Multifunctional aerogel composite thermal insulation material and preparation method thereof

Abstract

The invention relates to the technical field of aerogel thermal insulation materials, in particular to a multifunctional aerogel composite thermal insulation material and a preparation method thereof. According to the preparation method, red brick waste is used as a silicon source, a density-variable gradient pore channel structure is constructed in a wet gel matrix in one step through a two-way freezing technology, and the preparation method has mechanical enhancement and load presetting functions. Then, by means of the bridging effect of gamma-aminopropyltriethoxysilane, NH2-ZIF-8 and N-TiO2 (at) GQDs are subjected to in-situ assembly and chemical anchoring in a pore channel of a matrix, and a stable adsorption-catalysis micro-unit is formed. According to the obtained material, the utilization rate of red brick waste is 90% or above, the compression modulus can reach 8.5 MPa or above, the excellent visible light driven self-cleaning capacity is achieved, the 24-hour formaldehyde adsorption capacity can reach 170 mg / g or above, the decomposition rate can reach 90% or above, and the low-cost, high-strength and long-acting air purification functions are integrated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aerogel thermal insulation materials, in particular to a multifunctional aerogel composite thermal insulation material and a preparation method thereof. BACKGROUND

[0002] In the field of building energy saving, aerogels have attracted extensive research due to their excellent thermal insulation performance. However, its large-scale application has been limited for a long time due to some problems, for example, the raw material depends on expensive chemical silicon precursor, resulting in high production cost; in addition, the inherent nano-porous structure of the material brings excellent thermal insulation performance, but also causes macroscopic brittleness and low strength, making it easy to be damaged in engineering application; at the same time, the single thermal insulation function cannot meet the demand of modern buildings for indoor environment active purification.

[0003] Currently, in order to introduce air purification function, the "post addition" method of physical blending or surface coating photocatalyst (such as TiO2) is generally used. Mechanical blending will damage the precise network skeleton of aerogel, sacrificing its fundamental thermal insulation performance; and the surface coating layer is easy to peel off under complex working conditions due to weak interfacial bonding force, resulting in rapid failure of function. More importantly, these methods are difficult to achieve uniform, stable and long-term loading of functional components in the three-dimensional space of the thermal insulation matrix.

[0004] Therefore, it is of great significance to develop an aerogel material with low raw material cost, high mechanical strength, good thermal insulation function and long-term purification function. SUMMARY

[0005] The present application aims to solve the problems of high raw material cost, insufficient mechanical strength of the material, and single thermal insulation function and difficulty in stable integration with long-term purification function in the prior art of thermal insulation aerogel used in building materials. A multifunctional aerogel composite thermal insulation material and a preparation method thereof are provided. The red brick waste is used as a silicon source to prepare a silica sol, realizing the resource utilization of building solid waste and reducing the raw material cost; a large number of stable "adsorption-catalysis" micro-units are successfully constructed inside (NH2-ZIF-8 is responsible for efficient enrichment of formaldehyde and other pollutants, and N-TiO2@GQDs is responsible for photocatalytic degradation), thereby showing excellent and long-term visible light driven self-cleaning ability, and having high adsorption and decomposition performance for formaldehyde.

[0006] The first aspect of the present application provides a preparation method of an aerogel composite thermal insulation material, comprising the following steps: Preparation of silica sol from red brick waste; Adding reinforcing materials into the silica sol to form a composite sol; Carrying out bidirectional freezing treatment on the composite sol, and carrying out aging treatment on the frozen product to obtain a wet gel matrix; The wet gel matrix is immersed into a composite photocatalytic solution containing NH2-ZIF-8 and N-TiO2@GQDs modified by γ-aminopropyl triethoxysilane for loading treatment; Drying to obtain the aerogel composite thermal insulation material.

[0007] The application provides a preparation method of an aerogel composite thermal insulation material. First, a silicon sol is prepared by taking red brick waste as a silicon source, so that resource utilization of building solid waste is realized and raw material cost is reduced. Second, a reinforcing material is introduced into the silicon sol, and a two-way freezing technology is used for molding. By using a temperature gradient unique to the technology, a wet gel matrix with a gradient pore structure with dense and sparse changes is constructed in one step. The structure has a mechanical reinforcing effect, and by qualitatively guiding the growth of ice crystals, dense and small pores are formed at one side of the structure at an ultralow temperature, and large pores with good orientation are formed at the other side of the structure at a relatively high temperature, so that a convenient transmission channel is provided for photocatalytic materials, and the specific surface area is increased to facilitate adsorption and fixation. Subsequently, the wet gel matrix is immersed in a composite solution composed of NH2-ZIF-8 and N-TiO2@GQDs modified by γ-aminopropyl triethoxysilane. Amino groups guide NH2-ZIF-8 to gather around N-TiO2@GQDs through hydrogen bonding, and the NH2-ZIF-8 is in-situ assembled into a cluster-shaped composite photocatalytic unit. Silicon hydroxyl groups generated by hydrolysis and hydroxyl groups in the gel network undergo condensation reaction, so that the unit is chemically anchored to the pore surface, and firm loading is realized. The finally obtained aerogel composite material not only realizes high-value utilization of building solid waste and improvement of the mechanical properties of the matrix, but also successfully constructs a large number of stable “adsorption-catalysis” micro-units in the material, in which NH2-ZIF-8 is responsible for efficient enrichment of pollutants such as formaldehyde, and N-TiO2@GQDs is responsible for photocatalytic degradation, so that the material exhibits excellent and persistent visible light-driven self-cleaning ability, and has high adsorption and decomposition performance for formaldehyde.

[0008] Further, the silicon sol is prepared by using red brick waste. The specific operation method is as follows: the red brick waste is subjected to alkali fusion treatment, then is dissolved in water and filtered, and the pH is adjusted to form a silicon sol; and / or, the alkali fusion treatment is performed by using sodium hydroxide, and the mass ratio of the red brick waste to the alkali is 1:1.5-2.5; and / or, the alkali fusion temperature is 300-400 DEG C; and / or, the solid content of the formed silicon sol is 30%-50%.

[0009] Further, the pH is adjusted to 9-10.

[0010] Further, the reinforcing material is inorganic fiber modified by a silane coupling agent; the mass fraction of the inorganic fiber modified by the silane coupling agent in the composite sol is 2%-10%.

[0011] Further, the specific operation process of modifying the inorganic fiber by γ-aminopropyl triethoxysilane is as follows: the inorganic fiber is immersed in a γ-aminopropyl triethoxysilane ethanol solution with a concentration of 3-6 wt%, and is incubated at 50-70°C for 2-4h.

[0012] Further, the inorganic fiber is at least one of modified glass fiber and basalt fiber, the fiber diameter is 10-15μm, and the length is 1-3mm.

[0013] Further, when the reinforcing material is added, graphene quantum dots (GQDs) are also added; the addition amount of the graphene quantum dots is 0.2%-0.5% of the total mass of the composite sol. Further, the particle size of the graphene quantum dots is 5-10nm.

[0014] The GQDs can be embedded into the gel network and fiber interface like nano rivets, and can synergistically improve the mechanical strength of the matrix, due to the high specific surface area and rich functional groups of the GQDs; at the same time, as an excellent electronic conductor, the GQDs can promote the separation and transmission of photo-generated electrons, and significantly improve the photocatalytic efficiency of the N-TiO2@GQDs.

[0015] Further, the bidirectional freezing process is as follows: the composite sol is placed in a mold, and cooling is applied in the top and bottom directions at different temperatures, wherein the top cooling temperature is-25°C--15°C and the bottom cooling temperature is-90°C--70°C, or the top cooling temperature is-90°C--70°C and the bottom cooling temperature is-25°C--15°C.

[0016] Further, the bidirectional freezing process forms a gradient pore structure with a surface layer pore of 20-50μm and a core layer pore of 1-5μm.

[0017] Further, the temperature of the aging treatment is 40°C-60°C, and the time is 12-24h.

[0018] During the aging process, the network structure of the wet gel matrix is further crosslinked and densified, improving the stability and mechanical properties of the matrix.

[0019] Further, the mass concentration of the composite photocatalytic solution is 10-30mg / mL; the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs is 3:1-5:1. Further, the particle size of the N-TiO2@GQDs is 80-100nm, and the N doping amount is 2-4at%; and / or, the particle size of the NH2-ZIF-8 is 80-100nm, and the specific surface area is ≥1200m² / g.

[0020] The amino groups guide NH2-ZIF-8 to gather around N-TiO2@GQDs by hydrogen bonding, and the cluster-shaped composite photocatalytic units (with a diameter of 150-200 nm, each cluster containing 3-5 NH2-ZIF-8 particles and 1-2 N-TiO2@GQDs particles) are assembled in situ; the condensation reaction between the silicon hydroxyl groups generated by the hydrolysis of gamma-aminopropyl triethoxysilane and the hydroxyl groups of the gel network chemically anchors the units on the channel surface, realizes firm loading, and avoids the functional components from falling off.

[0021] Further, the method further comprises immersing the treated material into a hydrophobic material solution, and drying to obtain the aerogel composite thermal insulation material; and / or the hydrophobic material solution is a methyltrimethoxysilane ethanol solution with a mass concentration of 5-8%.

[0022] Further, the drying is performed in a gradient heating mode; and / or the procedure is as follows: 50-70 DEG C, drying for 1-3 h, then 75-100 DEG C, drying for 1-3 h, and finally 110-120 DEG C, drying for 1-3 h.

[0023] The drying mode can avoid the collapse of the pore structure of the material caused by a sharp temperature rise, and ensure that the material maintains excellent thermal insulation and adsorption performance.

[0024] The second aspect of the present application provides an aerogel composite thermal insulation material prepared by the preparation method.

[0025] Compared with the prior art, the present application has the following beneficial effects: This invention provides a method for preparing an aerogel composite thermal insulation material and the prepared aerogel material. First, silica sol is prepared using waste red bricks as the silicon source, realizing the resource utilization of construction solid waste and reducing raw material costs. Second, reinforcing materials are introduced into the sol, and a bidirectional freezing technique is used for molding. Utilizing the unique temperature gradient of this technique, a wet gel matrix with a gradient pore structure exhibiting varying density is constructed in one step. This structure provides mechanical reinforcement and, through qualitative guidance of ice crystal growth, forms dense and fine pores on one side at ultra-low temperatures, while the other side, at relatively high temperatures, forms well-oriented macropores on the surface, providing convenient transport channels for photocatalytic materials and increasing the specific surface area for adsorption and fixation. Subsequently, the wet gel matrix is ​​impregnated in a composite solution composed of NH2-ZIF-8 and N-TiO2@GQDs modified with γ-aminopropyltriethoxysilane. Amino groups guide the aggregation of NH2-ZIF-8 around N-TiO2@GQDs through hydrogen bonding, assembling in situ into clustered composite photocatalytic units. The silanol groups generated by hydrolysis undergo condensation reactions with the hydroxyl groups of the gel network, chemically anchoring the unit to the pore surface for robust loading. The resulting aerogel composite material not only achieves high-value utilization of construction solid waste and improves the mechanical properties of the matrix, but also exhibits excellent and long-lasting visible light-driven self-cleaning ability due to the successful construction of a large number of stable "adsorption-catalysis" microunits (NH2-ZIF-8 is responsible for the efficient enrichment of pollutants such as formaldehyde, and N-TiO2@GQDs are responsible for photocatalytic degradation). It also possesses highly efficient adsorption and decomposition performance for formaldehyde. The final prepared aerogel material achieves a utilization rate of over 90% for red brick waste, a compressive modulus of over 8.5 MPa, and excellent visible light-driven self-cleaning ability. Its 24-hour adsorption capacity for formaldehyde reaches over 170 mg / g, and its decomposition rate reaches over 90%, integrating low cost, high strength, and long-lasting air purification functions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the implementation of bidirectional freezing technology in some embodiments of the present invention.

[0027] Figure 2 This is a SEM image of the cluster structure formed in the gel by the composite photocatalytic solution in Example 2.

[0028] Figure 3 SEM images of the gradient honeycomb structure on the inner and outer sides of the aerogel material prepared in Example 2. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0030] The first aspect of the embodiment provides a preparation method of aerogel composite thermal insulation material, comprising the following steps: Preparation of silica sol using red brick waste; Adding reinforcing materials into the silica sol to form a composite sol; Carrying out bidirectional freezing treatment on the composite sol, and carrying out aging treatment on the frozen product to obtain a wet gel matrix; Immersion of the wet gel matrix into a composite photocatalytic solution containing NH2-ZIF-8 and N-TiO2@GQDs modified by γ-aminopropyl triethoxysilane for loading treatment; Drying to obtain the aerogel composite thermal insulation material.

[0031] Firstly, the silica sol is prepared using red brick waste as a silicon source, realizing the resource utilization of construction solid waste and reducing the raw material cost; secondly, the reinforcing materials are introduced into the silica sol and the bidirectional freezing technology is used for molding, and the temperature gradient of the technology is used to construct the wet gel matrix with gradient pore structure with dense and sparse changes in one step. The structure has mechanical reinforcement effect, and by guiding the growth of ice crystals, dense and small pores are formed at one side of the ultra-low temperature, and large pores with good orientation are formed at the other side of the relatively high temperature, which can provide a convenient transport channel for the photocatalytic material, and increase the specific surface area for adsorption and fixation. Then, the wet gel matrix is immersed in a composite solution composed of NH2-ZIF-8 and N-TiO2@GQDs modified by γ-aminopropyl triethoxysilane. The amino groups guide the aggregation of NH2-ZIF-8 around N-TiO2@GQDs through hydrogen bonding, and in-situ assemble into cluster-shaped composite photocatalytic units; the silicon hydroxyl groups generated by hydrolysis condense with the hydroxyl groups of the gel network, thereby chemically anchoring the units on the pore surface and achieving firm loading. The final aerogel composite material not only realizes the high-value utilization of construction solid waste and the improvement of the mechanical properties of the matrix, but also successfully constructs a large number of stable “adsorption-catalysis” micro-units in the interior (wherein NH2-ZIF-8 is responsible for efficient enrichment of formaldehyde and other pollutants, and N-TiO2@GQDs is responsible for photocatalytic degradation), thereby showing excellent and persistent visible light driven self-cleaning ability, and having high adsorption and decomposition performance for formaldehyde.

[0032] In some embodiments, silica sol is prepared from red brick waste, and the specific operation method is as follows: the red brick waste is subjected to alkali fusion treatment, then dissolved in water and filtered, and the pH is adjusted to form silica sol; and / or, the alkali fusion treatment is performed using sodium hydroxide, the mass ratio of red brick waste to alkali is 1:1.5~2.5 and / or, the alkali fusion temperature is 300~400℃; and / or, the solid content of the formed silica sol is 30%-50%. Reasonable control of the amount of NaOH and a suitable high-temperature environment can fully destroy the crystal structure of the red brick, maximizing the conversion of silicon and aluminum components into soluble aluminosilicates, thereby achieving the high-value utilization target of ≥90% for waste; at the same time, this parameter range effectively avoids the residual impurity ions caused by excessive NaOH or the surge in energy consumption and component segregation caused by excessively high temperatures. For example, the mass ratio of NaOH to red brick waste is 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, or 2.5:1. The alkali fusion temperature is 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃.

[0033] In some embodiments, the pH is adjusted to 9-10.

[0034] In some embodiments, the reinforcing material is an inorganic fiber with a surface modified by a silane coupling agent; the inorganic fiber with a surface modified by a silane coupling agent has a mass fraction of 2% to 10% in the composite sol.

[0035] In some embodiments, the specific procedure for modifying inorganic fibers with γ-aminopropyltriethoxysilane is as follows: the inorganic fibers are immersed in a 3-6 wt% γ-aminopropyltriethoxysilane ethanol solution and kept at 50-70°C for 2-4 hours. The modified inorganic fibers have amino and hydroxyl groups introduced onto their surface, which can form strong covalent bonds (Si-O-Si) with the silica sol matrix, effectively transferring stress from the brittle gel matrix to the high-strength fibers and significantly improving the material's mechanical properties.

[0036] In some embodiments, the inorganic fiber is at least one of modified glass fiber and basalt fiber, with a fiber diameter of 10-15 μm and a length of 1-3 mm. This parameter range ensures that the fiber forms a uniform three-dimensional support network in the matrix, avoiding performance defects caused by fiber agglomeration.

[0037] In some embodiments, graphene quantum dots (GQDs) are also added when adding reinforcing materials; the amount of graphene quantum dots added is 0.2% to 0.5% of the total mass of the composite sol. In some embodiments, the particle size of the graphene quantum dots is 5 to 10 nm.

[0038] In terms of mechanics, GQDs, with their high specific surface area and abundant functional groups, can be embedded in the interface between the gel network and the fiber like nano-rivets, effectively transferring and dispersing stress, and synergistically improving the matrix strength with macroscopic fibers. Secondly, in terms of function, GQDs are excellent electron conductors, which can significantly promote the separation and transmission of photogenerated electrons in the composite photocatalytic unit, thereby directly improving the photocatalytic efficiency of N-TiO2@GQDs, which is the key to achieving high formaldehyde decomposition rate.

[0039] In some embodiments, the bidirectional freezing process involves placing the composite sol in a mold and simultaneously applying cooling at different temperatures to the top and bottom, wherein the top cooling temperature is -25°C to -15°C and the bottom cooling temperature is -90°C to -70°C, or the top cooling temperature is -90°C to -70°C and the bottom cooling temperature is -25°C to -15°C. Figure 1 As shown.

[0040] Furthermore, the two-way cooling process takes 3-5 hours.

[0041] This process guides ice crystal growth by establishing an extremely differentiated temperature gradient field: on one side, ultra-low temperatures (-90℃ to -70℃) rapidly freeze the solvent, forming dense and fine core pores (1~5μm); on the other side, relatively high temperatures (-25℃ to -15℃) allow ice crystals to grow in a fully oriented manner, forming well-oriented surface macropores (20~50μm), ultimately constructing a gradient pore structure that is sparse on the outside and dense on the inside. This structure not only enhances the mechanical properties of the material but also provides a convenient transport channel for photocatalytic materials, while increasing the specific surface area to facilitate adsorption and fixation.

[0042] For example, the top temperature of double-sided freezing is -25℃ and the bottom temperature is -90℃; the top temperature is -15℃ and the bottom temperature is -70℃; the top temperature is -22℃ and the bottom temperature is -80℃; the top temperature is -20℃ and the bottom temperature is -85℃. Freezing times can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours. All methods are effective.

[0043] In some embodiments, the aging treatment is performed at a temperature of 40°C-60°C for 12-24 hours.

[0044] In some embodiments, the mass concentration of the composite photocatalytic solution is 10-30 mg / mL; the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs is 3:1 to 5:1. Furthermore, the N-TiO2@GQDs have a particle size of 80-100 nm and an N doping amount of 2-4 at%; and / or, the NH2-ZIF-8 has a particle size of 80-100 nm and a specific surface area ≥1200 m² / g, with 80 nm, 85 nm, 90 nm, or 100 nm sizes being acceptable.

[0045] The amino group guides NH2-ZIF-8 to aggregate around N-TiO2@GQDs through hydrogen bonding, assembling in situ into clustered composite photocatalytic units (150-200 nm in diameter, each cluster containing 3-5 NH2-ZIF-8 particles and 1-2 N-TiO2@GQDs particles); the silanol groups generated by the hydrolysis of γ-aminopropyltriethoxysilane undergo a condensation reaction with the hydroxyl groups of the gel network, chemically anchoring the unit to the pore surface, achieving a firm loading and preventing the functional components from falling off.

[0046] For example, the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs is 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0047] In some embodiments, the process further includes immersing the loaded material in a hydrophobic material solution and drying it to obtain an aerogel composite thermal insulation material; and / or, the hydrophobic material solution is an ethanol solution of methyltrimethoxysilane with a mass concentration of 5% to 8%. Reasonably controlling the mass concentration of the methyltrimethoxysilane (MTMS) ethanol solution helps ensure that the hydrophobic groups (-Si(CH3)3) generated after MTMS hydrolysis can fully cover and chemically bond to the entire surface of the aerogel network, forming a stable covalent bond, rather than physical adhesion. The formed hydrophobic layer can effectively block water vapor and liquid water from penetrating the material, preventing moisture from damaging the chemical bonding interface between the inorganic fibers and the matrix, avoiding mechanical property degradation; preventing moisture from eroding the two-dimensional intercalated microstructure of graphene quantum dots and silica sol composites, maintaining its stability; more importantly, it can prevent water molecules from poisoning or blocking the active sites of the NH2-ZIF-8 / N-TiO2@GQDs bifunctional clusters, ensuring that its formaldehyde adsorption and photocatalytic decomposition functions remain efficient and durable in humid environments. For example, in some embodiments, the mass concentration of the ethanol solution of methyltrimethoxysilane is 5%, 6%, 7%, or 8%.

[0048] In some embodiments, drying is carried out using a gradient temperature increase method; and / or, the procedure is: drying at 50°C to 70°C for 1 to 3 hours, then drying at 75°C to 100°C for 1 to 3 hours, and finally drying at 110°C to 120°C for 1 to 3 hours. For example, a gradient temperature increase drying process is: drying at 50°C for 3 hours, then at 75°C for 3 hours, and finally at 110°C for 3 hours. For example, a gradient temperature increase drying process is: drying at 70°C for 1 hour, then at 100°C for 1 hour, and finally at 120°C for 1 hour. For example, a gradient temperature increase drying process is: drying at 55°C for 2 hours, then at 95°C for 2 hours, and finally at 115°C for 2 hours.

[0049] The second aspect of this embodiment provides an aerogel composite thermal insulation material prepared by the preparation method described above.

[0050] To better understand the technical solutions of the above embodiments, the following more detailed experimental examples are provided for further explanation.

[0051] In the following examples and comparative examples, the sources of each raw material are as follows: BF is basalt fiber, purchased from Sichuan Juyuan Basalt Fiber Technology Co., Ltd., with specifications of fiber diameter 10-15μm and length 1-3mm.

[0052] GQDs purchased materials from Nanjing Xianfeng Nanomaterials Technology Co., Ltd., with a particle size of 5nm and a purity of ≥99%.

[0053] The N-TiO2@GQDs were purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd. The customization requirements were 3 at% N doping, 80 nm particle size, surface modification with γ-aminopropyltriethoxysilane (APTES) (grafting rate ≥1.2 mmol / g), and purity ≥98%.

[0054] NH2-ZIF-8 was purchased from Shanghai Maclean Biotechnology Co., Ltd., with specifications of 80nm particle size and specific surface area ≥1200m². 2 / g, purity ≥99%.

[0055] Example 1 (1) Preparation of silica sol: 100g of red brick waste (particle size 50μm) was mixed with 150g of NaOH, alkali-fused at 300℃ for 1h, cooled and then 500mL of deionized water was added and stirred for 30min. The mixture was filtered through a 0.22μm filter membrane to obtain an aluminosilicate solution (SiO2 concentration 8.1wt%). The pH was adjusted to 9.5 with 1M NaOH to form a silica sol with a solid content of 30%. (Direct pH adjustment can convert to silica sol. If the solid content is too low, rotary evaporation can be used to concentrate it to the target range. If the solid content is too high, a small amount of deionized water can be added to dilute and adjust it.) (2) Preparation of composite sol: 6g BF was added to 100mL of 5wt% APTES ethanol solution, kept at 60℃ for 3h, and 10g of 30wt% silica sol was added and stirred for 1h. After modification, the amino content on the surface of BF was 1.8mmol / g, forming a BF-SiO2 transition layer. Add the modified BF to 30wt% silica sol (80g) and ultrasonically disperse at 300W for 25min; Add 0.5g GQDs (particle size 5nm) and 10g 30wt% silica sol, stir for 1h to obtain a uniform composite sol.

[0056] (3) Two-way freezing and aging: The composite sol was injected into a 20×10×1cm³ mold and frozen for 4 hours in a two-way freezing device (top direction -20℃, bottom direction -80℃); Take out the sample and age it at 50℃ for 12 hours; (4) Loading and hydrophobic modification: 0.5g N-TiO2@GQDs (N doping amount 3at%) was added to 50mL of 2wt% APTES ethanol solution and stirred at 50℃ for 2h; 2g of NH2-ZIF-8 was mixed with the above-modified N-TiO2@GQDs, and 150mL of ethanol was added for ultrasonic dispersion for 20min to prepare a composite loading solution; The aged wet gel was immersed in the composite loading solution and kept at 60°C for 6 hours. After being removed, it was immersed in 8wt% MTMS ethanol solution and modified at 25°C for 2 hours.

[0057] (5) Gradient drying: The modified sample was dried at 60℃ for 2h, then at 80℃ for 2h, and then at 120℃ for 2h to obtain the aerogel product.

[0058] Example 2 Compared with Example 1, Example 2 only changed the amount of NaOH and the alkali fusion temperature in step (1). In Example 2, the amount of NaOH was 200g and the alkali fusion temperature was 350℃. The other preparation processes were the same as in Example 1.

[0059] In Example 2, the SiO2 content in the filtered aluminosilicate solution was 8.5 wt%, and the final silica sol had a solid content of 40%.

[0060] Example 3 Compared with Example 1, Example 3 only changed the amount of NaOH and the alkali melting temperature in step (1). In Example 3, the amount of NaOH was 250g and the alkali melting temperature was 400℃. The other preparation processes were the same as in Example 1.

[0061] In Example 3, the SiO2 content in the filtered aluminosilicate solution was 9.8 wt%, and the final silica sol had a solid content of 50%.

[0062] Example 4 Compared with Example 2, Example 4 adjusted the amount of BF added. In step (2) of Example 4, the amount of BF added was 7.5g, and the mass fraction of modified BF (relative to the total mass of the sol) was adjusted from 6% in Example 2 to 7.5% in Example 4. The other preparation process was completely the same as that in Example 2.

[0063] Example 5 Compared with Example 2, Example 5 adjusted the amount of BF added. In step (2) of Example 5, the amount of BF added was 9g, and the mass fraction of modified BF (relative to the total mass of the sol) was adjusted from 6% in Example 2 to 9% in Example 5. The other preparation process was completely the same as that of Example 2.

[0064] Example 6 Compared with Example 2, Example 6 adjusted the amount of GQDs added. In step (2) of Example 6, the amount of GQDs added was adjusted to 0.75g (0.75%). The other preparation process was completely the same as that of Example 2.

[0065] Example 7 Compared with Example 2, Example 7 adjusted the amount of GQDs added. In step (2) of Example 7, the amount of GQDs added was adjusted to 1g (1%). The other preparation process was completely the same as that of Example 2.

[0066] Example 8 Compared with Example 2, Example 8 only adjusted the amount of NH2-ZIF-8 and N-TiO2@GQDs. In step (3) of Example 8, the amount of NH2-ZIF-8 added was adjusted to 1.5g, and the amount of N-TiO2@GQDs added was still 0.5g (mass ratio 3:1). The other preparation process was exactly the same as that of Example 2.

[0067] Example 9 Compared with Example 2, Example 9 only adjusted the amount of NH2-ZIF-8 and N-TiO2@GQDs. In step (3) of Example 9, the amount of NH2-ZIF-8 added was adjusted to 2.5g, and the amount of N-TiO2@GQDs added was still 0.5g (mass ratio 5:1). The other preparation process was exactly the same as that of Example 2.

[0068] Example 10 Compared with Example 2, Example 10 only adjusted the mass concentration of the MTMS ethanol solution. In step (3) of Example 10, the mass concentration of the MTMS ethanol solution was adjusted to 6.5%, and the other preparation processes were exactly the same as those in Example 2.

[0069] Example 11 Compared with Example 2, Example 11 only adjusted the mass concentration of MTMS ethanol solution. In step (3) of Example 11, the mass concentration of MTMS ethanol solution was adjusted to 5%, and the other preparation process was exactly the same as that of Example 2.

[0070] Example 12 Compared with Example 2, Example 12 only adjusted the freezing temperature in the top direction and the freezing temperature in the bottom direction. In step (3) of Example 12, the freezing temperature in the top direction is -15℃ and the freezing temperature in the bottom direction is -70℃. The other preparation processes are exactly the same as those in Example 2.

[0071] Example 13 Compared with Example 2, Example 13 only adjusted the freezing temperature in the top direction and the freezing temperature in the bottom direction. In step (3) of Example 13, the freezing temperature in the top direction is -25°C and the freezing temperature in the bottom direction is -90°C. The other preparation processes are exactly the same as those in Example 2.

[0072] Performance testing The samples prepared in Examples 1-13 were subjected to the following performance tests, and the test results are shown in Tables 1 and 2.

[0073] (1) Mechanical property testing (compression modulus, fracture strength, compressive stress retention rate) Test standard: GB / T 1041-2008 "Determination of compressibility of plastics" (adjusting parameters for porous rigid materials), Instron 5969, equipped with a 500N pressure sensor (accuracy ±0.5%), compression rate: 1mm / min; compression strain range: 0~60%; data acquisition frequency: 10Hz.

[0074] (2) Formaldehyde adsorption capacity and decomposition rate test The testing standards are based on: GB / T 30737-2014 "Purification Performance of Indoor Air Purification Functional Coating Materials", HJ571-2010 "Determination of Formaldehyde in Ambient Air and Exhaust Gas - Acetylacetone Spectrophotometric Method" and GB / T 18204.24-2000 "Determination of Carbon Dioxide in Air in Public Places".

[0075] Sample Preparation: Sample Specifications: The aerogel was pulverized into 1–2 mm particles (simulating the contact area with air in actual use). 1.000 g ± 0.001 g of sample was placed in a 50 mm × 10 mm quartz sample dish (quartz does not adsorb formaldehyde and causes no interference). The sample was dried in a 120℃ vacuum drying oven for 2 hours to remove adsorbed moisture and impurities. After cooling to room temperature, the sample was tested immediately.

[0076] Test procedure: To 1m 3A formaldehyde standard solution was injected into the test chamber to achieve an initial concentration of 1.0 mg / m³. 3 ±0.1mg / m 3 Close the chamber door, turn on the fan (0.5 m / s) and mix for 30 minutes. Measure the initial concentration using a gas chromatograph. Place the pretreated sample dish into the chamber, turn on the visible light source (wavelength 400~760 nm), and take samples (50 mL each time) every 2 hours. Measure the formaldehyde concentration using a gas chromatograph, and simultaneously measure the change in CO2 concentration inside the chamber using a CO2 analyzer.

[0077] (3) Antibacterial test (Escherichia coli, Staphylococcus aureus) The testing standard is based on GB / T 21866-2008 "Determination of antibacterial properties and antibacterial effects of antibacterial coatings (films)", with Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 29213) as standard strains (purchased from China Microbial Culture Collection Center).

[0078] (4) Hydrophobicity test (water contact angle) The testing standard is based on GB / T 30693-2014, "Method for measuring the contact angle of plastic films and sheets".

[0079] (5) Long-term stability test (damp heat aging, cyclic stability) The testing standard is based on GB / T 18244-2000 "Test Method for Aging of Building Waterproofing Materials" (Damp Heat Aging Conditions).

[0080] Table 1

[0081] Table 2

[0082] The test results in Tables 1 and 2 show that: Analysis of the test results of Examples 1-3: (1) When the amount of NaOH increased from 1.5:1 to 2:1, the amount of OH in the alkali fusion system... - Increasing the concentration promotes the dissolution of SiO2 and Al2O3 from the red brick (reaction formula: SiO2 + 2NaOH → Na2SiO3 + H2O), increasing the utilization rate from 90.2% to 92.5%; when further increased to 2.5:1, excess NaOH leads to Na... +Aggregation in solution inhibits the dissolution of some aluminosilicates, and the utilization rate is slightly reduced to 91.8%, but still ≥90%. (2) As the alkali fusion temperature increases from 300℃ to 400℃, the reaction rate accelerates, the aluminosilicates dissolve more fully, and the SiO2 concentration in the solution increases from 8.1wt% to 9.8wt%. At the same time, the higher the concentration of silica sol, the denser the network structure is formed, and the matrix bearing capacity is improved. Therefore, the compressive modulus increases from 7.5MPa to 8.3MPa, and the fracture strength increases from 1.2MPa to 1.4MPa. (3) The adsorption capacity increases with the increase of NaOH dosage: more aluminosilicate dissolution provides more loading sites for bifunctional clusters (NH2-ZIF-8 / N-TiO2@GQDs), and the ZIF-8 content increases indirectly, thus improving the adsorption capacity. (4) Decomposition first increases and then decreases: The purity of the dissolved aluminosilicate is the highest (few impurities) at 350℃, and N-TiO2@GQDs are more uniformly dispersed, with a decomposition rate of 88%; at 400℃, excess Na + Residual inhibition of TiO2 photocatalytic activity slightly reduced the decomposition rate to 85%. Conclusion: Within this parameter range, the utilization rate of red bricks is ≥90%, and all core properties (mechanical properties, formaldehyde treatment, antibacterial properties, hydrophobicity, and stability) far exceed existing technologies.

[0083] The test results of Examples 2 and 4-5 were analyzed: (1) The modified BF (APTES-silica sol dual modification) has hydroxyl groups on its surface and forms covalent bonds (Si-O-Si) with the aluminosilicate matrix. As the dosage increases from 6% to 9%, the three-dimensional support network formed by the fiber in the matrix becomes denser. The fiber can transfer stress through the bridging effect (when the material is compressed, the fiber bears part of the load and inhibits crack propagation). Therefore, the compressive modulus, stress retention rate and fracture strength are effectively improved. (2) The increase in BF dosage makes the pore structure of the material more stable (reduces pore collapse during compression) and the formaldehyde diffusion channel is more unobstructed. Therefore, the adsorption and decomposition performance is slightly improved (3%~4%), but the effect is weaker than the mechanical properties (because BF does not directly participate in the formaldehyde reaction). Conclusion: Within the range of 6% to 9% by mass of modified BF, the aerogel compressive modulus is 7.5 to 9.5 MPa (a significant improvement over existing technologies), and all properties show a stable optimization trend with increasing fiber content, proving that this range can continuously achieve structural reinforcement-functional synergy, covering different mechanical requirement scenarios.

[0084] The test results of Examples 2 and 6-7 were analyzed: (1) Antibacterial performance: GQDs (graphene quantum dots) have an edge effect, and their abundant oxygen-containing functional groups (-OH, -COOH) on the surface can destroy bacterial cell membranes (through oxidative stress); when the dosage increases from 0.5% to 1.0%, the concentration of GQDs per unit volume increases, the probability of contact with bacteria increases, and the antibacterial rate increases by 0.6% to 0.7%. (2) Photocatalysis and stability: GQDs are excellent electron acceptors and can inhibit the recombination of photogenerated electron-hole pairs in N-TiO2 (extending carrier lifetime); after the dosage increases, more GQDs form "heterojunctions" with N-TiO2, the visible light response efficiency increases from 75% to 85%, and the formaldehyde decomposition rate increases by 5%; at the same time, the "skeleton support" effect of GQDs reduces the aggregation of TiO2 particles, and the decomposition efficiency increases by 3% after 10 cycles. Conclusion: Within the range of 0.5% to 1% addition of GQDs, the antibacterial rate is ≥99%, the formaldehyde decomposition rate under visible light is 85-90% (solving the problem of pure TiO2's dependence on ultraviolet light), and the stability is not reduced.

[0085] The test results of Examples 2 and 8-9 were analyzed: (1) Seesaw effect of adsorption and decomposition: NH2-ZIF-8 is a porous adsorbent (pore size 0.5-1nm), which is specifically used to adsorb formaldehyde molecules; N-TiO2@GQDs is a photocatalyst, which is responsible for oxidizing formaldehyde to CO2; when the ratio increases from 3:1 to 5:1, the ZIF-8 content increases by 33%, the adsorption sites increase, and the adsorption capacity increases by 17%; however, the relative proportion of TiO2 decreases, the catalytic sites decrease, and the decomposition rate decreases by 5%. (2) CO2 selectivity: ZIF-8 enhances the pre-enrichment effect of formaldehyde (the concentration of formaldehyde on the catalyst surface is higher when the ratio is high), and reduces the residue of intermediate products (such as formic acid), so the CO2 selectivity increases from 95% to 97%. Conclusion: In the mass ratio range of 3:1~5:1, the formaldehyde adsorption capacity is 145~170mg / g, the decomposition rate is 85%~90%, and there is no desorption at 30-120℃ (avoiding secondary pollution). All performance meets the requirements of adsorption-decomposition integration.

[0086] Analysis of the test results of Examples 2 and 10-11: (1) Hydrophobicity: MTMS (methyltrimethoxysilane) hydrolyzes to generate -Si(CH3)3 groups, which cover the material surface to form a hydrophobic layer; when the concentration increases from 5wt% to 8wt%, the density of hydrophobic groups on the surface increases, and the water contact angle increases by 8°, from "hydrophobic" (132°) to close to superhydrophobic (140°). (2) Functional stability: Higher concentrations of MTMS form a denser hydrophobic layer, which hinders water molecules from penetrating into the material interior and reduces the hydrolysis and deactivation of N-TiO2@GQDs; therefore, after damp heat aging (70℃ / 95% RH), the formaldehyde decomposition rate increases from 80% to 83%, proving that the hydrophobic protection effect is enhanced. Conclusion: In the range of MTMS concentration of 5~8wt%, the water contact angle is 132-140° (hydrophobic stability), and the formaldehyde decomposition rate after damp heat aging is ≥80% (resolving the conflict between hydrophobicity and function).

[0087] Analysis of the test results of Examples 2 and 12-13: (1) Pore structure optimization: The bidirectional freezing temperature is reduced (lower temperature), the ice crystal growth rate is slowed down, and the pores formed are finer and more uniformly distributed; the surface pores are reduced from 40~50μm to 20~35μm (enhancing the isolation ability of the external powder layer, but ensuring the air exchange capacity), and the core pores are reduced from 4~5μm to 1~3μm (enhancing the ability to support catalysts and increasing the density of functional sites). (2) Mechanical and mass transfer performance: The honeycomb structure with fine pores has a stronger load-bearing capacity (similar to the mechanical optimization of honeycomb), and the compression modulus is increased by 5%; the reduction in the core pore size makes the diffusion path of formaldehyde molecules shorter (reducing the mass transfer resistance), and the contact with functional clusters is more sufficient, so the adsorption and decomposition performance is improved by 3%~4%.

[0088] Conclusion: Within this temperature range, a gradient pore structure is formed with a loose surface layer and a dense core layer (20~50μm for the surface layer and 1~5μm for the core layer), with a formaldehyde diffusion rate ≥0.8cm / s (high mass transfer efficiency), and all performance characteristics are high-efficiency, stable and meet the standards.

[0089] This invention employs a multi-scale hierarchical structural design: like Figure 2 and Figure 3 As shown.

[0090] Macroscopic scale (1-10mm): A two-way freezing process (top direction -15~-25℃, bottom direction -70~-90℃) is used to construct a gradient pore structure with a loose surface layer and a dense core layer: surface pores 20~50μm (providing large pores to facilitate air exchange), core pores 1~5μm (ensuring rapid diffusion of formaldehyde to functional sites); Microscale (1~100nm): NH2-ZIF-8 / N-TiO2@GQDs bifunctional clusters (diameter 150~200nm) are loaded in the two-dimensional intercalation of SiO2-GQDs. Each cluster contains 3~5 NH2-ZIF-8 particles and 1~2 N-TiO2@GQDs particles, forming an "adsorption-decomposition" micro-unit to achieve uniform distribution of functional sites.

[0091] Comparative Example 1 Compared to Example 2, the inorganic fibers in Comparative Example 1 were not modified with γ-aminopropyltriethoxysilane, but the other preparation processes were the same as in Example 2.

[0092] Comparative Example 2 Compared to Example 2, Comparative Example 2 did not use a two-way freezing process, but instead used a one-way freezing process; otherwise, it was the same as Example 2.

[0093] Specifically, after injecting the composite sol into the mold, only the bottom of the mold is placed on a -20°C cold source for unidirectional freezing for 4 hours.

[0094] Comparative Example 3 Compared to Example 2, Comparative Example 3 did not use a two-way freezing process, but instead used a one-way freezing process; otherwise, it was the same as Example 2.

[0095] Specifically, after injecting the composite sol into the mold, only the bottom of the mold is placed on a -90℃ cold source for unidirectional freezing for 4 hours.

[0096] Comparative Example 4 Compared to Example 2, Comparative Example 4 did not use the two-way freezing process, but instead used static gelation at room temperature. Otherwise, it was the same as Example 2.

[0097] Comparative Example 5 Compared to Example 2, Comparative Example 5 did not add N-TiO2@GQDs, but only added NH2-ZIF-8. The other preparation processes were the same as in Example 2.

[0098] Comparative Example 6 Compared to Example 2, Comparative Example 6 did not add NH2-ZIF-8, but only added N-TiO2@GQDs. The other preparation processes were the same as in Example 2.

[0099] Comparative Example 7 Compared to Example 2, Comparative Example 7 was prepared using a physical blending sol-gel method, and the raw materials were exactly the same as those in Example 2.

[0100] Mix 100g of red brick waste with 200g of NaOH and alkali melt at 350℃ for 1 hour. After cooling, add 500mL of deionized water and stir for 30 minutes. Filter through a 0.22μm filter membrane to obtain an aluminosilicate solution. Adjust the pH to obtain a silica sol.

[0101] Direct mixing: 6g of unmodified BF, 0.75g of GQDs, 2g of NH2-ZIF-8, 0.5g of unmodified N-TiO2@GQDs, and the calculated mass of silica sol (total amount equivalent to the matrix solid content in Example 2) were all mixed at one time to obtain composite silica sol.

[0102] Stirring: Ultrasonic dispersion at 300W power for 25 minutes, followed by mechanical stirring for 1 hour to obtain a suspension containing all components.

[0103] Room temperature gelation: Inject the above suspension into the mold and let it stand at room temperature (25°C) for 12 hours to allow it to gel naturally.

[0104] Drying under normal pressure: The obtained wet gel block is placed directly into an oven and dried at 120°C under normal pressure for 6 hours to obtain the final aerogel material.

[0105] Comparative Example 8 Compared to Example 2, Comparative Example 8 only changed the temperature of the bidirectional freezing process. Specifically, the freezing temperature in the top direction was -30°C and the freezing temperature in the bottom direction was -50°C. The rest of the operation was the same as in Example 2.

[0106] Comparative Example 9 Compared to Example 2, Comparative Example 9 only changed the temperature of the bidirectional freezing process. Specifically, the freezing temperature in the top direction was -5°C and the freezing temperature in the bottom direction was -100°C. The rest of the operation was the same as in Example 2.

[0107] Comparative Example 10 Compared to Example 2, Comparative Example 10 changed the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs modified with γ-aminopropyltriethoxysilane to 1:1, while everything else was exactly the same as Example 2.

[0108] Comparative Example 11 Compared to Example 2, Comparative Example 11 changed the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs modified with γ-aminopropyltriethoxysilane to 8:1, while everything else was exactly the same as Example 2.

[0109] Comparative Example 12 Compared to Example 2, Comparative Example 12 used N-TiO2@GQDs that were not modified with γ-aminopropyltriethoxysilane, while the rest of the operation was the same as in Example 2.

[0110] Using the same test procedures as Tables 1 and 2, the samples prepared in Comparative Examples 1 to 11 were subjected to performance tests, and the test results are shown in Tables 3 and 4.

[0111] Table 3

[0112] Table 4

[0113] Comparative Example 1 (Unmodified Inorganic Fiber): Interfacial bonding failure led to performance degradation. The compressive modulus was 5.2 MPa (35% lower than Example 2), the tensile strength was 0.8 MPa (38% lower), and the stress retention rate at 60% compressive strain was 65% (26% lower). The core reason is that in Example 2, the inorganic fiber was modified with γ-aminopropyltriethoxysilane (APTES), introducing amino and hydroxyl groups onto the surface, forming strong Si-O-Si covalent bonds with the silica sol matrix, achieving efficient stress transfer. In Comparative Example 1, the unmodified inorganic fiber only achieved physical filling, resulting in weak interfacial bonding with the matrix. Under compression, the fiber easily peeled off from the matrix, failing to form a continuous three-dimensional support network, leading to a significant decrease in mechanical load-bearing capacity. The formaldehyde adsorption capacity, decomposition rate, and decomposition rate after 24-hour aging all decreased. This is because there are voids at the interface between the unmodified fiber and the matrix. Although these voids have little impact on the adsorption capacity, moisture can easily penetrate through them, disrupting the loading stability of the bifunctional clusters (NH2-ZIF-8 / N-TiO2@GQDs) and leading to a significant decrease in the decomposition rate after aging. The interfacial voids also reduce the continuity of the hydrophobic layer, and the uneven fiber dispersion affects the uniformity of the graphene quantum dots (GQDs) distribution, thus weakening the antibacterial effect.

[0114] Comparative Example 2 (unidirectional -20℃ freezing): Unidirectional low-temperature freezing only forms a uniform macroporous structure (30~60μm) without gradient distribution. The core layer lacks dense pore support and has insufficient mechanical load-bearing capacity. At the same time, the macroporous structure leads to a reduction in the loading sites of bifunctional clusters, and the diffusion path of formaldehyde molecules is too long, resulting in a decrease in mass transfer efficiency and a simultaneous decline in adsorption and catalytic performance.

[0115] Comparative Example 3 (unidirectional -90℃ freezing): Unidirectional ultra-low temperature freezing forms a uniform microporous structure (5~10μm). Although the specific surface area increases slightly, the pores are too dense, which increases the resistance to formaldehyde diffusion. N-TiO2@GQDs cannot fully contact the pollutants, resulting in a decrease in catalytic efficiency. Moreover, the uniform microporous structure has obvious stress concentration, which is prone to cracking when compressed, and its mechanical properties are weaker than those of the gradient pore structure.

[0116] In Comparative Examples 2 and 3, the formaldehyde decomposition rate and decomposition efficiency after 10 cycles of wet heat aging both decreased significantly. This is because a single-pore structure cannot balance mechanical support and mass transfer efficiency, and the loose pore wall structure allows moisture to easily penetrate and damage functional components, leading to a significant deterioration in stability. Therefore, the gradient structure of "20-50 μm macropores on the surface + 1-5 μm micropores in the core" constructed by bidirectional freezing is the core to achieve mechanical enhancement and functional synergy. Unidirectional freezing results in a uniform pore distribution, failing to balance load-bearing capacity and mass transfer efficiency, leading to a significant decrease in overall performance.

[0117] Comparative Example 4 (room temperature gelation) exhibited the worst mechanical properties among all samples. Room temperature gelation lacked temperature gradient guidance, resulting in randomly distributed pores (10–80 μm). Furthermore, the pore walls were thin, the network connections were loose, and the lack of directional structural support led to pore collapse under compression, failing to form an effective load-bearing structure. (The random pores resulted in uneven loading of bifunctional clusters, with functional sites clustering in some areas and blank areas in others. The tortuous mass transfer channels made it difficult for formaldehyde molecules to fully contact the catalytic sites, leading to a simultaneous and significant decrease in adsorption and decomposition efficiency. The loose network structure was susceptible to moisture erosion and collapse, resulting in substantial loss of functional components and extremely poor stability. Therefore, temperature gradient-guided directional pore construction is crucial for ensuring the material's structural density and uniformity. Room temperature gelation cannot form an effective supporting structure, leading to a complete collapse of both mechanical and functional properties.)

[0118] Comparative Example 5 (without N-TiO2@GQDs): The lack of catalytic function leads to purification failure. While the 24-hour formaldehyde adsorption capacity is high, the decomposition rate is only 12%, and after damp heat aging, the decomposition rate is 8%. NH2-ZIF-8, as a highly efficient adsorbent, can rapidly enrich formaldehyde, but lacks the photocatalytic degradation function of N-TiO2@GQDs. Once adsorption reaches saturation, it cannot be regenerated, and the adsorbed formaldehyde is easily desorbed, causing secondary pollution. It completely lacks long-term purification capabilities. Antibacterial performance mainly depends on GQDs and is unrelated to the catalytic component, therefore showing no significant change; hydrophobic properties are unaffected by the lack of the catalytic component and remain stable. N-TiO2@GQDs are the core component for formaldehyde degradation. Retaining only NH2-ZIF-8 only achieves physical adsorption and cannot complete the "adsorption-degradation" cycle, failing to meet the requirements for long-term air purification.

[0119] Comparative Example 6 (without NH2-ZIF-8): Lack of adsorption enrichment leads to inefficient catalysis. Formaldehyde adsorption capacity was low after 24 hours, with a decomposition rate as low as 26.1%. N-TiO2@GQDs rely on the pre-enrichment effect of NH2-ZIF-8 to increase local formaldehyde concentration. In Comparative Example 6, the absence of this component makes it difficult for low-concentration formaldehyde to be captured by the catalyst, significantly reducing the catalytic reaction rate. Simultaneously, insufficient adsorption sites result in a significant decrease in overall purification efficiency. Without the protection of NH2-ZIF-8, N-TiO2@GQDs are directly exposed to the environment, making them susceptible to moisture erosion and impurity adhesion, leading to a continuous decline in catalytic activity. Therefore, the adsorption enrichment of NH2-ZIF-8 and the catalytic degradation of N-TiO2@GQDs form a synergistic effect; the absence of adsorbent components leads to a significant reduction in catalytic efficiency, preventing the achievement of high-efficiency purification.

[0120] Comparative Example 7 (Preparation by Physical Blending): Network framework destruction leads to complete failure. Compressive modulus, tensile strength, and stress retention are all significantly reduced. Physical blending mixes all components at once, causing inorganic fibers, GQDs, and bifunctional clusters to agglomerate, disrupting the integrity of the silica sol network framework and creating numerous structural defects. Under compression, the network easily collapses, resulting in a complete breakdown of mechanical properties. Component agglomeration leads to uneven distribution of functional sites, and some catalytic sites are encapsulated, preventing contact with formaldehyde; simultaneously, the disrupted network structure hinders mass transfer, further reducing purification efficiency. The agglomerated components have extremely weak bonding with the matrix, easily detaching and leaking under humid and hot conditions, exhibiting extremely poor stability. Therefore, the process of "stepwise matrix construction and in-situ loading of functional components" is crucial to ensuring the integrity of the network framework and the uniform dispersion of functional components. Physical blending leads to component agglomeration and structural destruction, resulting in a comprehensive deterioration of all core properties.

[0121] Comparative Example 8 (top direction -30℃, bottom direction -50℃): The temperature in the top direction is lower than the design range (-25℃~-15℃), while the temperature in the bottom direction is higher than the design range (-90℃~-70℃), resulting in insufficient temperature gradient, indistinct gradient channel structure, and reduced difference in pore size between the surface and core layers (surface layer 30~40μm, core layer 5~8μm). Insufficient pore density in the core layer reduces mechanical load-bearing capacity; excessively large pores in the surface layer reduce the density of functional sites, affecting mass transfer efficiency.

[0122] Comparative Example 9 (top direction -5℃, bottom direction -100℃): The excessively high temperature at the top and the excessively low temperature at the bottom resulted in an imbalance in the ice crystal growth rate, leading to excessive surface pore growth (10~20μm) and overly dense core pores (0.5~2μm). The excessively large surface pores resulted in insufficient mechanical support, while the overly dense core pores increased mass transfer resistance, leading to a decline in overall performance. The incomplete gradient channel structure reduced the material's structural stability, making it easier for moisture to penetrate and disrupt the functional component loading state. Therefore, the temperature parameters for bidirectional freezing (top direction -25℃~-15℃, bottom direction -90℃~-70℃) are crucial for constructing a complete gradient channel. Temperature deviations resulted in an indistinct gradient structure, failing to balance mechanical load-bearing capacity and mass transfer efficiency, resulting in performance weaker than Example 2.

[0123] Comparative Example 10 (mass ratio 1:1): The proportion of NH2-ZIF-8 was too low, resulting in insufficient adsorption sites and an inability to effectively enrich formaldehyde. This led to a lack of sufficient raw materials for the catalytic reaction of N-TiO2@GQDs. Although the catalytic sites were relatively sufficient, the overall purification efficiency decreased due to limitations imposed by the adsorption process. Comparative Example 11 (mass ratio 8:1): The proportion of NH2-ZIF-8 was too high, resulting in sufficient adsorption sites but insufficient catalytic sites. The adsorbed formaldehyde could not be degraded in time, leading to rapid saturation of the adsorption sites. Furthermore, excess NH2-ZIF-8 tended to aggregate, hindering the diffusion of formaldehyde molecules to the catalytic sites and further reducing decomposition efficiency. This imbalance resulted in some functional sites being idle or overloaded, making them more susceptible to deactivation when exposed to moisture, thus reducing stability. Therefore, a mass ratio of NH2-ZIF-8 to N-TiO2@GQDs of 3:1 to 5:1 is crucial for achieving a synergistic match between adsorption and catalysis. Deviations in this ratio lead to an excess of one function and an insufficient function of the other, significantly reducing both purification efficiency and stability.

[0124] Comparative Example 12 (N-TiO2@GQDs unmodified): In Example 2, after N-TiO2@GQDs were modified with APTES, the silanol groups generated by hydrolysis underwent a condensation reaction with the gel network, achieving chemical anchoring. In Comparative Example 12, the unmodified N-TiO2@GQDs were only loaded through physical adsorption, resulting in weak binding to the matrix and easy detachment during testing, leading to a continuous reduction in catalytic sites. After water infiltration, the physically adsorbed functional particles were more easily detached from the matrix, and water accelerated particle aggregation, further reducing catalytic activity. The unmodified treatment did not affect the matrix structure or the loading of the adsorbed components, thus maintaining stable mechanical and adsorption properties.

[0125] This application provides an aerogel composite thermal insulation material with a multi-level, multi-scale synergistic structural design. Specifically, firstly, aluminosilicates derived from the alkali fusion of red brick waste are used as the matrix to achieve high-value utilization of solid waste; then, inorganic fibers are compositely modified using γ-aminopropyltriethoxysilane and silica sol to construct a reinforcing skeleton that is strongly bonded to the matrix; subsequently, a bidirectional freezing process with controlled specific temperature parameters is used to directionally form a gradient pore structure with a dense surface layer and a loose core layer, and the core layer has an in-plane micro-wrinkled honeycomb structure to enhance toughness and light scattering; finally, bifunctional clusters with a specific mass ratio (3:1~5:1) and a nanocluster structure (diameter 150-200nm, 3-5 NH2-ZIF-8 surrounding 1-2 N-TiO2@GQDs) are in situ loaded using the active interface of the wet gel, and then modified hydrophobically with methyltrimethoxysilane. Structurally, it achieves integrated synergy from fiber-reinforced skeleton (macroscopic), gradient pores (mesoscopic), to two-dimensional intercalation and bifunctional clusters (microscopic), resulting in a material compressive modulus of 7.5~8.5MPa and a fracture strength ≥1.2MPa. Functionally, the unique structural design ensures uniform and robust loading of functional components and creates a highly efficient adsorption-catalysis microenvironment, enabling the material to exhibit excellent formaldehyde purification capacity under visible light (24h adsorption capacity 150-170mg / g, decomposition rate 85%~90%), antibacterial rate ≥99%, and water contact angle of 132°~140°.

[0126] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aerogel composite thermal insulation material, characterized in that, Includes the following steps: Silica sol was prepared using waste red bricks; Reinforcing materials are added to silica sol to form a composite sol; The composite sol was subjected to bidirectional freezing treatment, and the frozen product was aged to obtain a wet gel matrix. The wet gel matrix was immersed in a composite photocatalytic solution containing NH2-ZIF-8 and N-TiO2@GQDs modified with γ-aminopropyltriethoxysilane for loading treatment; After drying, an aerogel composite insulation material is obtained.

2. The preparation method according to claim 1, characterized in that, The specific operation method for preparing silica sol using red brick waste is as follows: the red brick waste is subjected to alkali fusion treatment, then dissolved in water and filtered, and the pH is adjusted to form silica sol; and / or, the alkali fusion treatment is performed using sodium hydroxide, the mass ratio of red brick waste to alkali is 1:1.5~2.5 and / or, the alkali fusion temperature is 300~400℃; and / or, the solid content of the formed silica sol is 30%-50%.

3. The preparation method according to claim 1, characterized in that, The reinforcing material is an inorganic fiber modified with a silane coupling agent; and / or, the inorganic fiber is at least one of modified glass fiber and basalt fiber, with a fiber diameter of 10-15 μm and a length of 1-3 mm.

4. The preparation method according to claim 1, characterized in that, When adding reinforcing materials, graphene quantum dots are also added; and / or, the graphene quantum dots have a particle size of 5~10 nm.

5. The preparation method according to claim 1, characterized in that, The bidirectional freezing process is as follows: the composite sol is placed in the mold, and cooling at different temperatures is applied simultaneously in the top and bottom directions. The top cooling temperature is -25℃ to -15℃ and the bottom cooling temperature is -90℃ to -70℃, or the top cooling temperature is -90℃ to -70℃ and the bottom cooling temperature is -25℃ to -15℃.

6. The preparation method according to claim 1, characterized in that, The aging treatment temperature is 40℃~60℃, and the time is 12~24h.

7. The preparation method according to claim 1, characterized in that, The composite photocatalytic solution has a mass concentration of 10-30 mg / mL; the mass ratio of NH2-ZIF-8 to N-TiO2@GQDs is 3:1 to 5:1; and / or, the particle size of N-TiO2@GQDs is 80-100 nm, and the N doping amount is 2-4 at%; and / or, the particle size of NH2-ZIF-8 is 80-100 nm, and the specific surface area is ≥1200 m². 2 / g.

8. The preparation method according to claim 1, characterized in that, It also includes immersing the loaded material in a hydrophobic material solution and drying it to obtain an aerogel composite thermal insulation material; and / or, the hydrophobic material solution is an ethanol solution of methyltrimethoxysilane with a mass concentration of 5% to 8%.

9. The preparation method according to any one of claims 1-8, characterized in that, Drying is carried out using a gradient temperature increase method; and / or the program is as follows: 50℃~70℃, drying for 1~3 hours, then 75℃~100℃, drying for 1~3 hours, and finally drying at 110℃~120℃ for 1~3 hours.

10. The aerogel composite thermal insulation material prepared by the preparation method according to any one of claims 1-9.

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