Preparation method and application of CNTs (at) MnO2 composite material for formaldehyde purification

Abstract

The invention relates to the field of air purification, and discloses a preparation method and application of a CNTs (at) MnO2 composite material for formaldehyde purification, and the preparation method comprises the following steps: S1, completely immersing CNTs in a nitric acid solution, and pretreating the CNTs to remove impurities so as to obtain CNTs powder; and S2, mixing the pretreated CNTs powder with a KMnO4 solution, carrying out ultrasonic dispersion, feeding into a reaction kettle, carrying out a hydrothermal reaction, repeatedly cleaning and centrifuging to be neutral after the reaction, and drying to obtain the CNTs and MnO2 composite material. The CNTs-MnO2 composite material with excellent formaldehyde adsorption performance is prepared by loading mesoporous manganese dioxide on carbon nanotubes to form complementary advantages, and the CNTs-MnO2 composite material also has a corresponding air purification effect when applied to ink and filter paper and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the field of air purification, and in particular to a preparation method and application of a CNTs@MnO2 composite material for formaldehyde purification. Background Art

[0002] With the construction of numerous high-end buildings and the upgrading of residential interior decoration and furniture, indoor air pollution has become increasingly prominent. Indoor pollutants released during home renovations, such as formaldehyde (HCHO), carbon oxides (COx), nitrogen oxides (NOx), sulfur oxides (SOx), and volatile organic compounds (VOCs), have gradually attracted widespread attention. Human health is closely linked to indoor air quality, and formaldehyde, in particular, poses irreversible risks to human health.

[0003] Formaldehyde has been classified as a Class 1 carcinogen by the WHO and the International Agency for Research on Cancer (IARC). For the sake of human health, people usually eliminate most existing environmental pollutants through purification and other means after the interior decoration is completed, and enter the indoor environment for normal use after there is no obvious odor; the current methods for controlling indoor formaldehyde pollution include: ventilation technology, biodegradation, physical adsorption, etc.; the ventilation method is based on the dilution principle, and brings outdoor air into the room to reduce the indoor formaldehyde concentration. It is the simplest way to improve indoor air quality, but the process of formaldehyde volatilization is slow and long-lasting. Relying solely on ventilation can only reduce the indoor formaldehyde concentration in the short term, and the effect is easily affected by weather and seasonal changes; the biodegradation method mainly uses microorganisms and plants to degrade formaldehyde. The branches and leaves of plants can absorb formaldehyde. At the same time, microorganisms can work synergistically with plants to promote the decomposition of formaldehyde, but long-term air purification using plants and soil microorganisms will produce pollutants. At the same time, slight changes in temperature and humidity may have a significant impact on the degradation performance of plants and microorganisms. The physical adsorption method uses intermolecular van der Waals forces to adsorb formaldehyde on adsorbents with high porosity and high specific surface area, and reduce the formaldehyde concentration through adsorption. The current main adsorbents are divided into carbon-based adsorbents, silica-based adsorbents, porous organic polymers, metal-organic frameworks and other new adsorbents. However, the physical adsorption method usually improves the adsorbent under dry conditions with oxygen groups on the surface, showing better formaldehyde adsorption effect. As the relative humidity increases, the interaction between water molecules and oxygen groups is enhanced, affecting its ability to adsorb formaldehyde, resulting in a decrease in the performance of the adsorption material.

[0004] The above-mentioned formaldehyde removal methods all have certain limitations in practical applications. Therefore, it is necessary to find a new formaldehyde purification solution to make up for the shortcomings of the existing technology. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a preparation method and application of a CNTs@MnO2 composite material for formaldehyde purification.

[0006] To achieve the above objectives, one of the technical solutions provided by the present invention is a method for preparing a CNTs@MnO2 composite material for formaldehyde purification, comprising the following steps:

[0007] S1, immersing CNTs in a nitric acid solution with a pH value of 1-6, stirring at 50-60°C and 80-100 rpm for 10-15 minutes, then centrifuging and washing, ultrasonically cleaning until neutral, and drying to obtain pretreated CNTs powder;

[0008] S2. The pretreated CNTs powder was mixed with 0.07-0.09 mol / L KMnO4 solution at a mass ratio of 1:400-1:100, ultrasonically dispersed for 20-30 minutes, and then placed in a polytetrafluoroethylene reactor for hydrothermal reaction at 90-240°C for 2-8 hours. After washing and drying, a CNTs@MnO2 composite material was obtained.

[0009] In a preferred embodiment of the present invention, in step S1, the nitric acid solution is prepared by mixing concentrated nitric acid and water in a volume ratio of 1:3-1:10.

[0010] In a preferred embodiment of the present invention, in step S2, the temperature of the hydrothermal reaction is 90° C.-240° C., and the reaction time is 2-8 hours.

[0011] In a preferred embodiment of the present invention, in step S2, the mass ratio of CNTs powder to KMnO4 solution is 1:400-1:100.

[0012] In a preferred embodiment of the present invention, in step S2, the cleaned CNTs@MnO2 composite material is vacuum dried at 60-80°C for 12-16 hours.

[0013] The second technical solution provided by the present invention is a CNTs@MnO2 composite material prepared based on any of the methods described above.

[0014] The third technical solution provided by the present invention is a functional product comprising the above-mentioned composite material, wherein the product is selected from functional ink or air filter paper.

[0015] A fourth technical solution provided by the present invention is a method for preparing a functional ink, comprising the following steps:

[0016] S1. Mix the gelatin granules with water in a mass ratio of 1:5-1:20 and stir at 65-75°C for 0.5-2h until the granules are completely melted;

[0017] S2, mixing CNTs@MnO2 powder with water in a mass ratio of 1:10-1:20, and ultrasonically dispersing at 30-50°C for 20-40 minutes;

[0018] S3. Mix the solutions obtained in steps S1 and S2, add 0.1%-0.5% methanol to adjust the viscosity, and stir for 2-4 hours to obtain functional ink.

[0019] A fifth technical solution provided by the present invention is a method for preparing air filter paper, comprising the following steps:

[0020] S1. Add CNTs@MnO2 composite material into water and ultrasonically disperse for 30-45 minutes;

[0021] S2. Mixing the mixed solution obtained in step S1 with glass fiber, cellulose fiber and 0.5%-1% plant gum, stirring for 0.5-1 hour, and filtering to form a composite material layer;

[0022] S3. Place the composite material obtained by filtration in step S2 on a PP non-woven fabric, compress and compound it using a sealing and molding machine to form a thin sheet, and dry it at 50-70° C. for 2-4 hours to obtain air filter paper.

[0023] In a preferred embodiment of the present invention, the mass of the CNTs@MnO2 composite material accounts for 1%-10% of the total mass of the filter paper.

[0024] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0025] (1) The present application provides a method for preparing a CNTs@MnO2 composite material for formaldehyde purification, which can prepare a composite material with excellent formaldehyde removal performance; the CNTs@MnO2 composite material with this structure has excellent formaldehyde removal performance. Compared with the common adsorption materials or single catalysts in the prior art, it not only has a higher removal rate, but also has good stability and reusability, thereby significantly improving the effect and efficiency of indoor air purification.

[0026] (2) The present application provides a method for preparing a functional ink, which combines a specific proportion of bone glue with a CNTs@MnO2 composite material, so that the ink not only has good writing and drawing properties, but also can effectively remove formaldehyde. Compared with traditional inks, the functional ink of the present application has a significant air purification function while maintaining good fluidity. It has unique advantages in the fields of interior decoration and artistic creation. It can not only provide traditional visual effects, but also continuously purify indoor air, reduce the harm of formaldehyde to the human body, and expand the application range and functional value of ink.

[0027] (3) The present application provides a method for preparing air filter paper. By organically combining CNTs@MnO2 composite materials with glass fibers and cellulose fibers, and utilizing a specific ratio and preparation process, the filter paper can effectively reduce the filtration resistance while maintaining high-efficiency filtration performance. It can not only effectively remove solid particulate pollutants in the air, but also continuously decompose harmful gas formaldehyde, providing a more comprehensive and efficient air purification solution, significantly improving indoor air quality, and providing strong protection for people's healthy breathing.

[0028] (4) The CNTs@MnO2 composite material of this application and its application have significant advantages in the field of air purification; the CNTs@MnO2 composite material combines the high specific surface area and good electrical conductivity of carbon nanotubes with the excellent catalytic performance of manganese dioxide. Through a special preparation process, the advantages of the two are complementary to each other, forming a composite structure with a synergistic effect; the functional ink prepared by reasonable combination with additives such as gelatin not only improves the stability and dispersibility of the ink, but also enables the ink to continuously release active sites during the writing or painting process, achieving a long-term and stable air purification effect. The air filter paper prepared by compounding with glass fiber and cellulose fiber not only enhances the physical properties of the filter paper, but also greatly improves its comprehensive purification ability for particulate matter and harmful gases, achieving a high-efficiency, low-resistance, and multifunctional air purification effect; this application provides an innovative and effective solution to the problem of indoor air pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the SEM image of CNTs@MnO2;

[0030] Figure 2 (ad) are the actual pictures of the five inks after 48 hours of sedimentation; (e) is the sedimentation rate of the five inks; (f) is the viscosity test of the five inks;

[0031] Figure 3 (a) shows the finished Chinese painting using functional ink; (b) shows SEM images of the ink sample in the Chinese painting frame at different magnifications.

[0032] Figure 4 XRD patterns of functional ink, CNTs@MnO2 and bone glue;

[0033] Figure 5 (a) N2 isothermal adsorption-desorption curves of functional ink and CNTs@MnO2, (b) N2 isothermal adsorption-desorption curves of functional ink and CNTs;

[0034] Figure 6 A self-built PM2.5 test chamber; (a) PM2.5 static test chamber; (b) PM2.5 cycle test chamber test;

[0035] Figure 7 (a) PM 2.5 dust removal performance experiment in static warehouse; (b) PM 2.5 change trend over time in static warehouse; (c) PM 2.5 dust removal performance experiment in circulating warehouse; (d) PM 2.5 change trend over time in circulating warehouse. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0038] The materials involved in this application, their specifications and sources are shown in Table 1 below:

[0039] Table 1 Experimental materials

[0040]

[0041]

[0042] Exemplary method 1:

[0043] A method for preparing a CNTs@MnO2 composite material for formaldehyde purification comprises the following steps:

[0044] S1. Concentrated nitric acid is diluted with clean water to a pH of 1-6. CNTs are completely immersed in the diluted nitric acid solution. The solution is stirred at 50-60°C and 80-100 rpm for 10-15 minutes and then centrifuged. The solution is then ultrasonically cleaned and centrifuged multiple times with clean water and an ultrasonic cleaner to remove residual nitric acid until the solution is neutral. Finally, the solution is dried to obtain impurity-free CNT powder.

[0045] S2. Prepare 0.07-0.09 mol / L KMnO4 solution, mix the CNTs powder obtained in S1 with the KMnO4 solution at a mass ratio of 1:400-1:100, and ultrasonically disperse for 20-30 min. Transfer the mixture to a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, and hydrothermally react at 90℃-240℃ for 2-8 h. After the reaction, centrifuge and wash, and vacuum dry overnight at 60-80℃ to obtain a CNTs@MnO2 composite material.

[0046] Exemplary method 2:

[0047] A method for preparing a functional ink comprises the following steps:

[0048] S1. Wash the gelatin particles with clean water and dry them in an electric blast drying oven at 40-50°C for 1-2 hours;

[0049] S2. After heating clean water to 65° C., add bone gelatin particles to the clean water in proportion and continue stirring until the bone gelatin particles are completely melted; wherein the mass ratio of bone gelatin particles to water is 1:5-1:20, the rotation speed is 200-400 r / min, and the stirring time is 0.5-2 h;

[0050] S3. Add CNTs@MnO2 powder to clean water in proportion and disperse it ultrasonically; wherein the mass ratio of CNTs@MnO2 powder to water is 1:10-1:20, the ultrasonic dispersion temperature is 30-50°C, and the time is 20-40 minutes;

[0051] S4. Mix and stir the solutions obtained in steps S2 and S3, add methanol dropwise into the mixture to adjust the viscosity and stir to obtain functional ink; wherein, the stirring speed after mixing is 80-120 r / min, the stirring time is 2-4 h, the amount of methanol added is 0.1%-0.5% of the mass of the mixed solution, and the stirring speed after adjusting the viscosity is 80-120 r / min, and the time is 20-40 min.

[0052] Exemplary method 3:

[0053] A method for preparing air filter paper comprises the following steps:

[0054] S1. Add the CNTs@MnO2 composite material to water and ultrasonically disperse it for 30-45 minutes; wherein the mass of the CNTs@MnO2 is 1%-10% of the mass of the filter paper to be produced;

[0055] S2. Mix the mixed solution obtained in step S1 with a mixed solution of glass fiber and cellulose fiber, stir for 0.5-1 h, add plant gum, add water and stir to obtain a mixed solution, and filter with an ultrafiltration bottle; wherein the mass of the glass fiber is 10%-50% of the mass of the air filter paper, the mass ratio of the cellulose fiber to the glass fiber is 30:1-10:1, the amount of plant gum is 0.5%-1% of the mass of the mixed solution, the amount of water added is up to 400-600 mL, and the stirring time is 0.5-1.5 h;

[0056] S3. Place the composite material obtained by filtration in step S2 on a PP non-woven fabric, compress and compound it using a sealing and molding machine to form a thin sheet, and place it in an electric heated blast drying oven at 50-70° C. and dry it for 2-4 hours to obtain air filter paper.

[0057] Example 1:

[0058] The preparation steps of CNTs@MnO2 composite materials are as follows:

[0059] S1. Concentrated nitric acid is diluted with water to a pH of 1, and CNTs are completely immersed in the diluted nitric acid solution. The solution is heated to 60°C in a water bath and stirred at 80-100 rpm for 10-15 minutes, followed by centrifugation. The solution is then ultrasonically cleaned and centrifuged multiple times with water and an ultrasonic cleaner to remove residual nitric acid until the solution is neutral, i.e., at a pH of 7. The solution is then dried in a constant temperature oven at 100°C to obtain impurity-free CNT powder.

[0060] S2. Prepare 20 mL of 0.07 mol / L KMnO4 solution; take 0.1 g of the CNTs powder obtained in step S1 and mix it with the KMnO4 solution, ultrasonically disperse it for 30 minutes, transfer the mixture to a 50 mL stainless steel high-pressure reactor with a polytetrafluoroethylene liner, and hydrothermally react at 120°C for 8 hours. After the reaction is completed, the reactor is cooled to ambient temperature and centrifuged, repeatedly rinsed with clean water and anhydrous ethanol, precipitated using a centrifuge, and dried in a vacuum oven at 80°C overnight to obtain a CNTs@MnO2 composite material.

[0061] Test Example 1:

[0062] Example 1 was observed and tested, and the test results were as follows: Figure 1 As shown in the figure, the CNTs@MnO2 composite material prepared according to the above embodiment 1 is tested to be a preferred embodiment. Under the conditions of KMnO4 concentration of 0.07 mol / L, 0.1 g of CNTs participating in the reaction, and reaction time of 8 h at 120 ° C, its mass growth rate reaches 129.5%; the CNTs@MnO2 with the best morphology of δ crystal form is obtained, and the specific surface area of ​​the CNTs@MnO2 material is 52.61 m 2 / g, significantly higher than the 15.66m / g of CNTs 2 / g specific surface area.

[0063] Example 2:

[0064] The specific steps for preparing functional ink are as follows:

[0065] S1. Wash the gelatin particles with clean water and dry them in an electric blast drying oven at 40°C for 2 hours;

[0066] S2. Heat 50 mL of water to 65°C using a constant temperature water bath magnetic stirrer. Add 10 g of gelatin particles to the water and stir at 300 rpm for 1 hour until the gelatin is completely dissolved.

[0067] S3, add 2 g of CNTs@MnO2 powder to 20 mL of water and disperse it at 40 °C for 30 min using an ultrasonic cleaner;

[0068] S4. Pour the solutions obtained in steps S2 and S3 into a beaker, mix, and stir at a speed of 100 r / min for 3 h using a magnetic stirring device. Add 2 drops of methanol to the mixture to eliminate bubbles and adjust the viscosity. Stir the ink at a speed of 100 r / min for 30 min to stabilize its dispersion, thereby preparing a functional ink with a gelatin:water ratio of 1:5.

[0069] Example 3:

[0070] Different from Example 2, in Example 3, the amount of gelatin particles added in step S2 was changed to 5 g, and a functional ink with a gelatin:water ratio of 1:10 was prepared. The remaining steps were the same as in Example 2.

[0071] Example 4:

[0072] Different from Example 2, in Example 4, the amount of gelatin particles added in step S2 was changed to 3.3 g, and a functional ink with a gelatin:water ratio of 1:15 was prepared. The remaining steps were the same as in Example 2.

[0073] Example 5:

[0074] Different from Example 2, in Example 5, the amount of gelatin particles added in step S2 was changed to 2.5 g, and a functional ink with a gelatin:water ratio of 1:20 was prepared. The remaining steps were the same as in Example 2.

[0075] Comparative Example 1:

[0076] S1. Weigh 20 mL of deionized water, add 2 g of CNTs@MnO2 powder, and disperse it in an ultrasonic cleaner at 40 °C for 30 min.

[0077] S2. Pour the CNTs@MnO2 solution dispersed in step S1 into a beaker and stir it with a magnetic stirring device at a speed of 100 r / min for 3 h to ensure that the CNTs@MnO2 is evenly dispersed.

[0078] S3. Add 1 to 2 drops of methanol to the dispersant to eliminate bubbles and adjust the viscosity. Stir the ink at 100 r / min for 30 minutes to stabilize the dispersion and obtain a blank sample without adding gelatin.

[0079] Test Example 2:

[0080] The inks in Examples 2-5 and Comparative Example 1 were numbered as #1-#5;

[0081] Sedimentation Test: The inks of Examples 2-5 and Comparative Example 1 were placed in stoppered measuring bottles and left at room temperature for 48 hours. The sedimentation of the inks was observed after 1 hour, 2 hours, 6 hours, 24 hours, and 48 hours, respectively. The flow properties of the inks were tested at room temperature using an NDJ-8S rotational viscometer with a No. 1 rotor at 60 rpm.

[0082] Field Emission Scanning Electron Microscopy (FE-SEM): The morphologies of the samples before and after the experiment were observed using a SIGMA-500 scanning electron microscope. To obtain high-quality SEM images, the scanning voltage was set to 10 kV, the scanning current was set to 10 mA, and the gold spraying treatment time was set to 120 s. Topographic images of the functional inks generated in Examples 2-5 and Comparative Example 1 were obtained. The sample morphologies were observed and analyzed at different magnifications.

[0083] X-ray diffraction test (XRD): The functional inks of Examples 2-5 were analyzed using a Bruker D8 X-ray diffractometer;

[0084] Surface area test: Using a BELSORP Max II analyzer, the BET values ​​of the dry functional ink powder and CNTs@MnO2 were obtained through N2 absorption experiments.

[0085] In-situ infrared testing: using a TENSOR27 spectrometer with a high-temperature resistant transmission in-situ cell (CaF2 window, temperature range 500°C); the spectrum acquisition range is 4000-600cm -1 , with a resolution of 4cm -1 Each spectrum was scanned 64 times to optimize the signal-to-noise ratio. The catalyst powder was pressed into a pellet and placed in a sample tank, where it was pretreated at 300°C in an Ar atmosphere for 1 hour to remove adsorbed water. The gas flow rate (5% CO / He, 30 mL / min) was then precisely controlled by the gas system, and in situ infrared spectra were collected every 30 seconds to continuously monitor the evolution of surface adsorption states and intermediates.

[0086] Formaldehyde removal performance test: The diluted formaldehyde solution was evenly sprayed onto the glass to simulate a closed indoor environment with high formaldehyde pollution. After the formaldehyde was evenly diffused and the portable formaldehyde analyzer displayed a stable value, 0.1g of CNTs@MnO2 catalyst was placed at the bottom of the glass bottle. Formaldehyde degradation tests were then conducted at room temperature in the laboratory.

[0087] Sedimentation and fluidity analysis of functional inks:

[0088] The results are as follows Figure 2 As shown, Figure 2 (ad) show the sedimentation of the five inks after 48 hours. Ink #1 completely settled at the bottom of the glass bottle after 48 hours. Ink #2, despite the addition of a small amount of gelatin, also exhibited significant stratification. Inks #4 and #5 were sufficiently stable to maintain a relatively constant state, while ink #3 exhibited minimal stratification. Ink stratification was positively correlated with gelatin concentration. Gelatin, acting as a stabilizer and dispersant in the ink, improves the properties of the liquid interface, allowing the CNTs@MnO2 powder to be evenly distributed in the aqueous solution, forming a relatively stable emulsion. Figure 2 (e) Further illustrates the change in sedimentation ratio of the five inks over time. The sedimentation ratio is the volume ratio of the upper clear liquid to the entire ink after stratification. Within the first hour, all inks had no obvious stratification. After about 6 hours, inks #1 and #2 began to precipitate significantly, with sedimentation rates reaching about 8% and 3%, respectively. Ink #5 has the best stability, with a sedimentation rate of less than 1% after 48 hours. For the functional inks in this study, which are used for painting or calligraphy creation, the entire process will not take more than 1 day, so the stability of the three inks #3, #4 and #5 can meet the creation requirements in a short time. However, inks with lower sedimentation rates are often accompanied by higher viscosities ( Figure 2 (f)), the viscosity of ink is positively correlated with the content of bone glue; based on the above two test results, the use of #4 with moderate viscosity and good sedimentation efficiency test can meet complex and comprehensive creative needs.

[0089] Analysis of the morphology of functional ink calligraphy and painting works:

[0090] The Chinese paintings drawn by CNTs@MnO2 functional ink prepared with gelatin solution as dispersant are as follows: Figure 3 (a) Compared with traditional ink, there is no difference in viewing effect. In order to deeply analyze its microstructure, a part of the Chinese painting was cut and characterized by scanning electron microscopy. The results are shown in Figure 3 (be) is shown. Figure 3(b) As can be observed in the figure, due to the uniform coverage of CNTs@MnO2 on the cellulose paper, the Chinese painting macroscopically shows a significant black feature, and the functional ink after drying forms a uniform coating on the surface of the cellulose fiber substrate, which effectively increases the contact area between CNTs@MnO2 and the air, facilitating contact with harmful gases in the air. Figure 3 (d) It can be seen that due to the adhesive effect of bone glue, CNTs@MnO2 is firmly attached to the surface of cellulose fiber paper, and CNTs@MnO2 will not fall off over time. However, bone glue partially blocks the microporous structure of the CNTs@MnO2 surface during the curing process, such as Figure 3 As shown in (e), this may have a certain negative impact on its catalytic performance of formaldehyde.

[0091] Analysis of the structural composition of functional ink:

[0092] The XRD spectra of functional ink, bone glue and CNTs@MnO2 are shown in Figure 2. Figure 4 As shown in the figure, it can be seen that the XRD of bone glue does not show obvious characteristic diffraction peaks, which is consistent with the essential characteristics of the amorphous structure of bone glue. Bone glue has an amorphous structure, its molecular arrangement is disordered, and the atomic arrangement does not have a periodic lattice structure, which leads to a significant decrease in the intensity of X-ray coherent scattering, making it difficult to form identifiable diffraction peaks. The functional ink material has absorption peaks at 12.2°, 26.5°, 36.7°, 42.3° and 65.4°. These peaks correspond to the standard card of δ-MnO2 (JCPDS: 80-1098), corresponding to the (001), (002), (110), (112) and (312) crystal planes, respectively. However, compared with CNTs@MnO2, the diffraction peak intensity of the functional ink is reduced overall, especially the (001) crystal plane peak at 12.2° is significantly attenuated. This difference is due to the composite effect of amorphous bone glue and CNTs@MnO2: bone glue is coated on the surface of MnO2, and its X-ray absorption and scattering interfere with the diffraction signal of the crystal structure, resulting in a weakening of the characteristic peak intensity;

[0093] Figure 5 The BET results of the specific surface areas of functional ink, CNTs@MnO2 and CNTs obtained through N2 adsorption and desorption experiments are shown. The BET data of functional ink and CNTs@MnO2 show similar characteristics, both showing the adsorption isotherm of δ-MnO2, and consistent with the V-type isotherm characteristics, showing a significant hysteresis loop in the high pressure stage. The specific surface area of ​​the CNTs@MnO2 composite material is 52.61m 2 / g, because of the coverage of bone gelatin, the specific surface area of ​​the functional ink is 37.83m 2 / , significantly higher than the original CNTs15.66m 2 / g specific surface area. The adsorption and desorption curves increase with the increase of relative pressure, such as Figure 5 As shown in (b), a clear hysteresis loop appears, which is the capillary condensation phenomenon of the mesopores. At high P / P0, there is no platform, showing a type IV isotherm (IUPAC) and an H4 hysteresis loop, that is, the presence of a typical mesoporous structure. The isotherm rises in the high pressure region, indicating that the pores on the CNTs@MnO2 surface are not completely blocked by the gelatin. The functional ink is evenly loaded on the surface of the paper, which directly increases the contact area between the CNTs@MnO2 and the air, compensating for the relative decrease in specific surface area. The density of active sites on the material surface increases, promoting the diffusion and adsorption of reactants such as formaldehyde in its mesopores, thereby significantly improving the catalytic degradation performance.

[0094] Formaldehyde performance test of functional ink:

[0095] In the formaldehyde removal test of functional ink, the formaldehyde removal rate of ink No. 1 (bone glue to water ratio 1:20) reached 87.06% within 240 minutes. The removal rate of ink No. 2 (ratio 1:15) was slightly lower than that of #1, and its removal rate was between the blank sample and #1. The specific surface area of ​​ink No. 3 (ratio 1:10) was 37.83m 2 / g, also achieving a formaldehyde removal rate of 87.06% within 240 minutes, close to the 90.33% achieved by pure CNTs@MnO2 powder. Ink #4 (1:5 ratio) also achieved a higher removal rate than the blank. Ink #5, a blank sample without added gelatin, achieved a formaldehyde removal rate of only 22.8% within 240 minutes.

[0096] Analysis reveals that the functional ink's formaldehyde removal ability stems primarily from the adsorption and catalytic degradation of the CNTs@MnO2 composite. Its mesoporous structure effectively adsorbs small gas molecules, while the reactive oxygen species and hydroxyl groups on the δ-MnO2 surface catalyze the gradual conversion of formaldehyde into formate and carbonate, ultimately producing CO2 and H2O. The addition of gelatin improves the dispersion of CNTs@MnO2 in aqueous solution and enhances ink stability. However, excessive gelatin increases solution viscosity, potentially partially blocking the microporous structure of the CNTs@MnO2 and affecting its adsorption performance. Ink #3, with a gelatin-to-water ratio of 1:10, achieves a balanced dispersion and stability, resulting in a more uniform distribution and numerous active sites while maintaining a high specific surface area. This results in excellent formaldehyde removal performance, approaching that of pure CNTs@MnO2 powder. Inks #1 and #2, with lower gelatin ratios, exhibit lower viscosities but suffer from insufficient dispersion, impacting removal efficiency. Ink #4 has a high proportion of gelatin, which increases viscosity and clogs the micropores, resulting in an unclear removal rate, but it is better than the blank. Blank sample #5 lacks gelatin, resulting in poor dispersion of CNTs@MnO2 and a significantly lower removal rate.

[0097] Example 6:

[0098] The preparation of air filter paper, the specific steps are as follows:

[0099] S1. Weigh 0.06 g of CNTs@MnO2 (the mass is 3% of the mass fraction of the filter paper), add appropriate amount of water and ultrasonically disperse for 30 min;

[0100] S2. Mix the mixture of S1 with the mixture of glass fiber and cellulose fiber, stir for 1 hour, add plant glue and fill with water to 500 mL, and continue stirring for 0.5 hour; wherein the mass of glass fiber is 30% of the mass of air filter paper; the mass ratio of cellulose fiber to glass fiber is 7:3 (70% cellulose: 30% glass fiber); the amount of plant glue is 0.8% of the mass of the mixture;

[0101] S3, the mixed solution of S2 is filtered with an ultrafiltration bottle, the filtered composite material is placed on a PP non-woven fabric, and compressed into a thin sheet using a sealing machine;

[0102] S4. Place the mixture in an electric blast drying oven and dry it at 60°C for 3 hours to obtain air filter paper.

[0103] Test Example 3:

[0104] A control group was set up, in which 30% glass fiber filter paper (i.e., 30% glass fiber and 70% cellulose) was not added with CNTs@MnO2;

[0105] Filtration performance test: The filter paper was tested using the TSI-8130A automatic filter material tester. The test flow rate was set to 32 L / min and the test area was 100 cm 2 The sample size was 15×15 cm, and each sample was tested 5 times and the average value was taken to ensure data reliability.

[0106] PM2.5 purification performance test: The PM2.5 purification performance test of the sample was carried out in a closed environment built by the laboratory ( Figure 6 ), and a PM2.5 concentration detector was used to measure the concentration of PM2.5. The test is divided into two experimental parts: a static chamber and a circulating chamber. In the static chamber test, the sample is fixed on the connecting window between the smoke chamber and the purification chamber, and the polluted environment is simulated by igniting mosquito-killing tablets, and the changes in PM2.5 concentration are recorded. In the circulating chamber test, the sample is pasted on the surface of the fan, smoke is introduced into the test chamber and the door is quickly closed. The fan is used to promote air flow to simulate the purification effect in a dynamic environment. Both tests simulate actual severe pollution scenarios by using particulate matter generated by the burning of mosquito-killing tablets, and record test data to evaluate the PM2.5 purification ability of the sample.

[0107] Formaldehyde degradation performance test: Use a formaldehyde detector to conduct real-time detection of the formaldehyde concentration in the circulating test chamber, dilute the formaldehyde solution, use a spray bottle to evenly spray formaldehyde in the test chamber, and record the real-time changes in formaldehyde concentration.

[0108] Results and Analysis:

[0109] The experimental results are as follows Figure 7 As shown, Example 6 is the best example for preparing air filter paper. The filter efficiency of the filter paper is 99.73% and the filtration resistance is 61.4 Pa when measured by TSI-8130A automatic filter material tester. PM 2.5 Purification test, in the static experiment, PM 2.5 The concentration was maintained at 25 μg / m 3 In the cycle experiment, PM 2.5 The peak value dropped to 44 μg / m 3 The formaldehyde degradation test showed that the formaldehyde concentration was catalytically degraded from the initial value to 0.18 mg / m within 600 seconds. 3 , and still maintains efficient degradation performance after 5 cycles.

[0110] The reasons are as follows:

[0111] The composite structure of cellulose fiber and glass fiber provides the basic filtration performance for the filter paper. Cellulose fiber has the advantages of biodegradability and low cost, while glass fiber enhances the filtration efficiency of the filter paper with its high specific surface area and chemical stability. By adjusting the ratio of cellulose fiber and glass fiber, the pore structure of the filter paper is optimized, so that the filter paper can effectively intercept particulate matter in the air while maintaining low airflow resistance.

[0112] The introduction of CNTs@MnO2 nanofibers not only improves the filtration efficiency of the filter paper but also enables it to degrade formaldehyde. Specifically, the high specific surface area and abundant active sites of CNTs@MnO2 nanofibers enable the filter paper to more effectively adsorb and capture formaldehyde molecules and other pollutants in the air. Furthermore, the catalytic properties of MnO2 oxidize and decompose formaldehyde into harmless substances, achieving efficient removal of harmful gases such as formaldehyde.

[0113] Overall, the composite structure of cellulose and glass fibers provides the filter paper's foundational filtration performance, while the catalytic and adsorption effects of the CNTs@MnO2 nanofibers enhance its ability to remove harmful gases. The optimized preparation process ensures uniform distribution and structural stability. This synergistic effect enables the air filter paper to maintain high filtration efficiency while effectively degrading harmful gases like formaldehyde, demonstrating exceptional air purification performance.

[0114] In summary, the cellulose fiber / glass fiber / CNTs@MnO2 nanofiber composite air filter paper of this application has high filtration efficiency, low airflow resistance and excellent formaldehyde degradation performance, providing a new idea for the design of high-performance air filtration materials.

[0115] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a CNTs@MnO2 composite material for formaldehyde purification, characterized in that: The following steps are involved: S1, immersing CNTs in a nitric acid solution with a pH value of 1-6, stirring at 50-60°C and 80-100 rpm for 10-15 minutes, then centrifuging and washing, ultrasonically cleaning until neutral, and drying to obtain pretreated CNTs powder; S2. The pretreated CNTs powder was mixed with 0.07-0.09 mol / L KMnO4 solution at a mass ratio of 1:400-1:100, ultrasonically dispersed for 20-30 minutes, and then placed in a polytetrafluoroethylene reactor for hydrothermal reaction at 90-240°C for 2-8 hours. After washing and drying, a CNTs@MnO2 composite material was obtained.

2. The method for preparing a CNTs@MnO2 composite material for formaldehyde purification according to claim 1, characterized in that: In step S1, the nitric acid solution is prepared by mixing concentrated nitric acid and clean water in a volume ratio of 1:3-1:

10.

3. The method for preparing a CNTs@MnO2 composite material for formaldehyde purification according to claim 1, characterized in that: In step S2, the temperature of the hydrothermal reaction is 90° C.-240° C., and the reaction time is 2-8 hours.

4. The method for preparing a CNTs@MnO2 composite material for formaldehyde purification according to claim 1, characterized in that: In step S2, the mass ratio of CNTs powder to KMnO4 solution is 1:400-1:

100.

5. The method for preparing a CNTs@MnO2 composite material for formaldehyde purification according to claim 1, characterized in that: In step S2, the cleaned CNTs@MnO2 composite material is vacuum dried at 60-80°C for 12-16 hours.

6. A CNTs@MnO2 composite material, characterized in that: Prepared based on the method according to any one of claims 1 to 5.

7. A functional product comprising the composite material according to claim 6, characterized in that: The product is selected from functional ink or air filter paper.

8. A method for preparing functional ink, characterized in that: The following steps are involved: S1. Mix the gelatin granules with water in a mass ratio of 1:5-1:20 and stir at 65-75°C for 0.5-2h until the granules are completely melted; S2, mixing CNTs@MnO2 powder with water in a mass ratio of 1:10-1:20, and ultrasonically dispersing at 30-50°C for 20-40 minutes; S3. Mix the solutions obtained in steps S1 and S2, add 0.1%-0.5% methanol to adjust the viscosity, and stir for 2-4 hours to obtain functional ink.

9. A method for preparing air filter paper, characterized in that: The following steps are involved: S1. Add CNTs@MnO2 composite material into water and ultrasonically disperse for 30-45 minutes; S2. Mixing the mixed solution obtained in step S1 with glass fiber, cellulose fiber and 0.5%-1% plant gum, stirring for 0.5-1 hour, and filtering to form a composite material layer; S3. Place the composite material obtained by filtration in step S2 on a PP non-woven fabric, compress and compound it using a sealing and molding machine to form a thin sheet, and dry it at 50-70° C. for 2-4 hours to obtain air filter paper.

10. The method for preparing air filter paper according to claim 9, characterized in that: The mass of the CNTs@MnO2 composite material accounts for 1%-10% of the total mass of the filter paper.

Images