A porous hierarchical structure formaldehyde removal coating and a preparation method thereof

Abstract

This invention discloses a porous, hierarchical formaldehyde-removing coating and its preparation method. The coating is prepared by thermally curing a formaldehyde-removing nano-catalyst coating at 50-200℃. By weight, the formaldehyde-removing nano-catalyst coating comprises: 40-60 parts of double-modified coconut shell activated carbon, 15-25 parts of calcium oxide, 10-35 parts of manganese dioxide, 2-20 parts of sodium bicarbonate, and 0-5 parts of adhesive. The double-modified coconut shell activated carbon is obtained by sequentially treating the coconut shell activated carbon with steam, a hydrophobic modifier, and a mixed solution of urea and citric acid. This invention, by introducing a double-modified coconut shell activated carbon carrier and a sodium bicarbonate pore-forming agent and optimizing the process flow, achieves the uniform dispersion of the active catalyst within the pore structure of the double-modified coconut shell activated carbon while simultaneously constructing a porous, hierarchical structure, thereby significantly improving the pore structure control capability and formaldehyde catalytic purification performance of the coating product.

Description

Technical Field

[0001] This invention relates to the field of air purification technology, and in particular to a porous, hierarchical formaldehyde-removing coating and its preparation method. Background Technology

[0002] As people pay increasing attention to indoor air quality, the concentrations of formaldehyde and volatile organic compounds (VOCs) in indoor air have become important indicators affecting the quality of living. Currently, indoor pollution control and treatment mainly include three aspects: ventilation, source control, and end-of-pipe purification. Even with ventilation and source control, the problem of excessive indoor formaldehyde levels persists, requiring additional end-of-pipe purification measures. Among these, catalytic decomposition products are gradually gaining attention due to their thorough formaldehyde removal. Precious metal catalysts (such as platinum, gold, and silver) can decompose formaldehyde adsorbed on surfaces into carbon dioxide and water, exhibiting high removal efficiency and stability; however, their high price hinders widespread application.

[0003] Besides precious metal catalysts, transition metal oxides (such as manganese and copper) also exhibit oxidative activity towards formaldehyde. They are relatively inexpensive and possess relatively high catalytic activity, making them widely used in formaldehyde purification research. However, existing transition metal oxides often exist in particulate or powder form, requiring in-situ loading onto a carrier using electrochemical methods or redox mechanisms. Furthermore, currently available activated carbon filters have low adsorption capacity, resulting in less than ideal formaldehyde removal efficiency. Therefore, developing a highly efficient transition metal oxide coating for formaldehyde removal and its preparation method to improve removal efficiency and lifespan has become a pressing technical challenge. For example, CN116673021A discloses a composite material and its preparation method, comprising a matrix material and a coating loaded on the surface of the matrix material. While this patent provides a composite material that prevents formaldehyde removal material from detaching and achieves high-efficiency formaldehyde purification, the selection of the matrix material and the ratio of coating components still require further optimization to improve removal efficiency and stability. Summary of the Invention

[0004] This invention aims to overcome the problems of low purification efficiency, short service life, high air resistance, and cumbersome processes caused by the easy agglomeration of formaldehyde removal materials in the prior art. It provides a porous, hierarchical formaldehyde removal coating and its preparation method. By introducing a double-modified coconut shell activated carbon carrier and sodium bicarbonate pore-forming agent and optimizing the process flow, the active catalyst is uniformly dispersed in the pore structure of the double-modified coconut shell activated carbon while the porous hierarchical structure is constructed. This significantly improves the pore structure control ability and formaldehyde catalytic purification performance of the coating product.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A porous, hierarchical formaldehyde-removing coating is prepared by thermal curing a formaldehyde-removing nano-catalyst coating at 50-200°C. By weight, the formaldehyde-removing nano-catalyst coating comprises: 40-60 parts of double-modified coconut shell activated carbon, 15-25 parts of calcium oxide, 10-35 parts of manganese dioxide, 2-20 parts of sodium bicarbonate, and 0-5 parts of adhesive. The modified coconut shell activated carbon is prepared by sequentially treating the coconut shell activated carbon with steam, a hydrophobic modifier, and a mixed solution of urea and citric acid.

[0006] This invention introduces a dual-modified coconut shell activated carbon carrier and sodium bicarbonate pore-forming agent into the coating material. The dual-modified coconut shell activated carbon carrier is prepared by sequentially treating coconut shell activated carbon with steam, a hydrophobic modifier, and a mixed solution of urea and citric acid. This invention uses high-temperature steam as an activator, which reacts with carbon at high temperature to produce gases such as CO and H2. Etching and pore-expanding further increase the specific surface area and the proportion of micropores, thereby effectively controlling the pore structure of the coconut shell carbon. The high specific surface area and well-developed hierarchical structure of micropores, mesopores, and macropores provide rapid mass transfer channels, while also providing a good pore structure for subsequent hydrophobic modification. The resulting hydrophobic surface reduces competitive adsorption of water molecules, thereby enhancing the physical adsorption of formaldehyde molecules. Meanwhile, the basic active adsorption sites introduced by the nitrogen-containing functional groups amino and amide groups can enhance the chemical adsorption of formaldehyde through Schiff base reactions. The introduction of citric acid can, on the one hand, introduce oxygen-containing functional groups such as carboxyl groups on the surface of coconut shell charcoal, increasing surface polarity and making it easier to adsorb polar molecules; on the other hand, it can optimize the pore distribution of coconut shell charcoal, making it more suitable for the adsorption of formaldehyde molecules; in addition, the introduction of citric acid can also strengthen the binding of formaldehyde gas molecules through chemical adsorption (hydrogen bonding, electrostatic interaction), reduce competitive adsorption, and increase the adsorption rate.

[0007] This invention uses sodium bicarbonate as a pore-forming agent. After dissolution, sodium bicarbonate is uniformly adsorbed onto the surface of the pore structure of the double-modified coconut shell activated carbon. This facilitates the construction of a porous, hierarchical structure of the formaldehyde-removing coating precursor by the thermal decomposition products of sodium bicarbonate during subsequent thermal curing. On one hand, the H2O and CO2 generated by the thermal decomposition of sodium bicarbonate overflow from the coating surface in gaseous form and form a bubble structure, which is beneficial for the adsorption, mass transfer, and activated catalytic degradation of formaldehyde on the coating surface. On the other hand, the difference in sodium bicarbonate content and slow decomposition at different locations in the formaldehyde-removing coating can form pore structures of different sizes, thus obtaining a hierarchical pore structure. At the same time, with the thermal decomposition of sodium bicarbonate, the contact between the components in the formaldehyde-removing coating becomes tighter and more reliable. This not only facilitates the interaction between the components in the coating and the generation of active free radicals, but also reduces the content of adhesives to a certain extent, thereby reducing the adverse effects of adhesives masking active sites on the formaldehyde-removing coating's purification of formaldehyde. This achieves a highly efficient adsorption-activation-degradation cycle of formaldehyde by the formaldehyde-removing coating, ensuring the rapid purification of formaldehyde on the coating surface.

[0008] Meanwhile, this invention uses sodium carbonate, a thermal decomposition product of calcium oxide and sodium bicarbonate, as an additive. During the thermosetting process, sodium bicarbonate improves the dispersibility of each component through thermal decomposition and prevents the agglomeration of manganese dioxide nanoparticles in the coating through electrostatic repulsion, thereby obtaining a highly dispersed transition metal oxide manganese dioxide active phase. Simultaneously, calcium oxide and sodium carbonate can neutralize acidic active sites on the catalyst surface, optimizing formaldehyde adsorption and catalytic degradation efficiency, preventing the masking of adsorption / catalytic active sites by formate and acidic carbon dioxide gas, and thus releasing active sites to promote the catalytic degradation reaction. Furthermore, calcium oxide enhances the thermal stability and anti-carbon deposition performance of the formaldehyde-removing coating. By stabilizing the structure of active components in the coating, it reduces the agglomeration of active components caused by high-temperature heat treatment, while inhibiting carbon deposition and extending the service life of the formaldehyde-removing coating. In addition, calcium carbonate and calcium oxide regulate the electronic state of nanoparticles by coordinating the metal oxide-carrier interaction, thereby enhancing the chemical adsorption to capture carbon dioxide generated by catalytic degradation, improving the catalytic activity of the coating, and promoting the continuous catalytic degradation of formaldehyde on the coating surface.

[0009] Therefore, this invention utilizes the large specific surface area and improved pore structure of the double-modified coconut shell activated carbon to provide more active sites and enhance the physical and chemical adsorption of formaldehyde; a porous hierarchical structure is constructed using the thermal decomposition products of sodium bicarbonate; and the sodium bicarbonate pyrolysis products, sodium carbonate and calcium oxide, not only inhibit the aggregation of active components and the formation of carbon deposits, but also enhance the interaction between the active catalytic components and the carrier coconut shell. Through the synergistic effect of these multiple mechanisms, the coating significantly enhances the adsorption-activation-degradation pathway of formaldehyde.

[0010] The porous, hierarchical formaldehyde-removing coating of this invention can achieve the following effects: 1) Formaldehyde removal rate ≥35% in 3 minutes, formaldehyde removal rate ≥90% in 40 minutes; 2) High temperature and high humidity stability: After treatment at 75 ℃ and 90% humidity for 48 hours, the formaldehyde removal rate is ≥90% after 40 minutes. 3) The formaldehyde removal filter produced was dropped from a height of 1.5 meters without any obvious powder falling off.

[0011] Preferably, when treating coconut shell activated carbon with steam, the mass ratio of steam to coconut shell activated carbon is 1:0.6~1.2, the treatment temperature is 800~1000℃, and the treatment time is 30~120min.

[0012] Preferably, the hydrophobic modifier is propyltrichlorosilane and / or hexadecyltrimethoxysilane; the coconut shell activated carbon is treated with the hydrophobic modifier by ultrasonic impregnation, and the ultrasonic impregnation time is 10~50 min.

[0013] Preferably, in the urea and citric acid mixed solution, the mass ratio of urea to citric acid is 2~5:1; when treating coconut shell activated carbon with the urea and citric acid mixed solution, the treatment temperature is 120~180℃ and the treatment time is 2~6h.

[0014] Preferably, the calcium oxide has a particle size of 0.5~2μm, and the manganese dioxide has a particle size of 10~50nm.

[0015] Preferably, the adhesive is selected from one or more of polyurethane adhesive, polyacrylic resin, and epoxy resin.

[0016] Preferably, the thickness of the porous, hierarchical formaldehyde-removing coating is 15~45μm.

[0017] The present invention also provides a method for preparing the above-mentioned porous hierarchical formaldehyde removal coating, comprising the following steps: (1) Preparation of double-modified coconut shell activated carbon; (2) Disperse the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate in water in sequence, stir and mix evenly, then add the adhesive and continue to stir evenly to obtain the formaldehyde removal nano catalyst coating. (3) The formaldehyde-removing nano-catalyst coating is applied to the inner and outer surfaces of the aluminum honeycomb panel and then heat-cured at 50~200℃ to obtain the porous graded structure formaldehyde-removing coating.

[0018] This invention utilizes the high specific surface area and well-developed pore structure of double-modified coconut shell activated carbon to provide more contact sites for nano-manganese dioxide and calcium oxide, enhancing the adhesion of manganese dioxide and calcium oxide to the coconut shell surface through hydrogen bonding, electrostatic interactions, and other forces. The mechanical action during stirring achieves uniform mixing of the components in the formaldehyde-removing coating precursor material. After mechanical mixing, the resulting mixture undergoes high-temperature heat treatment, further achieving a uniform and firm distribution of the formaldehyde-removing active components within the pore structure of the double-modified coconut shell activated carbon without affecting its specific surface area.

[0019] This invention involves thermosetting within a temperature range of 50~200℃. If the thermosetting temperature is too low, it hinders the decomposition of sodium bicarbonate, preventing the formation of a porous, hierarchical structure and affecting the adhesion of the formaldehyde-removing coating to the aluminum honeycomb surface. If the thermosetting temperature is too high, the adhesive in the formaldehyde-removing slurry will obscure the active components, both of which will negatively impact the formaldehyde removal effect.

[0020] This invention uses an aluminum honeycomb panel as a carrier. By coating the inner and outer surfaces of its pores with the formaldehyde-removing coating, complex loading processes such as electrochemical or redox treatments are eliminated, simplifying the preparation process. Placing the aluminum honeycomb panel coated with the porous, graded formaldehyde-removing coating on the air inlet surface of air handling equipment such as air filters and air conditioners allows the incoming air to be separated from the formaldehyde-removing coating material, thereby purifying and removing formaldehyde from the air in the test chamber.

[0021] Preferably, the stirring rate in step (2) is 400~800 r / min; the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate are dispersed in water in sequence and stirred for 3~8 h, and then added to the adhesive and stirred for 2~6 h.

[0022] Preferably, the drying time in step (3) is 4 to 6 hours.

[0023] Therefore, the present invention has the following beneficial effects: (1) Introducing double-modified coconut shell activated carbon carrier and sodium bicarbonate pore-forming agent into the coating material modifies the pore structure of the coating and scientifically proportions it with components such as calcium oxide, manganese dioxide, and adhesive to obtain a formaldehyde removal coating with a porous hierarchical structure. This is beneficial for the adsorption and mass transfer of formaldehyde in the formaldehyde removal coating, significantly improving the purification and removal of formaldehyde by the coating. It has excellent high temperature and high humidity resistance and can maintain a long-term stable purification effect. (2) Physical mixing and high-temperature activation are adopted, that is, the components in the coating are firmly and uniformly distributed with low content of adhesive, which is conducive to the exposure of more catalytic active sites and effectively solves the problems of easy detachment of traditional air catalyst filter material and high content of adhesive masking catalytic active sites and affecting catalytic performance. (3) Using aluminum honeycomb panels as carriers, the formaldehyde-removing coating is applied to the inner and outer surfaces of the pores, eliminating the need for complex loading treatments such as electrochemical or redox reactions, thus simplifying the preparation process. Attached Figure Description

[0024] Figure 1 This is a physical image of the porous, graded formaldehyde-removing coating described in Embodiment 2 of the present invention.

[0025] Figure 2 This is a pore size distribution diagram of the porous graded structure formaldehyde removal coating shown in Embodiment 2 of the present invention.

[0026] Figure 3 This is a SEM image of the porous, hierarchical formaldehyde-removing coating shown in Embodiment 2 of the present invention. Detailed Implementation

[0027] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0028] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0029] General Implementation Examples: A porous, hierarchical formaldehyde-removing coating is prepared by thermal curing a formaldehyde-removing nano-catalyst coating at 50-200°C. By weight, the formaldehyde-removing nano-catalyst coating comprises: 40-60 parts of double-modified coconut shell activated carbon, 15-25 parts of calcium oxide, 10-35 parts of manganese dioxide, 2-20 parts of sodium bicarbonate, and 0-5 parts of adhesive. The modified coconut shell activated carbon is prepared by sequentially treating the coconut shell activated carbon with steam, a hydrophobic modifier, and a mixed solution of urea and citric acid.

[0030] As one specific implementation method, when treating coconut shell activated carbon with steam, the mass ratio of steam to coconut shell activated carbon is 1:0.6~1.2, the treatment temperature is 800~1000℃, and the treatment time is 30~120min.

[0031] In one specific embodiment, the hydrophobic modifier is propyltrichlorosilane and / or hexadecyltrimethoxysilane; the coconut shell activated carbon is treated with the hydrophobic modifier by ultrasonic impregnation, and the ultrasonic impregnation time is 10~50 min.

[0032] In one specific implementation, the mass ratio of urea to citric acid in the urea and citric acid mixed solution is 2~5:1; when treating coconut shell activated carbon with the urea and citric acid mixed solution, the treatment temperature is 120~180℃ and the treatment time is 2~6h.

[0033] In one specific embodiment, the calcium oxide has a particle size of 0.5~2μm, and the manganese dioxide has a particle size of 10~50nm.

[0034] In one specific embodiment, the adhesive is selected from one or more of polyurethane adhesive, polyacrylic resin, and epoxy resin.

[0035] In one specific embodiment, the thickness of the porous, hierarchical formaldehyde-removing coating is 15~45μm.

[0036] The preparation method of the above-mentioned porous hierarchical formaldehyde removal coating includes the following steps: (1) Preparation of double-modified coconut shell activated carbon; (2) Disperse the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate in water in sequence, stir and mix evenly, then add the adhesive and continue to stir evenly to obtain the formaldehyde removal nano catalyst coating. (3) The formaldehyde-removing nano-catalyst coating is applied to the inner and outer surfaces of the aluminum honeycomb panel and then heat-cured at 50~200℃ to obtain the porous graded structure formaldehyde-removing coating.

[0037] As a specific implementation method, the stirring rate in step (2) is 400~800r / min; the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate are dispersed in water in sequence and stirred for 3~8h, and then added to the adhesive and stirred for 2~6h.

[0038] In one specific implementation, the drying time in step (3) is 4~6 hours.

[0039] Example 1: A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 50 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 50 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0040] Example 2: A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 ℃ for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 ℃ for 3 hours to obtain the porous hierarchical formaldehyde-removing coating. Its physical image is shown below. Figure 1 As shown in the figure; aperture distribution diagram as shown in the figure. Figure 2 As shown, from Figure 2 As can be seen from the image, the coating obtained by this invention has a hierarchical pore structure; the SEM image is shown below. Figure 3 As shown, from Figure 3 As can be seen, the coating thickness is 30 μm.

[0041] Example 3: A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 100 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 100 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0042] Example 4: A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 125 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 125 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0043] Example 5: A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 5 parts of sodium bicarbonate were dispersed in 120 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0044] Comparative Example 1 (no modification of coconut shell activated carbon): A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) By weight, 50 parts of coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (2) 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) were added dropwise to the slurry obtained in step (2) under rapid stirring, and then the mixture was rapidly stirred at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (3) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 ℃ for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 ℃ for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0045] Comparative Example 2 (without calcium oxide): A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 15 parts of nano MnO2 (particle size 1.5 μm) and 10 parts of sodium bicarbonate were dispersed in 125 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0046] Comparative Example 3 (without sodium bicarbonate): A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm) and 15 parts of nano MnO2 (particle size 30 nm) were dispersed in 125 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0047] Comparative Example 4 (Thermosetting temperature too low): A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium bicarbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 40 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 40 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0048] Comparative Example 5 (using sodium carbonate instead of sodium bicarbonate): A method for preparing a porous, hierarchical formaldehyde-removing coating, comprising the following steps: (1) Coconut shell activated carbon was treated with steam at 850 °C for 60 minutes. Then the dried product was immersed in propyltrichlorosilane and treated with ultrasonic impregnation for 2 hours. After centrifugation and drying, physically modified coconut shell activated carbon was obtained. Finally, the above product was dispersed in urea-citric acid solution (mass ratio of urea to citric acid was 2:1) for impregnation modification. After reflux treatment at 80 °C for 2 hours, the product was centrifuged, washed and dried to obtain double-modified coconut shell activated carbon. (2) By weight, 50 parts of double-modified coconut shell activated carbon, 10 parts of calcium oxide (particle size 1.5 μm), 15 parts of nano MnO2 (particle size 30 nm) and 10 parts of sodium carbonate were dispersed in 115 parts of deionized water and stirred rapidly at 600 r / min for 3 hours at room temperature to obtain a uniformly mixed slurry. (3) Add 0.05 parts of water-based acrylic emulsion (Changzhou Guangshu Chemical GS-200) dropwise to the slurry obtained in step (2) under rapid stirring, and then stir rapidly at room temperature for 2.5 hours to obtain formaldehyde removal nano-catalyst coating. (4) The formaldehyde-removing nano-catalyst coating obtained in step (3) is sprayed onto the inner and outer surfaces of the aluminum honeycomb panel using a high-pressure spray gun. After spraying, it is heated and dried at 75 °C for 30 minutes. Then, step (4) is repeated three times. The coated aluminum honeycomb panel is dried at 75 °C for 3 hours to obtain the porous graded structure formaldehyde-removing coating, wherein the coating thickness is 30 μm.

[0049] The performance of the formaldehyde-removing coatings obtained in the above embodiments and comparative examples was tested, and the results are shown in Table 1. All performance tests were conducted in a 3-cubic-meter test chamber at normal temperature and pressure (25 ℃, 1 atmosphere), with a filter size of 100 mm × 100 mm × 18 mm and an initial formaldehyde concentration of 0.9 ± 0.1 mg / m³. 3 Air volume controlled at 110 m³ 3 / h.

[0050] Table 1: Coating component ratio and formaldehyde removal effect As can be seen from the comparison of formaldehyde removal data in Table 1, the coatings prepared using the formula and method of this invention in Examples 1-5 achieve a combination of hierarchical structure and good catalytic removal function, while also achieving a combination of highly efficient adsorption-catalytic performance. The synergistic effect between the components such as double-modified coconut shell activated carbon, calcium oxide, pore-forming agent sodium bicarbonate, and adhesive, and nano-manganese dioxide, can maintain the highly efficient purification performance of the porous hierarchical structure coating for formaldehyde. Meanwhile, the data from Examples 1-4 show that 75℃ is the optimal thermosetting temperature. In Comparative Example 1, without modification of the coconut shell activated carbon, the formaldehyde removal performance is significantly lower than in the examples, indicating that double-modified coconut shell activated carbon can enhance the adsorption and enrichment of formaldehyde by the coating, which is beneficial to the catalytic removal by nano-manganese dioxide. In Comparative Example 2, without the addition of calcium oxide, the formaldehyde removal performance is also lower than in the examples, indicating that calcium oxide can provide an alkaline environment for the coating, further enhancing the adsorption of formaldehyde. In Comparative Example 3, no sodium bicarbonate was added; in Comparative Example 4, the thermosetting temperature was too low, and sodium bicarbonate could not be effectively decomposed; in Comparative Example 5, sodium carbonate was used instead of sodium bicarbonate, and the formaldehyde removal effect of the coating decreased compared with the examples. This indicates that compared with sodium carbonate, sodium bicarbonate can not only achieve the construction of a porous hierarchical structure in the coating, but also its decomposition products can reduce the accumulation of acidic products such as formate in the formaldehyde removal process, which is conducive to the catalytic removal of formaldehyde by the coating. Therefore, its formaldehyde purification effect is better than that of the formaldehyde removal coating containing sodium carbonate.

Claims

1. A porous, hierarchical formaldehyde-removing coating, characterized in that, It is prepared by thermal curing of formaldehyde-removing nano-catalyst coating at 50~200℃; The formaldehyde-removing nano-catalyst coating comprises, by weight, 40-60 parts of double-modified coconut shell activated carbon, 15-25 parts of calcium oxide, 10-35 parts of manganese dioxide, 2-20 parts of sodium bicarbonate, and 0-5 parts of adhesive. The modified coconut shell activated carbon is prepared by sequentially treating the coconut shell activated carbon with steam, a hydrophobic modifier, and a mixed solution of urea and citric acid.

2. The porous, hierarchical formaldehyde-removing coating according to claim 1, characterized in that, When treating coconut shell activated carbon with steam, the mass ratio of steam to coconut shell activated carbon is 1:0.6~1.2, the treatment temperature is 800~1000℃, and the treatment time is 30~120min.

3. The porous, hierarchical formaldehyde-removing coating according to claim 1 or 2, characterized in that, The hydrophobic modifier is propyltrichlorosilane and / or hexadecyltrimethoxysilane; the coconut shell activated carbon is treated with the hydrophobic modifier by ultrasonic impregnation, and the ultrasonic impregnation time is 10~50 min.

4. The porous, hierarchical formaldehyde-removing coating according to claim 1 or 2, characterized in that urea... In the urea and citric acid mixed solution, the mass ratio of urea to citric acid is 2~5:1; when treating coconut shell activated carbon with the urea and citric acid mixed solution, the treatment temperature is 120~180℃ and the treatment time is 2~6h.

5. The porous, hierarchical formaldehyde-removing coating according to claim 1, characterized in that, The calcium oxide has a particle size of 0.5~2μm, and the manganese dioxide has a particle size of 10~50nm.

6. The porous, hierarchical formaldehyde-removing coating according to claim 1, characterized in that, The adhesive is selected from one or more of polyurethane adhesive, polyacrylic resin, and epoxy resin.

7. The porous, hierarchical formaldehyde-removing coating according to claim 1, characterized in that, The thickness of the porous, hierarchical formaldehyde-removing coating is 15~45μm.

8. A method for preparing a porous, hierarchical formaldehyde-removing coating as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Preparation of double-modified coconut shell activated carbon; (2) Disperse the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate in water in sequence, stir and mix evenly, then add the adhesive and continue to stir evenly to obtain the formaldehyde removal nano catalyst coating. (3) The formaldehyde-removing nano-catalyst coating is applied to the inner and outer surfaces of the aluminum honeycomb panel and then heat-cured at 50~200℃ to obtain the porous graded structure formaldehyde-removing coating.

9. The method for preparing the porous hierarchical formaldehyde-removing coating according to claim 8, characterized in that, The stirring rate in step (2) is 400~800 r / min; after dispersing the double-modified coconut shell activated carbon, calcium oxide, manganese dioxide and sodium bicarbonate in water, stir for 3~8 h, and then add them to the adhesive and stir for 2~6 h.

10. The method for preparing the porous hierarchical formaldehyde-removing coating according to claim 8, characterized in that, The drying time in step (3) is 4 to 6 hours.

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