A δ-MnO2-GO catalyst, its preparation method, and its application in formaldehyde degradation at room temperature.

Abstract

The application discloses a kind of delta-MnO2-GO catalyst and its preparation method and application in room temperature formaldehyde degradation, it is related to inorganic catalyst technical field.The preparation method of delta-MnO2-GO catalyst of the application can significantly limit the growth of manganese dioxide nanosheet by doping with low amount of GO, to manufacture abundant mass transfer transmission channel, delta-MnO2-GO catalyst presents unique two-dimensional crown structure, two-dimensional coral-like hierarchical pore structure delta-MnO2 nanorod is uniformly dispersed on the GO of plane structure, greatly promote the exposure of catalytic site and the mass transfer of reactant, produce a large number of surface active oxygen ROS and hydroxyl radical-OH, greatly maintain the excellent catalytic activity and stability to HCHO degradation, stably realize nearly 100% HCHO elimination at room temperature.

Description

Technical Field

[0001] This invention relates to the field of inorganic catalyst technology, and more specifically, to a δ-MnO2-GO catalyst, its preparation method, and its application in formaldehyde degradation at room temperature. Background Technology

[0002] In recent years, with the improvement of living standards, interior decoration has become increasingly popular. Wooden furniture products made from engineered wood panels, such as TV cabinets, sofas, coffee tables, dining tables, dining chairs, and shoe cabinets, have become very common in interior decoration. However, the engineered wood panels used in these wooden furniture pieces often contain formaldehyde and other substances released from adhesives. These formaldehyde molecules not only bring an unpleasant sensory experience but may also harm human health, affecting the normal function of the respiratory and circulatory systems. As a typical VOC odor from interior decoration, formaldehyde has been clearly classified as a carcinogen by the International Agency for Research on Cancer (IARC). Long-term exposure to formaldehyde may lead to cancers of the ears, nose, and throat; even long-term low-dose exposure may cause discomfort such as coughing, tearing, sneezing, dizziness, nausea, and vomiting. Various technologies have been developed to remove formaldehyde, such as adsorption, plasma treatment, photocatalytic oxidation, and thermocatalytic oxidation. Among these, catalytic oxidation under environmental conditions without the aid of light / heat / electricity is considered the most promising method. This has been achieved through the design and development of highly efficient catalysts, including both precious and non-precious metals. Although noble metal catalysts exhibit good performance and stability for formaldehyde oxidation at room temperature, their scarcity and high cost make transition metal oxide catalysts a more favorable choice. Therefore, developing efficient and stable transition metal catalysts to eliminate widespread formaldehyde pollution is highly desirable. Among transition metal catalysts, manganate oxides (MnOx) often exhibit excellent formaldehyde catalytic oxidation capabilities at low temperatures. However, the self-assembled spherical structure of MnOx particles easily leads to severe pore blockage, and the exposure of HCHO adsorption / catalytic sites is low, resulting in extremely limited mass transfer of reactants and products. This makes it difficult to achieve efficient and stable formaldehyde catalytic oxidation with MnOx catalysts at room temperature, and they are prone to deactivation.

[0003] The prior art discloses a method for preparing graphene-sheet manganese dioxide, comprising the following steps:

[0004] (1) Weigh potassium permanganate and manganese sulfate, wherein the molar ratio of potassium permanganate to manganese sulfate is 10:1-2:1; (2) Disperse the weighed potassium permanganate in water and stir until there are no particles to obtain an aqueous solution of potassium permanganate; (3) Add the weighed manganese sulfate to the aqueous solution of potassium permanganate and stir for 0.5-2 hours to obtain a potassium permanganate-manganese sulfate mixture; (4) Weigh graphene oxide powder, wherein the amount of graphene oxide powder weighed is 0.5-10 wt% of the potassium permanganate-manganese sulfate mixture; (5) Add the weighed graphene oxide powder to water. (6) The graphene oxide aqueous solution was ultrasonically dispersed to obtain an aqueous solution of graphene oxide; (7) The aqueous solution of graphene oxide was added to the potassium permanganate-manganese sulfate mixture and stirred thoroughly to obtain a mixed solution; (8) The mixed solution prepared in step (6) was transferred to a hydrothermal reactor and reacted at 120-180℃ for 2-24 hours to obtain a reaction solution; (9) After the reaction was completed, the reaction solution was filtered and the solid obtained by filtration was washed with deionized water and ethanol, respectively; (10) The solid obtained by washing in step (8) was dried at 50-120℃ to obtain graphene-sheet manganese dioxide. The preparation of the above graphene-sheet manganese dioxide material requires hydrothermal aging, which involves high reaction temperature. Although it also has a high formaldehyde degradation efficiency at room temperature, it does not solve the deactivation problem and does not have a stable and efficient formaldehyde catalytic oxidation effect. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing graphene-manganese dioxide catalysts, such as harsh preparation conditions, poor dispersion and exposure of catalytic active sites, which leads to poor catalytic stability and efficiency. This invention provides a method for preparing a δ-MnO2-GO catalyst. By in-situ growing δ-MnO2 on a GO substrate, a two-dimensional coral-like hierarchical porous structure material is synthesized, and finally a δ-MnO2-GO catalyst with a unique two-dimensional crown-like morphology is prepared, which can achieve efficient and stable catalytic degradation of formaldehyde at room temperature.

[0006] Another object of the present invention is to provide a δ-MnO2-GO catalyst.

[0007] Another object of the present invention is to provide an application of δ-MnO2-GO catalyst in formaldehyde degradation at room temperature.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0010] S1. Prepare an aqueous solution of graphene oxide with a concentration of 1.6–10 g / L, and add manganese sulfate to the graphene oxide solution to make the concentration of manganese sulfate 50–300 g / L to obtain a mixed solution;

[0011] S2. Prepare a potassium permanganate aqueous solution with a concentration of 30-60 g / L;

[0012] S3. Add potassium permanganate solution to the mixed solution of S1, stir for 30 min, age at room temperature for more than 12 h, and dry to obtain δ-MnO2-GO catalyst.

[0013] It should be noted that:

[0014] The preparation method of the δ-MnO2-GO catalyst of the present invention adopts the in-situ growth method of manganese dioxide, and the preparation process does not require additional reaction condition control, and the preparation process is simple and easy.

[0015] By using GO as a steric hindrance regulator and electronic state modifier for subsequent reactions during the growth of manganese dioxide, the appearance of the grown manganese dioxide was adjusted to a two-dimensional coral-like hierarchical porous structure, rather than ordinary nanospheres, thus achieving special morphology control.

[0016] First, in S1, manganese sulfate is added to the graphene oxide solution. The manganese sulfate contains Mn... 2+ The ions electrostatically bind to the O atoms of the oxygen-containing functional groups on the GO plane. Subsequently, S3 reacts with potassium permanganate solution and MnO4 in the mixed solution. - Ions and Mn 2+ Ionic reactions form numerous crystal nuclei that densely adhere to the GO plane. Finally, the nuclei age at room temperature and gradually grow into δ-MnO2 nanorods. These nanorods grow in a crisscross pattern, forming a coral-like structure. SEM clearly shows that the δ-MnO2 morphology of this invention is a coral-like structure, and physical adsorption characterization confirms a hierarchical porous structure, further confirming that it grows manganese dioxide with a two-dimensional coral-like hierarchical porous structure.

[0017] Furthermore, by introducing graphene, the original growth mode of δ-MnO2 is changed, allowing it to self-assemble and grow along the GO plane. The low amount of GO doping can significantly limit the growth of manganese dioxide nanosheets, gradually growing into δ-MnO2 nanorods, creating abundant mass transfer channels. The resulting δ-MnO2-GO catalyst exhibits a unique two-dimensional crown structure, with δ-MnO2 nanorods uniformly dispersed on the planar GO structure, greatly promoting the exposure of catalytic sites and the mass transfer of reactants.

[0018] In the preparation method of the δ-MnO2-GO catalyst of the present invention, the order of addition of potassium permanganate and manganese sulfate is also crucial. The order of addition affects the formation of the two-dimensional coral-like hierarchical pore structure of δ-MnO2 and the unique two-dimensional crown structure of δ-MnO2-GO catalyst, as well as the exposure of catalytic sites of δ-MnO2-GO catalyst.

[0019] The order in which manganese sulfate is added to the graphene oxide solution first, followed by potassium permanganate solution, is controlled to ensure that sufficient Mn is adsorbed on the GO surface. 2+ Ions, facilitating subsequent reaction with MnO4 - Ionic reactions form δ-MnO2. The reaction temperature during room temperature aging can control the disorder of δ-MnO2. The aging temperature affects the crystal morphology and growth rate of manganese dioxide, exposing more defect sites.

[0020] The preparation method of the δ-MnO2-GO catalyst of the present invention synthesizes a two-dimensional coral-like hierarchical porous material (δ-MnO2@GO) by in-situ growth of δ-MnO2 on a graphene oxide (GO) substrate. The modification with graphene oxide (GO) effectively inhibits the excessive growth and aggregation of δ-MnO2, preventing it from agglomerating into large-sized nanospheres. The interaction between GO and MnO2 promotes the exposure of adsorption / catalytic active sites and the mass transfer efficiency of reactants and products. The abundant oxygen vacancies in the δ-MnO2@GO catalyst material rapidly convert adsorbed water into surface -OH groups. The surface -OH groups and ROS synergistically reduce the accumulation of intermediates, and formaldehyde oxidation follows the LH mechanism, maximizing the exposure of catalytic active sites.

[0021] LH mechanism: Formaldehyde and oxygen molecules in the gas phase are adsorbed onto the catalyst surface, forming adsorbed molecules. These two adjacent adsorbed molecules react on the catalyst surface, achieving formaldehyde degradation.

[0022] The preparation method of this invention successfully synthesized a δ-MnO2@GO catalyst by in-situ growth of δ-MnO2 on a graphene oxide (GO) substrate, and stably achieved nearly 100% HCHO elimination at room temperature. The δ-MnO2@GO catalyst exhibits a unique two-dimensional crown structure, with δ-MnO2 nanorods uniformly dispersed on the planar GO structure, greatly promoting the exposure of catalytic sites and the mass transfer of reactants. The highly exposed catalytic sites on δ-MnO2@GO-RT can rapidly activate O2 and H2O, generating a large amount of surface-active oxygen species (ROS) and hydroxyl groups (-OH), greatly maintaining excellent catalytic activity and stability for HCHO degradation.

[0023] In a specific embodiment, preferably, the addition rate of potassium permanganate in S3 is 5-8 μL / min, more preferably 6 μL / min.

[0024] Controlling the addition rate can regulate Mn 2+ Ions and MnO4 - The ionic reaction rate and δ-MnO2 growth rate are more conducive to controlling its morphology and maximizing the exposure of catalytic active sites.

[0025] In a specific embodiment, preferably, the concentration of the graphene solution in S1 is 3-5 g / L, more preferably 3 g / L.

[0026] In a specific embodiment, preferably, the concentration of manganese sulfate in S1 is 60-80 g / L, more preferably 75 g / L.

[0027] In a specific embodiment, preferably, the concentration of potassium permanganate solution in S2 is 40-60 g / L, more preferably 50 g / L.

[0028] In the preparation method of this invention, the concentration of graphene solution and potassium permanganate solution, i.e. the amount of water used to dissolve pure water, directly affect the contact and kinetic growth of raw materials. If the concentration is too high, crystallization may be too fast, the grains will become larger, there will be fewer unsaturated coordinated atoms on the surface, and the reactivity will be low. If the concentration is too low, the growth will be slow, and manganese dioxide crystals will not grow.

[0029] In a specific embodiment, preferably, the purity of the graphene oxide is 95-99%, such as industrial-grade graphene oxide.

[0030] The drying temperature in S3 is preferably 50–120°C, and more preferably 80°C. This relatively low temperature reduces energy consumption, and also helps retain the bound water on the material surface, providing raw materials for hydroxyl activation.

[0031] The present invention also specifically protects a δ-MnO2-GO catalyst prepared by the above-mentioned method for preparing the δ-MnO2-GO catalyst.

[0032] This invention also specifically protects the application of a δ-MnO2-GO catalyst in the degradation of formaldehyde at room temperature.

[0033] The highly exposed catalytic sites on the δ-MnO2-GO catalyst can rapidly activate O2 and H2O, generating a large amount of surface active oxygen (ROS) and hydroxyl groups (-OH), which greatly maintains the excellent catalytic activity and stability for HCHO degradation, and can be widely used for formaldehyde degradation at room temperature.

[0034] In specific applications, the preferred application conditions for the δ-MnO2-GO catalyst of the present invention are:

[0035] The initial concentration of formaldehyde for degradation was 100 ppm, and the space velocity was 72 L / gcat·h.

[0036] The δ-MnO2-GO catalyst of the present invention exhibits good catalytic performance under any air humidity conditions, such as 0%, 25%, 50%, 75%, or 100%.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The preparation method of the δ-MnO2-GO catalyst of the present invention uses low-amount GO doping, which can significantly limit the growth of manganese dioxide nanosheets and create abundant mass transfer channels. The δ-MnO2-GO catalyst exhibits a unique two-dimensional crown structure. The two-dimensional coral-like hierarchical pore structure of δ-MnO2 nanorods is uniformly dispersed on the planar structure of GO, which greatly promotes the exposure of catalytic sites and the mass transfer of reactants. The highly exposed catalytic sites can rapidly activate O2 and H2O, generating a large amount of surface active oxygen ROS and hydroxyl -OH, which greatly maintains the excellent catalytic activity and stability for the degradation of HCHO.

[0039] The catalyst prepared by this invention has high activity and high stability in formaldehyde removal efficiency, and stably achieves nearly 100% HCHO elimination at room temperature.

[0040] The preparation method of the δ-MnO2-GO catalyst of the present invention is simple, requires room temperature aging, does not require high-temperature hydrothermal reaction, and has low energy consumption. Attached Figure Description

[0041] Figure 1 The figures show the formaldehyde removal rate and corresponding carbon dioxide production of catalysts doped with 0.5%, 1%, 2%, 3%, and 4% GO and pure δ-MnO2.

[0042] Figure 2 This is a schematic diagram illustrating the preparation process of the δ-MnO2-GO-RT catalyst and the hydrothermal δ-MnO2@GO-HT catalyst of the present invention.

[0043] Figure 3 The images are FESEM, TEM, and HRTEM images of δ-MnO2-RT.

[0044] Figure 4 FESEM, TEM and HRTEM images of δ-MnO2@GO-RT.

[0045] Figure 5 The images are FESEM, TEM, and HRTEM images of δ-MnO2-HT.

[0046] Figure 6 FESEM, TEM and HRTEM images of δ-MnO2@GO-HT.

[0047] Figure 7 XRD patterns of δ-MnO2@GO-RT and other comparative materials.

[0048] Figure 8 The image shows the infrared detection results of δ-MnO2-RT.

[0049] Figure 9 Infrared detection results of δ-MnO2@GO-RT prepared at room temperature.

[0050] Figure 10 Infrared detection results for the hydrothermal preparation of δ-MnO2-HT.

[0051] Figure 11 Infrared detection results of δ-MnO2@GO-HT prepared by hydrothermal methods.

[0052] Figure 12 This is a diagram illustrating the reaction mechanism of HCHO oxidation.

[0053] Figure 13 The formaldehyde removal efficiency of δ-MnO2@GO-RT compared with other comparative materials.

[0054] Figure 14 The results are from long-term stability tests of δ-MnO2@GO-RT. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0056] Example 1

[0057] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0058] S1. Add 0.6g of graphene oxide to 200mL of pure water and stir for 8min to obtain a graphene oxide solution. Add 15g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0059] The concentration of graphene oxide was 3 g / L, and the concentration of manganese sulfate was 75 g / L.

[0060] S2. Add 30g of potassium permanganate to 600mL of pure water and mix well to obtain a potassium permanganate solution with a concentration of 50g / L;

[0061] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 80℃.

[0062] The potassium permanganate solution was added at a rate of 6 μL / min.

[0063] The graphene is industrial-grade graphene with a purity of 95-99%.

[0064] Example 2

[0065] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0066] S1. Add 0.6g of graphene oxide to 200mL of pure water and stir for 8min to obtain a graphene oxide solution. Add 15g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0067] The concentration of graphene oxide was 3 g / L, and the concentration of manganese sulfate was 75 g / L.

[0068] S2. Add 30g of potassium permanganate to 600mL of pure water and mix well to obtain a potassium permanganate solution with a concentration of 50g / L;

[0069] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 80℃.

[0070] The potassium permanganate solution was added at a rate of 10 μL / min.

[0071] The graphene is industrial-grade graphene with a purity of 95-99%.

[0072] Example 3

[0073] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0074] S1. Add 1g of graphene oxide to 200mL of pure water and stir for 8min to obtain a graphene oxide solution. Add 15g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0075] The concentration of graphene oxide was 5 g / L, and the concentration of manganese sulfate was 75 g / L.

[0076] S2. Add 30g of potassium permanganate to 600mL of pure water and mix well to obtain a potassium permanganate solution with a concentration of 50g / L;

[0077] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 80℃.

[0078] The potassium permanganate solution was added at a rate of 6 μL / min.

[0079] The graphene is industrial-grade graphene with a purity of 95-99%.

[0080] In the catalytic oxidation of formaldehyde, MnO2 is the active component; increasing the GO content in the mixed solution decreases the relative MnO2 content. The formaldehyde catalytic effect in Example 3 is not as good as in Example 1, and the catalyst stability is not significantly improved.

[0081] Figure 1 The figures show the formaldehyde removal rate and corresponding carbon dioxide production of catalysts doped with 0.5%, 1%, 2%, 3%, and 4% GO and pure δ-MnO2.

[0082] Figure 1 In the study, the removal rate of HCHO and the corresponding CO2 production of the δ-MnO2@xGO catalyst were (a) and (b) respectively (test conditions: formaldehyde concentration: 100 ppm; equilibrium gas: air; temperature: 25℃; relative humidity: 50%; mass hourly space velocity: 72,000 mL·gcat). -1 ·h -1 )

[0083] All catalysts shown in the figure achieved approximately 100% formaldehyde removal rate, the difference being the varying stability of catalysts with different GO doping concentrations. As the GO doping concentration increased from 0 to 2%, the catalyst stability increased from 100 min to 200 min; further increasing the GO doping concentration to 4% caused the catalyst stability to gradually decrease back to 100 min. In this system, MnO2 is the active component in the catalytic oxidation of formaldehyde. Excessive GO doping reduces the relative content of MnO2, decreases the active sites for formaldehyde catalytic oxidation, and reduces the reaction activity.

[0084] Example 4

[0085] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0086] S1. Add 0.6 g of graphene oxide to 200 mL of pure water and stir for 8 min to obtain a graphene oxide solution. Add 30 g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0087] The concentration of graphene oxide was 3 g / L, and the concentration of manganese sulfate was 150 g / L.

[0088] S2. Add 30g of potassium permanganate to 600mL of pure water and mix well to obtain a potassium permanganate solution with a concentration of 50g / L;

[0089] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 80℃.

[0090] The potassium permanganate solution was added at a rate of 6 μL / min.

[0091] The graphene is industrial-grade graphene with a purity of 95-99%.

[0092] Manganese sulfate, used as a manganese source, reacts with potassium permanganate to produce manganese dioxide. Excessive use leads to waste, and the residual sulfate ions are difficult to wash away, resulting in performance degradation. The catalytic performance of the δ-MnO2-GO catalyst in Example 4 was not improved compared to Example 1.

[0093] Comparative Example 1

[0094] δ-MnO2@GO-HT prepared hydrothermally (according to the method of this invention, but prepared under hydrothermal conditions)

[0095] A designed amount of GO (1% of the total catalyst, uniformly dispersed by thorough ultrasonic and magnetic stirring), 0.28 g MnSO4·H2O, and 1.50 g KMnO4 were added to 80 mL of deionized water. After magnetic stirring for 30 minutes, the colloidal suspension was transferred to a 100 mL PTFE-lined hydrothermal synthesis reactor. The reactor was then placed in an oven maintained at 120 °C for 12 hours.

[0096] The precipitate was washed by centrifugation with deionized water until the final clear liquid was colorless and transparent. The precipitate was dried at 80°C and named δ-MnO2@GO-HT.

[0097] Comparative Example 2:

[0098] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0099] S1. Add 0.5-1g of graphene oxide, 15g of manganese sulfate and 30g of potassium permanganate to 100-300mL of pure water and stir for 8min to obtain a mixed solution;

[0100] S2. Add potassium permanganate solution to the mixed solution of S1, stir for 30 min, age at room temperature, filter, heat and dry at 80℃ to obtain δ-MnO2-GO catalyst.

[0101] Since the two reactants are added at the same time, it is equivalent to the reaction starting in the liquid phase before the GO carrier is fully adsorbed. Some independently nucleated manganese dioxide may not be able to grow into two-dimensional sheets instead of coral-like structures due to the restriction of GO, resulting in a decrease in performance.

[0102] Comparative Example 3

[0103] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0104] S1. Add 0.6g of graphene oxide to 400mL of pure water and stir for 8min to obtain a graphene oxide solution. Add 15g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0105] The concentration of graphene oxide was 1.5 g / L, and the concentration of manganese sulfate was 37.5 g / L.

[0106] S2. Add 30g of potassium permanganate to 600mL of pure water and mix well to obtain a potassium permanganate solution;

[0107] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 80℃.

[0108] The potassium permanganate solution was added at a rate of 6 μL / min.

[0109] The graphene is industrial-grade graphene with a purity of 95-99%.

[0110] The formaldehyde catalytic performance of the catalyst decreased compared to the example.

[0111] Comparative Example 4: It is speculated that this will lead to a slight decrease in performance.

[0112] A method for preparing a δ-MnO2-GO catalyst includes the following steps:

[0113] S1. Add 0.6g of graphene oxide to 200mL of pure water and stir for 8min to obtain a graphene oxide solution. Add 15g of manganese sulfate to the graphene oxide solution to obtain a mixed solution.

[0114] The concentration of graphene oxide was 3 g / L, and the concentration of manganese sulfate was 75 g / L.

[0115] S2. Add 30g of potassium permanganate to 1200mL of pure water and mix well to obtain a potassium permanganate solution with a concentration of 25g / L;

[0116] S3. Add potassium permanganate solution to the mixed solution in S1, stir for 30 min, age at room temperature, filter, and then heat to dry to obtain δ-MnO2-GO catalyst at 50℃.

[0117] The potassium permanganate solution was added at a rate of 6 μL / min.

[0118] The graphene is industrial-grade graphene with a purity of 95-99%.

[0119] Result detection

[0120] The preparation process of the δ-MnO2-GO-RT (room temperature) catalyst of the present invention and the preparation process of the δ-MnO2@GO-HT catalyst of Comparative Example 1 are shown in the figure below. Figure 2 As shown.

[0121] δ-MnO2-RT was prepared at room temperature alone, following the preparation method in Example 1, without the addition of GO graphene oxide.

[0122] Hydrothermal preparation of δ-MnO2-HT: (Prepared under hydrothermal conditions according to the method of this invention, but without the addition of GO)

[0123] 0.28 g MnSO4·H2O and 1.50 g KMnO4 were added to 80 mL of deionized water. After magnetic stirring for 30 minutes, the colloidal suspension was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal synthesis reactor. The reactor was placed in an oven maintained at 120 °C for 12 hours. The resulting precipitate was washed with deionized water by centrifugation until the final clear liquid was colorless and transparent. The precipitate was dried at 80 °C and named δ-MnO2-HT.

[0124] (1) Morphology detection

[0125] The morphology of the δ-MnO2-GO-RT catalyst, δ-MnO2, δ-MnO2-RT, and δ-MnO2@GO-HT prepared in the embodiments of the present invention was analyzed. Specific results are shown in [link to results]. Figure 3-6 .

[0126] in, Figure 3 FESEM, TEM, and HRTEM images of δ-MnO2-RT (b1-b4)

[0127] b1 is the FESEM image, b2 is the TEM image, and b3 and b4 are the HRTEM images.

[0128] Figure 4 The images are FESEM, TEM, and HRTEM images of δ-MnO2@GO-RT (c1-c4), where c1 is the FESEM image, c2 is the TEM image, and c3 and c4 are the HRTEM images.

[0129] Figure 5 The images are FESEM, TEM and HRTEM images of δ-MnO2-HT (d1-d4), where d1 is the FESEM image, d2 is the TEM image, and d3 and d4 are the HRTEM images.

[0130] Figure 6 The images are FESEM, TEM, and HRTEM images (e1-e4) of δ-MnO2@GO-HT, where e1 is the FESEM image, e2 is the TEM image, and e3 and e4 are the HRTEM images.

[0131] From the above Figures 3-6 It can be seen that:

[0132] Two-dimensional coral-like δ-MnO2@GO was synthesized by in-situ growth of δ-MnO2 on a GO substrate, such as... Figure 3 As shown in the figure, SEM images b1-b2 reveal rough and irregular δ-MnO2-RT nanorods that aggregate into flower-like microspheres. After GO modification, the microsphere structure transforms into a planar structure, as shown in the figure. Figure 4 c1-c2(δ-MnO2@GO-RT).

[0133] The flower-like microsphere structure of cross-linked δ-MnO2-HT nanosheets is as follows Figure 5 As shown in d1-d2. Similarly, with GO modification, the flower-like microsphere structure is transformed into a planar structure (δ-MnO2@GO-HT).

[0134] δ-MnO2@GO-RT(c2) shows nanorods crisscrossing on a flat surface, much like the tentacles of a sea anemone. In contrast, δ-MnO2@GO-HT exhibits a hierarchical and interwoven microstructure, with the distance between two adjacent nanosheets being smaller than that of δ-MnO2-HT.

[0135] Therefore, the hydrothermal method can make the material structure smoother and more regular, and reduce surface defects, which may have a negative impact on catalytic activity.

[0136] (2) Crystallization detection

[0137] XRD analysis was performed on materials prepared at room temperature (δ-MnO2-RT), GO, hydrothermally (δ-MnO2-HT), room temperature (δ-MnO2@GO-RT), and hydrothermally (δ-MnO2@GO-HT). Specific results are shown below. Figure 7 As shown.

[0138] from Figure 7 As can be seen, the δ-MnO2@GO-RT prepared by the method of the present invention has a certain crystal structure. It has a peak at the position of the characteristic peak of manganese dioxide, but it is not a sharp peak, indicating that the crystals are weak and the crystal structure is weak. The existence of the weak crystal structure indicates that δ-MnO2 has abundant structural defects and oxygen vacancies, which lays the foundation for the activation of water and oxygen.

[0139] (3) Infrared detection

[0140] Infrared spectroscopy was performed on materials prepared at room temperature (δ-MnO2-RT), at room temperature (δ-MnO2@GO-RT), hydrothermally (δ-MnO2-HT), and hydrothermally (δ-MnO2@GO-HT). Specific detection results are as follows: Figure 8-11 As shown.

[0141] in, Figure 8 The image shows the infrared detection results of δ-MnO2-RT.

[0142] Figure 9 Infrared detection results of δ-MnO2@GO-RT prepared at room temperature.

[0143] Figure 10 Infrared detection results for the hydrothermal preparation of δ-MnO2-HT.

[0144] Figure 11 Infrared detection results of δ-MnO2@GO-HT prepared by hydrothermal methods.

[0145] from Figure 8 and 9 It can be seen that:

[0146] In-situ DRIFTS experiments were conducted at room temperature with an inlet flow rate of 100 ppm HCHO. At a depth of 1348 cm⁻¹... -1 1387cm -1 1589cm -1 and 2831cm -1 Four bands of formate were observed nearby, confirming that formate is the main surface intermediate produced by the partial oxidation of HCHO. The δ-MnO2@GO-RT spectrum showed relatively low intensity of the formate species, and at 1464 cm⁻¹... -1 There are no wavelengths belonging to DOM species nearby. DOM on the δ-MnO2@GO-RT surface can be rapidly converted to formate without accumulation, and compared with other catalysts, δ-MnO2@GO-RT has a stronger oxidation capacity for formate.

[0147] δ-MnO2-HT and δ-MnO2@GO-HT at 3300cm -1 and 3600cm -1 The two nearby wavelengths are attributed to adsorbed water δ(OH) and the formed surface -OH groups ν(OH), respectively. The intensity of the formed surface -OH groups initially increases and then gradually decreases, indicating that adsorbed water molecules are activated into -OH groups for formate oxidation. 1049 cm⁻¹ -1 The two nearby bands belong to carbonates, and the reduction indicates that the decomposition rate of carbonates on the catalyst surface is faster than the formation rate.

[0148] Only about 3300 cm⁻¹ was observed on δ-MnO₂-RT and δ-MnO₂@GO-RT. -1The adsorption bandwidth of water δ(OH) is wide. The adsorption strength of δ-MnO2@GO-RT is lower than that of δ-MnO2-RT, indicating that adsorbed water molecules can be rapidly activated and consumed during the catalytic oxidation of HCHO. The activation of water by the catalyst and the generation of reactive oxygen species is an important feature of this invention.

[0149] Based on the characterization results, the possible reaction mechanism of HCHO oxidation on δ-MnO2@GO-RT was determined. In-situ growth of δ-MnO2 nanoparticles on graphene oxide nanosheets increased the specific surface area of ​​the graphene oxide nanosheets, exposed more active sites, promoted the adsorption capacity of oxygen and water molecules, and improved the activation efficiency of ROS and -OH groups on the graphene oxide surface.

[0150] Therefore, the reaction mechanism of HCHO oxidation is as follows: Figure 12 It can be described as:

[0151] First, HCHO molecules form hydrogen bonds with surface -OH groups and are rapidly adsorbed onto the catalyst surface;

[0152] Subsequently, molecular oxygen is captured by surface oxygen vacancies and excited to ROS(O2). - O - In the process, ROS further oxidizes the adsorbed HCHO into DOM.

[0153] DOM is then rapidly oxidized to formate, carbonate, and carbon dioxide. In the absence of oxygen, water molecules can be directly captured by surface oxygen vacancies and activated to form surface -OH groups. These surface -OH groups coordinate well with reactive oxygen species, promoting the catalytic oxidation of HCHO.

[0154] (4) Formaldehyde degradation performance

[0155] The performance of δ-MnO2-RT, GO, δ-MnO2-HT prepared at room temperature, δ-MnO2@GO-RT prepared at room temperature in Examples 1-4, δ-MnO2@GO-HT prepared at hydrothermal temperature (Comparative Example 1), and materials from Comparative Examples 2-4 were tested. The test conditions were: HCHO concentration = 100 ppm, equilibrium gas was N2, RH = 50%, and GHSV = 72 L / gcat·h.

[0156] The test results are shown in Tables 1 and 2 below. Figure 13 :

[0157] Table 1. Formaldehyde Conversion Rate

[0158]

[0159] In Example 2, after accelerating the sample injection rate, the reaction between potassium permanganate and manganese sulfate was insufficient, resulting in incomplete formation of manganese dioxide crystals, ultimately leading to a slight decrease in formaldehyde degradation performance.

[0160] Table 2. Export carbon dioxide concentration (ppm)

[0161]

[0162]

[0163] The formaldehyde removal performance results of δ-MnO2@GO-RT compared with other comparative materials demonstrate that the δ-MnO2@GO-RT prepared by the method of this invention exhibits excellent formaldehyde removal efficiency and stability among numerous catalysts. This also indicates that the room-temperature preparation method of this invention is superior to hydrothermal conditions, thus possessing promising prospects for practical application.

[0164] The long-term stability of δ-MnO2@GO-RT-I in Example 1 was tested under the following specific test conditions:

[0165] Test conditions were: HCHO concentration = 10 ppm, air as a balance gas, temperature ~25℃, RH = 50%, GHSV = 72 L / gcat·h.

[0166] The results are as follows Figure 14 As shown, from Figure 14 It can be seen that the removal rate can be maintained at a stability of more than 40 hours, indicating that the catalyst prepared by this method has a bright prospect for industrial application.

[0167] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. The application of a δ-MnO2-GO catalyst in the degradation of formaldehyde at room temperature, characterized in that, The δ-MnO2-GO catalyst was prepared by the following steps: S1. Prepare a 3~5 g / L graphene oxide aqueous solution, add manganese sulfate to the graphene oxide solution to make the concentration of manganese sulfate 50~300 g / L, and obtain a mixed solution; S2. Prepare a potassium permanganate aqueous solution with a concentration of 40~60g / L; S3. Add potassium permanganate solution to the mixed solution of S1, stir for 30 min, age at room temperature for more than 12 h, and dry to obtain δ-MnO2-GO catalyst; The potassium permanganate solution in S3 is added at a rate of 5~8 μL / min.

2. The application as described in claim 1, characterized in that, The concentration of manganese sulfate in S1 is 60~80 g / L.

3. The application as described in claim 1, characterized in that, The purity of the graphene oxide is 95-99%.

4. The application as described in claim 1, characterized in that, The drying temperature is 50~80℃.

5. The application as described in claim 1, characterized in that, The aging time described in S3 is 12~24h.

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