A method for preparing metal-organic framework material by adopting ball milling-electrochemical degradation of waste PET

Abstract

The application belongs to the technical field of converting waste plastics into high value-added materials, and discloses a method for converting waste PET into metal-organic framework material by ball milling and electrochemical degradation, which comprises the following steps: S1, ball milling waste PET and solid strong base compound together; S2, dissolving the ball milling product in deionized water; S3, adding conductive salt to obtain electrolyte; S4, selecting corresponding metal element foil to obtain metal M sheet; S5, taking the metal M sheet as an anode to perform electrochemical reaction, and thus MOF material is obtained. The application improves the process flow design of the preparation method, degrades the waste PET into disodium terephthalate and ethylene glycol by mechanical ball milling to form electrolyte, and then performs subsequent electrochemical treatment, so that MOF is synthesized, and the obtained MOF has better oxygen evolution reaction (OER) performance than other MOF materials, which breaks through the expectation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resource conversion of waste plastics into high value-added materials, more specifically, relates to a method for degrading waste PET into metal-organic framework materials by ball milling-electrochemical degradation, which can realize the conversion of waste PET into high value-added MOF materials under normal temperature and pressure conditions. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a thermoplastic polyester plastic, which is widely used in the production of disposable packaging products due to its good physical and mechanical properties, stable chemical properties and low manufacturing and processing costs. However, a large amount of post-consumer PET not only exacerbates environmental pollution and threatens biological safety, but also wastes carbon resources. So far, common PET recycling methods include traditional methods, physical and chemical methods, and biological methods, each of which has its advantages and disadvantages. Traditional methods include landfill, incineration and mechanical recycling. Landfill has the advantages of short-term effectiveness, simplicity and ease of implementation, but it relies heavily on land resources. Incineration produces a variety of toxic gases including polycyclic aromatic hydrocarbons, as well as a large amount of dust smoke and greenhouse gases, which seriously pollute the atmospheric environment. Mechanical recycling is to grind waste polyester into secondary raw materials using mechanical force, which has the advantages of simple process and low cost, but mechanical recycling often leads to a decrease in the structure and performance of the recycled material, limiting its practical value. Physical and chemical methods mostly convert waste polyester into monomers or oligomeric compounds through various chemical schemes (such as hydrolysis, alcoholysis, ammonolysis, etc.), however, these strategies often produce a large amount of waste acid and waste alkali, which poses a greater threat to the environment than the economic benefits of PET recycling, making it difficult to achieve large-scale application. Biological methods mainly use microorganisms or active enzymes to degrade PET into monomers or oligomeric compounds, which has attracted widespread attention due to its low cost and high rate, but the cultivation conditions of the strains are harsh, which has limited the widespread application of this method. In recent years, in the pursuit of various strategies for circular economy, the upgrading chemical recycling of PET has attracted widespread attention, which is to resourcefully convert waste PET into metal-organic framework (MOF) materials under normal temperature and pressure conditions.

[0003] MOFs (Metal-Organic Facility Buildings) are typical porous crystalline materials constructed by orderly splicing organic interconnects between metal nodes. The unique framework and pore structure of MOFs determine their unique properties such as large specific surface area, high porosity, and chemical tunability, leading to their wide application in gas storage, adsorption separation, biotechnology, and catalysis. Terephthalic acid is a typical PET degradation product. Degrading waste PET into terephthalic acid, followed by a solvothermal reaction with metal salts, is a promising strategy for synthesizing MOFs from common waste resources. Xu et al. used waste PET bottles as a ligand source, adding them to a mixed solvent of 40 mL N,N-dimethylformamide (DMF), 5 mL HCl, and 20 mL deionized water. The reaction was carried out at 180 °C for 12 h to obtain a white powder of MIL-53(Al) (Xiaodong Xu, Jiaxin Li, Anna Dymerska, J. Justin Koh, Jiakang Min, Siqi Liu, Jalal Azadmanjiri, Ewa Mijowska. MIL-53(Al) assisted inupcycling plastic bottle waste into nitrogen-doped hierarchical porous carbon for high-performance supercapacitors. Chemosphere 2023, 340, 139865). However, these harsh synthesis conditions and time-consuming process significantly increased production costs and environmental safety, hindering industrial-scale production. He et al. degraded PET to disodium terephthalate and ethylene glycol through mechanical ball milling and solvent-free alkaline hydrolysis, then added metal salts and continued ball milling to form MOFs (Panpan He, Zhen Hu, Zhikui Dai, Huiying Bai, ZifenFan, Ran Niu, Jiang Gong, Qiang Zhao, Tao Tang. Mechanochemistry milling of waste poly(ethylene terephthalate) into metal-organic frameworks. ChemSusChem 2023, 16, e202201935). This method reduces the safety index of the production environment, but it has adverse effects such as uncontrollable reaction process, products containing a large number of insoluble impurities (especially iron filings and incompletely degraded PET powder), and high energy consumption in the reaction process.Recently, patent ZL202211401069.6 disclosed a ball milling-solution blending method for converting waste PET into MOF. This method involves ball milling PET with a strong alkali compound to obtain a mixture of disodium terephthalate and ethylene glycol, followed by solution precipitation to prepare MOF. The disadvantages of this method are that the preparation process is uncontrollable, the stirring time is long (usually 1–3 hours), and it generates a significant amount of wastewater. Furthermore, this method is unsuitable for preparing materials with poor stability in water, such as Zn-MOF.

[0004] If a method can be found that can rapidly degrade waste PET into MOF materials at room temperature and pressure, and is also suitable for preparing MOF materials with poor stability in water, it will undoubtedly further promote the resource-based upgrading and utilization of waste PET and the development and application of MOF materials. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a method for preparing metal-organic framework (MOF) materials using ball milling and electrochemical degradation of waste PET. This method improves the process flow design, developing a controllable and mild MOF material preparation method. In this invention, the ball milling and electrochemical degradation of waste PET to obtain MOF materials involves first mechanically ball milling waste PET into disodium terephthalate and ethylene glycol, then dissolving them to obtain a mixed solution of disodium terephthalate and ethylene glycol. A conductive salt is then added to form an electrolyte, and subsequent electrochemical treatment synthesizes the MOF. The resulting MOF exhibits superior oxygen evolution reaction (OER) performance compared to other MOF materials, exceeding expectations. This invention's method, employing ball milling combined with electrochemical treatment, offers advantages such as process control, mild synthesis conditions, and low cost, providing a new method for the industrial production of MOFs from waste PET degradation.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing metal-organic framework materials by ball milling-electrochemical degradation of waste PET is provided, characterized by comprising the following steps:

[0007] S1. Mix waste PET and solid strong alkali compound evenly and then dry ball mill to obtain the ball milled product;

[0008] S2. Dissolve the ball-milled product obtained in step S1 in deionized water to obtain a mixed solution of disodium terephthalate and ethylene glycol.

[0009] S3. Add a conductive salt to the mixed solution obtained in step S2 to obtain an electrolyte;

[0010] S4. Based on the target metal element M in the target metal-organic framework material, select the corresponding elemental metal foil, cut it to obtain the electrode sheet, denoted as metal M sheet;

[0011] S5. Prepare a DC power supply. Use the metal M sheet obtained in step S4 as the anode, and prepare a cathode. Connect them to the positive and negative terminals of the DC power supply, respectively. Place the anode and cathode above the electrolyte, and immerse them in the electrolyte. Then, apply electricity to carry out an electrochemical reaction. After the reaction is complete, remove the metal M sheet that served as the anode, and then separate the unreacted metal M sheet from the product. The product obtained is the MOF material. The metal elements in the MOF material are the same as those in the metal M sheet.

[0012] In step S5, the output voltage of the DC power supply is 0.5 to 30V, and the current is 0.1 to 0.3A.

[0013] As a further preferred embodiment of the present invention, in step S1, the solid strong alkali compound is sodium hydroxide or potassium hydroxide, and the waste PET and the solid strong alkali compound are mixed in a molar ratio of less than or equal to 1:1.

[0014] As a further preferred embodiment of the present invention, in step S1, the ball milling speed of the dry ball mill is 200-600 r / min, and the ball milling time is 2-5 h.

[0015] As a further preferred embodiment of the present invention, in step S2, the concentration of the mixed solution of disodium terephthalate and ethylene glycol is 0.10 to 0.15 mg / mL.

[0016] As a further preferred embodiment of the present invention, in step S3, the conductive salt is at least one of NaCl and KCl;

[0017] The concentration of the conductive salt in the electrolyte is 3–15 mg / mL.

[0018] As a further preferred embodiment of the present invention, in step S4, the elemental metal foil is specifically Al foil, Fe foil, Co foil, Zn foil, Ni foil, Cu foil, Sn foil, or Cr foil.

[0019] As a further preferred embodiment of the present invention, in step S5, the reaction time of the electrochemical reaction is 0.5 to 30 min.

[0020] As a further preferred embodiment of the present invention, in step S5, the electrode clip is a polytetrafluoroethylene platinum sheet electrode clip;

[0021] The process of fixing the electrode clamp specifically involves fixing the electrode clamp onto a polytetrafluoroethylene plate.

[0022] The separation of the unreacted metal M sheet from the product specifically involves placing the removed anode-connected metal M sheet in ethanol for ultrasonic separation.

[0023] According to another aspect of the present invention, the present invention provides a metal-organic framework material obtained by the above method.

[0024] The technical solution conceived in this invention, through a process design of ball milling followed by electrochemical treatment, can effectively transform waste PET into high-value MOF materials. The method of this invention first utilizes ball milling to safely and reliably degrade PET. During ball milling, the impact between the grinding balls and the milling jar grinds the PET and solid strong alkali compounds, converting mechanical energy into chemical energy, thereby driving the destruction of the molecular structure in PET, breaking surface chemical bonds, and promoting the PET degradation reaction. The degradation products are dissolved in water to obtain a completely degraded terephthalate and ethylene glycol solution, which is used as the electrolyte for the electrochemical synthesis of MOF materials. In the electrochemical reaction stage, by adjusting the output current and voltage of the DC power supply, the rate of conversion of elemental metals into metal ions can be precisely controlled, promoting the instantaneous combination of metal ions and terephthalate ions to form MOF materials.

[0025] This invention provides a method for rapidly degrading waste PET into MOF materials at room temperature and pressure. It also offers advantages such as mild reaction conditions, controllable morphology, low energy consumption, and low cost, making it suitable for preparing MOF materials with poor stability in water. This provides a new method for the industrial production of MOF materials from waste PET. Furthermore, the MOF materials prepared by this invention exhibit excellent oxygen evolution reaction (OER) performance.

[0026] Specifically, the method of this invention utilizes waste polyester to prepare MOF materials, which can achieve the following beneficial effects:

[0027] (1) The present invention uses waste PET as the organic ligand source required in the synthesis of MOF materials, which can simultaneously realize the recycling and degradation of waste PET and the production of MOF.

[0028] (2) This invention uses ball milling-electrochemical degradation of waste PET as MOF, which has instant adjustability. That is, according to different applications, the output voltage and current value of the preparation process can be adjusted to accurately and quickly prepare various types of MOF materials such as Zn-MOF with different morphologies and sizes, which are widely used in gas storage, adsorption separation, biology and catalysis.

[0029] (3) This invention uses ball milling-electrochemical degradation of waste PET to produce MOF. Compared with the previously reported PET ball milling degradation method, this invention directly utilizes the aqueous solution after degradation, avoiding acid and alkali treatment caused by adding large amounts of acid or alkali to the separated products. The electrode material production process is pollution-free, completely green, and low-cost, which is conducive to the popularization of PET degradation and MOF material preparation technology.

[0030] (4) This invention uses ball milling-electrochemical degradation of waste PET as MOF. Compared with the reported high-temperature hydrothermal synthesis technology that uses harsh synthesis conditions and time-consuming synthesis process, this invention completes the synthesis of MOF materials rapidly and controllably under normal temperature and pressure conditions, reduces external heat demand, reduces energy intake, and has high social and economic benefits.

[0031] (5) The present invention uses ball milling-electrochemical degradation of waste PET as MOF. Compared with the reported two-step ball milling method for synthesizing MOF, the present invention precisely controls the rate of metal element conversion into metal ions by adjusting the output current and voltage of DC power supply, promotes the directional combination of metal ions and terephthalate ions to form MOF, avoids the presence of a large number of insoluble impurities such as iron filings and incompletely degraded PET powder in the product, and improves the purity of the product.

[0032] (6) The present invention uses ball milling-electrochemical degradation of waste PET as MOF. The electrochemical reaction stage only requires 0.5 to 30 minutes, which greatly shortens the reaction time and reduces energy consumption. Attached Figure Description

[0033] Figure 1 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of the Al-MOF in Example 1. Figure 1 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 1 In the image, 'b' corresponds to a scanning electron microscope image. Figure 1 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 1 The 'd' in the diagram corresponds to the aperture distribution.

[0034] Figure 2 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, pore size distribution map, LSV polarization curve, and overpotential histogram of Fe-MOF in Example 2. Figure 2 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 2 In the image, 'b' corresponds to a scanning electron microscope image. Figure 2 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 2 In the diagram, d corresponds to the aperture distribution. Figure 2 The 'e' in the graph corresponds to the LSV polarization curve. Figure 2f in the graph corresponds to the overpotential histogram.

[0035] Figure 3 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of the Co-MOF in Example 3. Figure 3 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 3 In the image, 'b' corresponds to a scanning electron microscope image. Figure 3 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 3 The 'd' in the diagram corresponds to the aperture distribution.

[0036] Figure 4 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of Cu-MOF in Example 4. Figure 4 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 4 In the image, 'b' corresponds to a scanning electron microscope image. Figure 4 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 4 The 'd' in the diagram corresponds to the aperture distribution.

[0037] Figure 5 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of the Zn-MOF in Example 5. Figure 5 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 5 In the image, 'b' corresponds to a scanning electron microscope image. Figure 5 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 5 The 'd' in the diagram corresponds to the aperture distribution.

[0038] Figure 6 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of the Ni-MOF in Example 6. Figure 6 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 6 In the image, 'b' corresponds to a scanning electron microscope image. Figure 6 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 6 The 'd' in the diagram corresponds to the aperture distribution.

[0039] Figure 7 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of the Sn-MOF in Example 7. Figure 7 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 7 In the image, 'b' corresponds to a scanning electron microscope image. Figure 7 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 7 The 'd' in the diagram corresponds to the aperture distribution.

[0040] Figure 8 The images show the X-ray powder diffraction pattern, scanning electron microscope image, nitrogen adsorption-desorption curve, and pore size distribution of Cr-MOF in Example 8. Figure 8 In the diagram, 'a' corresponds to an X-ray powder diffraction pattern. Figure 8 In the image, 'b' corresponds to a scanning electron microscope image. Figure 8 In the curve, 'c' corresponds to the nitrogen adsorption-desorption curve. Figure 8 The 'd' in the diagram corresponds to the aperture distribution.

[0041] Figure 9 The image shows the X-ray powder diffraction pattern of Zn-MOF in Comparative Example 1. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] Example 1

[0044] S1. Add 12g of waste PET and 5g of sodium hydroxide to a ball mill jar. The ball-to-material ratio is 32:1 (mass ratio, the same below). Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0045] S2. Dissolve the white product from S1 in 120 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.108 mg / mL (the concentration of the PET degradation solution was calculated by taking 1 mL of PET degradation solution in a petri dish, drying it in a 90℃ oven for 2 hours, and weighing it; the same applies below).

[0046] S3. Add NaCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 11 mg / mL.

[0047] S4. Cut the Al foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Al sheets.

[0048] S5. Take two Al sheets from S4 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Al sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 30V and the output current to 0.3A, and react for 20 min before disconnecting the power supply. Remove the Al sheet connected to the anode and sonicate it in ethanol for 30 min to separate the Al sheet and the product. Wash and dry the product to obtain Al-MOF material with a yield of 99 wt%.

[0049] Figure 1 In the diagram, 'a' represents the X-ray powder diffraction pattern of Al-MOF. Figure 1 In the image, b is a scanning electron microscope image of Al-MOF. Figure 1 In the figure, c represents the nitrogen adsorption-desorption curve of Al-MOF. Figure 1 In the diagram, 'd' represents the pore size distribution of Al-MOF. X-ray powder diffraction patterns show that Al-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Al-MOF consists of irregular nanospheres with sizes ranging from 50 to 200 nm. Nitrogen adsorption and desorption curves demonstrate the presence of a distinct adsorption and desorption lag ring in Al-MOF. The pore size distribution indicates a large number of micropores (<2 nm) and a specific surface area of ​​369 m². 2 / g.

[0050] Example 2

[0051] S1. Add 24g of waste PET and 10g of sodium hydroxide into a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0052] S2. Dissolve the white product from S1 in 180 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.100 mg / mL.

[0053] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 3 mg / mL.

[0054] S4. Cut the Fe foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Fe sheets.

[0055] S5. Take two Fe sheets from S4 and install them onto two PTFE-platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Fe sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 5V and the output current to 0.1A, and turn off the power after reacting for 10 minutes. Remove the Fe sheet connected to the anode and sonicate it in ethanol for 30 minutes to separate the Fe sheet and the product. Wash and dry the product to obtain Fe-MOF material with a yield of 99 wt%.

[0056] S6. Ethanol and 5 wt% Nafion solution were uniformly mixed at a volume ratio of 980:20 to prepare Nafion dilution. Then, 20 mg of Fe-MOF prepared in S5 was added to 250 μL of the above Nafion dilution and ultrasonically dispersed to obtain a dispersion. The dispersion was then uniformly drop-coated onto nickel foam (NF) using a pipette. After drying, the working electrode was obtained. A three-electrode system was constructed with Hg / HgO electrode as reference electrode, carbon rod as counter electrode, and KOH solution as electrolyte to conduct OER performance testing under room temperature and atmospheric pressure conditions.

[0057] Figure 2 In the diagram, 'a' represents the X-ray powder diffraction pattern of Fe-MOF. Figure 2 In the image, b is a scanning electron microscope image of Fe-MOF. Figure 2 In the figure, c represents the nitrogen adsorption-desorption curve of Fe-MOF. Figure 2 In the diagram, d represents the pore size distribution of Fe-MOF. Figure 2 In the figure, 'e' represents the LSV polarization curves of Fe-MOF(BE)@NF, Fe-MOF(BB)@NF, IrO2@NF, and NF under the same conditions (Fe-MOF(BE)@NF is prepared by the ball milling-electrochemical method mentioned in this invention). Figure 3 f in the figure represents the LSV overpotential histogram of Fe-MOF(BE)@NF, Fe-MOF(BB)@NF, IrO2@NF and NF under the same conditions.

[0058] in:

[0059] Fe-MOF(BE)@NF is an electrode prepared by loading Fe-MOF on NF according to the ball milling-electrochemical method mentioned in this invention, and is used in the experimental group.

[0060] Fe-MOF(BB)@NF is an electrode prepared by loading Fe-MOF onto NF according to the S6 step described above, using a two-step ball milling method reported in the prior art (Panpan He, Zhen Hu, Zhikui Dai, Huiying Bai, Zifen Fan, Ran Niu, Jiang Gong, Qiang Zhao, Tao Tang. Mechanochemistry milling of waste poly(ethylene terephthalate) into metal-organic frameworks. ChemSusChem 2023, 16, e202201935). It serves as a control group.

[0061] IrO2 is currently recognized as the best OER noble metal material for electrode preparation. IrO2@NF is an electrode prepared by loading IrO2 (IrO2 purchased from Bide Pharmaceuticals, CAS: 12030-49-8) onto NF according to step S6. Control group.

[0062] NF is blank nickel foam, the control group.

[0063] X-ray powder diffraction (XRD) patterns revealed significant characteristic diffraction peaks in Fe-MOF, indicating successful synthesis. Scanning electron microscopy (SEM) images showed that Fe-MOF exhibited irregular nanosheet morphology with dimensions ranging from 50 to 100 nm. Nitrogen adsorption-desorption curves indicated the presence of a distinct adsorption-desorption lag ring in Fe-MOF. Pore size distribution maps revealed numerous micropores (<2 nm) and a specific surface area of ​​76 m². 2 / g. From the polarization curves and LSV overpotential histograms of Fe-MOF(BE)@NF, Fe-MOF(BB)@NF, IrO2@NF, and NF, it can be seen that Fe-MOF(BE)@NF has the best OER, requiring only 283mV overpotential to achieve 100mAcm. -2 The current density is significantly lower than that required for Fe-MOF(BB)@NF (327mV), IrO2@NF (462mV), and NF (545mV) materials; a current density of only 440mV is needed to achieve 500mA cm⁻¹. -2 The current density is much lower than that required for Fe-MOF(BB)@NF (535mV), IrO2@NF (721mV) and NF (826mV) materials.

[0064] Example 3

[0065] S1. Add 18g of waste PET and 8g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0066] S2. Dissolve the white product from S1 in 80 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.150 mg / mL.

[0067] S3. Add NaCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 10 mg / mL.

[0068] S4. Cut the Co foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Co sheets.

[0069] S5. Take two Co sheets from S4 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Co sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 10V and the output current to 0.1A, and react for 0.5 min before disconnecting the power supply. Remove the Co sheet connected to the anode and sonicate it in ethanol for 30 min to separate the Co sheet and the product. Wash and dry the product to obtain Co-MOF material with a yield of 99 wt%.

[0070] Figure 3 In the diagram, 'a' represents the X-ray powder diffraction pattern of Co-MOF. Figure 3 In the image, b is a scanning electron microscope image of Co-MOF. Figure 3 In the figure, c represents the nitrogen adsorption-desorption curve of Co-MOF. Figure 4 In the diagram, 'd' represents the pore size distribution of Co-MOF. X-ray powder diffraction patterns show that Co-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Co-MOF has an irregular nanosheet structure with dimensions ranging from 300 to 500 nm. Nitrogen adsorption and desorption curves show that Co-MOF possesses a distinct adsorption and desorption lag ring, with a specific surface area of ​​36 m². 2 / g.

[0071] Example 4

[0072] S1. Add 24g of waste PET and 10g of sodium hydroxide into a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0073] S2. Dissolve the white product from S1 in 180 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.100 mg / mL.

[0074] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 15 mg / mL.

[0075] S4. Cut the Cu foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Cu sheets.

[0076] S5. Take two Cu sheets from S4 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Cu sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 10V and the output current to 0.1A, and turn off the power after reacting for 2 minutes. Remove the Cu sheet connected to the anode and sonicate it in ethanol for 30 minutes to separate the Cu sheet and the product. Wash and dry the product to obtain Cu-MOF material with a yield of 98 wt%.

[0077] Figure 4 In the diagram, 'a' represents the X-ray powder diffraction pattern of Cu-MOF. Figure 4 In the image, b is a scanning electron microscope image of Cu-MOF. Figure 4 In the figure, c represents the nitrogen adsorption-desorption curve of Cu-MOF. Figure 5 In the diagram, 'd' represents the pore size distribution of Cu-MOF. X-ray powder diffraction patterns show that Cu-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Cu-MOF has an irregular nanorod structure with dimensions ranging from 300 to 500 nm. Nitrogen adsorption and desorption curves show that Cu-MOF possesses a distinct adsorption and desorption lag ring, with a specific surface area of ​​33 m². 2 / g.

[0078] Example 5

[0079] S1. Add 15g of waste PET and 7g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 600r / min and the ball milling time to 2h to obtain a white product.

[0080] S2. Dissolve the white product from S1 in 120 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.125 mg / mL.

[0081] S3. Add NaCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 3 mg / mL.

[0082] S4. Cut the Zn foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Zn sheets.

[0083] S5. Take two Zn sheets from S4 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Zn sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 8V and the output current to 0.2A, and turn off the power after reacting for 5 minutes. Remove the Zn sheet connected to the anode and sonicate it in ethanol for 30 minutes to separate the Zn sheet and the product. Wash and dry the product to obtain Zn-MOF material with a yield of 99 wt%.

[0084] Figure 5 In the diagram, 'a' represents the X-ray powder diffraction pattern of Zn-MOF. Figure 5 In the image, b is a scanning electron microscope image of Zn-MOF. Figure 5 In the figure, c represents the nitrogen adsorption-desorption curve of Zn-MOF. Figure 6 In the diagram, 'd' represents the pore size distribution of Zn-MOF. X-ray powder diffraction patterns show that Zn-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Zn-MOF has an irregular nanosheet structure with dimensions ranging from 100 to 800 nm. Nitrogen adsorption and desorption curves show that Zn-MOF possesses a distinct adsorption and desorption lag ring, with a specific surface area of ​​56 m². 2 / g.

[0085] Example 6

[0086] S1. Add 13g of waste PET and 6g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 500r / min and the ball milling time to 2.5h to obtain a white product.

[0087] S2. Dissolve the white product from S1 in 120 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.110 mg / mL.

[0088] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 11 mg / mL.

[0089] S4. Cut the Ni foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metallic Ni sheets.

[0090] S5. Take two Ni sheets from S4 and install them onto two PTFE-platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Ni sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 4V and the output current to 0.2A, and turn off the power after reacting for 5 minutes. Remove the Ni sheet connected to the anode and sonicate it in ethanol for 30 minutes to separate the Ni sheet and the product. Wash and dry the product to obtain Ni-MOF material with a yield of 99 wt%.

[0091] Figure 6 In the diagram, 'a' represents the X-ray powder diffraction pattern of Ni-MOF. Figure 6 In the image, b is a scanning electron microscope image of Ni-MOF. Figure 6 In the figure, c represents the nitrogen adsorption-desorption curve of Ni-MOF. Figure 7 In the diagram, 'd' represents the pore size distribution of Ni-MOF. X-ray powder diffraction patterns show that Ni-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Ni-MOF has an irregular nanosheet structure with dimensions ranging from 100 to 500 nm. Nitrogen adsorption and desorption curves show that Ni-MOF possesses a distinct adsorption and desorption lag ring, with a specific surface area of ​​65 m². 2 / g.

[0092] Example 7

[0093] S1. Add 12g of waste PET and 5g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 200r / min and the ball milling time to 5h to obtain a white product.

[0094] S2. Dissolve the white product from S1 in 80 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.150 mg / mL.

[0095] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 15 mg / mL.

[0096] S4. Cut the Sn foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Sn sheets.

[0097] S5. Take two Sn sheets from S4 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Sn sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 30V and the output current to 0.1A, and react for 30 min before disconnecting the power supply. Remove the Sn sheet connected to the anode and sonicate it in ethanol for 30 min to separate the Sn sheet and the product. Wash and dry the product to obtain Sn-MOF material with a yield of 99 wt%.

[0098] Figure 7 In the diagram, 'a' represents the X-ray powder diffraction pattern of Sn-MOF. Figure 7 In the image, b is a scanning electron microscope image of Sn-MOF. Figure 7 In the figure, c represents the nitrogen adsorption-desorption curve of Sn-MOF. Figure 8 In the diagram, 'd' represents the pore size distribution of Sn-MOF. X-ray powder diffraction patterns show that Sn-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Sn-MOF has an irregular nanorod structure with dimensions ranging from 1 to 3 μm. Nitrogen adsorption and desorption curves show that Sn-MOF possesses a distinct adsorption and desorption lag ring, with a specific surface area of ​​41 m². 2 / g.

[0099] Example 8

[0100] S1. Add 12g of waste PET and 5g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 600r / min and the ball milling time to 2h to obtain a white product.

[0101] S2. Dissolve the white product from S1 in 80 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.150 mg / mL.

[0102] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 3 mg / mL.

[0103] S4. Cut the Cr foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metallic Cr sheets.

[0104] S5. Take two Cr sheets from S4 and install them onto two PTFE-platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Cr sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 0.5V and the output current to 0.3A, and turn off the power after reacting for 10 minutes. Remove the Cr sheet connected to the anode, place it in ethanol, and sonicate for 30 minutes to separate the Cr sheet and the product. The product is washed and dried to obtain Cr-MOF material with a yield of 99 wt%.

[0105] Figure 8 In the diagram, 'a' represents the X-ray powder diffraction pattern of Cr-MOF. Figure 8 In the image, b is a scanning electron microscope image of Cr-MOF. Figure 8 In the figure, c represents the nitrogen adsorption-desorption curve of Cr-MOF. Figure 9 In the diagram, 'd' represents the pore size distribution of Cr-MOF. X-ray powder diffraction patterns show that Cr-MOF exhibits significant characteristic diffraction peaks, indicating successful synthesis. Scanning electron microscopy images reveal that Cr-MOF consists of irregular nanospheres with dimensions ranging from 20 to 50 nm. Nitrogen adsorption and desorption curves demonstrate the presence of a distinct adsorption and desorption lag ring in Cr-MOF. The pore size distribution indicates a large number of micropores (<2 nm) and a specific surface area of ​​163 m². 2 / g.

[0106] Comparative Example 1

[0107] S1. Add 12g of waste PET and 5g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0108] S2. Dissolve the white product from S1 in 120 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.108 mg / mL.

[0109] S3. Add KCl to the PET degradation solution in S2 to obtain an electrolyte with a conductive salt concentration of 3 mg / mL.

[0110] S4. Cut the Zn foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Zn sheets.

[0111] S5. Take two Zn sheets from S4 and mount them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S3, ensuring the Zn sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 5V and the output current to 0.35A, and turn off the power after reacting for 10 minutes. Remove the Zn sheet connected to the anode and sonicate it in ethanol for 30 minutes to separate the Zn sheet and the product. Wash and dry the product to obtain Zn-MOF material.

[0112] Figure 9 The X-ray powder diffraction pattern of Zn-MOF shows that Zn-MOF has weak characteristic diffraction peaks (6.84°, 9.69°), but other stronger diffraction peaks are also present. For example, compared with Example 5, ​ The X-ray powder diffraction pattern shown exhibits distinct peaks at 31.8°, 34.4°, 36.3°, 47.5°, and 56.6°, corresponding to peaks of ZnO compounds (PDF#36-1451). This indicates that excessive applied current may cause Zn to be oxidized to ZnO under the influence of the current, resulting in a large amount of ZnO in the formed Zn-MOF. Therefore, a suitable current needs to be set when preparing MOFs using ball milling-electrochemical methods.

[0113] Comparative Example 2

[0114] S1. Add 12g of waste PET and 5g of sodium hydroxide to a ball mill jar with a ball-to-material ratio of 32:1. Set the ball mill speed to 400r / min and the ball milling time to 3.5h to obtain a white product.

[0115] S2. Dissolve the white product from S1 in 120 mL of deionized water, stir and filter to obtain a PET degradation solution with a concentration of 0.108 mg / mL, which is used directly as the electrolyte.

[0116] S3. Cut the Cu foil into 1cm×1.5cm electrode sheets, and ultrasonically clean them in ethanol and deionized water for 10 minutes in sequence to obtain clean metal Cu sheets.

[0117] S4. Take two Cu sheets from S3 and install them onto two PTFE platinum electrode holders respectively. Then fix the two electrodes onto a PTFE plate, 3 cm apart. Place the electrode holders vertically in the electrolyte obtained in S2, ensuring the Cu sheets are completely submerged. Connect the positive and negative terminals of a DC power supply to the top of the electrode holders respectively. Turn on the DC power supply, set the output voltage to 10V and the output current to 0.1A, and turn off the power after reacting for 30 minutes. Remove the Cu sheet connected to the anode; no Cu-MOF has formed on the Cu sheet.

[0118] The above embodiments are merely examples. For instance, in step S5, besides using two M-plates from S4 as the anode and cathode respectively, only one M-plate can be used as the anode, and the cathode can be made of other conductive materials (such as carbon rods or platinum sheets) without affecting the electrochemical reaction. As another example, the above embodiments use a 1:1 molar ratio of waste PET and solid strong alkali compound. In actual operation, the solid strong alkali compound can be used in excess.

[0119] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing metal-organic framework materials by ball milling-electrochemical degradation of waste PET, characterized in that, Includes the following steps: S1. Mix waste PET and solid strong alkali compound evenly and then dry ball mill to obtain the ball milled product; S2. Dissolve the ball-milled product obtained in step S1 in deionized water to obtain a mixed solution of disodium terephthalate and ethylene glycol. S3. Add a conductive salt to the mixed solution obtained in step S2 to obtain an electrolyte; wherein the conductive salt is at least one of NaCl and KCl, and the concentration of the conductive salt in the electrolyte is 3~15 mg / mL. S4. Based on the target metal element M in the target metal-organic framework material, select the corresponding elemental metal foil, cut it to obtain the electrode sheet, denoted as metal M sheet; S5. Prepare a DC power supply. Use the metal M sheet obtained in step S4 as the anode, and prepare a cathode. Connect them to the positive and negative terminals of the DC power supply, respectively. Place the anode and cathode above the electrolyte, and immerse them in the electrolyte. Then, apply electricity to carry out an electrochemical reaction. After the reaction is complete, remove the metal M sheet that served as the anode, and then separate the unreacted metal M sheet from the product. The product obtained is the MOF material. The metal elements in the MOF material are the same as those in the metal M sheet. In step S5, the output voltage of the DC power supply is 0.5~30 V, the current is 0.1~0.3 A, and the reaction time of the electrochemical reaction is 0.5~30 min.

2. The method as described in claim 1, characterized in that, In step S1, the solid strong alkali compound is sodium hydroxide or potassium hydroxide, and the waste PET and the solid strong alkali compound are mixed in a molar ratio of less than or equal to 1:

1.

3. The method as described in claim 1, characterized in that, In step S1, the ball milling speed of the dry ball mill is 200~600 r / min, and the ball milling time is 2~5 h.

4. The method as described in claim 1, characterized in that, In step S2, the concentration of the mixed solution of disodium terephthalate and ethylene glycol is 0.10~0.15 mg / mL.

5. The method as described in claim 1, characterized in that, In step S4, the metal elemental foil is specifically Al foil, Fe foil, Co foil, Zn foil, Ni foil, Cu foil, Sn foil, or Cr foil.

6. The method as described in claim 1, characterized in that, In step S5, the anode and the cathode are connected to the positive and negative terminals of the DC power supply respectively via electrode clamps, wherein the electrode clamps are polytetrafluoroethylene platinum sheet electrode clamps; the electrode clamps are fixed on the polytetrafluoroethylene plate; The separation of the unreacted metal M sheet from the product specifically involves placing the removed anode-connected metal M sheet in ethanol for ultrasonic separation.

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