Aluminum-iron heterometallic organic framework materials, their preparation methods and applications

Abstract

This invention relates to the field of catalytic materials technology, and more particularly to aluminum-iron heterometallic organic framework materials, their preparation methods, and applications. This invention constructs an AlFe bimetallic MOF using 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid as a ligand. The ligand precisely immobilizes Al through "regional coordination." 3+ with Fe 3+ This forms a co-catalytic center. The two carboxylic acid groups and two phenolic hydroxyl groups in its molecular structure can act as hard bases, preferentially reacting with hard acids like Al. 3+ Coordination forms stable secondary structural units; while its phenanthrene nitrogen atom acts as an intermediate base, selectively reacting with Fe. 3+ Metal coordination makes it an ideal "platform-type" ligand for constructing heterometallic bimetallic MOFs. The aluminum-iron heterometallic organic framework material prepared by the above method has both high catalytic activity and excellent thermal stability, and as a heterogeneous catalyst, it is easy to separate and recycle, providing a new solution for efficient and environmentally friendly PET polymerization catalysts.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and in particular to aluminum-iron heterometallic organic framework materials, their preparation methods and applications. Background Technology

[0002] Polyethylene terephthalate (PET) is one of the most widely used polyester materials worldwide, with applications in fibers, bottle flakes, and films. Industrially, PET is mainly synthesized through the esterification and polycondensation reaction of terephthalic acid and ethylene glycol. This process typically requires heavy metal catalysts such as antimony, germanium, and titanium. However, antimony compounds are toxic and have potential bioaccumulation, which may affect the safe application of the product in food packaging and other fields; germanium catalysts are extremely expensive; titanium catalysts, especially tetrabutyl titanate (TBT), were once extensively studied due to their high catalytic activity, but numerous studies and industrial practices have shown that TBT, as a homogeneous catalyst, has inherent defects such as causing severe yellowing of polyester products, sensitivity to hydrolysis, and difficulty in separating and recovering from the products. In recent years, researchers have improved its performance through ligand modification or immobilization. For example, the literature (European Polymer Journal, 2023, 186, 111870) developed a titanium-amino acid complex catalyst, which improved the color of the product to some extent, but still cannot fully meet the requirements of high-end applications and increases the complexity and cost of synthesis. Therefore, developing a novel catalyst system that combines high activity, excellent selectivity (good color), and easy recovery remains an urgent problem to be solved in this field.

[0003] Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. They possess ultra-high specific surface area, tunable pore structure, and well-defined and designable active sites, demonstrating great potential in the field of catalysis. Using MOFs as heterogeneous catalysts in PET synthesis is expected to solve problems such as difficult product purification, metal residue, and poor color control associated with traditional homogeneous catalysts. Currently, some studies have attempted to use single-metal MOFs for PET catalysis. The literature (Turk. J. Chem., 2022, 46, 1281-1290) studied the use of metal-organic framework material MIL-53 (Al) for the catalytic synthesis of PET. Under optimized conditions (catalyst molar content 0.05%, reaction temperature 280℃, reaction time 150 min), PET with an intrinsic viscosity of about 0.714 dL / g can be obtained, proving its feasibility as a heterogeneous catalyst. However, it is limited by the mass transfer resistance caused by the microporous structure and the lack of synergistic catalytic effect of the single aluminum metal center, resulting in low utilization of active sites and consistently low catalytic performance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide aluminum-iron heterometallic organic framework materials, their preparation methods and applications. The prepared aluminum-iron heterometallic organic framework materials have both high catalytic activity and excellent thermal stability. They exhibit excellent catalytic activity and selectivity in both esterification and polycondensation stages, significantly reducing the reaction activation energy and improving polymerization efficiency.

[0005] The following is a summary of this disclosure to provide a basic understanding of some aspects. This summary is not intended to identify key or important elements, nor is it intended to limit the implementation or any aspects of the claims. Furthermore, this summary provides a simplified overview of some aspects that can be described in more detail in other parts of this disclosure.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] The first aspect of this invention provides a method for preparing an aluminum-iron heterometallic organic framework material, comprising the following steps:

[0008] Dissolve 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid in NaOH solution, then dilute with N,N-dimethylformamide and filter to obtain the ligand solution;

[0009] Weigh out aluminum nitrate nonahydrate and add it to deionized water to prepare an aluminum nitrate solution; weigh out ferric nitrate nonahydrate and add it to N,N-dimethylformamide to prepare a ferric nitrate solution.

[0010] Under stirring conditions, aluminum nitrate solution and ferric nitrate solution were added to the ligand solution, and tetrafluoroboric acid and formic acid were added dropwise until a dark brown suspension was formed. The dark brown suspension was transferred to a high-pressure reactor, heated to 120-130 °C, and reacted at a constant temperature for 20-24 h. After the reaction was completed, the temperature was lowered to room temperature, the resulting reaction solution was filtered, washed, and replaced with acetone for 20-24 h. The solution was then dried at room temperature to obtain the AlFe-MOF catalyst.

[0011] In the above preparation method, AlFe bimetallic MOFs are constructed using 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid as a ligand. The ligand precisely immobilizes Al through "partition coordination". 3+ with Fe 3+ This forms a co-catalytic center. The two carboxylic acid groups and two phenolic hydroxyl groups in its molecular structure can act as hard bases, preferentially reacting with hard acids like Al. 3+ Coordination forms stable secondary structural units; and its phenanthroline nitrogen atom acts as an intermediate base, selectively reacting with Fe. 3+Metal coordination, with its "partitioned coordination" characteristic, makes it an ideal "platform-type" ligand for constructing heterometallic bimetallic MOFs. The aluminum-iron heterometallic organic framework material prepared by the above method exhibits both high catalytic activity and excellent thermal stability, and as a heterogeneous catalyst, it is easy to separate and recover, providing a new solution for efficient and environmentally friendly PET polymerization catalysts.

[0012] Preferably, the molar ratio of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid to NaOH is 1:(4-5), and the concentration of the NaOH solution is 1 mol / L.

[0013] Preferably, the molar ratio of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid, zinc nitrate hexahydrate, and ferric nitrate nonahydrate is 1:1:1.

[0014] Preferably, the mixed solution is heated to 120-130 °C in a high-pressure reactor at a heating rate of 5 °C / min; after the reaction is completed, it is cooled to room temperature at a rate of 0.5 °C / min.

[0015] As a preferred embodiment, the preparation method of the 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid is as follows:

[0016] Weigh out 4,7-dicarboxylic acid-1,10-phenanthroline and dissolve it in sulfuric acid solution. Cool to 0–5 °C, add FeSO4·7H2O, and dropwise add 30 wt% hydrogen peroxide solution while controlling the temperature ≤10 °C. After the hydrogen peroxide solution is completely added, stir the reaction at room temperature for 2–4 h. Monitor the reaction progress by TLC. After the reaction is complete, quench excess H2O2 with Na2SO3 solution, extract with ethyl acetate, collect the aqueous phase, acidify to pH=2, filter the precipitated solid, dry the solid product, and recrystallize with an ethanol / water mixed solvent to obtain 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0017] In the above method for preparing 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid, FeSO4·7H2O dissociates in sulfuric acid to release Fe 2+ It reacts with H2O2 to generate hydroxyl radicals (·OH) and Fe. 3+ Fe 3+ It can also be reduced to Fe by excess H2O2. 2 + A catalytic cycle is formed; hydroxyl radicals (·OH) attack the 3 and 8 aromatic carbons of 4,7-dicarboxylic acid-1,10-phenanthroline, undergoing electrophilic substitution, introducing two hydroxyl groups, and generating 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0018] Preferably, the concentration of the sulfuric acid solution is 1 mol / L, and the mass-to-volume ratio of the 4,7-dicarboxylic acid-1,10-phenanthroline to the sulfuric acid solution is 0.5 g:(25-40 mL); and / or,

[0019] The molar volume ratio of the 4,7-dicarboxylic acid-1,10-phenanthroline, FeSO4·7H2O and hydrogen peroxide solution is (1.8–2.0) mmol:(0.3–0.5) mmol:1 mL.

[0020] As a preferred embodiment, the preparation method of the 4,7-dicarboxylic acid-1,10-phenanthroline is as follows:

[0021] Weigh 4,7-dimethyl-1,10-phenanthroline and dissolve it in 1 mol / L NaOH solution. Add KMnO4 in portions, heat to 40-60 °C, and reflux for 4-6 h. Cool to room temperature, filter, and acidify the filtrate to pH 2 with dilute HCl. Filter again, wash the precipitate with water, dry it, and recrystallize it with an ethanol / water mixed solvent to obtain 4,7-dicarboxylic acid-1,10-phenanthroline.

[0022] In the above method for preparing 4,7-dicarboxylic acid-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline is oxidized by KMnO4 under alkaline (NaOH) and heating conditions, wherein the methyl group (-CH3) is oxidized to the carboxyl group (-COOH), and KMnO4 is reduced to MnO2 to obtain the disodium salt of 4,7-dicarboxylic acid-1,10-phenanthroline; the disodium salt of 4,7-dicarboxylic acid-1,10-phenanthroline reacts with dilute HCl, and after acidification, the carboxyl group is freed, and the product precipitates in the form of carboxylic acid, thus obtaining 4,7-dicarboxylic acid-1,10-phenanthroline.

[0023] Preferably, the molar volume ratio of the 4,7-dimethyl-1,10-phenanthroline, KMnO4 and NaOH solution is (3.5-4.5):(28-36):50 mL.

[0024] A second aspect of the present invention provides an aluminum-iron heterometallic organic framework material, which is prepared by the preparation method described in the first aspect.

[0025] The third aspect of the present invention provides the application of the aluminum-iron heterometallic organic framework material described in the second aspect as a catalyst in the synthesis of polyethylene terephthalate, wherein the polyethylene terephthalate is synthesized using terephthalic acid and ethylene glycol as the main raw materials, and the amount of the aluminum-iron heterometallic organic framework material is 199 to 500 ppm of terephthalic acid.

[0026] The method for preparing the aluminum-iron heterometallic organic framework material of the present invention utilizes the "partition coordination" characteristic of the 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid ligand to successfully construct an AlFe bimetallic MOF. This MOF material has a robust framework that can withstand the high temperature of 280 °C during PET polymerization, maintains a stable crystal structure, and the active sites (Al / Fe heterometallic nodes) do not undergo significant sintering, loss, or deactivation, ensuring the stable progress of the catalytic process. In addition, it exhibits excellent catalytic activity in both the esterification and polycondensation stages, significantly reducing the reaction activation energy and improving the polymerization efficiency.

[0027] The aluminum-iron heterometallic organic framework material of the present invention has both high catalytic activity and excellent thermal stability. Fe and Al form a synergistic catalytic effect, exhibiting excellent catalytic activity and selectivity in both esterification and polycondensation stages, significantly reducing the reaction activation energy and improving polymerization efficiency.

[0028] Compared with traditional titanium-based catalysts, the aluminum-iron heterometallic organic framework material of this invention is stable at high temperatures and does not trigger side reactions. The PET prepared by this invention has a lower b-value (yellow index), better color, and higher quality. Attached Figure Description

[0029] Figure 1 This is the XRD pattern of the AlFe-MOF catalyst prepared in Example 1;

[0030] Figure 2 This is a cyclic stability diagram of the AlFe-MOF catalyst prepared in Example 1. Detailed Implementation

[0031] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0032] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] This application discloses an aluminum-iron heterometallic organic framework material and its preparation method. An AlFe bimetallic MOF is constructed using 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid as a ligand. The ligand precisely immobilizes Al through "regional coordination". 3+ with Fe 3+This forms a co-catalytic center. The two carboxylic acid groups and two phenolic hydroxyl groups in its molecular structure can act as hard bases, preferentially reacting with hard acids like Al. 3+ Coordination forms stable secondary structural units; and its phenanthroline nitrogen atom acts as an intermediate base, selectively reacting with Fe. 3+ Metal coordination, with its "partitioned coordination" characteristic, makes it an ideal "platform-type" ligand for constructing heterometallic bimetallic MOFs. The aluminum-iron heterometallic organic framework material of this application combines high catalytic activity with excellent thermal stability, and as a heterogeneous catalyst, it is easy to separate and recycle, providing a new solution for efficient and environmentally friendly PET polymerization catalysts.

[0034] Specifically, the preparation method of the aluminum-iron heterometallic organic framework material of this application includes the following steps:

[0035] Dissolve 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid in a 1 mol / L NaOH solution, then dilute with N,N-dimethylformamide. Filter through a 0.22 µm membrane to remove insoluble impurities, obtaining the ligand solution. Weigh aluminum nitrate nonahydrate and add it to deionized water, sonicating until completely dissolved to prepare an aluminum nitrate solution. Weigh ferric nitrate nonahydrate and add it to N,N-dimethylformamide, sonicating until completely dissolved to prepare a ferric nitrate solution. Under stirring conditions, aluminum nitrate solution and ferric nitrate solution were added to the ligand solution, and tetrafluoroboric acid (HBF4) and formic acid (HCOOH) were added dropwise, immediately forming a dark brown suspension. The dark brown suspension was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and the temperature was increased to 120-130 ℃ at a heating rate of 5 ℃ / min, and the reaction was maintained at this temperature for 20-24 h. After the reaction was completed, the temperature was lowered to room temperature at a rate of 0.5 ℃ / min, and a reaction solution with brown-black blocky crystals settled at the bottom of the reactor was obtained. The reaction solution was removed, filtered, and washed twice each with DMF and hot water at 60 ℃, respectively. Then, it was replaced with acetone for 20-24 h and dried at room temperature to obtain the AlFe-MOF catalyst.

[0036] The preparation method of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid is as follows:

[0037] Weigh 4,7-dimethyl-1,10-phenanthroline and dissolve it in 1 mol / L NaOH solution. Add KMnO4 in portions, heat to 40-60 °C, and reflux for 4-6 h until the purple color fades. Cool to room temperature, filter to remove MnO2 precipitate, and acidify the filtrate with dilute HCl to pH=2 to precipitate a white or pale yellow solid. Filter, wash the precipitate with water, dry it, and recrystallize it with an ethanol / water mixed solvent to obtain 4,7-dicarboxylic acid-1,10-phenanthroline. Weigh out 4,7-dicarboxylic acid-1,10-phenanthroline and dissolve it in 1 mol / L sulfuric acid solution. Cool to 0–5 °C, add FeSO4·7H2O, and slowly add 30 wt% hydrogen peroxide solution while controlling the temperature ≤10 °C. After the hydrogen peroxide solution is added, stir the reaction at room temperature for 2–4 h. Monitor the reaction progress by TLC. After the reaction is complete, quench excess H2O2 with Na2SO3 solution, extract with ethyl acetate, collect the aqueous phase, acidify to pH=2, filter the precipitated solid, dry the solid product, and recrystallize with an ethanol / water mixed solvent to obtain 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0038] In the preparation of 4,7-dicarboxylic acid-1,10-phenanthroline, under alkaline conditions, KMnO4 acts as a strong oxidizing agent, progressively oxidizing the methyl group (-CH3) of the aromatic ring side chain: first to hydroxymethyl (-CH2OH), then to an aldehyde group (-CHO), and finally to a carboxyl group (-COOH); MnO4⁻ (purple) is reduced to MnO2 (black precipitate), which is the basis for judging the reaction endpoint (the fading of purple). In the preparation of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid, the Fenton reaction-mediated electrophilic substitution reaction of the aromatic ring generates hydroxyl radicals (・OH) in the Fe²⁺ / H2O2 system, which attack the 3 and 8 positions (sites with higher electron cloud density) of the 1,10-phenanthroline ring, introducing hydroxyl groups (-OH).

[0039] The ethanol / water mixed solvent used in the embodiments of this application is a mixed solvent of ethanol and water in a volume ratio of 2:1, and the dilute hydrochloric acid is a hydrochloric acid solution with a mass fraction of 15%.

[0040] The following examples 1-7 will provide a detailed description of the aluminum-iron heterometallic organic framework material of this application, its preparation method, and its application:

[0041] Example 1

[0042] The preparation method of the aluminum-iron heterometallic organic framework material in this embodiment includes the following steps:

[0043] (1) Preparation of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid

[0044] Weigh 0.83 g of 4,7-dimethyl-1,10-phenanthroline and dissolve it in 50 mL of 1 mol / L NaOH solution. Add 4.74 g of KMnO4 in portions, heat to 50 °C, and reflux for 5 h until the purple color fades. Cool to room temperature, filter to remove the MnO2 precipitate, and acidify the filtrate with dilute HCl to pH=2 to precipitate a white or pale yellow solid. Filter, wash the precipitate with water, dry it, and recrystallize it with an ethanol / water mixed solvent to obtain 4,7-dicarboxylic acid-1,10-phenanthroline.

[0045] Weigh 0.5 g of 4,7-dicarboxylic acid-1,10-phenanthroline and dissolve it in 30 mL of 1 mol / L sulfuric acid solution. Cool to 5 °C, add 0.1 g of FeSO4·7H2O, and slowly add 1 mL of 30 wt% hydrogen peroxide solution, controlling the temperature to ≤10 °C. After the hydrogen peroxide solution is added, stir the reaction at room temperature for 3 h. Monitor the reaction progress by TLC. After the reaction is complete, quench excess H2O2 with Na2SO3 solution, extract with ethyl acetate, collect the aqueous phase, acidify to pH=2, filter the precipitated solid, dry the solid product, and recrystallize with an ethanol / water mixed solvent to obtain 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0046] (2) Preparation of aluminum-iron heterometallic organic framework materials

[0047] Weigh 30.0 mg of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid and dissolve it in 0.5 mL of 1 mol / L NaOH solution. Then, dilute with 4 mL of N,N-dimethylformamide. Filter through a 0.22 µm filter membrane to remove insoluble impurities and obtain the ligand solution. Weigh 37.5 mg of aluminum nitrate nonahydrate and add it to 1 mL of deionized water. Sonicate until completely dissolved to prepare an aluminum nitrate solution. Weigh 40.4 mg of ferric nitrate nonahydrate and add it to 2 mL of N,N-dimethylformamide. Sonicate until completely dissolved to prepare a ferric nitrate solution. Under stirring conditions, aluminum nitrate solution and ferric nitrate solution were added to the ligand solution, and 60 μL of tetrafluoroboric acid (HBF4) and 50 μL of formic acid (HCOOH) were added dropwise. A dark brown suspension was immediately formed. The dark brown suspension was transferred to a high-pressure reactor lined with polytetrafluoroethylene and heated to 130 °C at a heating rate of 5 °C / min. The reaction was held at this temperature for 24 h. After the reaction was completed, the temperature was lowered to room temperature at a rate of 0.5 °C / min, and a reaction solution with brown-black blocky crystals settled at the bottom of the reactor was obtained. The reaction solution was removed, filtered, and washed twice each with DMF and hot water at 60 °C. Then, it was replaced with acetone for 24 h and dried at room temperature to obtain the AlFe-MOF catalyst, i.e., aluminum-iron heterometallic organic framework material.

[0048] Example 2

[0049] The preparation method of the aluminum-iron heterometallic organic framework material in this embodiment includes the following steps:

[0050] (1) Preparation of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid

[0051] Weigh 0.728 g of 4,7-dimethyl-1,10-phenanthroline and dissolve it in 50 mL of 1 mol / L NaOH solution. Add 4.42 g of KMnO4 in portions, heat to 40 °C, and reflux for 6 h until the purple color fades. Cool to room temperature, filter to remove MnO2 precipitate, and acidify the filtrate with dilute HCl to pH=2 to precipitate a white or pale yellow solid. Filter, wash the precipitate with water, dry it, and recrystallize it with an ethanol / water mixed solvent to obtain 4,7-dicarboxylic acid-1,10-phenanthroline.

[0052] Weigh 0.48 g of 4,7-dicarboxylic acid-1,10-phenanthroline and dissolve it in 30 mL of 1 mol / L sulfuric acid solution. Cool to 3 °C, add 0.08 g of FeSO4·7H2O, and slowly add 1 mL of 30 wt% hydrogen peroxide solution, controlling the temperature to ≤10 °C. After the hydrogen peroxide solution is added, stir the reaction at room temperature for 2 h. Monitor the reaction progress by TLC. After the reaction is complete, quench excess H2O2 with Na2SO3 solution, extract with ethyl acetate, collect the aqueous phase, acidify to pH=2, filter the precipitated solid, dry the solid product, and recrystallize with an ethanol / water mixed solvent to obtain 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0053] (2) Preparation of aluminum-iron heterometallic organic framework materials

[0054] Weigh 30.0 mg of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid and dissolve it in 0.4 mL of 1 mol / L NaOH solution. Then, dilute with 4 mL of N,N-dimethylformamide. Filter through a 0.22 µm filter membrane to remove insoluble impurities and obtain the ligand solution. Weigh 37.5 mg of aluminum nitrate nonahydrate and add it to 1 mL of deionized water. Sonicate until completely dissolved to prepare an aluminum nitrate solution. Weigh 40.4 mg of ferric nitrate nonahydrate and add it to 2 mL of N,N-dimethylformamide. Sonicate until completely dissolved to prepare a ferric nitrate solution. Under stirring conditions, aluminum nitrate solution and ferric nitrate solution were added to the ligand solution, and 60 μL of tetrafluoroboric acid (HBF4) and 50 μL of formic acid (HCOOH) were added dropwise, immediately forming a dark brown suspension. The dark brown suspension was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and the temperature was increased to 125 °C at a heating rate of 5 °C / min, and the reaction was maintained at this temperature for 22 h. After the reaction was completed, the temperature was lowered to room temperature at a rate of 0.5 °C / min, and a reaction solution with brown-black blocky crystals settled at the bottom of the reactor was obtained. The reaction solution was removed, filtered, and washed twice each with DMF and hot water at 60 °C. Then, it was replaced with acetone for 24 h and dried at room temperature to obtain the AlFe-MOF catalyst, i.e., aluminum-iron heterometallic organic framework material.

[0055] Example 3

[0056] The preparation method of the aluminum-iron heterometallic organic framework material in this embodiment includes the following steps:

[0057] (1) Preparation of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid

[0058] Weigh 0.936 g of 4,7-dimethyl-1,10-phenanthroline and dissolve it in 50 mL of 1 mol / L NaOH solution. Add 5.69 g of KMnO4 in portions, heat to 60 °C, and reflux for 4 h until the purple color fades. Cool to room temperature, filter to remove MnO2 precipitate, and acidify the filtrate with dilute HCl to pH=2 to precipitate a white or pale yellow solid. Filter, wash the precipitate with water, dry it, and recrystallize it with an ethanol / water mixed solvent to obtain 4,7-dicarboxylic acid-1,10-phenanthroline.

[0059] Weigh 0.536 g of 4,7-dicarboxylic acid-1,10-phenanthroline and dissolve it in 30 mL of 1 mol / L sulfuric acid solution. Cool to 0 °C, add 0.13 g of FeSO4·7H2O, and slowly add 1 mL of 30 wt% hydrogen peroxide solution, controlling the temperature to ≤10 °C. After the hydrogen peroxide solution is added, stir the reaction at room temperature for 4 h. Monitor the reaction progress by TLC. After the reaction is complete, quench excess H2O2 with Na2SO3 solution, extract with ethyl acetate, collect the aqueous phase, acidify to pH=2, filter the precipitated solid, dry the solid product, and recrystallize with an ethanol / water mixed solvent to obtain 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid.

[0060] (2) Preparation of aluminum-iron heterometallic organic framework materials

[0061] Weigh 30.0 mg of 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid and dissolve it in 0.45 mL of 1 mol / L NaOH solution. Then, dilute with 4 mL of N,N-dimethylformamide. Filter through a 0.22 µm filter membrane to remove insoluble impurities and obtain the ligand solution. Weigh 37.5 mg of aluminum nitrate nonahydrate and add it to 1 mL of deionized water. Sonicate until completely dissolved to prepare an aluminum nitrate solution. Weigh 40.4 mg of ferric nitrate nonahydrate and add it to 2 mL of N,N-dimethylformamide. Sonicate until completely dissolved to prepare a ferric nitrate solution. Under stirring conditions, aluminum nitrate solution and ferric nitrate solution were added to the ligand solution, and 60 μL of tetrafluoroboric acid (HBF4) and 50 μL of formic acid (HCOOH) were added dropwise, immediately forming a dark brown suspension. The dark brown suspension was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and the temperature was increased to 120 °C at a heating rate of 5 °C / min, and the reaction was maintained at this temperature for 20 h. After the reaction was completed, the temperature was lowered to room temperature at a rate of 0.5 °C / min, and a reaction solution with brown-black blocky crystals settled at the bottom of the reactor was obtained. The reaction solution was removed, filtered, and washed twice each with DMF and hot water at 60 °C. Then, it was replaced with acetone for 20 h and dried at room temperature to obtain the AlFe-MOF catalyst, i.e., aluminum-iron heterometallic organic framework material.

[0062] Example 4

[0063] In this embodiment, polyethylene terephthalate was prepared by the following method:

[0064] 166 g of terephthalic acid (PTA), 124 g of ethylene glycol (EG), and 33 mg of the AlFe-MOF catalyst prepared in Example 1 were added to a polymerization reactor equipped with a fractionating column and a stirring device. Under nitrogen protection, the temperature was gradually increased to 250 °C for esterification until the amount of water distilled reached more than 90% of the theoretical value and the reaction system became clear and transparent. Then, the temperature was gradually increased to 280 °C while a vacuum was slowly drawn to allow the system pressure to drop steadily from atmospheric pressure to below 100 Pa within 60 min. Once the pressure stabilized at <100 Pa, the temperature was maintained at approximately 280 °C for polycondensation. The reaction endpoint was determined by monitoring the stirring torque, and PET polymer was obtained.

[0065] Example 5

[0066] This example prepared polyethylene terephthalate, which differed from Example 4 in that it used 50 mg of the AlFe-MOF catalyst prepared in Example 1.

[0067] Example 6

[0068] This example prepared polyethylene terephthalate, which differs from Example 4 in that it used 66 mg of the AlFe-MOF catalyst prepared in Example 1.

[0069] Example 7

[0070] This example prepared polyethylene terephthalate, which differed from Example 4 in that it used 83 mg of the AlFe-MOF catalyst prepared in Example 1.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 5 is that the tetrabutyl titanate catalyst is used instead of the AlFe-MOF catalyst prepared in Example 1; otherwise, they are the same.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 5 is that the Al-MOF catalyst prepared in Example 1 is replaced with an Al-MOF catalyst; all other aspects are the same.

[0075] Performance testing:

[0076] (1) Using the aluminum-iron heterometallic organic framework material prepared in Example 1 as a sample, the XRD pattern of the AlFe-MOF catalyst prepared in Example 1 is shown below. Figure 1 As shown.

[0077] (2) The AlFe-MOF catalyst prepared in Example 1 was used for the catalytic synthesis of PET, and its cycle stability was tested. The results are as follows: Figure 2 As shown.

[0078] (3) PET samples prepared in Examples 4-6 and Comparative Examples 1 and 2 were used for performance testing. The results are shown in Table 1.

[0079] Table 1 PET Performance Test Results

[0080] Sample source catalyst Dosage (ppm) Intrinsic viscosity (dL / g) Chromaticity (b-value) <![CDATA[Carboxyl end group content (mol / 10 6 g)]]> Example 4 AlFe-MOF 200 0.660 2.6 23 Example 5 AlFe-MOF 300 0.680 2.4 19 Example 6 AlFe-MOF 400 0.705 2.1 15 Comparative Example 1 Tetrabutyl titanate 300 0.665 4.7 24 Comparative Example 2 Al-MOF 300 0.615 3.0 36

[0081] The data in Table 1 show that the intrinsic viscosity of PET synthesized by AlFe-MOF is superior to that of the conventional catalyst TBT and the comparative Al-MOF at the same dosage. In particular, Example 6 (400 ppm) achieved the highest intrinsic viscosity of 0.705 dL / g, demonstrating its strongest ability to catalyze the formation of high molecular weight PET. The b-value (yellow index) of the PET obtained from the AlFe-MOF series is significantly lower than that of the TBT catalyst, resulting in a whiter product with better color. This is attributed to the mild catalytic properties of AlFe-MOF, which effectively suppresses the thermal oxidative degradation side reactions at high temperatures. The performance of Comparative Example 2 (Al-MOF) is far inferior to that of this invention, demonstrating that the introduction of Fe and Al form a synergistic catalytic effect, jointly enhancing catalytic activity and selectivity.

[0082] Figure 1 The image shows the XRD pattern of the AlFe-MOF catalyst. The diffraction peaks of the experimental sample are consistent with the main peak type of the simulated model of the AlFe-MOF catalyst, indicating that the AlFe-MOF catalyst was successfully synthesized. Figure 2 The cyclic stability of the AlFe-MOF catalyst was demonstrated. After five cycles, the intrinsic viscosity of PET synthesized by AlFe-MOF catalyst decreased slightly from 0.705 dL / g initially to 0.69 dL / g in the fifth cycle, with an activity retention rate as high as 96.0%. This slight decrease in intrinsic viscosity is within the industrial tolerance range, indicating that the AlFe-MOF catalyst maintains a stable crystal structure under harsh polymerization conditions (high temperature, high vacuum), and that the active sites (Al / Fe heterometallic nodes) did not undergo significant sintering, loss, or deactivation. Through simple centrifugation, washing, and drying steps, the catalyst recovery gradually decreased from 99.0% to 96.0%, with an average recovery rate greater than 97.0% after five cycles. This demonstrates that the AlFe-MOF catalyst possesses good mechanical strength and is not easily pulverized during the reaction and post-processing. The slight decrease in recovery rate is mainly attributed to physical losses during experimental operations.

[0083] In summary, the aluminum-iron heterometallic organic framework material prepared by this invention is stable at high temperatures and does not trigger side reactions. When used as a catalyst in the synthesis of PET, the resulting PET exhibits a lower b-value (yellow index), better color, and higher quality. Therefore, the aluminum-iron heterometallic organic framework material of this invention can be used as a catalyst for the catalytic synthesis of PET.

[0084] The foregoing description includes examples from this specification. Of course, for the purposes of describing this specification, it is impossible to describe every conceivable combination of components or methods; however, those skilled in the art will understand that many other combinations and arrangements are possible. Therefore, this specification is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, with regard to the use of the term "comprising" in the detailed description or claims, the term is intended to be inclusive in a manner similar to the term "including," as interpreted when "comprising" is used as a transitional word in the claims.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the preparation of an aluminum-iron heterometallic organic framework material, characterized in that, The method comprises the following steps: The 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid is dissolved in a NaOH solution, diluted with N,N-dimethylformamide, and filtered to obtain a ligand solution; Aluminum nitrate nonahydrate is weighed and added to deionized water to prepare an aluminum nitrate solution; iron nitrate nonahydrate is weighed and added to N,N-dimethylformamide to prepare an iron nitrate solution; The aluminum nitrate solution and the iron nitrate solution are added to the ligand solution under stirring, and tetrafluoroboric acid and formic acid are added dropwise until a dark brown suspension is formed, the dark brown suspension is transferred to a high-pressure reaction kettle, heated to 120-130°C, and kept at a constant temperature for 20-24 hours, the reaction is completed, the reaction liquid is cooled to room temperature, filtered, washed, and replaced with acetone for 20-24 hours, and dried at room temperature to obtain an AlFe-MOF catalyst.

2. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 1, characterized in that, The molar ratio of the 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid to NaOH is 1:(4-5), and the concentration of the NaOH solution is 1 mol / L.

3. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 1, characterized in that, The molar ratio of the 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid, zinc nitrate hexahydrate, and iron nitrate nonahydrate is 1:1:

1.

4. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 1, characterized in that, The mixed solution is heated to 120-130°C at a heating rate of 5°C / min in a high-pressure reaction kettle; and after the reaction is completed, the temperature is lowered to room temperature at a rate of 0.5°C / min.

5. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 1, characterized in that, The preparation method of the 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid is as follows: 4,7-dicarboxylic acid-1,10-phenanthroline is weighed and dissolved in a sulfuric acid solution, cooled to 0-5°C, FeSO4·7H2O is added, a 30wt% hydrogen peroxide solution is added dropwise, the temperature is controlled to be ≤10°C, after the hydrogen peroxide solution is added dropwise, the reaction is stirred at room temperature for 2-4 hours, the reaction progress is monitored by TLC, after the reaction is completed, the excess H2O2 is quenched with a Na2SO3 solution, extracted with ethyl acetate, the obtained aqueous phase is acidified to PH=2, the precipitated solid is filtered, the obtained solid product is dried, recrystallized with an ethanol / water mixed solvent, and 3,8-dihydroxy-1,10-phenanthroline-4,7-dicarboxylic acid is obtained.

6. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 5, characterized in that, The concentration of the sulfuric acid solution is 1 mol / L, and the mass / volume ratio of the 4,7-dicarboxylic acid-1,10-phenanthroline to the sulfuric acid solution is 0.5g:(25-40mL); and / or, The molar volume ratio of the 4,7-dicarboxylic acid-1,10- phenanthroline, FeSO4·7H2O, and hydrogen peroxide solution is (1.8-2.0) mmol:(0.3-0.5) mmol:1 mL.

7. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 5, characterized in that, The preparation method of the 4,7-dicarboxylic acid-1,10-phenathroline is as follows: The 4,7-dimethyl-1,10-phenanthroline is weighed and dissolved in a 1 mol / L NaOH solution, KMnO4 is added in batches, the temperature is raised to 40-60 DEG C, and heated to reflux for 4-6 h, cooled to room temperature, the obtained filtrate is acidified with dilute HCl to PH = 2, filtered, the obtained precipitate is washed with water and dried, recrystallized with ethanol / water mixed solvent to obtain 4,7-dimethyl-1,10-phenanthroline.

8. The method for preparing the aluminum-iron heterometallic organic framework material according to claim 7, characterized in that, The molar volume ratio of the 4,7-dimethyl-1,10-phenanthroline, KMnO4 and NaOH solution is (3.5-4.5):(28-36):50 mL.

9. An aluminum-iron heterometallic organic framework material, characterized in that, The aluminum-iron heterometallic organic framework material is prepared by the preparation method of any one of claims 1-8.

10. The use of the aluminum-iron heterometallic organic framework material of claim 9 as a catalyst in the synthesis of polyethylene terephthalate, which is synthesized by using terephthalic acid and ethylene glycol as main raw materials, and the aluminum-iron heterometallic organic framework material is used in an amount of 199-500 ppm of terephthalic acid.

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