised to (200, 201, 202, 203, 204, 205, 206, 207, 208, 209, or 210)°C and held for 0.5 h. Then, raise the temperature to (520, 522, 524, 526, 528, 530, 532, 534, 536, 538, or 540)℃ and hold for 0.5h. Then switch to a mixed gas with a N2 to CO2 volume ratio of 1:1 and a total flow rate of 1.5 L / min, raise the temperature to (790, 791, 792, 793, 794, 795, 796, 797, 798, 799, or 800)℃ and hold for 40min. Switch back to nitrogen and allow to cool naturally to ≤150℃ before removing from the furnace. However, this process is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] In a preferred embodiment of the present invention, in step S4, the solid-liquid ratio of the finished precursor to the hydrochloric acid solution is 1:20.

[0039] In some optional embodiments, the concentration of the hydrochloric acid solution is 1M.

[0040] In some optional embodiments, the pickling time is 2-3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In some optional embodiments, the concentration of the ammonium bicarbonate solution is 0.1M.

[0042] In some alternative embodiments, the soaking time is 1-2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] In some optional embodiments, the short-time annealing is: annealing at 350-360°C for 0.5 hours in a mixed atmosphere with a N2 to NH3 volume ratio of 9:1 and a total flow rate of 1 L / min, followed by natural cooling to room temperature with nitrogen. For example, it can be: annealing at (350, 351, 352, 353, 354, 355, 356, 357, 358, 359, or 360)°C for 0.5 hours in a mixed atmosphere with a N2 to NH3 volume ratio of 9:1 and a total flow rate of 1 L / min, followed by natural cooling to room temperature with nitrogen. However, it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0044] Secondly, the present invention provides a porous structure-controlled activated carbon for adsorbing formaldehyde, prepared by the preparation method described in the first aspect.

[0045] Compared with existing technologies, the beneficial effects of this invention are as follows: By pre-forming eutectic microparticles with potassium-containing activators and nitrogen-containing precursors, highly uniform dispersion of activation sites and doping sites in the raw materials is achieved, enabling simultaneous and synergistic micropore etching and nitrogen atom doping during heat treatment. The resulting activated carbon has richer ultraporous / microporous structures and higher nitrogen doping efficiency, enhancing its physical adsorption and chemical anchoring capabilities for formaldehyde molecules. Using polymeric complex microgels as mesoporous templates and surface functionalization precursors, these gels construct interconnected mesoporous channels in situ during carbonization, improving the internal mass transfer efficiency of the material and allowing formaldehyde molecules to quickly reach the internal microporous adsorption sites. Simultaneously, the nitrogen-rich framework left after carbonization introduces a large number of alkaline sites onto the material surface, enhancing its chemical affinity for formaldehyde. By introducing inorganic nano-framework reinforcing agents during the forming stage and employing a microgel-based curing strategy for the particle surface, the mechanical strength and wear resistance of the raw carbon particles and even the final product are improved, broadening its engineering application scenarios. Detailed Implementation

[0046] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0047] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0048] Example 1

[0049] This embodiment provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The preparation method specifically includes the following steps:

[0050] S1, 30g of anhydrous potassium carbonate and 60g of urea are dissolved in 100g of deionized water, stirred at 90°C for 1.5h under nitrogen atmosphere and dehydrated under reduced pressure until a uniform high-viscosity eutectic slurry is formed, and spray dried to obtain K2CO3-urea eutectic microparticles, wherein the D50 of the K2CO3-urea eutectic microparticles is 10μm;

[0051] S2, 10g of tannic acid was dispersed in 1000mL of Tris buffer. At 15℃, 1000mL of 20mg / mL polyethyleneimine aqueous solution was added to Tris buffer and sheared to form a milky white microgel emulsion. The pH was adjusted to 7.8 and 1.0g of 40wt.% glyoxal aqueous solution was added for crosslinking for 30min. After centrifugation, washing, and freeze-drying, complexed microgel powder was obtained.

[0052] S3, 100g coconut shell powder, 12g sucrose, 15g complexed microgel powder, and 30g K2CO3-urea eutectic microparticles are dry-mixed, and deionized water is added to a pressure of 3,000 mPa·s. Then, 13.5g of 30wt.% silica sol is added in two batches, and deionized water is added again to a pressure of 6,500 mPa·s. The mixture is granulated / extruded to obtain wet granules with a D50 of 0.75mm. The surface of the wet granules is microgelled by spraying with a 0.5wt.% glacial acetic acid solution for 20s, followed by graded drying. The drying process involved sequentially drying at 45℃ for 2 hours, 80℃ for 2 hours, and 120℃ for 2 hours to obtain raw green pellets. The raw green pellets were then subjected to a carbonization-activation process. The carbonization-activation process involved a nitrogen atmosphere, raising the temperature to 210℃ from room temperature and holding for 0.5 hours, then raising it to 520℃ and holding for 0.5 hours. Subsequently, the mixed gas was switched, with N2:CO2 = 1:1 (volume ratio) and a total flow rate of 1.5 L / min, raising the temperature to 800℃ and holding for 40 minutes. The process was then switched back to nitrogen atmosphere and allowed to cool naturally to ≤150℃ before being removed from the furnace to obtain the finished product precursor.

[0053] S4. The product precursor is added to 1M hydrochloric acid solution and stirred and acid-washed at room temperature for 3 hours to remove soluble metal salts and then dried. The solid-liquid ratio of the product precursor to the hydrochloric acid solution is 1:20. Then, it is impregnated with 0.1M ammonium bicarbonate solution for 1 hour and dried to complete the re-alkalization. Then, it is annealed for a short time. The short-time annealing is carried out in a mixed atmosphere with N2:NH3 = 9:1 (volume ratio) and a total flow rate of 1L / min. The annealing is carried out at 360℃ for 0.5 hours. Then, nitrogen gas is switched and the mixture is naturally cooled to room temperature to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0054] Example 2

[0055] This embodiment provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The preparation method specifically includes the following steps:

[0056] S1, 33g of anhydrous potassium carbonate and 54g of urea are dissolved in 120g of deionized water, stirred at 80°C for 2.0h under nitrogen atmosphere and dehydrated under reduced pressure until a uniform high-viscosity eutectic slurry is formed, and spray dried to obtain K2CO3-urea eutectic microparticles, wherein the D50 of the K2CO3-urea eutectic microparticles is 2μm;

[0057] S2, 12g of tannic acid was dispersed in 1000mL of Tris buffer. At 10℃, 1000mL of 20mg / mL polyethyleneimine aqueous solution was added to Tris buffer and sheared to form a milky white microgel emulsion. The pH was adjusted to 8.2 and 0.5g of 40wt.% glyoxal aqueous solution was added for crosslinking for 40min. After centrifugation, washing, and freeze-drying, complexed microgel powder was obtained.

[0058] S3, 100g coconut shell powder, 10g sucrose, 18g complexed microgel powder, and 25g K2CO3-urea eutectic microparticles are dry-mixed, and deionized water is added to a pressure of 4,000 mPa·s. Then, 13.5g of 35wt.% silica sol is added in two batches, followed by further addition of deionized water to a pressure of 4,500 mPa·s. The mixture is then granulated / extruded to obtain wet granules with a D50 of 0.85mm. The surface of the wet granules is microgelled by spraying with a 0.2wt.% glacial acetic acid solution for 40s, followed by graded drying. The drying process involved sequentially drying at 45℃ for 2 hours, 80℃ for 2 hours, and 120℃ for 2 hours to obtain raw green pellets. The raw green pellets were then subjected to a carbonization-activation process. The carbonization-activation process involved a nitrogen atmosphere, raising the temperature from room temperature to 200℃ and holding for 0.5 hours, then raising it to 540℃ and holding for 0.5 hours. Subsequently, the mixed gas was switched, with N2:CO2 = 1:1 (volume ratio) and a total flow rate of 1.5 L / min, raising the temperature to 790℃ and holding for 40 minutes. The process was then switched back to nitrogen atmosphere and allowed to cool naturally to ≤150℃ before being removed from the furnace to obtain the finished product precursor.

[0059] S4. The product precursor is added to a 1M hydrochloric acid solution and stirred and acid-washed at room temperature for 2 hours to remove soluble metal salts and then dried. The solid-liquid ratio of the product precursor to the hydrochloric acid solution is 1:20. Then, it is impregnated with a 0.1M ammonium bicarbonate solution for 2 hours and dried to complete the re-alkalization. Then, it is annealed for a short time. The short-time annealing is carried out in a mixed atmosphere with N2:NH3 = 9:1 (volume ratio) and a total flow rate of 1L / min at 350℃ for 0.5 hours. Then, nitrogen is switched and the mixture is naturally cooled to room temperature to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0060] Example 3

[0061] This embodiment provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The preparation method specifically includes the following steps:

[0062] S1, 31g of anhydrous potassium carbonate and 58g of urea are dissolved in 110g of deionized water, stirred at 85°C for 1.8h under nitrogen atmosphere and dehydrated under reduced pressure until a uniform high-viscosity eutectic slurry is formed, and spray dried to obtain K2CO3-urea eutectic microparticles, wherein the D50 of the K2CO3-urea eutectic microparticles is 5μm;

[0063] S2, 11g of tannic acid was dispersed in 1000mL of Tris buffer. At 12℃, 1000mL of 20mg / mL polyethyleneimine aqueous solution was added to Tris buffer and sheared to form a milky white microgel emulsion. The pH was adjusted to 8.0 and 0.8g of 40wt.% glyoxal aqueous solution was added for crosslinking for 35min. After centrifugation, washing, and freeze-drying, complexed microgel powder was obtained.

[0064] S3, 100g coconut shell powder, 11g sucrose, 16g complexed microgel powder, and 28g K2CO3-urea eutectic microparticles are dry-mixed, and deionized water is added to a pressure of 3500mPa·s. Then, 13.2g and 32wt.% silica sol are added in two batches, followed by further addition of deionized water to a pressure of 5000mPa·s. The mixture is granulated / extruded to obtain wet granules with a D50 of 0.80mm. The surface of the wet granules is microgelled by spraying with a 0.4wt.% glacial acetic acid solution for 30s, followed by graded drying. The drying process involves sequentially drying at 45℃ for 2 hours, 80℃ for 2 hours, and 120℃ for 2 hours to obtain raw green granules. The raw green granules are then subjected to a carbonization-activation process. The carbonization-activation process is as follows: under a nitrogen atmosphere, the temperature is raised from room temperature to 205℃ and held for 0.5 hours, then raised to 530℃ and held for 0.5 hours. Subsequently, the mixed gas is switched, with N2:CO2 = 1:1 (volume ratio) and a total flow rate of 1.5 L / min, and the temperature is raised to 795℃ and held for 40 minutes. The process is then switched back to nitrogen and allowed to cool naturally to ≤150℃ before being removed from the furnace to obtain the finished product precursor.

[0065] S4. The product precursor is added to a 1M hydrochloric acid solution and stirred and acid-washed at room temperature for 2.5 hours to remove soluble metal salts and then dried. The solid-liquid ratio of the product precursor to the hydrochloric acid solution is 1:20. Then, it is impregnated with a 0.1M ammonium bicarbonate solution for 1.5 hours and dried to complete the re-alkalization. Then, it is annealed for a short time. The short-time annealing is carried out in a mixed atmosphere with N2:NH3 = 9:1 (volume ratio) and a total flow rate of 1L / min at 355℃ for 0.5 hours. Then, nitrogen gas is switched and the mixture is naturally cooled to room temperature to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0066] Example 4

[0067] This embodiment provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The preparation method specifically includes the following steps:

[0068] S1, 32g of anhydrous potassium carbonate and 56g of urea are dissolved in 115g of deionized water, stirred at 82°C for 1.6h under nitrogen atmosphere and dehydrated under reduced pressure until a uniform high-viscosity eutectic slurry is formed, and spray dried to obtain K2CO3-urea eutectic microparticles, wherein the D50 of the K2CO3-urea eutectic microparticles is 8μm;

[0069] S2, 11.5 g of tannic acid was dispersed in 1000 mL of Tris buffer. At 14 °C, 1000 mL of 20 mg / mL polyethyleneimine aqueous solution was added to the Tris buffer and sheared to form a milky white microgel emulsion. The pH was adjusted to 7.9 and 0.6 g of 40 wt.% glyoxal aqueous solution was added for crosslinking for 32 min. After centrifugation, washing, and freeze-drying, complexed microgel powder was obtained.

[0070] S3, 100g coconut shell powder, 11.5g sucrose, 17g complexed microgel powder, and 26g K2CO3-urea eutectic microparticles are dry-mixed, and deionized water is added to a pressure of 3800mPa·s. Then, 13.8g and 34wt.% silica sol are added in two batches, and deionized water is added again to a pressure of 6000mPa·s. The mixture is granulated / extruded to obtain wet granules with a D50 of 0.82mm. The surface of the wet granules is microgelled by spraying with a 0.3wt.% glacial acetic acid solution for 25s, followed by graded drying. The drying process involved sequentially drying at 45℃ for 2 hours, 80℃ for 2 hours, and 120℃ for 2 hours to obtain raw green pellets. The raw green pellets were then subjected to a carbonization-activation process. The carbonization-activation process involved a nitrogen atmosphere, raising the temperature to 208℃ from room temperature and holding for 0.5 hours, then raising it to 535℃ and holding for 0.5 hours. Subsequently, the mixed gas was switched, with N2:CO2 = 1:1 (volume ratio) and a total flow rate of 1.5 L / min, raising the temperature to 792℃ and holding for 40 minutes. The process was then switched back to nitrogen atmosphere and allowed to cool naturally to ≤150℃ before being removed from the furnace to obtain the finished product precursor.

[0071] S4. The product precursor is added to 1M hydrochloric acid solution and stirred and acid-washed at room temperature for 2.2h to remove soluble metal salts and then dried. The solid-liquid ratio of the product precursor to the hydrochloric acid solution is 1:20. Then, it is impregnated with 0.1M ammonium bicarbonate solution for 1.8h and dried to complete the re-alkalization. Then, it is annealed for a short time. The short time annealing is carried out in a mixed atmosphere with N2:NH3=9:1 (volume ratio) and a total flow rate of 1L / min at 352℃ for 0.5h. Then, nitrogen gas is switched and the mixture is naturally cooled to room temperature to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

[0072] Comparative Example 1

[0073] This comparative example provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The difference between this example and Example 1 is that no complexed microgel powder is added in S3, while other process parameters and operating conditions are exactly the same as in Example 1.

[0074] Comparative Example 2

[0075] This comparative example provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The difference between this example and Example 1 is that K2CO3-urea eutectic particles are not added in S3, while other process parameters and operating conditions are exactly the same as in Example 1.

[0076] Comparative Example 3

[0077] This comparative example provides a porous structure-controlled activated carbon for adsorbing formaldehyde and its preparation method. The difference between this example and Example 1 is that no silica sol is added in S3, and no surface microgelation treatment with glacial acetic acid spray is performed. Other process parameters and operating conditions are exactly the same as in Example 1.

[0078] Static saturated adsorption capacity test method: 1.000 g of the porous structure-regulated activated carbon sample to be tested was evenly spread in an open glass weighing bottle at the bottom of a 10 L sealed glass desiccator that had been pre-equilibrated at 25℃ and 50% relative humidity (RH) for 24 h and had established a stable formaldehyde concentration (C0, 100 ppm). The desiccator was quickly sealed, and the formaldehyde concentration change in the desiccator over time was monitored and recorded in real time using a formaldehyde detector. At 48 hours, the final equilibrium formaldehyde concentration C1 was recorded. Static saturated adsorption capacity (48 h, mg / g) = [(C0 – C1) × V × M / 24.45] / 1.000, where V is the effective volume of the desiccator (m³ / h). 3 M represents the molar mass of formaldehyde (30.03 g / mol). Simultaneously, a desiccator without the sample was placed under the same initial conditions as a blank control to correct for the natural decay of formaldehyde.

[0079] Dynamic breakthrough test method: 1.000 g of the porous activated carbon sample to be tested was uniformly filled into a quartz adsorption tube with an inner diameter of 10 mm, and both ends were fixed with quartz wool. The adsorption tube was placed in the test system, and a mixed gas flow was introduced, which had been treated at constant temperature and humidity to 25℃, 50% RH, a total flow rate of 1000 mL / min, and a constant formaldehyde inlet concentration (C-in) of 50 ppm. The formaldehyde concentration (C-out) at the outlet of the adsorption tube was continuously monitored using an online formaldehyde analyzer. When the outlet concentration (C-out) reached 5% of the inlet concentration (C-in), the time was recorded, which is the breakthrough time t (min). The breakthrough adsorption capacity Qb (mg / g) was calculated by integrating the breakthrough curve from 0 to t.

[0080] Wear rate test method: Weigh 10.00 g of intact porous activated carbon sample particles as the initial mass m0 and place it in a 50 mL rigid polypropylene centrifuge tube. Fix the centrifuge tube on a vortex mixer and vortex at maximum speed for 5 minutes. After vortexing, pour all the material in the tube onto a 0.5 mm standard sieve, collect and weigh the mass of the intact particles remaining on the sieve, and record it as the final mass m1. Wear rate (%) = [(m0 – m1) / m0] × 100%.

[0081] The test results are shown in Table 1.

[0082] Table 1. Test results of porous structure-regulated activated carbon particles in Examples 1-4 and Comparative Examples 1-3

[0083] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Static saturated adsorption capacity (mg / g) 1.044 1.021 1.033 1.028 0.860 0.430 0.737 Penetration adsorption capacity (mg / g) 9.33 9.30 9.27 9.36 7.00 2.63 5.25 Wear rate (%) 1.5 1.6 1.6 1.7 1.8 1.2 5.0

[0084] As shown in Table 1, compared to Example 1, Comparative Example 1 showed a decrease in static saturated adsorption capacity, a decrease in breakthrough saturated adsorption capacity, and an increase in wear rate; Comparative Example 3 showed a decrease in static saturated adsorption capacity, a decrease in breakthrough saturated adsorption capacity, and an increase in wear rate. This is because the carbonization of the complexed microgel powder provides a loose, soft template to open mesoporous channels and introduces alkaline nitrogen-containing sites for addition / condensation fixation with formaldehyde. In Comparative Example 1, no complexed microgel powder was added, resulting in a more tortuous diffusion path and weaker chemical fixation, thus leading to a decrease in both static saturated adsorption capacity and breakthrough saturated adsorption capacity. The eutectic microparticles, after dehydration under reduced pressure, are uniformly dispersed in a quasi-eutectic form. During pre-carbonization and activation, intercalation and departure occur, along with etching, primarily generating ultrapores / micropores. Simultaneously, urea pyrolysis acts as a nitrogen source, promoting the formation of surface alkaline sites. In Comparative Example 2, no eutectic microparticles were added, resulting in a decrease in both static saturated adsorption capacity and breakthrough saturated adsorption capacity. The spraying of glacial acetic acid pulls the pH of the particle surface to a range conducive to silanol condensation, promoting the rapid gelation of silica sol to form a Si-O-Si network. This provides a support shell for the drying and pre-carbonization stages and inhibits pulverization. In Comparative Example 3, no silica sol was added, and no surface microgelation treatment was performed by spraying with glacial acetic acid. Under the activation of high burn-off rate, the particles became more brittle and more prone to powdering and breakage. Under the action of airflow, channeling and fine powder entrainment appeared in the bed, resulting in a decrease in static saturated adsorption capacity, a decrease in breakthrough saturated adsorption capacity, and an increase in wear rate.

[0085] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing porous structure-controlled activated carbon for adsorbing formaldehyde, characterized in that, The preparation method includes: S1, anhydrous potassium carbonate and urea are dissolved in deionized water, stirred and dehydrated under reduced pressure, and spray dried to obtain K2CO3-urea eutectic microparticles; S2, Tannic acid is dispersed in Tris buffer, polyethyleneimine aqueous solution is added to Tris buffer and sheared to form a milky white microgel emulsion, pH is adjusted to 7.8-8.2 and glyoxal aqueous solution is added to obtain complexed microgel powder; S3, coconut shell powder, sucrose, complexed microgel powder and K2CO3-urea eutectic microparticles are dry mixed, deionized water is added to the target slurry viscosity, then silica sol is added in two batches, and deionized water is added to the final viscosity to obtain wet particles. The surface of the wet particles is microgelled by spraying with glacial acetic acid solution, and then graded and dried to obtain green granules. The green granules are then subjected to a carbonization-activation process to obtain the finished product precursor. S4. The precursor of the finished product is added to hydrochloric acid solution for acid washing, then impregnated with ammonium bicarbonate solution, and then annealed for a short time to obtain porous structure-controlled activated carbon particles for formaldehyde adsorption.

2. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S1: The mass ratio of anhydrous potassium carbonate, urea and deionized water is (30-33):(54-60):(100-120). The D50 of the K2CO3-urea eutectic microparticles is 2-10 μm.

3. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S2: The mass-to-volume ratio of the tannic acid, Tris buffer solution, polyethyleneimine aqueous solution and glyoxal aqueous solution is (10-12) g: 1000 mL: 1000 mL: (0.5-1) g.

4. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S2: The number-average molecular weight of the polyethyleneimine is 10,000; The concentration of the glyoxal aqueous solution is 35-40 wt.%.

5. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S3: The mass ratio of coconut shell powder, sucrose, complexed microgel powder, K2CO3-urea eutectic microparticles to silica sol is 100: (10-12): (15-18): (25-30): (13-14).

6. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S3: The target slurry has a viscosity of 3,000-4,000 mPa·s at 25°C. The final viscosity is 4,500-6,500 mPa·s at 25°C.

7. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S3: The graded drying process involves sequentially drying at 45℃ for 2 hours, at 80℃ for 2 hours, and at 120℃ for 2 hours.

8. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S3: The carbonization-activation process is as follows: under a nitrogen atmosphere, the room temperature is raised to 200-210℃ and held for 0.5 h, then raised to 520-540℃ and held for 0.5 h. Subsequently, a mixed gas is switched, with a N2 to CO2 volume ratio of 1:1 and a total flow rate of 1.5 L / min, and the temperature is raised to 790-800℃ and held for 40 min. The process is then switched back to nitrogen and allowed to cool naturally to ≤150℃ before being removed from the furnace.

9. The method for preparing porous structure-controlled activated carbon for formaldehyde adsorption according to claim 1, characterized in that, In S4: The solid-liquid ratio of the finished product precursor to the hydrochloric acid solution is 1:20; The short-time annealing is performed in a mixed atmosphere with a N2 to NH3 volume ratio of 9:1 and a total flow rate of 1L / min. Annealing is carried out at 350-360℃ for 0.5h, followed by natural cooling to room temperature with nitrogen.

10. A porous structure-controlled activated carbon for adsorbing formaldehyde obtained by the preparation method according to any one of claims 1-9.