Method for removing microporous molecular sieve template agent through cooperation of ultraviolet and ozone

Abstract

The invention discloses a method for removing a microporous molecular sieve template agent through cooperation of ultraviolet and ozone, and the efficient decomposition of an organic template agent in a pore channel is successfully realized by utilizing the synergistic effect of dual-band ultraviolet light (185nm and 254nm). The ultraviolet light of 185 nm has higher photon energy and can directly excite water molecules (H2O) to generate a large number of hydroxyl radicals (. OH) and monatomic oxygen (O), and meanwhile oxygen (O2) in the solution is converted into ozone (O3). 254nm ultraviolet light further enhances the concentration of free radicals generated by ozone decomposition, and improves the efficiency of oxidation reaction. The 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 thorough removal of the template agent is achieved.

Description

Technical Field

[0001] The invention relates to the field of synthesis of molecular sieve materials, and in particular to a method for removing microporous molecular sieve templates in a coordinated manner using ultraviolet and ozone. Background Art

[0002] Molecular sieves are a class of inorganic materials with regular microporous structures, which are widely used in gas separation, catalysis and adsorption. In the synthesis process of molecular sieves, templates are an indispensable key component used to induce crystal growth and regulate pore structure. However, since templates occupy the pores of molecular sieves, thus limiting their practical application, the templates must be completely removed after synthesis. At present, the commonly used methods for removing templates include high-temperature calcination, solvent extraction, chemical oxidation and plasma treatment. Among them, high-temperature calcination is the most widely used industrial method because it is efficient in oxidative decomposition of templates and is easy to operate; while solvent extraction and chemical oxidation are removed by dissolution or decomposition, and the operating conditions are relatively mild. Plasma technology has also received some attention due to its low temperature and high efficiency. These methods meet the needs of template removal to a certain extent, but there are also many shortcomings.

[0003] The main problems with existing methods are: high-temperature calcination can easily cause local collapse of the molecular sieve structure or interlayer stacking of two-dimensional molecular sieves, significantly reducing the dispersibility and utilization rate of the material; although solvent extraction and chemical oxidation have little effect on the structure, the removal efficiency of organic templates contained in microporous materials is very low and the cost is high; and plasma treatment is difficult to promote on a large scale due to expensive equipment and complex operation. In addition, these methods generally have problems such as high energy consumption and severe environmental pollution, and are particularly unsuitable for two-dimensional molecular sieves with high surface area and ultra-thin characteristics. Therefore, developing a green, low-cost and non-destructive method for removing templates has become one of the key challenges to achieving the industrialization and efficient application of molecular sieves. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for removing the template of microporous molecular sieve in collaboration with ultraviolet ozone, which is particularly suitable for removing the template of two-dimensional molecular sieve materials.

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

[0006] A method for removing a template agent in a microporous molecular sieve by ultraviolet ozone technology, comprising:

[0007] (1) directly dispersing the synthesized molecular sieve nanosheets in water to form a molecular sieve aqueous solution;

[0008] (2) irradiating the molecular sieve aqueous solution with dual-band ultraviolet light having wavelengths of 185 and 254 nm, and continuously stirring and reacting until the suspension becomes a transparent solution;

[0009] (3) The transparent solution obtained in step (2) is filtered to collect the solid product by vacuum filtration to obtain the molecular sieve nanosheets with the template removed.

[0010] This method uses the synergistic effect of dual-band ultraviolet light (185nm and 254nm) to successfully achieve efficient decomposition of organic templates in the pores. The 185nm ultraviolet light has higher photon energy and can directly excite water molecules (H2O) to generate a large number of hydroxyl radicals (·OH) and monatomic oxygen (O), while converting oxygen (O2) in the solution into ozone (O3). The 254nm ultraviolet light further enhances the concentration of free radicals generated by ozone decomposition and improves the efficiency of the oxidation reaction. These highly active oxidants can react quickly with organic templates, decomposing them into harmless small molecules such as carbon dioxide (CO2) and water (H2O), and ultimately achieving complete removal of the template. This method is suitable for removing the pore structure occupied by the organic template in the molecular sieve nanosheets, thereby restoring the micropore distribution characteristics of the molecular sieve. In the process of removing the template, the high-temperature calcination step is avoided, effectively preventing the agglomeration and performance degradation of the nanosheets, and achieving complete removal of the template. This method does not produce corrosive waste liquid, only uses water and ultraviolet light, and meets environmental protection requirements. In addition, it does not require complex multi-step rinsing, and the treatment can be completed after illumination. It is simple to operate and safer. Compared with traditional high-temperature roasting and piranha solution treatment methods, this technology not only performs better in removal efficiency and structural protection, but also significantly improves the safety and environmental protection of the experiment, providing a better alternative for the preparation process 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 nanosheet is a microporous material.

[0013] Furthermore, the concentration of the molecular sieve aqueous solution ranges from 1 mg / 80 ml to 1 mg / 4 ml. If the concentration is too high, ultraviolet light cannot penetrate the solution, resulting in a decrease in the content of active oxygen or a lower removal efficiency of the template.

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

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

[0016] Furthermore, in step (1), stirring and reacting are continued for at least three days, during which water needs to be added regularly. On the one hand, water molecules are decomposed after being irradiated by the ultraviolet lamp, and on the other hand, the irradiation of the ultraviolet lamp generates heat, which increases the temperature of the reaction system and causes the volatilization of water.

[0017] Furthermore, in step (2), the initial state of the suspension is a uniform milky white solution, which becomes a transparent colorless solution after being treated with ultraviolet ozone. The initial milky white state is caused by the opacity of the template. After the template is removed, the pores are opened and the suspension becomes transparent after light is transmitted.

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

[0019] The technical solution provided by the embodiments of the present application may have the following beneficial effects:

[0020] As can be seen from the above embodiments, the present application uses ultraviolet ozone treatment technology to efficiently remove the organic template in the molecular sieve under mild conditions, thereby overcoming the disadvantages of the traditional high-temperature calcination method in damaging the molecular sieve structure, and avoiding the limitations of other methods in terms of energy consumption, cost and applicability. The method excites the oxygen in the aqueous solution to form active oxygen species (such as ozone and hydroxyl radicals) through the dual-band ultraviolet light generated by the ultraviolet lamp, thereby oxidizing and degrading the template molecules, converting them into carbon dioxide and water, and completely removing the template residues. The present application has a number of advantages: first, the method is carried out at a lower temperature and aqueous solution system, avoiding the stacking and structural damage of the molecular sieve caused by high-temperature calcination, effectively preventing the agglomeration and performance degradation of the nanosheets, and removing the organic template occupied in 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; secondly, the method does not require the use of expensive or toxic reagents, is low in cost, and does not require complex equipment, and has good industrialization potential; finally, the ultraviolet ozone treatment process is clean and environmentally friendly, and the reaction only generates harmless carbon dioxide and water, which meets the requirements of sustainable development. In summary, the present invention provides a new method for removing templates that is efficient, green and scalable, providing important support for the industrial production and application of molecular sieve materials.

[0021] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] Figure 1 A schematic diagram of a method for gently removing molecular sieve nanosheet template provided in this application.

[0024] Figure 2 Comparison of the reaction solution before and after removing the template.

[0025] Figure 3 The scanning electron microscope pictures before and after the template is removed in Example 1.

[0026] Figure 4 This is the Fourier transform image before and after removing the template in Example 1.

[0027] Figure 5 This is the thermogravimetric curve before and after removing the template in Example 1.

[0028] Figure 6 ] are the nitrogen adsorption-desorption curves and pore size distribution before and after the template agent is removed in Example 1, wherein A is the nitrogen adsorption isotherm curve before and after ultraviolet treatment, and B is the pore size distribution of the nanosheets before and after ultraviolet treatment. DETAILED DESCRIPTION

[0029] Here, exemplary embodiments are described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application.

[0030] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0031] In order to more effectively remove the template in the molecular sieve nanosheets while maintaining the integrity of its microporous structure, the present invention provides a low-temperature treatment method based on ultraviolet ozone technology, and the specific implementation steps are as follows:

[0032] Example 1: UV-ozone method to remove the template in the molecular sieve nanosheets, such as Figure 1 As shown, the method includes:

[0033] (1) dispersing the synthesized molecular sieve nanosheets (such as b-axis oriented ultrathin MFI nanosheets) 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 evenly distributed by moderate stirring to form a milky white emulsion. In this embodiment, the molecular sieve nanosheets used have a microporous structure, and the pore size along the b-axis is 0.53×0.56 nanometers;

[0035] (2) placing the nanosheet dispersion obtained in step (1) in a reaction container, controlling the reaction temperature at 58° C., irradiating the emulsion with an ultraviolet lamp having a wavelength of 185-254 nm, stirring with a magnetic stirrer, and setting the rotation speed between 500 and 1000 rpm. The reaction container is tightly wrapped with aluminum foil to prevent damage to the human body caused by ultraviolet rays;

[0036] Specifically, the irradiation of the ultraviolet lamp excites the oxygen to decompose and generate ozone, and the ozone reacts with the template to produce carbon dioxide gas (such as Figure 2 The treatment process lasts for about 3 days until the emulsion gradually changes from milky white to a transparent colorless solution, as shown in FIG. Figure 2 This process avoids the high energy consumption and damage to the nanosheet structure of the traditional high-temperature calcination method, and can achieve gentle and thorough template removal.

[0037] (3) Solid collection and purification steps

[0038] To further remove possible byproducts or residues, the clear solution obtained in step (2) is filtered by vacuum to collect the solid product. The obtained solid is then redispersed in deionized water to form a uniformly dispersed nanosheet solution, such as Figure 3 As shown in the scanning electron microscope images in the figure, the dispersion of the nanosheets before and after the reaction is very good, and there is no agglomeration phenomenon.

[0039] The template agent of the molecular sieve nanosheets treated by the above method is completely removed, and the complete microporous structure and excellent dispersion performance are retained. Figure 4 ) found that the wave number is 2700-3200cm -1 The characteristic peaks of organic matter at the position disappeared obviously, and the thermal gravimetric curve ( Figure 5 ), the nanosheets treated with UV light and calcined showed no thermal weight loss in the range of 300-500℃, but the synthesized nanosheets containing organic matter had a 14% thermal weight loss in this range. Finally, the nitrogen adsorption-desorption curve ( Figure 6 ) verified that the nanosheets after UV treatment have microporous structures, such as Figure 6 A in, 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 residue, the crystal structure is complete, and the micropore size distribution is uniform.

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

[0041] In order to remove the template in the MFI nanosheets, the dried nanosheet samples were placed in a tube furnace and treated with high-temperature calcination. The specific steps are as follows: the sample was placed in a porcelain boat and placed in a tube furnace. Under air atmosphere conditions, 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 the calcination process, the template decomposed and volatilized to form a pure inorganic framework structure.

[0042] After calcination, the sample was cooled to room temperature and taken out. It was observed that the calcined MFI nanosheets agglomerated into white agglomerates, and the strong van der Waals interaction between the particles made it difficult to redisperse them in the solution. This agglomeration phenomenon may have an adverse effect on the subsequent dispersibility and application performance of the nanosheets.

[0043] Further analysis shows that high temperature calcination can effectively remove the template ( Figure 4 , Figure 5 , Figure 6 ), but at the same time, the surface of the nanosheets will shrink or have defects to a certain extent, thus limiting subsequent applications. In addition, the calcination method has high energy consumption and is accompanied by the emission of harmful gases. These phenomena suggest that other methods of removing the template (such as low-temperature UV-ozone treatment) need to be explored to reduce the agglomeration effect and maintain the good dispersion of the nanosheets.

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

[0045] In order to remove the organic template in the pores of the molecular sieve nanosheets, a highly active piranha solution (a mixed solution of concentrated sulfuric acid and hydrogen peroxide) (pH = 0-1) was used for treatment. This method uses the strong oxidizing property of the piranha solution to oxidize and decompose the organic template in the pores. However, the experimental results show that ( Figure 4 , Figure 5 , Figure 6 ), although part of the template was effectively removed, there was still a small amount of residue that was difficult to completely remove. By Fourier transform infrared spectroscopy (FTIR) ( Figure 4 ) found that the wave number is 2700-3200cm -1 The characteristic peaks of organic matter still exist, and the thermal gravimetric curve ( Figure 5 ), the nanosheets treated with ozone showed obvious thermal weight loss in the range of 300-500℃. Finally, the nitrogen adsorption-desorption curve ( Figure 6 ) verified that the nanosheets treated with piranha solution did not have a microporous structure. Figure 6 In A, there is no micropore adsorption curve. Figure 6Figure B also shows that there are no micropores in the nanosheet, and organic matter is still blocked in the pores. These residual organic matter may hinder the complete penetration and reaction of the piranha solution and active hydroxyl groups due to the high depth of the pores and the complex pore structure. In addition, this treatment method has the disadvantages of cumbersome operation steps and high safety risks. Especially in the preparation and treatment of the solution, extreme caution is required to avoid the danger of high temperature or volatile reactions. After treatment, multiple steps of deionized water and ethanol rinsing are required to completely remove residual chemical reagents. This inefficient treatment method not only increases the 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] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application.

Claims

1. A method for removing microporous molecular sieve templates by synergistic use of ultraviolet and ozone, characterized in that: include: (1) directly dispersing the synthesized molecular sieve nanosheets in water to form a molecular sieve aqueous solution; (2) irradiating the molecular sieve aqueous solution with dual-band ultraviolet light having wavelengths of 185 and 254 nm, and continuously stirring and reacting until the suspension becomes a transparent solution; (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 nanosheet is a microporous material.

4. The method according to claim 1, characterized in that: The concentration of the nanosheet aqueous solution ranges 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 being treated with ultraviolet ozone.

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

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