Method for preparing nano-porous titanium nitride aerogel by template method

Abstract

The invention relates to nano porous titanium nitride aerogel prepared by a template method, and belongs to the technical field of aerogel material preparation processes. The preparation method comprises the following steps: delignification is carried out by taking wood as an organic precursor, then wood aerogel is prepared by adopting a freeze-drying method, titanium sol-loaded porous wet gel is obtained by adopting an impregnation process, and then the lightweight nano-porous blocky TiN aerogel is prepared through the processes of supercritical drying, carbon thermal reduction and the like. The nano-porous TiN aerogel prepared by the invention not only has a complete blocky structure, but also has the characteristics of low density, high specific surface area, high temperature resistance, high heat insulation and the like, and has important significance in realizing the application of a TiN aerogel material in multiple fields of aerospace, high-temperature kilns, building energy conservation and the like.

Description

Technical Field

[0001] The present invention belongs to the field of aerogel material preparation technology, and relates to a method for preparing nanoporous titanium nitride aerogel by a template method, preparing a porous wet gel loaded with titanium sol by an impregnation process, and then combining freeze drying and high-temperature carbon thermal reduction process to prepare nanoporous titanium nitride (TiN) aerogel. Background Art

[0002] Aerogel is a nanoporous material composed of nanoparticles with an ultra-low bulk density (0.03-0.35 g·cm -3 ), high porosity (80-99%) and high surface area (500-1500m 2 ·g -1 ) and other unique properties. They have shown excellent performance in thermal insulation, catalyst carriers, drug carriers, cosmic particle collectors, energy conversion, storage materials, sensors and many other applications. Ceramic aerogels have excellent fire resistance and corrosion resistance and are considered to be one of the most promising candidates for thermal insulation materials. However, their practical applications are severely limited by their brittleness and volume shrinkage at high temperatures. Compared with traditional nitride ceramics, nanoporous TiN aerogels have good conductivity and attractive metallic luster, which gives them broad application prospects in the field of new ceramics. Zhang et al. (Materials Chemistry and Physics, 2021, 273: 125085.) prepared precursor wet gels using citric acid, tetrabutyl titanate and sodium carbonate as raw materials, and then prepared TiN aerogels by carbon thermal reduction. As far as we know, the TiN aerogels reported in the report were obtained by mixing TiO2 powder with different carbon sources, while there are few reports on synthesizing TiN aerogels by atomic mixing of carbon sources and titanium sources to prepare TiN aerogels with more uniform structure and excellent thermal insulation properties.

[0003] Therefore, in order to meet the growing demand for sustainable and high-performance materials, people are paying more and more attention to the development of bio-based ceramic aerogels with excellent thermal and mechanical properties. Among them, TiN ceramic aerogels synthesized from biological precursors have attracted widespread attention due to their potential applications in various fields such as aerospace engineering and energy storage. Han et al. (Journal of the European Ceramic Society, 2021, 41(10): 5127-37.) used titanium dioxide and chitosan as raw materials, and prepared TiN aerogels by freeze casting and CRN method at 1200 ° C. Although this method is technically feasible, it relies on chemically synthesized raw materials, which inevitably leads to high energy consumption and chemical pollution in the production process, which runs counter to the concept of sustainable development. In addition, these chemical raw materials also have obvious limitations in cost control and resource utilization efficiency. Therefore, in order to overcome the above defects and problems, it is still a huge challenge to synthesize efficient and environmentally friendly biomass titanium nitride ceramic aerogels and realize their application in aerospace, high-temperature kilns, building energy conservation and other fields. Summary of the Invention

[0004] The present invention aims to address the shortcomings of existing technologies by providing a method for preparing nanoporous titanium nitride aerogels using a template method. This method produces aerogels at a lower cost, with a larger specific surface area, higher porosity, higher temperature resistance, and greater thermal insulation properties. This method is of great significance for the application of TiN aerogels in a variety of fields, including aerospace, high-temperature furnaces, and building energy conservation.

[0005] The technical solution of the present invention is: a method for preparing nanoporous titanium nitride aerogel by a template method, the specific steps of which are as follows:

[0006] (1) Soaking the original wood in an alkaline solution and heating it in a water bath to 30-100°C for delignification treatment;

[0007] (2) performing solvent replacement on the sample obtained in step (1) in deionized water to remove impurities, freezing the sample in liquid nitrogen, and then freeze-drying the sample to obtain wood aerogel;

[0008] (3) mixing a titanium source, alcohol, acid solution, and water in a proportion at 15-40° C. to form a TiO sol, placing the wood aerogel obtained in step (2) in a sealed container, and immersing the aerogel in the TiO sol to age to obtain a composite wet gel;

[0009] (4) taking out the composite wet gel obtained in step (3) and soaking it in alcohol to remove impurities;

[0010] (5) drying the wet gel after removing impurities in step (4) to obtain an organic-inorganic hybrid aerogel;

[0011] (6) The organic-inorganic hybrid aerogel obtained by drying in step (5) is subjected to high-temperature heat treatment under nitrogen conditions to finally obtain biomass nanoporous TiN aerogel.

[0012] Preferably, in step (1), the native wood is balsa, pine, eucalyptus, willow or poplar; the mass ratio of wood to alkaline solution is 1:(1.5-10), the soaking times are 2-6 times, each time for 3-9 hours; the alkaline solution is one or more mixtures of sodium hydroxide or potassium hydroxide; and the mass concentration of the alkaline solution is 3-50%.

[0013] Preferably, the solvent replacement time in step (2) is 12 to 72 hours; the drying temperature of freeze drying is -60 to -5°C, and the drying time is 12 to 66 hours.

[0014] Preferably, in step (3), the titanium source is tetrabutyl titanate or one or more mixtures of isopropyl titanate; the alcohol is one of methanol, ethanol, propanol, butanol or ethylene glycol or a mixture thereof; the acid solution is one of hydrochloric acid, boric acid, phosphoric acid, hypochlorous acid or perchloric acid or a mixture thereof, wherein the mass concentration of the acid solution is 3-40%; the mass ratio of the titanium source, alcohol, acid solution and water is 1:(3-10):(1-4.5):(0.2-1), and the aging time is 5-36h.

[0015] Preferably, the alcohol in step (4) is one of ethanol, methanol, propanol, n-pentanol or isopropanol or a mixture thereof; the soaking times are 3 to 9 times, and the soaking time each time is 4 to 10 hours.

[0016] Preferably, the drying method described in step (5) is a carbon dioxide supercritical drying method: carbon dioxide is used as the drying medium, the reaction temperature is 40-70°C, the drying pressure is 8-15 MPa, the degassing rate is 4-16 L / min, and the drying time is 5-14 h.

[0017] Preferably, the high temperature heat treatment temperature in step (6) is 1000-1500° C., the heating rate is 2-8° C. / min, and the holding time is 2-7 h.

[0018] Beneficial effects:

[0019] The method of the present invention and the high-temperature resistant nanoporous TiN aerogel material using wood as raw material prepared by the method have the following characteristics:

[0020] (1) Using wood as raw material, the organic aerogel prepared by freeze-drying method has a typical aerogel porous structure, and the porous wet gel loaded with titanium sol is prepared by impregnation process. Then, the nanoporous TiN aerogel with low thermal conductivity is finally obtained by supercritical drying and carbon thermal reduction, realizing the successful preparation of high-temperature resistant nanoporous TiN aerogel.

[0021] (2) The obtained TiN ceramic aerogel material has high porosity, high specific surface area and nano-scale pores, and is in a complete block shape, which has positive significance for the application of aerogel materials in the field of thermal insulation.

[0022] (3) Novel process. The innovation of this work lies in the use of biomass materials as organic precursors to prepare lightweight porous bulk nanoporous TiN aerogels, abandoning the TiO2 nanopowder used in the traditional preparation of nanoporous TiN. This invention provides a new idea for the preparation of bulk porous nanoporous TiN aerogel materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The sample pictures of wood aerogel and nanoporous TiN aerogel in Example 1; (a) wood aerogel (b) nanoporous TiN aerogel

[0024] Figure 2 is the XRD pattern of the nanoporous TiN aerogel prepared in Example 2;

[0025] Figure 3 is a SEM image of the nanoporous TiN aerogel prepared in Example 3. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to examples, but the scope of protection is not limited thereto.

[0027] Example 1

[0028] Balsa wood blocks were delignified by soaking them in a 3% potassium hydroxide solution heated to 100°C in a waterbath at a mass ratio of 1:1.5. The samples were immersed in deionized water for 12 hours, then frozen in liquid nitrogen and freeze-dried at -60°C for 12 hours to produce wood aerogels. A TiO2 sol was prepared by mixing tetrabutyl titanate, ethanol, hydrochloric acid (3% by mass), and water in a mass ratio of 1:3:1:0.2 at 15°C. The resulting wood aerogels were placed in a sealed container and aged for 36 hours in the TiO2 sol to produce a composite wet gel. The composite wet gel was then removed and soaked in ethanol three times for 10 hours each to remove impurities. The wet gel after impurities were removed was subjected to supercritical carbon dioxide drying at a reaction temperature of 40°C, a drying pressure of 8 MPa, a degassing rate of 4 L / min, and a drying time of 14 hours to obtain an organic-inorganic hybrid aerogel. The obtained organic-inorganic hybrid aerogel was heat-treated in a nitrogen atmosphere at a temperature of 1000°C, a heating rate of 2°C / min, and a holding time of 7 hours to obtain a nanoporous TiN aerogel. Figure 1 (a) is a photo of the obtained wood aerogel placed on a leaf, showing that the aerogel has the characteristics of low density and light weight. Figure 1 (b) is a physical picture of the nanoporous TiN aerogel, in which the nanoporous TiN aerogel is a complete block structure with a black surface. After characterization, its specific surface area is 233 cm 2 / g, and thermal conductivity is 0.032W / (m·K).

[0029] Example 2

[0030] Eucalyptus wood blocks were delignified by soaking them in a 15% sodium hydroxide solution heated to 86°C in a waterbath at a mass ratio of 1:3.2. The immersion process lasted five 4-hour soaks. The delignified samples were then replaced in deionized water for 27 hours, frozen in liquid nitrogen, and freeze-dried at -43°C for 26 hours to obtain wood aerogels. A TiO2 sol was prepared by mixing isopropyl titanate, methanol, perchloric acid (8% by mass), and water at a mass ratio of 1:4.1:1.7:0.3 at 22°C. The resulting wood aerogels were placed in a sealed container and aged for 31 hours in the TiO2 sol to produce a composite wet gel. The composite wet gel was then removed and soaked in isopropyl alcohol five times for 7 hours each to remove impurities. The wet gel after impurities were removed was subjected to supercritical carbon dioxide drying at a reaction temperature of 47°C, a drying pressure of 9 MPa, a degassing rate of 7 L / min, and a drying time of 11 hours to obtain an organic-inorganic hybrid aerogel. The obtained organic-inorganic hybrid aerogel was heat-treated in a nitrogen atmosphere at a temperature of 1400°C, a heating rate of 4°C / min, and a holding time of 3 hours to obtain a nanoporous TiN aerogel. Figure 2 The XRD spectrum of the obtained nanoporous TiN aerogel is shown in Figure 1. Its diffraction peaks completely correspond to the standard spectrum of TiN, and there are no diffraction peaks of other impurities, proving that the sample is a pure phase nanoporous TiN aerogel. After characterization, its specific surface area is 469 cm 2 / g, and thermal conductivity is 0.029W / (m·K).

[0031] Example 3

[0032] Poplar wood blocks were delignified by soaking them in a 29% potassium hydroxide solution heated to 65°C in a waterbath at a mass ratio of 1:5.8. The samples were immersed three times for 5 hours each. The delignified samples were then replaced in deionized water for 41 hours, frozen in liquid nitrogen, and freeze-dried at -30°C for 32 hours to obtain wood aerogels. A TiO2 sol was prepared by mixing tetrabutyl titanate, propanol, boric acid (40% by mass), and water at a mass ratio of 1:6.6:2.5:0.6 at 29°C. The resulting wood aerogels were placed in a sealed container and aged for 26 hours in the TiO2 sol to produce a composite wet gel. The composite wet gels were then removed and soaked in n-pentanol six times for 6 hours each to remove impurities. The wet gel after impurities were removed was subjected to supercritical carbon dioxide drying, wherein the reaction temperature was 55°C, the drying pressure was 11 MPa, the degassing rate was 11 L / min, and the drying time was 9 hours, thereby obtaining an organic-inorganic hybrid aerogel. The obtained organic-inorganic hybrid aerogel was heat-treated in a nitrogen atmosphere at a heat treatment temperature of 1200°C, a heating rate of 5°C / min, and a holding time of 5 hours, and finally a nanoporous TiN aerogel was obtained. Its SEM image is shown as follows: Figure 3 As shown in Figure 2, the nanoporous TiN aerogel has the typical three-dimensional nanoporous characteristics of aerogels. After characterization, it was found that its specific surface area is 411 cm 2 / g, and thermal conductivity is 0.042W / (m·K).

[0033] Example 4

[0034] Pine wood blocks were delignified by soaking them in a 38% potassium hydroxide solution heated to 50°C in a waterbath at a mass ratio of 1:8.1. The immersion process lasted two 7-hour soaks. The delignified samples were then replaced in deionized water for 55 hours, frozen in liquid nitrogen, and freeze-dried at -17°C for 41 hours to produce wood aerogels. A TiO2 sol was prepared by mixing isopropyl titanate, butanol, phosphoric acid (13% by mass), and water at a mass ratio of 1:8.2:3.8:0.8 at 33°C. The resulting wood aerogels were placed in a sealed container and aged for 12 hours in the TiO2 sol to produce a composite wet gel. The composite wet gel was then removed and soaked in methanol seven times for 5 hours each to remove impurities. The wet gel after impurities were removed was subjected to supercritical carbon dioxide drying, wherein the reaction temperature was 61°C, the drying pressure was 14 MPa, the degassing rate was 13 L / min, and the drying time was 7 h, thereby obtaining an organic-inorganic hybrid aerogel. The obtained organic-inorganic hybrid aerogel was heat-treated in a nitrogen atmosphere at a heat treatment temperature of 1300°C, a heating rate of 7°C / min, and a holding time of 4 h, ultimately obtaining a nanoporous TiN aerogel. Characterization showed that its specific surface area was 189 cm 2 / g, and thermal conductivity is 0.054W / (m·K).

[0035] Example 5

[0036] Willow wood was delignified by soaking it in a 50% sodium hydroxide solution heated to 30°C in a waterbath at a mass ratio of 1:10. The immersion process lasted two 9-hour soaks. The delignified sample was then replaced in deionized water for 72 hours, then frozen in liquid nitrogen and freeze-dried at -5°C for 66 hours to produce a wood aerogel. A TiO2 sol was prepared by mixing isopropyl titanate, ethylene glycol, hypochlorous acid (25% by mass), and water at a mass ratio of 1:10:4.5:1 at 40°C. The resulting wood aerogel was placed in a sealed container and aged for 5 hours in the TiO2 sol to produce a composite wet gel. The composite wet gel was then removed and soaked in propanol nine times for 4 hours each to remove impurities. The wet gel after impurities were removed was subjected to supercritical carbon dioxide drying, wherein the reaction temperature was 70°C, the drying pressure was 15MPa, the degassing rate was 16L / min, and the drying time was 5h, thereby obtaining an organic-inorganic hybrid aerogel. The obtained organic-inorganic hybrid aerogel was heat-treated in a nitrogen atmosphere at a heat treatment temperature of 1500°C, a heating rate of 8°C / min, and a holding time of 2h, finally obtaining a nanoporous TiN aerogel. After characterization, it was found that its specific surface area was 348cm 2 / g, and thermal conductivity is 0.039W / (m·K).

Claims

1. A method for preparing nanoporous titanium nitride aerogel by a template method, the specific steps of which are as follows: (1) Soaking the original wood in an alkaline solution and heating it in a water bath to 30-100°C for delignification treatment; (2) performing solvent replacement on the sample obtained in step (1) in deionized water to remove impurities, freezing the sample in liquid nitrogen, and then freeze-drying the sample to obtain wood aerogel; (3) mixing a titanium source, alcohol, acid solution, and water in a proportion at 15-40° C. to form a TiO sol, placing the wood aerogel obtained in step (2) in a sealed container, and immersing the aerogel in the TiO sol to age to obtain a composite wet gel; (4) taking out the composite wet gel obtained in step (3) and soaking it in alcohol to remove impurities; (5) drying the wet gel after removing impurities in step (4) to obtain an organic-inorganic hybrid aerogel; (6) The organic-inorganic hybrid aerogel obtained by drying in step (5) is subjected to high-temperature heat treatment under nitrogen conditions to finally obtain biomass nanoporous TiN aerogel.

2. The method according to claim 1, characterized in that In step (1), the native wood is balsa wood, pine wood, eucalyptus wood, willow wood or poplar wood; the mass ratio of the wood to the alkaline solution is 1: (1.5-10), the soaking times are 2-6 times, each time for 3-9 hours; the alkaline solution is one or more mixtures of sodium hydroxide or potassium hydroxide; and the mass concentration of the alkaline solution is 3-50%.

3. The method according to claim 1, characterized in that The solvent replacement time in step (2) is 12 to 72 hours; the drying temperature of freeze drying is -60 to -5°C, and the drying time is 12 to 66 hours.

4. The method according to claim 1, characterized in that In step (3), the titanium source is one or more mixtures of tetrabutyl titanate or isopropyl titanate; the alcohol is one or a mixture of methanol, ethanol, propanol, butanol or ethylene glycol; the acid solution is one or a mixture of hydrochloric acid, boric acid, phosphoric acid, hypochlorous acid or perchloric acid, wherein the mass concentration of the acid solution is 3-40%; the mass ratio of the titanium source, alcohol, acid solution and water is 1:(3-10):(1-4.5):(0.2-1), and the aging time is 5-36 hours.

5. The method according to claim 1, characterized in that In step (4), the alcohol is one of ethanol, methanol, propanol, n-pentanol or isopropanol or a mixture thereof; the soaking times are 3 to 9 times, and the soaking time each time is 4 to 10 hours.

6. The method according to claim 1, characterized in that The drying method described in step (5) is a carbon dioxide supercritical drying method: carbon dioxide is used as the drying medium, the reaction temperature is 40-70°C, the drying pressure is 8-15 MPa, the degassing rate is 4-16 L / min, and the drying time is 5-14 h.

7. The method according to claim 1, characterized in that In step (6), the high temperature heat treatment temperature is 1000-1500° C., the heating rate is 2-8° C. / min, and the holding time is 2-7 h.

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