Preparation method of flaky mesoporous material with consideration of specific surface area and mechanical strength

Abstract

This invention discloses a method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength, comprising: S1, taking organic additives and inorganic ordered mesoporous material powder in a mass ratio of 0.2~1.0:100 and spray coating them to form a premix; S2, pressing and shaping the premix to obtain a sheet-like preform; S3, heating the sheet-like preform to 500℃ and holding it at that temperature to obtain the sheet-like mesoporous material. This method achieves a dynamic balance between pore structure retention and mechanical enhancement through hydrogen bonding / complexation between additive molecules and silanol groups, two-stage stress regulation during the pressing process, and a slow-release stress mechanism during sintering. The resulting sheet-like mesoporous material SBA-15 has a specific surface area retention rate ≥76%, pore size retention rate ≥85%, pore order retention rate ≥80%, compressive modulus ≥41.38MPa, and fracture energy ≥0.238MPa.

Description

Technical Field

[0001] This invention relates to the field of inorganic porous material forming and structure control technology, specifically to a method for preparing sheet-like mesoporous materials that balances specific surface area and mechanical strength. Background Technology

[0002] Mesoporous molecular sieve materials (such as SBA-15) have broad application prospects in adsorption separation, catalytic reactions, energy storage, and biomedicine due to their regular pore structure, high specific surface area, and tunable pore size distribution. However, in practical applications, these materials usually need to be prepared into bulk, sheet, or particle forms with certain morphology and size to meet the operational strength and cycle stability requirements of industrial use.

[0003] Existing methods for forming mesoporous molecular sieve materials typically include direct pressing, organic additive molding, sol-gel casting, and inorganic binder or filler reinforcement. However, among these methods, direct pressing results in brittle, easily broken sheets with low mechanical strength. High-strength sheets usually require high binder content, but this sacrifices pore structure and specific surface area. For example, in organic additive molding, binders are introduced to improve formability, but during subsequent high-temperature processing, the binders are prone to rapid pyrolysis, leading to pore collapse or partial deactivation of the pore structure, resulting in a significant decrease in specific surface area. In inorganic binder or filler reinforcement, mechanical reinforcement is achieved by doping with alumina, silica, or other inorganic particles, but these methods introduce additional non-mesoporous components, weakening the mesoporous order and purity of the material, which is detrimental to catalytic and adsorption performance.

[0004] In summary, existing technologies generally suffer from the following problems: First, it is difficult to balance maintaining pore structure and mechanical enhancement. Conventional methods either maintain specific surface area but lack sufficient strength and are prone to breakage, or improve mechanical properties but are accompanied by a severe decrease in pore order and specific surface area. Second, they have poor cyclic stability. Under repeated loading or water treatment environments, both mechanical strength and pore structure are prone to degradation, making it difficult to meet the needs of sustainable applications. Finally, existing technologies have limited applicability. Most methods are only applicable to a single system and lack universality for promotion to other mesoporous materials such as MCM-41 and KIT-6. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing sheet-like mesoporous materials that combine specific surface area and mechanical strength. This invention can solve the problem of difficulty in simultaneously maintaining pore structure and enhancing mechanical strength in existing inorganic ordered mesoporous materials, especially in the SBA-15 molding technology.

[0006] A method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength includes the following steps: S1. Weigh out organic additives and inorganic ordered mesoporous material powder in a mass ratio of 0.2~1.0:100; dissolve the organic additives in deionized water to form an additive aqueous solution with a mass concentration of 5%; atomize the additive aqueous solution into fine droplets through an atomizing nozzle and spray it evenly onto the surface of the inorganic ordered mesoporous material powder to obtain wet powder; dry the wet powder at a temperature of 50~70℃ until completely dry to obtain premix; S2. Place the premixed material into the tableting mold, pre-press it for 30 seconds under a pressure of 50MPa, and then final press it for 10 minutes under a pressure of 200~230MPa to obtain a sheet-like preform. S3. The sheet-like preform is heated in air or an inert atmosphere at a heating rate of 1~3℃ / min until it reaches 500℃. Then, it is held at that temperature for 5 hours to obtain a sheet-like mesoporous material.

[0007] Explanation: The above method controls the ratio of organic additives to inorganic ordered mesoporous materials and the atomization spraying process to achieve uniform dispersion and efficient adsorption of additives on the material surface. Combined with staged gradient pressure molding and heat treatment, it significantly improves the mechanical strength and thermal stability of the material while retaining the high specific surface area and ordered pore structure of the mesoporous material. It effectively solves key problems in traditional methods such as uneven additive distribution, easy cracking during molding, and pore collapse caused by high-temperature sintering.

[0008] Furthermore, the inorganic ordered mesoporous material powder is one of SBA-15 powder, MCM-41 powder, and KIT-6 powder.

[0009] Note: The above examples of typical inorganic ordered mesoporous material powders such as SBA-15, MCM-41, or KIT-6 demonstrate that the method can effectively avoid the pore collapse and decrease in specific surface area caused by traditional high-temperature sintering, and can significantly enhance the compressive strength and thermal stability of the material.

[0010] Furthermore, the SBA-15 powder has a pore size of 2~15nm and a specific surface area of ​​600~1000m². 2 / g.

[0011] Note: The above method further limits the properties of the powder, providing specific parameters for optimizing the prepared sheet material.

[0012] Further, in S1, the organic additive is any one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylamide, or polyvinylpyrrolidone.

[0013] Note: The above-mentioned organic additives undergo slow pyrolysis during sintering, forming a stress buffer layer, thereby reducing the risk of pore collapse and improving the mechanical properties of the finished product. Among them, polyvinyl alcohol provides excellent film-forming and bonding properties, sodium carboxymethyl cellulose enhances powder dispersion stability, polyacrylamide improves slurry rheology and anti-settling properties, and polyvinylpyrrolidone has both solubility and surface activity. Single or composite additives can be flexibly selected according to the specific application scenario of the target mesoporous material, and the mechanical strength, pore structure retention rate and surface functionalization effect during the material forming process can be precisely controlled, providing multi-dimensional performance optimization technical support for the large-scale preparation of high-performance mesoporous materials.

[0014] Furthermore, the thickness of the sheet-like blank is 1~3 mm, and the diameter is 12.7 mm.

[0015] Note: By limiting the thickness and diameter of the sheet-like blank, the above measures ensure that the blank has suitable heat transfer efficiency and uniform stress distribution during subsequent heat treatment. This size range takes into account both the mechanical strength and functional density of the material, providing a key structural parameter control basis for the stable preparation and industrial application of high-performance mesoporous materials.

[0016] Furthermore, the inert atmosphere is argon or helium.

[0017] Note: In the presence of an inert gas, oxidative decomposition or pore structure collapse of mesoporous materials during high-temperature heat treatment can be prevented, while ensuring thermal conductivity and diffusion reaction, thus improving the process reliability and product consistency of high-performance mesoporous material preparation.

[0018] The beneficial effects of this invention are: This invention balances pore structure preservation and mechanical enhancement, solving the problems of pore collapse and insufficient mechanical properties after inorganic ordered mesoporous material powder molding. The sheet-like SBA-15 material possesses high specific surface area and high porosity, enabling efficient adsorption of organic pollutants and heavy metal ions in water treatment. Its excellent mechanical strength allows for recycling and reuse, demonstrating significant economic efficiency and sustainability. This method can also be extended to mesoporous materials such as MCM-41 and KIT-6, and can be widely applied in catalysis, adsorption separation, and other applications. This invention also has the following advantages: Balancing pore structure and mechanical properties: Through the synergistic effect of the interaction between the additive and silanol groups, and two-stage tableting and programmed sintering, a balance between pore structure preservation and mechanical enhancement is achieved, resulting in excellent mechanical and cyclic stability. Furthermore, it requires no additional inorganic fillers, is simple to operate, and has a wide range of applications, making it suitable for large-scale preparation of inorganic ordered mesoporous material systems such as MCM-41 and KIT-6. Attached Figure Description

[0019] Figure 1 This is a graph showing the effect of different tableting pressures on the pore size and specific surface area of ​​SBA-15. Figure 2 This is a graph showing the effect of different sintering temperatures on the pore size and specific surface area of ​​SBA-15. Figure 3 This is a graph showing the effect of different compression pressures on the mechanical properties of SBA-15. Figure 4 This is a graph showing the effect of different additive amounts on the mechanical properties of SBA-15; Figure 5 It is a nitrogen adsorption-desorption curve of SBA-15 with H1 type hysteresis loop; Figure 6 This is the aperture distribution diagram of SBA-15. Detailed Implementation

[0020] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0021] As can be seen from the background art, existing methods often improve the mechanical strength of mesoporous materials while causing pore collapse, loss of specific surface area and pore order, or insufficient mechanical properties while maintaining the pore structure, resulting in materials that are brittle, have poor cycle stability, and are difficult to meet the engineering requirements of long-term use and water treatment. Furthermore, existing methods lack universality and are difficult to extend to other mesoporous material systems. Therefore, this invention provides specific methods in the following embodiments: Example 1: A method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength; this example illustrates the preparation method of sheet-like SBA-15: Step 1: Preparation of SBA-15 powder; 100 mL of ultrapure water was mixed with 20 mL of 38% hydrochloric acid solution, and 3.2 g of triblock copolymer P123 was added. The mixture was stirred at 50 °C and 400 rpm to dissolve the copolymer. After P123 was completely dissolved, different doses of decane (or trimethylbenzene) were added as pore expanders, and the mixture was stirred for another 30 min. Then, 9 mL of tetraethyl orthosilicate (TEOS) was added as a silicon source, and the mixture was stirred under heating conditions for 24 h. The resulting mixed solution was subjected to a hydrothermal reaction at 100 °C for 24 h to obtain a white precipitate. The product was centrifuged, filtered, and washed with water, then dried at 60 °C and calcined at 550 °C to remove the template agent, yielding SBA-15 powder with an ordered hexagonal mesoporous structure. The pore size of SBA-15 can be effectively controlled by adjusting the amount of pore expander (decane or trimethylbenzene). Step 2: BET specific surface area and pore size analysis; The SBA-15 powder obtained in step one was vacuum dried at 120℃ for 12h to remove surface adsorbed moisture, and then analyzed using a nitrogen adsorption-desorption tester at 77K; the mass of the test sample was approximately 200mg, the specific surface area was calculated using the multi-point BET method, and the pore size distribution was calculated using the BJH method. Figure 5 , Figure 6 Test results show that the specific surface area of ​​SBA-15 powder is 820 m². 2 / g, with an average pore size of 4.5nm, and the nitrogen adsorption-desorption isotherm exhibits a typical type IV curve with a distinct H1 type hysteresis loop, indicating that the material has a high specific surface area and an ordered mesoporous structure; this result serves as a basic performance reference before subsequent molding. Step 3: Forming and sintering sheet-like SBA-15; S1. Weigh out the organic additive and inorganic ordered mesoporous material powder SBA-15 powder at a mass ratio of 0.5:100. The pore size of the SBA-15 powder is 2~15nm, and the specific surface area of ​​the SBA-15 powder is 600~1000 m². 2 / g; the organic additive is polyvinyl alcohol; Organic additives are dissolved in deionized water to form an additive aqueous solution with a mass concentration of 5%. The additive aqueous solution is atomized into fine droplets through an atomizing nozzle and evenly sprayed onto the surface of inorganic ordered mesoporous material powder to obtain wet powder. The wet powder is dried completely at a temperature of 60°C to obtain premix. S2. Place the premixed material into a tableting mold with a diameter of 1 / 2 inch (i.e. 12.7 mm). First, pre-press it under a pressure of 50 MPa for 30 seconds to form the shape, and then final press it under a pressure of 217 MPa for 10 minutes to solidify it, so as to obtain a sheet-like preform. The thickness of the sheet-like preform is 2 mm. S3. Under an argon atmosphere, the sheet-like preform is heated at a heating rate of 2℃ / min until it reaches 500℃. Then, it is held at that temperature for 5 hours to obtain the sheet-like mesoporous material. During the sintering process, PVA gradually pyrolyzes and releases gas, forming a stress-relieving layer that effectively prevents the pore walls from collapsing, ultimately resulting in a sheet-like SBA-15 material with both high porosity and mechanical strength. The additives form a stress buffer layer during the slow-release pyrolysis process, effectively preventing the pore walls from collapsing, thus obtaining a sheet-like SBA-15 finished product with both high specific surface area and mechanical strength. Through the above technical solutions, the embodiments of the present invention significantly improve the mechanical properties of SBA-15 material while maintaining its ordered pore structure and high specific surface area. Specifically, the obtained sheet-like SBA-15 has a specific surface area retention rate of ≥76%, a pore size retention rate of ≥85%, a compressive modulus of ≥41.38 MPa, a fracture energy of ≥0.238 MPa, and retains ≥90% of its compressive modulus after at least 5 cycles of loading and unloading, demonstrating excellent cyclic stability. In existing technologies, mesoporous materials typically have a specific surface area of ​​60-70% and a pore size of 70-80%. After being compressed into tablets, they generally have a compressive modulus of 10-20 MPa and a fracture energy of less than 0.1 MPa. Conventional technologies consider that it is difficult for such materials to simultaneously achieve both adsorption performance (specific surface area and pore size) and mechanical properties (compressive modulus and fracture energy). When the specific surface area and pore size increase, their compressive modulus and fracture energy will decrease accordingly. In existing technologies, in order to ensure one application, the other application is often sacrificed. As a result, the application range of mesoporous materials is greatly limited. Compared with existing technologies, the embodiments of the present invention solve the technical contradiction of "difficulty in maintaining pore structure and mechanical enhancement" in traditional processes through the synergistic effect of organic additive-silanol interaction, two-stage tableting and programmed temperature-controlled sintering. It avoids pore collapse and specific surface area loss, and achieves a dynamic balance between pore structure integrity and mechanical strengthening. At the same time, this method does not require the introduction of additional inorganic fillers, the process is simple and has good universality, and can be widely applied to various mesoporous materials such as MCM-41 and KIT-6, with significant engineering application value and sustainability.

[0022] (1) Investigate the effect of the dosage of adjuvants on the performance of SBA-15 tablets; Comparative Example 1: The difference from Example 1 is that the amount of organic additive is different, and the amount of organic additive is 0.1%.

[0023] like Figure 4 As shown, comparing Example 1 of the present invention with Comparative Example 1, the results show that the specific surface area retention rate of the sintered SBA-15 material decreased to 62%, the pore size retention rate was only 72%, the compressive modulus decreased to 23.5 MPa, and the fracture energy was only 0.118 MPa. During cyclic loading, the sample was prone to fracture, and the modulus retention rate was less than 70%. This indicates that when the amount of additives is insufficient, the flexible support layer cannot be effectively formed, and the pore structure is prone to collapse during sintering, resulting in a decrease in both pore structure and mechanical properties.

[0024] Example 2: The difference from Example 1 is that the amount of organic additive is different, and the amount of organic additive is 0.2%.

[0025] Example 3: The difference from Example 1 is that the amount of organic additive is different, and the amount of organic additive is 1%.

[0026] Comparing Example 1 with Examples 2 and 3 of this invention, i.e., comparing the molding effects of different amounts of additives, it was found that when the amount of organic additive added is controlled at 0.2-1%, the resulting sheet-like SBA-15 material can achieve a good balance between mechanical properties and pore structure maintenance. On the one hand, the amount of additive within this range is sufficient to form a uniform support layer on the powder surface, thereby significantly improving the strength and fracture toughness after tableting. On the other hand, this amount will not cause excessive blockage of mesoporous channels, ensuring the integrity and orderliness of pore size distribution. Further exploration showed that when the amount of additive added is 0.5%, the molding effect is optimal, and the resulting material has both high compressive modulus and fracture energy, while maintaining good specific surface area and pore size orderliness. In conventional powder forming processes (such as tableting and granulation), adding a certain proportion of organic binder (such as polymers) is standard practice to obtain a green body with sufficient mechanical strength. However, in traditional technologies, the proportion of organic binder added is generally between 3% and 20% to ensure that the powder particles are fully coated and adhered to, so as to withstand the pressure during the pressing process and the strength requirements after demolding. If the amount of binder is drastically reduced to 0.2% to 1.0% using traditional technologies, problems such as loose tablets, cracking, or even failure to form tablets at all may occur.

[0027] This invention precisely locates the critical parameter range of 0.2~1.0% by optimizing the dosage of additives and the spray coating process. It proposes a step of first spray coating, followed by two-stage stress control and sintering temperature selection. The atomized and uniformly dispersed organic additives form a continuous flexible support layer on the powder surface, thereby achieving effective molding even under low addition conditions. At the same time, it significantly improves the compressive modulus and fracture energy of the sheet, and maintains the pore size distribution and pore channel order. (2) Investigate the effect of sintering temperature on the properties of sheet-like SBA-15; Comparative Example 2: The difference from Example 1 is that the temperature was raised to 800 °C and then kept at that temperature.

[0028] Comparative Example 3: The difference from Example 1 is that the temperature was raised to 400 °C and then kept at that temperature.

[0029] like Figure 2 As shown, under the conditions of Comparative Example 2, the specific surface area retention of the sample decreased to 39%, and the pore size shrank by more than 50%. Although the compressive modulus increased slightly to 47 MPa, the nitrogen adsorption-desorption curve showed that the pore structure was completely disordered and no longer exhibited the typical H1-type loop curve, indicating that the mesoporous structure was severely damaged. The results of the cyclic experiment further showed that the modulus retention was less than 60%, and the long-term performance of the material was poor. This result indicates that excessively high sintering temperature can cause the silicon wall to shrink or even partially crystallize, thereby causing the pore structure to collapse. Although the mechanical properties are improved, the mesoporous characteristics are sacrificed.

[0030] Under the conditions of Comparative Example 3, the specific surface area and pore size retention rate of the sample were basically maintained above 70%, indicating that the low temperature did not cause significant damage to the pore structure. However, due to the insufficient temperature to effectively trigger the bonding effect between particles, the internal bonding force of the sheet was limited, resulting in a compressive modulus of only 18.6 MPa and a fracture energy of less than 0.12 MPa. Microcracks were easily generated during cyclic loading, and the overall mechanical strength was low. This result indicates that it is difficult to form a stable particle bridging structure when the sintering temperature is too low. Although the material can maintain the pore characteristics, its mechanical properties are insufficient to meet the requirements of long-term application.

[0031] (3) Investigate the effect of tableting process on the performance of SBA-15 tablets; Comparative Example 4: The difference from Example 1 is that the tableting process uses a single compression, that is, it is directly compressed at a pressure of 217 MPa for 10 min without pre-compression.

[0032] Test results showed that the specific surface area retention rate decreased to 54%, the pore size retention rate was 65%, the compressive modulus was 29.6 MPa, and the fracture energy was 0.162 MPa. Compared with Example 1, this sample showed obvious edge cracks during loading, and the cyclic modulus retention rate was only 72%. The results indicate that stress concentration during a single high-pressure tableting process can easily lead to pore wall failure, resulting in the pore structure and mechanical properties not reaching the optimal level. The results from the combined examples and comparative examples show that the present invention, through multi-parameter synergistic optimization of additive-silanol interaction, two-stage tableting, and programmed temperature-controlled sintering, significantly improves the mechanical strength and cycle stability of sheet-like SBA-15 while maintaining the integrity of the pore structure and high specific surface area. In contrast, insufficient additives, excessively high sintering temperatures, or single-stage tableting can all cause pore collapse or a decrease in mechanical properties, making it impossible to achieve both. The process proposed in this invention achieves a dynamic balance between maintaining the pore structure and enhancing mechanical properties, demonstrating significant advantages.

[0033] Example 4: The difference from Example 1 is that in S2, the material is first pre-pressed at 50MPa for 30s to form, and then finally pressed at 200MPa for 10min to set.

[0034] Example 5: The difference from Example 1 is that in S2, the material is first pre-pressed at 50MPa for 30s to form, and then finally pressed at 230MPa for 10min to solidify.

[0035] like Figure 1 and Figure 3As shown, comparing the molding effects under different final pressures reveals that when the final pressure is 200 MPa, although the resulting sheet has a certain degree of formability, the interparticle bonding is not tight enough, resulting in low compressive modulus and fracture energy, and insufficient mechanical properties. When the final pressure is further increased to 230 MPa, although the mechanical strength is improved, excessive pressure can cause local collapse of the pore walls, leading to a decrease in specific surface area and pore size retention, and disruption of the pore structure order. Considering both mechanical properties and pore structure retention, a final pressure of 217 MPa achieves the best balance between compaction and pore retention. The resulting sheet possesses both high compressive modulus and fracture toughness, while maintaining good specific surface area and pore size distribution, thus representing the optimal pressure condition.

[0036] (4) Investigate the effect of heating rate on the performance of sheet-like SBA-15; Example 6: The difference from Example 1 is that the heating rate in S3 is 1℃ / min.

[0037] Example 7: The difference from Example 1 is that the heating rate in S3 is 3℃ / min.

[0038] Comparing the experimental results (Examples 1, 6, and 7) under different heating rates, it can be seen that when the heating rate is 1℃ / min, the temperature change of the system is too slow. Although the pore structure can be well maintained, the sintering effect between particles is insufficient, and the improvement of the mechanical properties of the sheet is limited. The compressive modulus and fracture energy are both lower than the ideal values. When the heating rate is increased to 3℃ / min, although a strong sintering bond can be achieved in a short time, the stress accumulation caused by the rapid heating is prone to cause pore wall collapse and cracks, resulting in a decrease in specific surface area and pore size retention. Considering the mechanical enhancement effect and the pore structure retention, the heating rate of 2℃ / min can achieve the best balance, which can ensure the compressive modulus and fracture toughness of the sheet, and maintain a high degree of pore structure integrity and order.

[0039] Example 2: The difference between this example and Example 1 is that the organic additive is sodium carboxymethyl cellulose and the inorganic ordered mesoporous material is MCM-41.

[0040] Example 3: The difference between this example and Example 1 is that the organic additive is a mixture of polyacrylamide and polyvinylpyrrolidone in a mass ratio of 1:1, and the inorganic ordered mesoporous material is KIT-6.

Claims

1. A method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength, characterized in that, Includes the following steps: S1. Weigh out organic additives and inorganic ordered mesoporous material powder in a mass ratio of 0.2~1.0:100; dissolve the organic additives in deionized water to form an additive aqueous solution with a mass concentration of 5%; atomize the additive aqueous solution into fine droplets through an atomizing nozzle and spray it evenly onto the surface of the inorganic ordered mesoporous material powder to obtain a wet powder; dry the wet powder at 50~70℃ until completely dry to obtain a premix. S2. Place the premixed material into the tableting mold, pre-press it for 30 seconds under a pressure of 50MPa, and then final press it for 10 minutes under a pressure of 200~230MPa to obtain a sheet-like preform. S3. Under an inert atmosphere, the sheet-like preform is heated at a heating rate of 1~3℃ / min until it reaches 500℃. Then, it is held at that temperature for 5 hours to obtain a sheet-like mesoporous material. The inorganic ordered mesoporous material powder is one of SBA-15 powder, MCM-41 powder, and KIT-6 powder; In S1, the organic additive is one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylamide, or polyvinylpyrrolidone.

2. The method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength as described in claim 1, characterized in that, The SBA-15 powder has a pore size of 2~15 nm and a specific surface area of ​​600~1000 m². 2 / g.

3. The method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength as described in claim 1, characterized in that, The sheet-like blank described in S2 has a thickness of 1~3mm and a diameter of 12.7mm.

4. The method for preparing a sheet-like mesoporous material that balances specific surface area and mechanical strength as described in claim 1, characterized in that, The inert atmosphere is argon or helium.

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