Method for removing template of microporous molecular sieve by ultraviolet ozone cooperation

Abstract

The application discloses a method for removing a microporous molecular sieve template agent by ultraviolet ozone cooperation, and utilizes the synergistic effect of double-band ultraviolet light (185 nm and 254 nm) to successfully realize efficient decomposition of an organic template agent in a channel. The ultraviolet light of 185 nm has higher photon energy, can directly excite water molecules (H2O) to generate a large amount of hydroxyl radicals (·OH) and monatomic oxygen (O), and simultaneously converts oxygen (O2) in a solution into ozone (O3). The ultraviolet light of 254 nm further enhances the concentration of radicals generated by the decomposition of the ozone, and improves the efficiency of the oxidation reaction. These high-activity oxidants can rapidly react with the organic template agent to decompose the organic template agent into harmless small molecules such as carbon dioxide (CO2) and water (H2O), and finally realize complete removal of the template agent.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve material synthesis, and in particular to a method for the synergistic removal of microporous molecular sieve template agents by ultraviolet ozone. Background Technology

[0002] Molecular sieves are a class of inorganic materials with regular microporous structures, widely used in gas separation, catalysis, and adsorption. In the synthesis of molecular sieves, template agents are an indispensable key component, used to induce crystal growth and regulate pore structure. However, because template agents occupy the pores of molecular sieves, thus limiting their practical applications, the synthesized template agents must be completely removed. Currently, commonly used methods for template agent removal include high-temperature calcination, solvent extraction, chemical oxidation, and plasma treatment. Among these, high-temperature calcination is the most widely used industrial method due to its high efficiency in oxidative decomposition of template agents and its simple operation; while solvent extraction and chemical oxidation achieve removal through dissolution or decomposition, with relatively mild operating conditions. Plasma technology has also attracted some attention due to its low-temperature and high-efficiency characteristics. These methods meet the needs of template agent removal to a certain extent, but they also have many shortcomings.

[0003] The main problems with existing methods are: high-temperature calcination easily causes local collapse of the molecular sieve structure or interlayer stacking of two-dimensional molecular sieves, significantly reducing the material's dispersibility and utilization rate; solvent extraction and chemical oxidation, although having less impact on the structure, have low efficiency and high cost in removing organic template agents contained in microporous materials; and plasma treatment is difficult to scale up due to expensive equipment and complex operation. Furthermore, these methods generally suffer from high energy consumption and significant environmental pollution, and are particularly unsuitable for two-dimensional molecular sieves with high surface area and ultrathin properties. Therefore, developing a green, environmentally friendly, low-cost, and non-destructive method for removing template agents has become one of the key challenges in realizing the industrialization and efficient application of molecular sieves. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for the synergistic removal of template agents from microporous molecular sieves using ultraviolet ozone, which is particularly suitable for the removal of template agents from two-dimensional molecular sieve materials.

[0005] The technical solution involved in this invention is as follows:

[0006] A method for removing template agents from microporous molecular sieves using ultraviolet ozone technology includes:

[0007] (1) The synthesized molecular sieve nanosheets were directly dispersed in water to form a molecular sieve aqueous solution;

[0008] (2) Irradiate the molecular sieve aqueous solution with dual-band ultraviolet light with wavelengths of 185 and 254 nm, and continue stirring and reacting until the suspension becomes a transparent and clear solution.

[0009] (3) The transparent and clear solution obtained in step (2) is collected by vacuum filtration to obtain molecular sieve nanosheets with template agent removed.

[0010] This method utilizes the synergistic effect of dual-band ultraviolet light (185nm and 254nm) to successfully achieve the efficient decomposition of organic template agents within the pores. The 185nm ultraviolet light, with its higher photon energy, can directly excite water molecules (H2O) to generate a large number of hydroxyl radicals (·OH) and monatomic oxygen (O), while simultaneously converting oxygen (O2) in the solution into ozone (O3). The 254nm ultraviolet light further enhances the concentration of free radicals generated by ozone decomposition, improving the efficiency of the oxidation reaction. These highly reactive oxidants can rapidly react with the organic template agent, decomposing it into harmless small molecules such as carbon dioxide (CO2) and water (H2O), ultimately achieving complete removal of the template agent. This method is suitable for removing the pore structure occupied by organic template agents in molecular sieve nanosheets, thereby restoring the micropore distribution characteristics of the molecular sieve. It avoids the high-temperature calcination step during template agent removal, effectively preventing nanosheet aggregation and performance degradation, while simultaneously achieving complete removal of the template agent. This method produces no corrosive waste liquid, using only water and ultraviolet light, thus meeting environmental protection requirements. Furthermore, it eliminates the need for complex multi-step washing; treatment is completed immediately after light exposure, making it simpler and safer to operate. Compared to traditional high-temperature calcination and piranha solution treatment methods, this technology not only demonstrates superior removal efficiency and structural protection but also significantly improves experimental safety and environmental friendliness, providing a superior alternative for the preparation of molecular sieve materials.

[0011] Furthermore, in step (1), the molecular sieve nanosheets are MFI type nanosheets.

[0012] Furthermore, in step (1), the molecular sieve nanosheets are microporous materials.

[0013] Furthermore, the concentration range of the molecular sieve aqueous solution is from 1 mg / 80 mL to 1 mg / 4 mL. If the concentration is too high, ultraviolet light will not be able to penetrate the solution, resulting in a decrease in the content of reactive oxygen species or a decrease in the removal efficiency of the template agent.

[0014] Further, in step (1), the molecular sieve nanosheets are dispersed in deionized water.

[0015] Further, in step (2), the intensity of the ultraviolet light is 24800-27600 μW / cm. 2 .

[0016] Furthermore, in step (1), the mixture is continuously stirred and reacted for at least three days, during which time water needs to be added periodically. This is because water molecules decompose after being irradiated by the ultraviolet lamp, and because the ultraviolet lamp generates heat, which raises the temperature of the reaction system and causes the water to evaporate.

[0017] Furthermore, in step (2), the suspension is initially a uniform milky white solution, which becomes a transparent and colorless solution after ultraviolet ozone treatment. The initial milky white state is due to the opacity of the template agent. After the template agent is removed, the pores are opened, and the solution becomes transparent after light passes through.

[0018] Furthermore, in step (3), the solid product obtained by vacuum filtration is redispersed in deionized water to maintain the stable dispersion of the molecular sieve nanosheets.

[0019] The technical solutions provided by the embodiments of this application may include the following beneficial effects:

[0020] As can be seen from the above embodiments, this application utilizes ultraviolet ozone treatment technology to efficiently remove organic template agents from molecular sieves under mild conditions, overcoming the drawbacks of traditional high-temperature calcination methods that damage the molecular sieve structure, while avoiding the limitations of other methods in terms of energy consumption, cost, and applicability. This method uses dual-band ultraviolet light generated by an ultraviolet lamp to excite oxygen in the aqueous solution to form reactive oxygen species (such as ozone and hydroxyl radicals), thereby oxidizing and degrading template agent molecules, converting them into carbon dioxide and water, and thoroughly removing template agent residues. This application has several advantages: First, the method is carried out at a lower temperature and in an aqueous solution system, avoiding molecular sieve stacking and structural damage caused by high-temperature calcination, effectively preventing the aggregation and performance degradation of nanosheets, while removing organic template agents occupying the pore structure of the molecular sieve nanosheets, thereby restoring the micropore distribution characteristics of the molecular sieve and maintaining the high dispersibility and utilization rate of the two-dimensional molecular sieve; second, this method does not require expensive or toxic reagents, is low in cost, and does not require complex equipment, possessing good industrialization potential; finally, the ultraviolet ozone treatment process is clean and environmentally friendly, with the reaction only generating harmless carbon dioxide and water, meeting the requirements of sustainable development. In summary, this invention provides a novel, efficient, green, and scalable method for template agent removal, offering significant support for the industrial production and application of molecular sieve materials.

[0021] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0023] Figure 1 A schematic diagram illustrating a method for the gentle removal of molecular sieve nanosheet template agents provided in this application.

[0024] Figure 2 A comparison of the reaction solutions before and after template removal.

[0025] Figure 3 These are scanning electron microscope images of Example 1 before and after template removal.

[0026] Figure 4 These are Fourier transform images of Example 1 before and after template removal.

[0027] Figure 5 The thermogravimetric curves before and after removing the template agent in Example 1 are shown.

[0028] Figure 6 The figures show the nitrogen adsorption-desorption curves and pore size distribution before and after template removal in Example 1, where A is the nitrogen adsorption isotherm before and after UV treatment, and B is the pore size distribution of the nanosheets before and after UV treatment. Detailed Implementation

[0029] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0030] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0031] To more effectively remove template agents from molecular sieve nanosheets while maintaining the integrity of their microporous structure, this invention provides a low-temperature treatment method based on ultraviolet ozone technology, the specific implementation steps of which are as follows:

[0032] Example 1: Removal of template agents from molecular sieve nanosheets using ultraviolet ozone method, such as... Figure 1 As shown, the method includes:

[0033] (1) The synthesized molecular sieve nanosheets (such as b-axis oriented ultrathin MFI nanosheets) are dispersed in deionized water to form a diluted nanosheet aqueous solution. The preferred concentration range of the nanosheet aqueous solution is 1 mg / 80 mL to 1 mg / 4 mL;

[0034] Specifically, during the dispersion process, the nanosheets are uniformly distributed by moderate stirring to form a milky white emulsion. In this embodiment, the molecular sieve nanosheets used have a microporous structure with a pore size of 0.53 × 0.56 nanometers oriented along the b-axis.

[0035] (2) Place the nanosheet dispersion obtained in step (1) into a reaction vessel, control the reaction temperature at 58°C, irradiate the emulsion with an ultraviolet lamp with a wavelength of 185-254 nm, and stir with a magnetic stir bar at a speed of 500-1000 rpm. The reaction vessel should be tightly wrapped with aluminum foil to prevent ultraviolet rays from harming the human body.

[0036] Specifically, ultraviolet light irradiation excites oxygen to decompose and generate ozone. The ozone then reacts with the template agent in an oxidation reaction, producing carbon dioxide gas (e.g., ...). Figure 2 (As shown), the template agent is gradually degraded. The treatment process lasts approximately 3 days, until the emulsion gradually changes from milky white to a transparent, colorless solution, as shown. Figure 2 As shown. This process avoids the high energy consumption and damage to the nanosheet structure of traditional high-temperature calcination methods, and can achieve gentle and thorough removal of the template agent.

[0037] (3) Solid collection and purification steps

[0038] To further remove any potential byproducts or residues, the clear solution obtained in step (2) was collected by vacuum filtration to obtain the solid product. The resulting solid was then redispersed in deionized water to form a uniformly dispersed nanosheet solution, such as... Figure 3 As shown in the scanning electron microscope images, the nanosheets were very well dispersed before and after the reaction, and no agglomeration or clumping was observed.

[0039] The template agent on the molecular sieve nanosheets treated by the above method was completely removed, while retaining the complete microporous structure and excellent dispersibility. Fourier transform infrared spectroscopy (FTIR) was used to further analyze the results. Figure 4 It was found that at wavenumbers of 2700-3200 cm⁻¹ -1 The characteristic peaks of organic matter at that location disappeared significantly, and the thermogravimetric curve ( Figure 5 In the study, nanosheets treated with UV light and calcined showed no thermal weight loss in the 300-500℃ range, but the synthesized nanosheets containing organic matter experienced a 14% thermal weight loss in this range. Finally, nitrogen adsorption-desorption curves were used to determine the final result. Figure 6 This verified that the UV-treated nanosheets possess a microporous structure, such as... Figure 6 In A, at the same time, Figure 6 B in the figure also shows a pore size distribution of 0.5-0.6 nm. The above characterization proves that the obtained nanosheets have no organic template agent residue, a complete crystal structure, and a uniform micropore size distribution.

[0040] Comparative Example 1: Removal of template agent from nanosheets by high-temperature calcination

[0041] To remove the template agent from MFI nanosheets, the dried nanosheet samples were placed in a tube furnace and treated with a high-temperature calcination method. The specific steps are as follows: the sample was placed in a ceramic boat and then placed in the tube furnace. Under air atmosphere, the temperature was gradually increased to 500°C at a rate of 50°C / hour, and then calcined at this temperature for 10 hours. During calcination, the template agent decomposed and volatilized, generating a pure inorganic framework structure.

[0042] After calcination, the samples were cooled to room temperature and removed. Observation revealed that the calcined MFI nanosheets agglomerated into white clumps, with strong van der Waals interactions between the particles making them difficult to redisperse in solution. This agglomeration may adversely affect the subsequent dispersibility and application performance of the nanosheets.

[0043] Further analysis showed that although high-temperature calcination could effectively remove the template agent ( Figure 4 , Figure 5 , Figure 6 However, calcination can cause some shrinkage or defects on the surface of nanosheets, limiting their subsequent applications. Furthermore, calcination is energy-intensive and involves the emission of harmful gases. These phenomena suggest the need to explore other methods for removing template agents (such as low-temperature ultraviolet ozone treatment) to reduce agglomeration and maintain good dispersibility of the nanosheets.

[0044] Comparative Example 2: Removal of template agent from nanosheets using piranha solution

[0045] To remove the organic template agent from the pores of molecular sieve nanosheets, a highly active piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide) (pH = 0-1) was used for treatment. This method utilizes the strong oxidizing properties of the piranha solution to oxidize and decompose the organic template agent within the pores. However, experimental results showed ( Figure 4 , Figure 5 , Figure 6 Although some template agent was effectively removed, a small amount of residue remained and was difficult to completely eliminate. Fourier transform infrared spectroscopy (FTIR) was used to investigate this. Figure 4 It was found that at wavenumbers of 2700-3200 cm⁻¹ -1 The characteristic peaks of organic matter at that location still exist, and the thermogravimetric curve ( Figure 5 In the study, ozone-treated nanosheets exhibited significant thermogravimetric loss in the 300-500℃ temperature range. Finally, nitrogen adsorption-desorption curves were used to determine the final result. Figure 6 This verified that the nanosheets treated with piranha solution did not possess a microporous structure. Figure 6 In A, no microporous adsorption curve appeared, and at the same time, Figure 6B in the figure also shows that the nanosheets lack micropores, and organic matter remains trapped within the channels. This residual organic matter may hinder the complete penetration and reaction of the piranha solution and active hydroxyl groups due to the high depth and complex pore structure of the channels. Furthermore, this treatment method suffers from cumbersome procedures and high safety risks, especially during solution preparation and handling, requiring extreme caution to avoid the dangers of high temperatures or volatile reactions. After treatment, multiple steps of rinsing with deionized water and ethanol are necessary to thoroughly remove residual chemical reagents. This inefficient treatment method not only increases experimental time and reagent consumption but also poses a potential threat to the integrity of the nanosheet structure, limiting the convenience and feasibility of its practical application.

[0046] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A method for the synergistic removal of microporous molecular sieve template agents by ultraviolet ozone, characterized in that, include: (1) The synthesized molecular sieve nanosheets are directly dispersed in water to form a molecular sieve aqueous solution; (2) Irradiate the molecular sieve aqueous solution with dual-band ultraviolet light with wavelengths of 185 and 254 nm, continuously stir and react to prevent nanosheet aggregation and performance degradation, remove the organic template agent occupying the pore structure of molecular sieve nanosheets, restore the micropore distribution characteristics of molecular sieve, until the suspension becomes a transparent and clear solution, in which the reaction only produces carbon dioxide and water. (3) Collect the solid product from the solution obtained in step (2) by vacuum filtration and redisperse it in deionized water for use.

2. The method according to claim 1, characterized in that, In step (1), the molecular sieve nanosheets are MFI type nanosheets.

3. The method according to claim 1, characterized in that, In step (1), the molecular sieve nanosheets are microporous materials.

4. The method according to claim 1, characterized in that, The concentration range of the nanosheet aqueous solution is from 1 mg / 80 mL to 1 mg / 4 mL.

5. The method according to claim 1, characterized in that, In step (1), molecular sieve nanosheets are dispersed in deionized water.

6. The method according to claim 1, characterized in that, In step (2), the intensity of the ultraviolet light is 24800-27600 μW / cm. 2 .

7. The method according to claim 1, characterized in that, In step (2), the initial state of the suspension is a uniform milky white solution, which becomes a transparent colorless solution after ultraviolet ozone treatment.

8. The method according to claim 1, characterized in that, In step (2), the stirring speed is 500-1000 rpm.

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