A diatomaceous earth-based composite material, its preparation method and application

Abstract

This invention relates to a diatomaceous earth-based composite material, its preparation method, and its application. The method includes: dissolving a zinc salt in a first solvent, then adding diatomaceous earth to form a first solution; adding a second solvent to a ligand to form a second solution; subsequently adding the second solution to the first solution and stirring to obtain a ZIF-8 / diatomaceous earth composite material; calcining the composite material by first heating in two stages and then cooling it down, followed by natural cooling to room temperature to obtain a ZIF-8-derived carbon / diatomaceous earth composite substrate; dissolving a manganese salt in a third solvent to form a third solution; adding a fourth solvent to the composite substrate and soaking it to form a fourth solution; subsequently adding the solid material filtered from the fourth solution to the third solution, stirring, and calcining to obtain a manganese dioxide@ZIF-8-derived carbon / diatomaceous earth composite material. Compared with the prior art, this invention has excellent volatile organic compound adsorption performance, light absorption performance, photothermal conversion performance, and photothermal catalytic performance, and can be recycled multiple times.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and relates to a diatomaceous earth-based composite material, its preparation method, and its application. Background Technology

[0002] In recent years, due to the widespread use of paints and coatings, the formaldehyde gas they release over a long period of time has seriously affected indoor air quality and greatly threatened people's health, thus attracting widespread attention (IU C, MIAO X, LIJ. Outdoor formaldehyde matters and substantially impacts indoor formaldehyde concentrations[J]. Building and Environment,2019,158:145-150.).In recent years, to remove indoor formaldehyde, people have developed strategies such as physical adsorption, membrane separation, and primary biological filtration. Among these, physical adsorption is favored due to its advantages of ease of use, high efficiency, and speed. Examples of effective methods include molecular sieves (SHEN X, DU X, YANG D, et al. Influence of physical structures and chemical modification on VOCs adsorption characteristics of molecular sieves [J]. Journal of Environmental Chemical Engineering, 2021, 9(6): 106729.) and activated carbon (SHEN X, DU X, YANG D, et al. Influence of physical structures and chemical modification on VOCs adsorption characteristics of molecular sieves [J]. Journal of Environmental Chemical Engineering, 2021, 9(6): 106729.). Porous materials such as diatomite (CHEN Z, ZHANG H, LUO W, et al. Diatomite in situ loaded by MOF(ZIF-8) and its application in removing methylene orange from aqueous solutions[J]. Bioresources, 2019, 15(1): 265-275.) have received widespread attention.

[0003] Diatomite (DA) has received considerable attention in recent years due to its advantages of low cost, environmental friendliness, and excellent adsorption capacity for volatile organic compounds (VOCs), and has been successfully commercialized as an adsorbent coating. However, the mechanism of formaldehyde removal by DA is mainly adsorption based on intermolecular forces. Once exposed to high temperatures, the adsorbed formaldehyde will desorb, causing secondary pollution. Because DA is rich in hydroxyl groups (-OH) and has a regular morphology, it is extremely suitable as a matrix material for catalysts (LI C, WANG M, CHEN Z, et al. Enhanced thermal conductivity and photo-to-thermal performance of diatomite-based composite phase change materials for thermal energy storage[J]. Journal of Energy Storage, 2021, 34: 102-171.), catalyst modification is a promising solution. Manganese dioxide (MnO2) is an excellent thermal catalyst that can rapidly degrade formaldehyde into water and carbon dioxide at certain temperatures, potentially mitigating the problem of secondary pollution caused by DA at high temperatures. However, the temperature provided by high temperatures is still somewhat different from the temperature required for catalysis, which is insufficient to fully activate MnO2 catalysis, thus limiting its catalytic efficiency. Reports indicate that under infrared light, MnO2 undergoes non-radiative recombination of electrons, releasing heat and exhibiting strong photothermal conversion capabilities. Therefore, under sunlight, MnO2 can provide the heat required for catalysis, enabling photothermal degradation of formaldehyde (HUANG J, ZHONG S, DAI Y, et al. Effect of MnO2 Phase Structure on the Oxidative Reactivity toward Bisphenol A Degradation[J]. Environmental Science & Technology, 2018, 52(19): 11309-11318.). Therefore, utilizing MnO2 composite DA catalyst (MD) for photothermal degradation of formaldehyde to avoid secondary pollution from diatomaceous earth has good application prospects. However, the low thermal conductivity and weak light absorption of diatomaceous earth limit the photothermal conversion capability of the composite material, thus limiting its photothermal catalytic effect.

[0004] In recent years, metal-organic frameworks (MOFs) have been widely used in gas adsorption, catalysis, and other fields due to their large specific surface area and excellent micro-mesoporous structure. It has been reported that ZIF-8 (a Zn...) 2+Microporous carbon materials with a microporous structure can be obtained by high-temperature carbonization of ZIF-8 carbides in an inert gas atmosphere. Therefore, they are used to improve the light absorption, photothermal conversion and thermal conductivity of materials (Cao Fengli, Teng Shuai, Gao Yang, et al. Effect of different carbonization temperatures on the catalytic activity of ZIF-8 carbides [J]. Shandong Chemical Industry, 2018, 47(7):4-6.). In addition, some studies have shown that ZIF-8 can grow uniformly on the surface of diatomaceous earth using -OH as anchor points, thereby improving the adsorption performance of the material. Therefore, using carbonized ZIF-8 to modify MD is expected to enhance its light absorption, photothermal conversion and thermal conductivity, while further improving its adsorption capacity and promoting catalysis.

[0005] Patent CN111715287A discloses a ZIF-67 / GO photocatalytic-photothermal composite film, its preparation method, and its application, comprising the following steps: adding graphene oxide to ultrapure water and sonicating to obtain a homogeneous solution of graphene oxide, which is a GO aqueous solution; filtering the GO aqueous solution onto a PTFE membrane and drying it at room temperature to obtain a GO membrane; pouring a Co(NO3)2·6H2O solution into a petri dish containing the GO membrane and maintaining it at 35-45℃ for 8-24 hours, then discarding the solution and washing the membrane with methanol; then pouring a 2-methylimidazole solution into a petri dish containing a GO membrane soaked in the Co(NO3)2·6H2O solution and maintaining it at 35-45℃ for 8-24 hours, then discarding the solution and washing the membrane with methanol; finally drying it in a vacuum drying oven at 60℃ to obtain the ZIF-67 / GO photocatalytic-photothermal composite film. However, the preparation process of this patented composite film material is time-consuming, and the prepared ZIF-67 / GO photocatalytic-photothermal composite film has a sheet structure, making it difficult to prepare on a large scale and unable to meet the needs of large-scale applications. At the same time, the composite film prepared above can only catalytically reduce metal ions under photocatalytic-photothermal synergistic catalysis conditions, and it is still unknown whether it can catalytically reduce metal ions under thermal catalysis. In terms of application scenarios, in addition to catalytically reducing metal ions, whether it can catalytically degrade VOCs in the air is also a very critical issue. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one defect of the prior art by providing a diatomaceous earth-based composite material, its preparation method and application. This invention has excellent volatile organic compound adsorption performance, light absorption performance, photothermal conversion performance and photothermal catalytic performance, and can be recycled multiple times.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide a method for preparing a diatomaceous earth-based composite material, the method comprising the following steps:

[0009] (1) Dissolve the zinc salt in the first solvent, then add diatomaceous earth (DA), and stir vigorously overnight to allow zinc ions (Zn) to dissolve. 2+ The ligands are linked to hydroxyl groups (-OH) on the surface of diatomaceous earth to form the first solution. A second solvent is added to the ligands and stirred thoroughly until dissolved to form the second solution. The second solution is then slowly added to the first solution while stirring. The ligands will coordinate and assemble around the zinc ions, thereby growing ZIF-8 on the surface of diatomaceous earth. The product is centrifuged, washed, and dried overnight to obtain a ZIF-8 / diatomaceous earth (ZIF-8 / DA, ZD) composite material. The ZIF-8 / diatomaceous earth composite material is calcined by first heating in two stages and then cooling down, and then naturally cooled to room temperature to obtain a ZIF-8 derived carbon / diatomaceous earth (ZIF-8-C / DA, ZCD) composite substrate.

[0010] (2) Dissolve the manganese salt in the third solvent and stir until completely dissolved to obtain the third solution; add the fourth solvent to the ZIF-8 derived carbon / diatomite composite substrate, seal and soak to allow the fourth solvent to attach to the hydroxyl groups on the surface of the diatomite to obtain the fourth solution; then add the solid material after filtering the fourth solution to the third solution under stirring, seal and stir, centrifuge, wash, dry overnight and calcine to remove the residual fourth solvent to obtain the manganese dioxide@ZIF-8 derived carbon / diatomite (MnO2@ZIF-8-C / DA, MZCD) composite material.

[0011] Further, in step (1), the zinc salt includes zinc nitrate (Zn(NO3)2) or zinc carbonate (Zn(CO3)2), and the first solvent includes methanol or ethanol;

[0012] The ligands include 2-methylimidazole or 4-methylimidazole, and the second solvent includes methanol or ethylene glycol.

[0013] Further, in step (1), the zinc ion concentration is 40-50 mmol / L, and the mass ratio of zinc ions to diatomaceous earth is (0.005-0.009):1;

[0014] The ligand concentration was 170-180 mmol / L, and the molar ratio of zinc ions to ligands was 1:(4-4.2).

[0015] Furthermore, the stirring and soaking time in steps (1) and (2) is 10-13 hours.

[0016] As a preferred technical solution, the washing solvent in step (1) is methanol or ethanol.

[0017] As a preferred technical solution, the drying temperature in steps (1) and (2) is 50-70℃.

[0018] As a preferred technical solution, the calcination environment in step (1) is argon or helium.

[0019] Furthermore, in step (1), the heating rate of the calcination stage is 3-6℃ / min, the temperature is 250-350℃, and the holding time is 2-4h;

[0020] The second stage heating rate is 4-6℃ / min, the temperature is 750-850℃, and the holding time is 2-4h;

[0021] The cooling rate is 1-3℃ / min, the temperature is 150-250℃, and the holding time is 8-12min.

[0022] Furthermore, in step (2), the manganese salt includes potassium permanganate (KMnO4) or potassium manganate (K2MnO4), and the third solvent includes water or methanol;

[0023] The fourth solvent includes n-butanol, ethanol, or methanol.

[0024] Furthermore, the concentration of manganese ions in step (2) is 50-450 mmol / L;

[0025] The concentration of the ZIF-8 derived carbon / diatomite composite substrate is 20-30 g / L, and the molar / mass ratio of manganese ions to the ZIF-8 derived carbon / diatomite composite substrate is (2-18 mmol):1 g.

[0026] As a preferred technical solution, the washing solvent in step (2) is ethanol or methanol.

[0027] Furthermore, in step (2), the calcination heating rate is 3-6℃ / min, the temperature is 150-250℃, and the time is 1-3h.

[0028] One of the technical solutions of the present invention is to provide a diatomite-based composite material prepared by the method described above, wherein the composite material is a metal-organic framework (MOF) derived carbon-modified diatomite loaded with manganese dioxide (MnO2).

[0029] One of the technical solutions of the present invention is to provide an application of a diatomaceous earth-based composite material, wherein the composite material is used for the adsorption and catalytic degradation of volatile organic compounds.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) In this invention, ZIF-8 / diatomite composite material is obtained by uniformly loading ZIF-8 on diatomite through in-situ growth. Then, ZIF-8-derived C / diatomite composite substrate is obtained by carbonization. Finally, manganese dioxide is loaded on the composite substrate by redox method and in-situ growth method to obtain manganese dioxide@ZIF-8-derived C / diatomite composite material. Compared with traditional diatomite materials, the composite material has a larger specific surface area, better adsorption capacity of volatile organic compounds, and photothermal catalytic degradation capacity of volatile organic compounds.

[0032] (2) The present invention not only has a shorter synthesis time, but also has a large specific surface area of ​​composite material, and the presence of pore structure further increases the efficiency of catalytic degradation.

[0033] (3) The present invention has good adsorption degradation efficiency and photothermal conversion characteristics, and can significantly improve the light absorption efficiency and photothermal catalytic degradation ability of the material;

[0034] (4) This invention can generate heat quickly and completely degrade volatile organic compounds into non-toxic and harmless water and carbon dioxide, and can be recycled multiple times. It can easily and thoroughly eliminate indoor volatile organic compounds and can be used as a wall coating with a wider application area and scope. Attached Figure Description

[0035] Figure 1 These are field emission scanning electron microscope (FE-SEM) images of diatomaceous earth-based materials at different magnifications in Embodiment 3 and Comparative Examples 1 to 4 of the present invention;

[0036] Figure 2 The images shown are scanning electron microscope (SEM) images, EDS images, and mapping images of diatomaceous earth-based materials at 10kx magnification in Embodiment 3 and Comparative Examples 1 to 4 of the present invention.

[0037] Figure 3 The X-ray diffraction (XRD) spectra of the materials in Embodiment 3 and Comparative Examples 1 to 3, 5 and 6 of this invention are shown below.

[0038] Figure 4 The Fourier transform infrared (FTIR) spectra of the materials in Embodiment 3 and Comparative Examples 1 to 3, 5 and 6 of this invention are shown below.

[0039] Figure 5 The images show the overall and enlarged views of the BET nitrogen adsorption-desorption curves of the materials in Example 3 and Comparative Examples 3, 4 and 6 of this invention.

[0040] Figure 6 The above are X-ray photoelectron spectroscopy (XPS) spectra of the diatomaceous earth-based composite materials in Example 3 and Comparative Example 4 of this invention.

[0041] Figure 7 The figures show the fitting results of pseudo-first-order and pseudo-second-order adsorption kinetics of diatomaceous earth-based materials in Example 3 and Comparative Examples 1 and 3 of the present invention.

[0042] Figure 8 The thermocatalytic effect diagrams of the diatomaceous earth-based materials in Example 3 and Comparative Examples 1 and 4 of this invention are shown.

[0043] Figure 9 The diffuse reflectance spectra of ultraviolet-visible-near-infrared (UV-vis-NIR) transmittance, reflectance, and absorbance of the diatomaceous earth-based materials in Example 3 and Comparative Examples 1, 3, and 4 of the present invention, as well as the photothermal conversion effect diagram, are shown.

[0044] Figure 10 The images show the photothermal catalytic effects of diatomaceous earth-based materials in the embodiments of the present invention and comparative examples 1, 3 and 4, including photothermal catalytic formaldehyde degradation rate diagrams of different concentration examples, photothermal catalytic formaldehyde degradation rate diagrams of different samples, photothermal catalytic formaldehyde mineralization effect diagrams of different samples, and cyclic catalytic formaldehyde degradation rate diagram of example 3.

[0045] Figure 11 This is a graph showing the catalytic formaldehyde degradation rate of the diatomaceous earth-based composite material under different conditions in Example 3 of the present invention;

[0046] Figure 12 The images show the photothermal conversion effect of the diatomaceous earth-based composite material under ultraviolet-visible light and the Tauc plot in Example 3 of this invention.

[0047] Figure 13 This is a schematic diagram illustrating the catalytic degradation mechanism of formaldehyde by diatomaceous earth-based composite materials under ultraviolet-visible light in an embodiment of the present invention;

[0048] Figure 14 This is a schematic diagram of the overall catalytic mechanism of the diatomaceous earth-based composite material in an embodiment of the present invention. Detailed Implementation

[0049] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0050] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0051] Examples 1 to 4:

[0052] A diatomaceous earth-based composite material and its preparation method are described below:

[0053] (1) Preparation of ZIF-8 derived carbon / diatomite (ZIF-8-C / DA, ZCD) composite substrate:

[0054] Place 0.64 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in a beaker, add 50 mL of methanol, then add 2 g of diatomaceous earth (DA), and stir vigorously overnight to allow zinc ions (Zn) to dissolve. 2+ ) is attached to the hydroxyl group (-OH) on the surface of DA, as solution A; 0.72 g of 2-methylimidazole is placed in a beaker, 50 mL of methanol is added, and the mixture is stirred thoroughly until dissolved, as solution B; then solution B is slowly added to solution A, and the mixture is stirred for 12 h. 2-methylimidazole will then be attached to Zn 2+ ZIF-8 was grown on the DA surface through surrounding coordination assembly. The product was centrifuged and washed three times with methanol, then dried overnight in a 60°C oven to obtain the ZIF-8 / diatomite (ZIF-8 / DA, ZD) composite material. ZD was placed in a tube furnace and calcined under argon atmosphere according to the following procedure: the temperature was increased to 300°C at a rate of 5°C / min and held for 3 hours, then increased to 800°C at a rate of 5°C / min and held for 3 hours, then decreased to 200°C at a rate of 2°C / min and held for 10 minutes, and then naturally cooled to room temperature to obtain a black powder product, which is ZCD.

[0055] (2) Preparation of manganese dioxide@ZIF-8 derived C / diatomite (MnO2@ZIF-8-C / DA, MZCD) composite material:

[0056] 0.316 g, 0.623 g, 0.948 g, and 1.264 g of potassium permanganate (KMnO4) were placed in beakers, 20 mL of deionized water was added, and the mixture was stirred until the KMnO4 was completely dissolved, preparing solutions of 100 mmol / L, 200 mmol / L, 300 mmol / L, and 400 mmol / L, respectively. 0.5 g of ZCD was placed in a beaker, 20 mL of n-butanol was added, the beaker was sealed, and the solution was soaked for 12 h to allow the n-butanol to attach to the -OH group on the DA surface. Excess n-butanol was then filtered off, and the remaining solid was added to the KMnO4 solution under stirring. The solution was sealed and stirred for 12 h, then centrifuged and washed three times with ethanol. The product was dried overnight in a 60 °C oven. The product was then calcined in a muffle furnace at 200 °C for 2 h at a heating rate of 5 °C / min to remove residual n-butanol. The collected product was xMZCD, where x = 100, 200, 300, or 400.

[0057] Comparative Example 1:

[0058] Diatomaceous earth was purchased directly from Aladdin Company. During the experiment, the diatomaceous earth was soaked in methanol to increase the dispersibility of DA.

[0059] Comparative Example 2:

[0060] The ZIF-8 / diatomite composite material was prepared using the same method as ZD in the examples.

[0061] Comparative Example 3:

[0062] The ZIF-8 derived carbon / diatomite composite substrate was prepared using the same method as the ZCD preparation method in the examples.

[0063] Comparative Example 4:

[0064] A manganese dioxide@diatomite (MnO2@DA, MD) composite material and its preparation method are described below:

[0065] Place 0.948 g KMnO4 in a beaker, add 20 mL of deionized water, and stir until the KMnO4 is completely dissolved. Place 0.5 g DA in a beaker, add 20 mL of n-butanol, seal the beaker, and soak for 12 h. Then filter off the excess n-butanol. Add the remaining solid to the KMnO4 solution while stirring, seal the beaker, and stir for 12 h. Centrifuge and wash three times with ethanol, then dry in a 60 °C oven overnight. Place the product in a muffle furnace and calcine at 200 °C for 2 h at a heating rate of 5 °C / min to remove residual n-butanol. Collect the product as MD.

[0066] Comparative Example 5:

[0067] A ZIF-8 and its preparation method, the specific steps of which are as follows:

[0068] 0.3 g of zinc acetate was placed in a beaker and dissolved in 10 mL of deionized water to obtain solution A; 1.12 g of 2-methylimidazole was placed in a beaker and dissolved in 10 mL of deionized water to obtain solution B; solution B was then slowly added to solution A, and the mixture was stirred at room temperature (~33℃) for 24 h. The product was centrifuged and washed three times with deionized water, and then dried in an oven at 40℃ for 5 h to obtain ZIF-8.

[0069] Comparative Example 6:

[0070] A manganese dioxide (MnO2) and its preparation method, the specific steps of which are as follows:

[0071] 79 mg of KMnO4 was placed in a beaker and dissolved in 10 mL of deionized water. Then, 5 mL of 2-(N-morpho)ethanesulfonic acid buffer solution (MES buffer, pH 6.5, 0.1 M) was added. The solution was stirred for 30 min until the redox reaction was completed. The product was centrifuged and washed three times with deionized water. Then, it was dried in an oven at 40 °C for 5 h to obtain a brownish-black product, which is MnO2.

[0072] like Figure 1 As shown, A represents Comparative Example 1 (DA), B represents Comparative Example 2 (ZD), C represents Comparative Example 3 (ZCD), D represents Example 3 (MZCD), and E represents Comparative Example 4 (MD). It can be seen that in Example 3, a metal-organic framework (MOF) was successfully loaded onto DA, and the pore structure of DA was well preserved and was not damaged or covered.

[0073] like Figure 2 As shown, the small particles on Comparative Example 2ZD are ZIF-8; Mn signals appeared in both Comparative Example 4MD and Example 3MZCD, indicating the successful introduction of MnO2; the presence of C signals in Example 3MZCD further indicates the successful loading and carbonization of ZIF-8.

[0074] The experiment employed X-ray diffraction analysis, using an X-ray diffractometer with Cu-Kα as the radiation source, a voltage of 40 kV, a current of 200 mA, a scanning range of 5-80°, and a scanning rate of 10° / min.

[0075] like Figure 3 As shown, the characteristic peak of Comparative Example 2ZD is similar to that of Comparative Example 5ZIF-8, proving the successful loading of ZIF-8; the characteristic peak of Example 3MZCD is similar to that of Comparative Example 6MnO2, proving the successful introduction of MnO2; the characteristic peak of Example 3MZCD is similar to that of Comparative Example 1DA, Comparative Example 2ZD and Comparative Example 3ZCD, proving the successful synthesis of MZCD.

[0076] like Figure 4 As shown, the absorption peak of Comparative Example 2ZD is similar to that of Comparative Example 5ZIF-8, proving the successful loading of ZIF-8; the absorption peak of Example 3MZCD is similar to that of Comparative Example 6MnO2, proving the successful introduction of MnO2; the absorption peak of Example 3MZCD is similar to that of Comparative Example 1DA, Comparative Example 2ZD and Comparative Example 3ZCD, proving the successful synthesis of MZCD.

[0077] like Figure 5 As shown in the curve, it can be seen that the introduction of MnO2 did not cover the original pores of Example 3MZCD (Comparative Example 3ZCD), and further improved the overall specific surface area of ​​Example 3MZCD.

[0078] like Figure 6 As shown, A to C represent comparative example 4MD, and D to F represent example 3MZCD. By comparing the peaks of Mn, O, C and Si, it can be seen that compared with comparative example 4MD, example 3MZCD can capture more free oxygen, which plays a key role in promoting the oxygen replenishment process in the catalytic cycle.

[0079] To investigate the effect of ZIF-8-C and MnO2 addition on the formaldehyde adsorption capacity of the material, we tested the material's formaldehyde adsorption capacity over 180 minutes. The specific steps are as follows:

[0080] A mixture of formaldehyde and air at a volume ratio of 4:1 was introduced into a 500 mL quartz bottle. The formaldehyde gas concentration was allowed to stabilize at 180 mg / m³. 3 Then, the quartz bottle was sealed and a quartz tube (with 0.1g of sample placed inside) was connected. The delivery tube of the quartz tube was quickly transferred to a gas monitor, and the change in formaldehyde concentration in the system was recorded over 3 hours.

[0081] like Figure 7 As shown, after the introduction of ZIF-8-C, the adsorption performance of the material for formaldehyde increased from 0.11 mg / g in Comparative Example 1DA to 0.35 mg / g in Comparative Example 3ZCD. After the introduction of MnO2, its adsorption performance was further improved to 0.42 mg / g in Example 3MZCD. This indicates that the introduction of ZIF-8-C and MnO2 significantly improved the adsorption performance of the material for formaldehyde. This is because the introduction of ZIF-8-C and MnO2 improved the pore structure and specific surface area of ​​the material, thereby increasing the adsorption capacity.

[0082] To verify that the material can completely remove formaldehyde under heat, its thermocatalytic effect at 100℃ was tested. The specific steps are as follows:

[0083] A mixture of formaldehyde and air at a volume ratio of 4:1 was introduced into a 500 mL quartz bottle. The formaldehyde gas concentration was allowed to stabilize at 180 mg / m³. 3 Then, the quartz bottle was sealed and placed in a device system of a muffle furnace and a gas monitor (the tube furnace was preheated to 100°C, and 0.1g of sample was placed in the internal quartz tube), and the change in formaldehyde concentration in the system was recorded over 2 hours.

[0084] like Figure 8As shown, under 100℃ conditions, the formaldehyde in the system was reduced to a certain extent. Comparative Example 1DA, Comparative Example 4MD, and Example 3MZCD reduced formaldehyde by 17.91%, 59.17%, and 79.76%, respectively, indicating that the incorporation of MnO2 under heat significantly improved the formaldehyde removal performance of the material. Comparative Example 4MD and Example 3MZCD both produced a certain amount of carbon dioxide (CO2), indicating that MD and MZCD promoted the degradation of formaldehyde, with MZCD causing complete degradation of formaldehyde, producing water (H2O) and CO2. However, DA did not produce CO2, indicating that the formaldehyde reduction caused by DA was due to chemisorption, which is consistent with the adsorption kinetics study results. In addition, the CO2 content was much higher than the theoretical yield. This is because the formaldehyde gas in this experiment originated from the volatilization of the formaldehyde solution. During this process, some methanol contained in the formaldehyde solution volatilized and was degraded along with the formaldehyde gas, thus resulting in a CO2 yield much higher than the theoretical yield.

[0085] The photothermal conversion efficiency was tested by irradiating the material with full-spectrum light and recording the temperature change of the material from the moment the light was turned on using an AS877 dual-channel thermocouple thermometer. The recording was done every 15 seconds for 10 minutes.

[0086] like Figure 9 As shown, Comparative Example 1DA only has a certain absorption capacity for ultraviolet light below 320nm, and exhibits strong reflection and transmission capabilities for light in other wavelength bands. After doping with ZIF-8-C (Comparative Example 3ZCD), the light absorption capacity of the material is greatly improved, showing good absorption across the entire wavelength band. When MnO2 is added (Example 3MZCD), the light absorption capacity of the material in the ultraviolet-visible region is further enhanced. Although the absorption capacity in the near-infrared region decreases slightly, it is still much stronger than that of Comparative Example 1DA. This indicates that the introduction of ZIF-8-C successfully improves the light absorption capacity of the material, while the introduction of the MnO2 catalyst does not reduce the light absorption performance, which is in line with expectations. At the same time, compared with Comparative Example 4MD without ZIF-8-C, the full-spectrum absorption capacity of Example 3MZCD is much stronger. This is because the presence of carbon greatly improves the light absorption capacity of the material, thus making MZCD exhibit strong light absorption.

[0087] Under full-spectrum xenon lamp irradiation, the temperature of Comparative Example 1DA rose to approximately 64.5°C. When ZIF-8-C was introduced (Comparative Example 3ZCD), its photothermal temperature rise increased to 79.5°C. This is because the introduction of carbon enhanced the absorption of DA in the infrared region, reduced reflection and transmission, and increased the thermal effect of infrared light, leading to a temperature increase. With the further introduction of MnO2 (Example 3MZCD), the photothermal temperature rise of the material further increased to 132.6°C. This is due to the extremely high photothermal conversion efficiency of MnO2. Compared with Comparative Example 4MD, the photothermal temperature rise of Example 3MZCD increased by 27.7°C. This is because the introduction of ZIF-8-C improved the light absorption performance of the material, allowing MnO2 to obtain more light energy, ultimately resulting in a better photothermal effect for MZCD.

[0088] To select the optimal MnO2 loading, we tested the catalytic effect of MZCD prepared under different KMnO4 concentrations, and performed five consecutive cycles of catalytic degradation of formaldehyde using the 300MZCD composite material. The specific steps are as follows:

[0089] A mixture of formaldehyde and air at a volume ratio of 4:1 was introduced into a 500 mL quartz bottle. The formaldehyde gas concentration was allowed to stabilize at 180 mg / m³. 3 Afterwards, the quartz bottle was sealed and a quartz tube (with 0.1g of sample placed inside) was connected. The delivery tube of the quartz tube was quickly transferred to a gas monitor, and the change in formaldehyde concentration in the system was recorded over 2-3 hours. The above experiment was repeated 5 times.

[0090] like Figure 10As shown, the catalytic formaldehyde degradation rates of the materials in the examples all reached over 80%. When using 300 mmol / L KMnO4 (Example 3 300MZCD), the catalytic degradation effect was the best, reaching 99.71%. Comparative Example 3 ZCD and Comparative Example 1DA both had some formaldehyde removal effect, but their CO2 production was almost zero, indicating that both were mainly adsorption-based. According to adsorption kinetic analysis, ZCD had a higher proportion of chemical adsorption than DA, therefore the gas adsorbed by ZCD was more difficult to desorb, resulting in a relatively higher formaldehyde removal rate, consistent with the experimental results. Comparative Example 4MD and Example 3MZCD showed degradation rates of 92.48% and 99.71%, respectively. The system generates a large amount of CO2, indicating that both can promote the degradation of formaldehyde. MZCD exhibits stronger catalytic activity because, compared to MD, the introduction of ZIF-8-C gives MZCD a stronger photothermal conversion capacity. MZCD operates at a higher temperature, and the catalytic activity of MnO2 on the composite material is temperature-dependent, resulting in stronger catalytic activity for MZCD. Furthermore, the introduction of ZIF-8-C improves the pore structure of the material, giving it better adsorption performance and gradually transforming it from physical adsorption to chemical adsorption. In addition, according to... Figure 6 As a result, the addition of ZIF-8-C gave the material more Mn. 3+ This indicates that the increased number of oxygen vacancies allows for the capture of more oxygen, thereby promoting the catalytic reaction.

[0091] In each of the five cycles, the formaldehyde degradation rate reached over 99%, indicating that Example 3 300MZCD has good reusability and can be used repeatedly without significant deactivation.

[0092] To determine the catalytic mechanism of MZCD, we tested the material's formaldehyde degradation effect under two different conditions: 130℃ (determined by photothermal conversion) and simulated sunlight irradiation. The specific steps are as follows:

[0093] A mixture of formaldehyde and air at a volume ratio of 4:1 was introduced into a 500 mL quartz bottle. The formaldehyde gas concentration was allowed to stabilize at 180 mg / m³. 3 Afterwards, the quartz bottle was sealed and placed in a device system of a muffle furnace and a gas monitor (the tube furnace was preheated to 130°C, and 0.1g of Example 3 MZCD was placed in the internal quartz tube), and the change in formaldehyde concentration in the system was recorded over 2 hours.

[0094] A mixture of formaldehyde and air at a volume ratio of 4:1 was introduced into a 500 mL quartz bottle. The formaldehyde gas concentration was allowed to stabilize at 180 mg / m³. 3Afterwards, the quartz bottle was sealed and a quartz tube was connected (0.1g of Example 3MZCD was placed inside the quartz tube). The conduit of the quartz tube was quickly transferred into the gas monitor, and the quartz tube was irradiated with a xenon lamp. The changes in formaldehyde concentration in the system within 2 hours were recorded.

[0095] like Figure 11 As shown, at 130℃, the formaldehyde degradation rate reached 94.55% within 2 hours, while under simulated sunlight, the degradation efficiency reached 99.71%, and the catalytic rate was even faster. This indicates that the material not only degrades formaldehyde through thermocatalysis, but also that light plays a certain role. Considering that the photothermal effect of the material is mainly generated by infrared light, we tested the ultraviolet-visible light catalytic effect of the material. The results showed that its formaldehyde degradation rate reached 86.44%, which indicates that MZCD also has a certain ultraviolet-visible light catalytic effect.

[0096] like Figure 12 As shown, under UV-Vis irradiation, the MZCD in Example 3 can reach 60.7°C within 600s. At this temperature, δ-MnO2 can degrade formaldehyde gas to a certain extent, but its efficiency is low. In addition, we studied the band gap of MZCD by Taucplot method, and the band gap of MZCD is 1.94eV.

[0097] like Figure 13 As shown, when MZCD absorbs ultraviolet-visible light, electrons jump from the valence band to the conduction band, creating holes in the valence band. OH- on the catalyst surface occupies these holes and is converted into ·OH. ·OH has a very strong oxidative degradation ability, which in turn degrades formaldehyde. It can be seen that the catalytic process of MZCD involves not only thermocatalysis but also photocatalysis. Therefore, the catalytic rate and efficiency of MZCD under full-spectrum irradiation are higher than those of pure thermocatalysis.

[0098] like Figure 14 As shown, formaldehyde first connects to the hydroxyl groups on the DA surface of MZCD via hydrogen bonds, adsorbing onto the MZCD surface. Under sunlight, the temperature of MnO2 in the MZCD increases, and photocatalytic and thermocatalytic degradation of formaldehyde begins simultaneously. After absorbing sunlight, electrons in MnO2 undergo transitions, forming photogenerated holes at the valence band position, converting OH- to ·OH. The ·OH further degrades formaldehyde into H2O and CO2. Simultaneously, after absorbing sunlight, MnO2 converts sunlight into heat. Under the influence of heat, adsorbed oxygen on its surface is converted into reactive oxygen species (ROS) by MnO2, simultaneously forming a positively charged oxygen vacancy. The ROS further oxidizes and degrades formaldehyde into H2O and CO2. Meanwhile, MnO2... 4+ Reduced to Mn 3+ Subsequently, positively charged oxygen vacancies capture oxygen from the air, and Mn is then converted back into oxygen. 3+ Oxidized to Mn 4+ This completes one cycle.

[0099] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An application of a diatomaceous earth-based composite material for the adsorption and photothermal catalytic degradation of volatile organic compounds, characterized in that, The preparation method of this diatomaceous earth-based composite material includes the following steps: (1) Dissolve zinc salt in the first solvent, then add diatomite as the first solution; add the second solvent to the ligand as the second solution; then add the second solution to the first solution, stir, and centrifuge the product to obtain ZIF-8 / diatomite composite material; calcine the ZIF-8 / diatomite composite material by first heating and then cooling it in two stages, and then naturally cool it to room temperature to obtain ZIF-8 derived carbon / diatomite composite substrate; (2) Dissolve the manganese salt in the third solvent to obtain the third solution; add the fourth solvent to the ZIF-8 derived carbon / diatomite composite substrate and soak it to obtain the fourth solution; then add the solid material after filtering the fourth solution to the third solution, stir, and centrifuge and calcine the product to obtain manganese dioxide@ZIF-8 derived carbon / diatomite composite material. In step (2), the concentration of manganese ions is 50-450 mmol / L; The concentration of the ZIF-8 derived carbon / diatomite composite substrate is 20-30 g / L, and the molar / mass ratio of manganese ions to the ZIF-8 derived carbon / diatomite composite substrate is (2-18 mmol):1 g.

2. The application according to claim 1, characterized in that, In step (1), the zinc salt is zinc nitrate or zinc carbonate, and the first solvent is methanol or ethanol; The ligand is 2-methylimidazole or 4-methylimidazole, and the second solvent is methanol or ethylene glycol.

3. The application according to claim 1, characterized in that, In step (1), the zinc ion concentration is 40-50 mmol / L, and the mass ratio of zinc ions to diatomaceous earth is (0.005-0.009):1; The ligand concentration was 170-180 mmol / L, and the molar ratio of zinc ions to ligands was 1:(4-4.2).

4. The application according to claim 1, characterized in that, The stirring and soaking time in steps (1) and (2) is 10-13 h.

5. The application according to claim 1, characterized in that, In step (1), the heating rate of the calcination stage is 3-6 ℃ / min, the temperature is 250-350 ℃, and the holding time is 2-4 h; The second-stage heating rate is 4-6 ℃ / min, the temperature is 750-850 ℃, and the holding time is 2-4 h; The cooling rate is 1-3 ℃ / min, the temperature is 150-250 ℃, and the holding time is 8-12 min.

6. The application according to claim 1, characterized in that, In step (2), the manganese salt is potassium permanganate or potassium manganate, and the third solvent is water or methanol; The fourth solvent is one of n-butanol, ethanol, or methanol.

7. The application according to claim 1, characterized in that, In step (2), the calcination heating rate is 3-6 ℃ / min, the temperature is 150-250 ℃, and the time is 1-3 h.

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