Hydrotalcite supported MOFs composite material, and preparation method and application thereof

Abstract

This invention discloses a hydrotalcite-loaded MOFs composite material, its preparation method, and its application, belonging to the field of inorganic functional material synthesis. This invention uses magnesium-aluminum hydrotalcite as a carrier to load MOFs onto it, forming a hydrotalcite-loaded MOFs composite material. By expanding the main layers of the hydrotalcite and assembling them with the MOFs, the MOFs can be inserted into the interlayer, structurally supporting the hydrotalcite, delaying the collapse of the hydrotalcite's layered structure, thereby improving the thermal stability of the hydrotalcite and increasing the thermal stabilizing effect of magnesium-aluminum hydrotalcite on PVC.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional material synthesis. Specifically, it relates to a hydrotalcite-supported MOF composite material, its preparation method, and its application. Background Technology

[0002] Polyvinyl chloride (PVC) is an important basic raw material widely used in many industrial fields. PVC resin has poor light and heat stability, and its molecular chain contains unstable structures and residual free radicals. At temperatures above 100°C or under prolonged exposure to sunlight, PVC decomposes and releases hydrogen chloride (HCl). HCl further catalyzes the degradation reaction, resulting in a significant decrease in its physical and mechanical properties. With the rapid development of the PVC industry, various products exhibit significant differences in key indicators such as weather resistance, processing performance, and thermal stability.

[0003] Currently, the most mature heat stabilizers on the market are lead salts, organotin compounds, and calcium-zinc compounds. Layered double hydroxides (LDHs) possess unique pH-regulating capabilities and biocompatibility advantages, making them suitable as novel environmentally friendly materials for heat stabilization systems in PVC products. Compared to traditional lead salts (containing heavy metals), metal soaps (easily oxidized and degraded), and organotin compounds (high raw material costs), LDHs, through the dynamic exchange mechanism of interlayer anions and the synergistic effect of alkaline sites on the layers, demonstrate the feasibility of replacing existing systems and show significant application value in the field of green polymer materials.

[0004] Hydrotalcite (LDH) is a two-dimensional layered composite metal hydroxide. As the basic building block of layered double hydroxides, its main layers are composed of divalent (M... 2+ ) and trivalent (M 3+ Metal cations are bridged by hydroxyl groups to form M 2+ 1-X M 3+ X (OH)2 structural unit, this layer is exchangeable with anionic guests (such as NO3⁻, CO3⁻) between layers. 2- They are arranged in an orderly manner through electrostatic interactions, while retaining a specific amount of water of crystallization molecules in the interlayer domains. Their general chemical formula is: [M... 2+ 1-X M 3+ X (OH)2] X+ [An - ] X / n•zH2O. Due to the special nature of this structure, hydrotalcite is alkaline and reacts with HCl gas produced during the thermal degradation of PVC, thereby improving the thermal stability of PVC. However, because hydrotalcite is significantly hydrophilic, has poor thermal stability, weak bonding with PVC, and tends to agglomerate, its effect on improving the thermal stability of PVC is not good. Summary of the Invention

[0005] To address the technical problem of poor thermal stability in existing hydrotalcite materials, which leads to unsatisfactory thermal stability against PVC, this invention provides a hydrotalcite-loaded MOF composite material, its preparation method, and its application. This invention uses magnesium-aluminum hydrotalcite as a carrier to load MOFs onto it, forming a hydrotalcite-loaded MOF composite material.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first objective of this invention is to provide a hydrotalcite-loaded MOFs composite material, which uses magnesium aluminum hydrotalcite as a carrier to load MOFs onto the magnesium aluminum hydrotalcite to form a hydrotalcite-loaded MOFs composite material.

[0008] The MOFs account for 4.76% to 35% of the total mass of the hydrotalcite-loaded MOFs composite material.

[0009] The MOFs are ZIF-7 and ZIF-8.

[0010] The second objective of this invention is to provide a method for preparing hydrotalcite-supported MOFs composite materials, comprising the following steps: Soluble aluminum salt, soluble magnesium salt, precipitant and MOFs are ultrasonically mixed in a solvent and reacted at 100℃~190℃ to obtain hydrotalcite-supported MOFs composite material.

[0011] In a preferred embodiment, the mass ratio of the soluble aluminum salt, the soluble magnesium salt, and the precipitant is 1–2:3–4:1.

[0012] In a preferred embodiment, the soluble aluminum salt is aluminum nitrate nonahydrate and the soluble magnesium salt is magnesium nitrate hexahydrate.

[0013] In a preferred embodiment, the precipitant is urea, ammonium bicarbonate, or hexamethylenetetramine.

[0014] In a preferred embodiment, the solvent is a 50% (v / v) aqueous solution of ethanol. The volume ratio of ethanol to water is 1:1.

[0015] In a preferred embodiment, the solvothermal reaction takes 12 hours.

[0016] A third objective of this invention is to provide the application of the hydrotalcite-supported MOFs composite material as a stabilizer for polyvinyl chloride, wherein the application method is to heat and mix polyvinyl chloride and the hydrotalcite-supported MOFs composite material at 180°C.

[0017] In a preferred embodiment, the mass ratio of the hydrotalcite-loaded MOFs composite material to polyvinyl chloride is 1:3.2 to 41.8.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The metal-organic framework (MOF) materials of this invention utilize imidazole organic ligands to chemically replace the bridging oxygen groups of traditional zeolite molecular sieves, forming a coordination network between the metal central cation and the imidazole nitrogen atoms, ultimately resulting in a zeolite-like topology with a regular channel system. This invention uses magnesium-aluminum hydrotalcite (LDH) as a carrier to load MOFs onto it, forming a hydrotalcite-loaded MOF composite material. By expanding the main layers of the hydrotalcite and assembling it with the MOFs, the MOFs can be inserted into the interlayer, structurally supporting the LDH and delaying the collapse of the LDH's layered structure. This improves the performance of the hydrotalcite, increases its thermal stability against PVC, and solves the problem of weak bonding and agglomeration between existing hydrotalcites and PVC, resulting in poor performance of hydrotalcite in improving the thermal stability of PVC. Attached Figure Description

[0019] Figure 1 The images show XRD comparisons of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 9 of this invention and the urea hydrotalcite obtained in Comparative Example 1. Specifically, image a shows the XRD comparison of the hydrotalcite-loaded MOFs composite materials obtained in Examples 6 to 9 and Example 2 and the urea hydrotalcite obtained in Comparative Example 1; image b shows the XRD comparison of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 5.

[0020] Figure 2 The figures show a comparison of thermogravimetric analysis (TGA) results of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 9 of this invention and the urea hydrotalcite obtained in Comparative Example 1. Specifically, Figure a shows a comparison of the TGA results of the hydrotalcite-loaded MOFs composite materials obtained in Examples 6 to 9 and Example 2 and the urea hydrotalcite obtained in Comparative Example 1; Figure b shows a comparison of the TGA results of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 5.

[0021] Figure 3The infrared spectra of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 9 of the present invention and the urea hydrotalcite obtained in Comparative Example 1 are shown. Among them, Figure a shows the infrared spectra of the hydrotalcite-loaded MOFs composite materials obtained in Examples 6 to 9 and Example 2 and the urea hydrotalcite obtained in Comparative Example 1; Figure b shows the infrared spectra of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 5. Detailed Implementation

[0022] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0023] Hydrotalcite (LDH) is a two-dimensional layered composite metal hydroxide. As the basic building block of layered double hydroxides, its main layers are composed of divalent (M... 2+ ) and trivalent (M 3+ Metal cations are bridged by hydroxyl groups to form M 2+ 1-X M 3+ X(OH)2 + Structural unit, the layer with exchangeable anionic guests (such as NO3) between layers. - CO3 2- They are arranged in an orderly manner through electrostatic interactions, while retaining a specific amount of water of crystallization molecules in the interlayer domains. Their general chemical formula is: [M... 2+ 1-X M 3+ X (OH)2] X+ [An - ] X / n •zH2O. Due to the unique structure of this compound, hydrotalcite is alkaline and neutralizes the HCl gas produced during the thermal degradation of PVC, thereby improving the thermal stability of PVC. However, because hydrotalcite is significantly hydrophilic, has poor thermal stability, weak bonding with PVC, and is prone to agglomeration, its effect on PVC thermal stability is unsatisfactory. Based on the above problems, this invention provides a hydrotalcite-supported MOFs composite material, its preparation method, and its application.

[0024] The technical solution of the present invention will be analyzed in detail below.

[0025] This invention provides a hydrotalcite-loaded MOFs composite material, which uses magnesium aluminum hydrotalcite as a carrier and loads MOFs onto the magnesium aluminum hydrotalcite to form a hydrotalcite-loaded MOFs composite material; the mass percentage of the MOFs in the hydrotalcite-loaded MOFs composite material is 4.76% to 35%; the MOFs are ZIF-7 or ZIF-8.

[0026] In the above technical solution, the present invention modifies magnesium aluminum hydrotalcite with MOFs, loads MOFs on magnesium aluminum hydrotalcite, and prepares hydrotalcite-loaded MOFs composite material as a new type of heat stabilizer material, thereby increasing the heat stabilizing effect of hydrotalcite on PVC.

[0027] The technical solution of the present invention will be further illustrated below through the following embodiments and comparative examples.

[0028] Example 1 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 (Zn) crystalline material.

[0029] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.1g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 9.09%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 130℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (130℃).

[0030] Example 2 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0031] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.2g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 16.67%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 130℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (0.2g).

[0032] Example 3 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0033] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.3g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 23.08%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 130℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (0.3g).

[0034] Example 4 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0035] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g of aluminum nitrate nonahydrate, 6.4g of magnesium nitrate hexahydrate, 2.1g of urea, and 0.4g of ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 28.57%). Add 100mL of anhydrous ethanol and 100mL of water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 130℃ for 12h. After filtration and washing, dry at 60℃ for 24h, and grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (0.4g).

[0036] Example 5 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0037] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.5g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 33.33%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 130℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (0.5g).

[0038] Example 6 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0039] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.1g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 9.09%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 100℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (100℃).

[0040] Example 7 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0041] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.1g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 9.09%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 150℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (150℃).

[0042] Example 8 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0043] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.1g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 9.09%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 170℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (170℃).

[0044] Example 9 A method for preparing a hydrotalcite-supported MOF composite material includes the following steps: Synthesis of S1, ZIF-7 (Zn): 2.23 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 15 mL of N,N-dimethylformamide, labeled as solution A. Simultaneously, an organic ligand solution was prepared by dissolving 6.244 mmol of benzimidazole in 15 mL of methanol, labeled as solution B. Solution B was slowly added dropwise to solution A at room temperature, and the mixture was continuously magnetically stirred for 5 min to form a homogeneous mixture. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), sealed, and subjected to a solvothermal reaction at 120 °C for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature, collected, centrifuged, washed three times with methanol, and vacuum dried at 60 °C for 12 h to obtain a white powdery ZIF-7 crystalline material.

[0045] S2, Hydrotalcite-supported MOFs composite material: Weigh 3.75g aluminum nitrate nonahydrate, 6.4g magnesium nitrate hexahydrate, 2.1g urea, and 0.1g ZIF-7 (Zn) into a beaker (the mass percentage of MOFs in the hydrotalcite-supported MOFs composite material is 9.09%). Add 100mL anhydrous ethanol and 100mL water. Mix thoroughly by ultrasonic vibration for 20min at room temperature. Then, transfer the mixture to a 400mL reactor and react at 190℃ for 12h. After filtration and washing, dry at 60℃ for 24h, then grind into powder to obtain the hydrotalcite-supported MOFs composite material, denoted as LDH@ZIF-7 (190℃).

[0046] To further illustrate the effects of the present invention, comparative examples are also provided, as follows: Comparative Example 1 A method for preparing urea hydrotalcite includes the following steps: Weigh 2.1g of urea, 3.75g of aluminum nitrate nonahydrate, and 6.4g of magnesium nitrate hexahydrate into a 150mL beaker. Add 50mL of water and 50mL of anhydrous ethanol. Place a magnetic stir bar in the container and stir magnetically for 20 minutes at room temperature until completely dissolved. Transfer the solution to a reaction vessel, seal it tightly, and place it in a constant temperature drying oven at 150℃ for 12 hours. After the reaction is complete, remove the reaction vessel and allow it to cool naturally to room temperature. Filter and wash the suspension to obtain a white solid. Then, place it in a constant temperature drying oven at 60℃ for 24 hours. After drying, grind it into powder to obtain urea hydrotalcite.

[0047] Congo Red Performance Test The hydrotalcite-loaded MOFs composite material prepared in Examples 1 to 9 of this invention or the urea hydrotalcite prepared in Comparative Example 1 was mixed evenly with polyvinyl chloride resin in a test tube. Congo red test paper was suspended above the test tube, and the test tube was then heated in an oil bath at 180°C. Finally, the time it took for the Congo red test paper to turn from red to blue was taken as the evaluation index of thermal stability and was recorded as the static thermal stability time.

[0048] Table 1 shows that PVC exhibits the best thermal stability at a synthesis temperature of 130℃, with a Congo red time of 98 minutes. Using 130℃ as the optimal synthesis temperature, hydrotalcite-loaded MOF composites were synthesized by varying the amount of MOFs added. According to the thermal stability evaluation results, the hydrotalcite-loaded MOF composite material with 0.2g ZIF-7 added in Example 2 showed the best thermal stability, with a Congo red time of 128 minutes.

[0049] Figure 1The XRD patterns of the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 9 of this invention and the urea hydrotalcite obtained in Comparative Example 1 are shown. The XRD patterns show relatively stable diffraction peak baselines, with some minor impurities, but the peak widths are narrow and sharp. Five characteristic hydrotalcite diffraction peaks with relatively high diffraction intensity are observed at 2θ, appearing near 2θ values ​​of 11.6°, 23.4°, 35.4°, 39.5°, and 46.9°, indicating that this method successfully synthesized LDH@ZIF-7. The XRD patterns of LDH@ZIF-7 all show characteristic absorption peaks of hydrotalcite, but not those of ZIF-7, possibly because ZIF-7 exists in an amorphous form.

[0050] Figure 2 The thermogravimetric analysis (TGA) comparison charts are shown for the hydrotalcite-loaded MOFs composite materials obtained in Examples 1 to 9 of this invention and the urea hydrotalcite obtained in Comparative Example 1. The TGA curves of LDH@ZIF-7 synthesized at 100℃, 170℃, and 190℃ show significant deviations compared to the curves of urea hydrotalcite, possibly due to incomplete hydrotalcite growth or structural damage. LDH@ZIF-7 synthesized at 130℃ and 150℃, and LDH@ZIF-7 synthesized with different MOF ratios, exhibit three weight loss ranges: the first weight loss stage for LDH@ZIF-7 at different synthesis temperatures is from 40℃ to 221℃, primarily involving the removal of adsorbed water and residual solvents, with a weight loss rate of 13% at 221℃; the second weight loss stage is from 221℃ to 574℃, representing ligand decomposition, specifically the removal of carbonate ions and dehydration of lamellar hydroxyl groups. The third stage, from 570℃ to 800℃, involves structural collapse and framework disintegration. The first weight loss stage for LDH@ZIF-7 with different MOF ratios occurs between 40℃ and 220℃, presumably due to the release of adsorbed water on the LDH@ZIF-7 surface and crystal water between crystal layers; at this stage, the sample still maintains a layered structure. The second weight loss stage occurs between 221℃ and 560℃, corresponding to the decomposition reaction of interlayer carbonates; the mass loss mainly comes from carbonate removal and the dehydration of hydroxyl groups in the layers. As the temperature rises above 580℃, the material undergoes structural collapse, the layered framework completely disintegrates, and a mixed oxide is ultimately formed. The thermogravimetric curves show that the sample synthesized at 130℃ with the addition of 0.2g ZIF-7 exhibits a higher thermal stability compared to samples synthesized under other conditions, with the thermogravimetric curves shifting towards higher temperatures.

[0051] Figure 3 The images show the infrared spectra of the hydrotalcite-supported MOF composite materials obtained in Examples 1 to 9 of this invention, and the urea hydrotalcite obtained in Comparative Example 1. The peak shapes of LDH@ZIF-7 synthesized at different synthesis temperatures and with different MOF ratios are basically consistent, with the peak at 3446 cm⁻¹ being the most prominent. -1The positions on the left and right are attributed to the stretching vibration peaks of the hydroxyl groups and adsorbed water in hydrotalcite, at 1631 cm⁻¹. -1 The location is attributed to the bending vibration peak of H2O, at 1349 cm⁻¹. -1 Location belongs to CO3 2- Asymmetric stretching vibration. Furthermore, at 776 cm⁻¹... -1 684cm -1 549cm -1 A weak peak was observed, which is attributed to the lattice vibrations of oxides MgO and Al2O3. Therefore, LDH@ZIF-7 was successfully synthesized. The infrared analysis of LDH@ZIF-7 shows that the functional group structure is mainly composed of MgAl-LDHs.

[0052] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A hydrotalcite-loaded MOFs composite material, characterized in that, Using magnesium aluminum hydrotalcite as a carrier, MOFs are loaded onto magnesium aluminum hydrotalcite to form hydrotalcite-loaded MOFs composite materials. The MOFs account for 4.76% to 35% of the total mass of the hydrotalcite-loaded MOF composite material. The MOFs are ZIF-7 or ZIF-8.

2. A method for preparing the hydrotalcite-supported MOFs composite material according to claim 1, characterized in that, Includes the following steps: Soluble aluminum salt, soluble magnesium salt, precipitant and MOFs are ultrasonically mixed in a solvent and reacted at 100℃~190℃ to obtain hydrotalcite-supported MOFs composite material.

3. The method for preparing the hydrotalcite-supported MOFs composite material according to claim 2, characterized in that, The mass ratio of the soluble aluminum salt, soluble magnesium salt, and precipitant is 1–2:3–4:

1.

4. The method for preparing the hydrotalcite-supported MOFs composite material according to claim 2, characterized in that, The soluble aluminum salt is aluminum nitrate nonahydrate, and the soluble magnesium salt is magnesium nitrate hexahydrate.

5. The method for preparing the hydrotalcite-supported MOFs composite material according to claim 2, characterized in that, The precipitant is urea, ammonium bicarbonate, or hexamethylenetetramine.

6. The method for preparing the hydrotalcite-supported MOFs composite material according to claim 2, characterized in that, The solvent is a 50% (v / v) aqueous solution of ethanol.

7. The application of the hydrotalcite-supported MOFs composite material according to claim 1 as a stabilizer for polyvinyl chloride, characterized in that, The application method is as follows: polyvinyl chloride and the hydrotalcite-loaded MOFs composite material are heated and mixed at 180°C.

8. The application of the hydrotalcite-supported MOFs composite material according to claim 7 as a stabilizer for polyvinyl chloride, characterized in that, The mass ratio of the hydrotalcite-loaded MOFs composite material to polyvinyl chloride is 1:3.2 to 41.8.

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