Method for preparing MOF hydrogen storage material from waste PET and application thereof

Abstract

This invention discloses a method for preparing MOF hydrogen storage materials from waste PET and its application. The chemical formula of the MOF material is M₁. X M₂ᵧ(BDC)₂(H₂O)₂, where M₁ is Zn²⁺ or Cu²⁺, M₂ is Co²⁺, Ni²⁺ or Mg²⁺, BDC is terephthalate, 0.1≤x≤0.9, 0.1≤y≤0.9, and x+y=1. The preparation method employs a microwave-assisted solvothermal method, and the terephthalic acid (TPA) is derived from the chemical depolymerization product of waste polyethylene terephthalate. This invention is the first to specifically apply waste PET-derived MOF materials to the field of hydrogen storage. By precisely controlling the ratio of metal salt to organic ligand, reaction temperature, and time, MOF materials with high specific surface area, regular pore structure, and a large number of open metal sites are prepared in a short time. This invention also provides the application of the MOF material in hydrogen storage. The material exhibits a hydrogen storage capacity exceeding 6.5 wt% at 77 K and 100 bar, and exceeding 2.3 wt% at 298 K and 100 bar, while also demonstrating excellent cycle stability. This method offers advantages such as short reaction time, low energy consumption, and good product crystallinity, making it suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and waste resource utilization technology, and more specifically, relates to a method and application for preparing MOF hydrogen storage materials from waste PET. Background Technology

[0002] With the global energy crisis and environmental pollution becoming increasingly severe, hydrogen energy, as a clean and renewable energy carrier, has received widespread attention. However, the safe and efficient storage of hydrogen remains one of the bottlenecks restricting its large-scale application. Metal-organic framework materials, due to their high specific surface area, tunable pore structure, and surface chemistry, have shown great potential in the field of hydrogen storage.

[0003] Currently, classic MOF materials such as MOF-5 and MOF-177 exhibit excellent hydrogen storage performance at a low temperature of 77K, but their hydrogen storage capacity at room temperature remains low, making it difficult to meet practical application requirements. This is mainly due to the weak interaction between MOF materials and hydrogen molecules, with weak physical adsorption being the primary mechanism. Furthermore, the synthesis of traditional MOFs heavily relies on petroleum-based feedstocks (such as terephthalic acid), resulting in non-renewable feedstocks, high costs, and a high carbon footprint throughout their lifecycle, which contradicts the concept of green and sustainable development.

[0004] To improve the hydrogen storage performance of MOF materials, researchers have attempted methods such as introducing open metal sites. However, these improvements are mostly limited to material structure design and have failed to fundamentally address the issue of feedstock sustainability.

[0005] Chinese invention patent CN119955117A discloses a MOF catalyst derived from waste PET plastics and its preparation method. Terephthalic acid is obtained through alkaline alcoholysis of PET, followed by a solvothermal reaction with a metal salt to prepare MOF materials for catalytic olefin epoxidation. Chinese invention patent CN115960366B discloses a method for preparing MOF materials using waste PET and stainless steel pickling wastewater; the resulting materials are used for dye wastewater treatment. Furthermore, Wang Jiexin's research group at Beijing University of Chemical Technology published a study in the Journal of Materials Chemistry A in 2024, reporting the one-pot synthesis of MOFs using ZnO nanoparticles to catalyze the hydrolysis of PET for water adsorption and photocatalytic degradation of tetracycline. However, the above-mentioned existing technologies all apply waste PET-derived MOFs to catalysis, wastewater treatment, or water adsorption; there are no reports of their dedicated application to hydrogen storage, nor are there any technical solutions involving bimetallic design or exogenous metal modification to improve their hydrogen storage performance. In addition, the above methods mostly employ traditional solvothermal methods or hydrolysis with specific catalysts, which suffer from long reaction times or complex processes.

[0006] On the other hand, waste plastics, especially polyethylene terephthalate (PET), are produced in huge quantities globally each year, but the recycling rate is low, causing serious "white pollution." Depolymerizing waste PET into its monomer, terephthalic acid (TPA), through chemical recycling technologies (such as alcoholysis and hydrolysis) is a key approach to achieving closed-loop, high-value utilization of plastics. If this bio-based / recycled terephthalic acid can be used in the synthesis of high-performance MOFs, it will simultaneously solve two major problems: waste plastic pollution and the preparation of green hydrogen storage materials.

[0007] Therefore, developing a MOF hydrogen storage material that uses waste PET as a raw material, has an efficient preparation process, and possesses a high specific surface area and a large number of open metal sites is of great significance for promoting the coordinated development of the circular economy and hydrogen energy storage technology. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a green raw material, efficient preparation, and excellent performance MOF hydrogen storage material with open metal sites, as well as its preparation method and application.

[0009] The first objective of this invention is to provide a MOF hydrogen storage material with open metal sites.

[0010] The second objective of this invention is to provide a method for preparing the above-mentioned MOF hydrogen storage material, particularly a green preparation method using waste PET chemical depolymerization products as raw materials.

[0011] The third objective of this invention is to provide an exogenous metal-modified MOF hydrogen storage material.

[0012] A fourth objective of this invention is to provide the application of the above-mentioned MOF hydrogen storage material in hydrogen storage.

[0013] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0014] A MOF hydrogen storage material with open metal sites, wherein the chemical formula of the MOF material is M 1x M2ᵧ(BDC)2(H2O)2, wherein M1 is selected from Zn²⁺ or Cu²⁺, M2 is selected from Co²⁺, Ni²⁺ or Mg²⁺, BDC is terephthalate, 0.1≤x≤0.9, 0.1≤y≤0.9, and x+y=1; the specific surface area of ​​the MOF material is 2000-3500m² / g, and the pore size distribution is 0.5-2.0nm.

[0015] This invention introduces a second transition metal M2 to form a bimetallic MOF material with the main metal M1.

[0016] A large number of uniformly distributed open metal sites were created within the framework, serving as strong adsorption sites and significantly improving hydrogen storage capacity, especially at room temperature. More importantly, this invention is the first to specifically apply waste PET-sourced MOF materials to the field of hydrogen storage. Through targeted design of bimetallic combinations (Zn / Co, Cu / Ni, Zn / Mg) and exogenous metal modification strategies, the hydrogen storage capacity of the material is synergistically improved at low temperature of 77K and room temperature of 298K. This is an application direction and technical effect that has not been addressed in existing waste PET-sourced MOF technologies.

[0017] Preferably, M1 is Zn²⁺, M2 is Co²⁺, x=0.7, and y=0.3.

[0018] Furthermore, this invention claims protection for a method for preparing the above-mentioned MOF hydrogen storage material, comprising the following steps:

[0019] (1) Dissolve M1 metal salt, M2 metal salt and terephthalic acid in N,N-dimethylformamide in stoichiometric ratio to obtain a mixed solution. The terephthalic acid is preferably derived from the chemical depolymerization product of waste PET.

[0020] (2) Place the mixed solution obtained in step (1) in a microwave reactor and react at 100-150℃ for 10-60 min;

[0021] (3) Cool and filter the product obtained in step (2), wash it with DMF, and then vacuum dry it at 50-80℃ to obtain the MOF precursor.

[0022] (4) The MOF precursor was vacuum activated at 150-250℃ for 6-24h to obtain the MOF hydrogen storage material.

[0023] This invention employs a microwave-assisted synthesis method, which features short reaction time and high efficiency. Combined with bio-based raw materials, the entire process is green and highly efficient.

[0024] Preferably, in step (1), the M1 metal salt is zinc nitrate, the M2 metal salt is cobalt nitrate, and the molar ratio of M1 metal salt, M2 metal salt, and terephthalic acid is 0.7:0.3:1. Preferably, the total concentration of metal salts in the mixed solution in step (1) is 0.1-0.5 mol / L. Preferably, the power of the microwave reaction in step (2) is 300-800W. Preferably, the conditions for vacuum activation in step (4) are: vacuum degree ≤10⁻³ Torr, temperature 200℃, and time 12h.

[0025] Furthermore, this invention also claims protection for an exogenous metal-modified MOF hydrogen storage material, obtained by mixing the MOF hydrogen storage material with a metal salt solution, impregnating and drying it, and then heat-treating it at 200-300°C for 2-6 hours under a protective atmosphere; the metal salt is selected from one or more of LiCl, LiNO3, and MgCl2. Preferably, the metal salt is LiCl, and its mass ratio to the MOF material is 1:10-1:20.

[0026] Furthermore, the present invention also claims protection for the application of the above-mentioned MOF hydrogen storage material in hydrogen storage.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention designs bimetallic MOF materials that, while maintaining a high specific surface area, introduce a large number of uniformly distributed open metal sites. These sites, as strong adsorption sites, significantly improve the hydrogen storage capacity of the material, especially under room temperature conditions.

[0029] 2. This invention is the first to apply chemically recycled waste PET products to the preparation of MOF hydrogen storage materials, pioneering a new technological path of "waste recycling - hydrogen storage material preparation". Unlike existing waste PET source MOF technologies (CN119955117A, CN115960366B, etc.) which focus on applications such as catalysis and wastewater treatment, this invention specifically develops a bimetallic MOF system suitable for hydrogen storage, expanding new directions for the high-value utilization of waste PET and combining environmental benefits with innovative energy material value.

[0030] 3. This invention uses a microwave-assisted synthesis method, which shortens the reaction time from more than 24 hours to less than 1 hour compared with the traditional solvothermal method, greatly reducing energy consumption and improving production efficiency.

[0031] 4. By modifying with exogenous metals, the hydrogen storage performance of MOF materials is further improved, especially the room temperature hydrogen storage capacity. Moreover, the preparation process is simple and easy to scale up.

[0032] 5. The MOF hydrogen storage material provided by this invention can achieve a hydrogen storage capacity of more than 6.5 wt% under 77 K and 100 bar conditions, and a hydrogen storage capacity of more than 2.3 wt% under 298 K and 100 bar conditions, and has excellent cycle stability, showing good application prospects. Attached Figure Description

[0033] Figure 1 A flowchart of a green preparation method for MOF hydrogen storage materials from recycled waste PET raw materials. Detailed Implementation

[0034] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0035] Example A: Preparation of a bio-based terephthalic acid

[0036] (1) Add 10g of cleaned and dried waste PET bottle flakes, 100mL of methanol, and 0.1g of zinc acetate catalyst to a high-pressure reactor. (2) React at 180℃ for 4 hours to carry out alcoholysis. After the reaction is completed, cool and filter to remove unreacted substances to obtain a methanol solution of dimethyl terephthalate (DMT). (3) Mix the above solution with 50mL of 10% NaOH aqueous solution and stir at 70℃ for 2 hours to hydrolyze DMT into sodium terephthalate. (4) Adjust the pH of the solution to 2-3 with hydrochloric acid, precipitate the solid, filter, and wash with deionized water until neutral. (5) Dry the solid under vacuum at 100℃ for 12 hours to obtain a white powder of bio-based terephthalic acid (Bio-TPA). The purity of the powder was ≥99.0% by high performance liquid chromatography (HPLC).

[0037] Example 1: Using a Commercial TPA

[0038] (1) Dissolve 2.10 mmol Zn(NO3)2·6H2O, 0.90 mmol Co(NO3)2·6H2O, and 3.00 mmol commercial terephthalic acid in 30 mL DMF and sonicate. (2) Transfer the mixed solution to a microwave reactor and react at 120 °C and 500 W for 30 min. (3) After the reaction, cool to room temperature, filter, wash three times with DMF, and vacuum dry at 60 °C for 12 h to obtain the MOF precursor. (4) Activate the MOF precursor at 200 °C and 10⁻³ Torr for 12 h to obtain Zn0.7Co0.3(BDC)2 MOF hydrogen storage material (labeled as C-MOF).

[0039] Example 2

[0040] (1) Dissolve 1.50 mmol Cu(NO3)2·3H2O, 1.50 mmol Ni(NO3)2·6H2O and 3.00 mmol commercial terephthalic acid in 30 mL DMF and sonicate. (2) React the mixed solution in a microwave reactor at 130 °C and 600 W for 20 min.

[0041] (3) After the reaction was completed, the mixture was cooled to room temperature, filtered, washed three times with DMF, and dried under vacuum at 60°C for 12 h to obtain the MOF precursor. (4) The MOF precursor was activated at 200°C and a vacuum of 10⁻³ Torr for 12 h to obtain Cu0.5Ni0.5(BDC)2 MOF hydrogen storage material.

[0042] Example 3

[0043] (1) Dissolve 2.40 mmol Zn(NO3)2·6H2O, 0.60 mmol Mg(NO3)2·6H2O and 3.00 mmol commercial terephthalic acid in 30 mL DMF and sonicate. (2) React the mixed solution in a microwave reactor at 110 °C and 400 W for 40 min.

[0044] (3) After the reaction was completed, the mixture was cooled to room temperature, filtered, washed three times with DMF, and dried under vacuum at 60°C for 12 h to obtain the MOF precursor. (4) The MOF precursor was activated at 200°C and a vacuum of 10⁻³ Torr for 12 h to obtain Zn0.8Mg0.2(BDC)2 MOF hydrogen storage material.

[0045] Example 4: Exogenous Metal Modification

[0046] (1) C-MOF materials were prepared according to the method in Example 1.

[0047] (2) Mix 1.0 g C-MOF with 10 mL of 0.1 mol / L LiCl methanol solution and impregnate at room temperature for 12 h by shaking. (3) Filter, vacuum dry at 80 °C for 6 h, and heat treat at 250 °C for 3 h under nitrogen protection to obtain Li⁺ modified MOF material (which can be represented as Li⁺@MOF).

[0048] Example 5: Exogenous Metal Modification

[0049] (1) C-MOF materials were prepared according to the method in Example 1.

[0050] (2) Mix 1.0 g C-MOF with 10 mL of 0.15 mol / L MgCl2 methanol solution and impregnate at room temperature for 10 h with shaking. (3) Filter, vacuum dry at 75 °C for 8 h, and heat treat at 220 °C for 4 h under nitrogen protection to obtain Mg²⁺ modified MOF material.

[0051] Example 6 Using Bio-based TPA

[0052] (1) Dissolve 2.10 mmol Zn(NO3)2·6H2O, 0.90 mmol Co(NO3)2·6H2O and 3.00 mmol Bio-TPA prepared in Example A in 30 mL DMF and sonicate to dissolve.

[0053] (2) The subsequent steps are exactly the same as (2)-(4) of Example 1.

[0054] (3) A bio-based Zn0.7Co0.3(BDC)2 MOF hydrogen storage material (labeled as B-MOF) was obtained.

[0055] Comparative Example 1

[0056] Following the method of Example 1, but without adding Co(NO3)2·6H2O, only 3.00 mmol Zn(NO3)2·6H2O and 3.00 mmol commercial terephthalic acid were used to prepare single-metal Zn(BDC) MOF materials.

[0057] Comparative Example 2

[0058] Following the method of Example 1, but replacing Co(NO3)2·6H2O with an equimolar amount of Ca(NO3)2·4H2O, Zn0.7Ca0.3(BDC)2 material was prepared.

[0059] Comparative Example 3

[0060] The method of Example 1 was followed, but the conventional solvothermal method was used, and the reaction was carried out in an oven at 120°C for 24 hours, while other conditions remained unchanged.

[0061] Comparative Example 4

[0062] Following the method of Example 6, but changing the metal ratio, using 0.90 mmol Zn(NO3)2·6H2O and 2.10 mmol Co(NO3)2·6H2O, Zn0.3Co0.7(BDC)2 material was prepared.

[0063] Comparative Example 5

[0064] B-MOF precursors were prepared according to the method of Example 6, but the high-temperature vacuum activation in step (4) was not performed; the tests were only conducted in the precursor stage.

[0065] Comparative Example 6

[0066] The B-MOF precursor was prepared according to the method in Example 6, but with modifications based on the preparation method of patent CN119955117A.

[0067] (1) Dissolve the Bio-TPA prepared in Example A and Cr(NO3)3·9H2O in DMF at a molar ratio of 1:1, and add an appropriate amount of deionized water.

[0068] (2) Transfer the mixed solution to a polytetrafluoroethylene-lined reactor and react at 180°C for 24 hours.

[0069] (3) After the reaction is complete, the mixture is cooled, centrifuged, washed with DMF and ethanol, and dried under vacuum at 80°C for 12 h. (4) The obtained material is labeled as the control sample PET-MIL-101(Cr) and used for hydrogen storage performance testing.

[0070] Comparative Example 7

[0071] B-MOF precursors were prepared according to the method in Example 6, but modified with reference to the one-pot method strategy in the literature from Beijing University of Chemical Technology.

[0072] (1) The PET hydrolysate obtained in step (2) of Example A (unpurified) was used directly as the ligand source. (2) 2.10 mmol Zn(NO3)2·6H2O and 0.90 mmol Co(NO3)2·6H2O were added to the above slurry, and DMF was added to 30 mL.

[0073] (3) Transfer the mixed solution to a microwave reactor and react at 120°C and 500W for 30 min. (4) Follow up with the same steps (3)-(4) as in Example 1. The resulting material is labeled as the control sample One-pot-MOF.

[0074] Test Example 1

[0075] The materials prepared in the above embodiments and comparative examples were characterized in structure and tested for hydrogen storage performance. The results are shown in Table 1.

[0076] Table 1

[0077] project Specific surface area (m² / g) Pore ​​volume (cm³ / g) Hydrogen storage capacity at 77K and 100 bar (wt%) Hydrogen storage capacity at 298K and 100 bar (wt%) Example 1 3150 1.35 6.78 2.41 Example 6 3080 1.32 6.70 2.38 Example 4 3050 1.30 7.05 2.65 Comparative Example 1 3200 1.38 5.92 1.75 Comparative Example 2 2650 1.15 5.35 1.62 Comparative Example 3 3080 1.32 6.65 2.35 Comparative Example 4 2850 1.20 5.80 1.90 Comparative Example 5 <800 0.35 0.95 0.30 Comparative Example 6 2650 1.12 4.85 1.32 Comparative Example 7 2750 1.18 5.21 1.48

[0078] As shown in Table 1, the B-MOF prepared using bio-based TPA in Example 6 exhibits almost identical specific surface area, pore volume, and hydrogen storage performance to that of Example 1 (C-MOF) using commercial TPA, demonstrating that waste PET can be used as a qualified raw material for high-performance MOFs. Furthermore, the B-MOF demonstrates significantly superior performance compared to the comparative examples, showcasing the combined advantages of the bimetallic design, microwave synthesis, and activation process of this invention.

[0079] The materials prepared in Comparative Examples 6 and 7, although also using waste PET as raw material, exhibited significantly lower hydrogen storage performance (especially hydrogen storage capacity at 298K room temperature) than those in Examples 1 and 6 of this invention. This demonstrates that the bimetallic system, microwave synthesis process, and activation conditions designed for hydrogen storage applications in this invention have unique technical effects on improving the hydrogen storage performance of waste PET source MOFs, which cannot be easily obtained by those skilled in the art from existing PET source MOF technologies.

[0080] Test Example 2

[0081] Cyclic stability tests were conducted on Example 1 (C-MOF) and Example 6 (B-MOF). After 100 hydrogen adsorption and desorption cycles at 77 K, the hydrogen storage capacity retention rate of C-MOF was 96.5%, and that of B-MOF was 96.8%, indicating that bio-based MOFs also have excellent cyclic stability.

[0082] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A MOF hydrogen storage material with open metal sites for hydrogen storage, characterized in that, The chemical formula of the MOF material is M 1x M2ᵧ(BDC)2(H2O)2, wherein M1 is selected from Zn²⁺ or Cu²⁺, M2 is selected from Co²⁺, Ni²⁺ or Mg²⁺, and BDC is terephthalate, wherein the terephthalate is derived from the chemical depolymerization product of waste polyethylene terephthalate; 0.1≤x≤0.9, 0.1≤y≤0.9, and x+y=1; the specific surface area of ​​the MOF material is 2000-3500m² / g, and the pore size distribution is 0.5-2.0nm.

2. The MOF hydrogen storage material according to claim 1, characterized in that, M1 is Zn²⁺, M2 is Co²⁺, x=0.7, y=0.

3.

3. A method for preparing the MOF hydrogen storage material according to claim 1 or 2, characterized in that, Includes the following steps: (1) Dissolve metal salt M1, metal salt M2 and terephthalic acid in N,N-dimethylformamide in stoichiometric ratio to obtain a mixed solution; (2) Place the mixed solution obtained in step (1) in a microwave reactor and react at 100-150℃ for 10-60 min; (3) Cool and filter the product obtained in step (2), wash it with DMF, and then vacuum dry it at 50-80℃ to obtain the MOF precursor. (4) The MOF precursor was vacuum activated at 150-250℃ for 6-24h to obtain the MOF hydrogen storage material.

4. The preparation method according to claim 3, characterized in that, In step (1), the M1 metal salt is zinc nitrate, the M2 metal salt is cobalt nitrate, and the molar ratio of the M1 metal salt, the M2 metal salt and terephthalic acid is 0.7:0.3:

1.

5. The preparation method according to claim 3 or 4, characterized in that, The total concentration of metal salts in the mixed solution in step (1) is 0.1-0.5 mol / L.

6. The preparation method according to claim 3, characterized in that, The power of the microwave reaction in step (2) is 300-800W.

7. The preparation method according to claim 3, characterized in that, The conditions for vacuum activation in step (4) are: vacuum degree ≤ 10⁻³ Torr, temperature 200℃, and time 12h.

8. The preparation method according to any one of claims 3-7, characterized in that, The terephthalic acid mentioned in step (1) is derived from the chemical depolymerization product of waste polyethylene terephthalate. The chemical depolymerization product of waste PET is being used for the first time in the preparation of MOF hydrogen storage materials.

9. A MOF hydrogen storage material modified with exogenous metal, characterized in that, The MOF hydrogen storage material according to any one of claims 1-2 or the MOF hydrogen storage material prepared by the preparation method according to any one of claims 3-7 is mixed with a metal salt solution, impregnated and dried, and then heat-treated at 200-300℃ for 2-6 hours under a protective atmosphere to obtain the final product; the metal salt is selected from one or more of LiCl, LiNO3, and MgCl2.

10. The exogenous metal-modified MOF hydrogen storage material according to claim 8, characterized in that, The metal salt is LiCl, and its mass ratio with the MOF material is 1:10-1:

20.

11. The application of the MOF hydrogen storage material according to any one of claims 1-2 or 9-10 in hydrogen storage.

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