Method for preparing MIL-53 (Al) material by degrading waste PET (Polyethylene Terephthalate) through ball milling-aqueous solution reflux

Abstract

The invention belongs to the technical field of green controllable degradation of waste plastics and preparation of metal-organic framework (MOF) materials, and discloses a method for preparing an MIL-53 (Al) material by degrading waste PET through ball milling-aqueous solution reflux, and the method comprises the following steps: (1) uniformly mixing the waste PET and a solid strong alkali compound, and carrying out ball milling to obtain a ball milling product; then, dissolving the ball-milled product in deionized water to obtain a mixed solution of terephthalic acid salt and ethylene glycol; and (2) mixing the mixed solution obtained in the step (1) with an aluminum salt solution, and performing reflux heating and stirring reaction to generate the MIL-53 (Al) material. According to the method, the waste PET is converted into the MOF with the high specific surface area through cooperation of ball milling treatment and aqueous solution reflux reaction, the method has the advantages of being low in cost, environmentally friendly, free of organic solvents, high in yield and easy to produce in an amplified mode, and a new scheme is provided for large-scale upgrading and chemical recovery of the waste PET into the MOF.

Description

Technical Field

[0001] The present invention belongs to the technical field of green and controllable degradation of waste plastics and preparation of metal-organic framework (MOF) materials. More specifically, it relates to a method for preparing MIL-53(Al) material by ball milling-aqueous solution reflux degradation of waste PET. Background Art

[0002] PET is the most important variety in thermoplastic polyesters. Due to its low cost, light weight, good processability and high durability, it is widely used in fields such as packaging, construction, automotive, and electronic products. However, at the same time, due to its high chemical stability, it is difficult to degrade under natural conditions. A large number of waste PET products such as beverage bottles and packaging materials have become an important source of white pollution, causing serious damage to ecological environments such as soil and water bodies. Waste PET will decompose into microplastics in the environment, enter the ocean, fish and other marine organisms, and even human livers, kidneys and placentas, posing a major threat to the ecosystem and human health. So far, the traditional disposal methods for waste PET include landfill, incineration and mechanical recycling. Landfill has the advantages of being effective in the short term, simple and easy to implement. However, the landfill method will occupy a large amount of land, leach harmful substances, and cause other environmental problems such as groundwater pollution. Incineration overcomes some limitations of landfill because it does not require a large amount of space and can even recover energy in the form of heat. However, incineration will produce a variety of toxic gases including polycyclic aromatic hydrocarbons, etc., and at the same time will produce a large amount of dust smoke and greenhouse gases, seriously polluting the atmospheric environment. Mechanical recycling is to grind waste PET into secondary raw materials by mechanical force. The advantages are simple process and low cost. However, mechanical recycling often leads to a decline in the structural properties of the recycled materials, limiting their practical value. Although the biodegradation of waste plastics has received high attention in recent years, due to reasons such as the poor thermal stability, high cost, short lifespan, and difficulty in recycling and reuse of enzyme catalysts, it is difficult to achieve large-scale industrialization of enzymatic degradation of waste plastics. And upgrading chemical recycling aims to convert waste plastics into high-value-added products through various chemical schemes, and has recently received increasing attention as an alternative recycling strategy.

[0003] Metal-organic framework materials (MOF) are porous crystalline materials self-assembled by metal centers (metal ions or metal clusters) and organic ligands through coordination bonds. MOF materials have characteristics such as abundant atomically dispersed metal sites, tunable pore structures, high specific surface areas and porosities, and tunable chemical compositions and functions, and are widely used in fields such as gas storage and separation, catalysis, drug delivery, and chemical / biological sensing. Terephthalic acid is the main monomer of PET and also a typical degradation product of PET, while terephthalic acid is at the same time one of the most common organic ligands for synthesizing MOF materials. Therefore, upgrading and recycling waste PET into MOF materials is an emerging and popular method of upgrading chemical recycling. Currently, the solvothermal method and the ball milling method are the main strategies for upgrading and recycling PET into MOF materials. Fan et al. used a one-pot solvothermal method to convert waste PET into Mn-MOF, that is, 12 mmol of waste PET and 12 mmol of MnCl2 were added to a mixed solvent of 30 mL of N,N-dimethylformamide (DMF) and 15 mL of deionized water, and the reaction was carried out at 180 °C for 24 h. The product was washed with DMF and dried to obtain Mn-MOF (Zifen Fan, Jiaxin Ren, Huiying Bai, Panpan He, Liang Hao, Ning Liu, Bingyu Chen, Ran Niu, Jiang Gong. Shape-controlled fabrication of MnO / C hybrid nanoparticle from waste polyester for solar evaporation and thermoelectricity generation. Chemical Engineering Journal 2023, 451, 138534). This method has harsh reaction conditions (high temperature and high pressure, such as usually 20-200 atmospheres), long reaction times (such as usually 24-48 h), consumes a large amount of organic solvents (such as DMF), has high costs and energy consumption, and is difficult to scale up production.He et al. converted waste PET into MOF materials through a two-step ball milling method. That is, first, PET was ball milled and degraded to obtain disodium terephthalate and ethylene glycol, and then metal salts were added and ball milled again to promote the coordination of terephthalic acid ions with metal ions to form MOF (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). The disadvantage of this method is that the product contains insoluble impurities (such as iron filings and incompletely degraded PET powders). These impurities are likely to damage the crystal structure of MOF, and the ball milling process is prone to blocking the MOF pore channels, resulting in a low specific surface area (less than 150 m 2 / g), which is not conducive to expanding the practical application of MOF materials. ZL202211401069.6 discloses a method for preparing MOF materials by ball milling-solution blending, that is, PET is ball milled with a solid strong base compound to obtain an intermediate terephthalate product, the intermediate product is dissolved in water to obtain a mixed solution, and then a metal salt solution is added to the mixed solution and stirred at room temperature until precipitation occurs. The precipitate is obtained as MOF after centrifugation, washing, and drying. CN202410847823.1 discloses a method for preparing MOF materials by ball milling-electrochemical degradation of PET. The specific surface area of the MOF prepared by these methods has been improved to a certain extent (369 m 2 / g). CN 202410063010.3 discloses a method for preparing MOF materials by two-step ball milling of PET assisted by trace organic solvents, with a medium specific surface area (539 - 605 m 2 / g). Nevertheless, there are still challenges in realizing the industrial production of MOF with a high specific surface area.

[0004] Therefore, there is an urgent need to develop a green and efficient method with mild reaction conditions, without consuming organic solvents, low cost and energy consumption, and easy to scale up production, to achieve continuous and large-scale controllable degradation of PET into MOF materials with a high specific surface area, so as to realize the green and controllable degradation and upgraded recycling of waste PET and make it move towards circular economy. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a method for preparing MIL-53(Al) material by ball milling-aqueous solution reflux degradation of waste PET. Through the cooperation of ball milling treatment and aqueous solution reflux reaction, waste PET is converted into MOF with high specific surface area, which has the advantages of low cost, environmental friendliness, no use of organic solvents, high yield, and easy large-scale production of MOF, providing a new solution for large-scale upgrading of chemical recycling of waste PET into MOF.

[0006] To achieve the above object, according to the present invention, there is provided a method for preparing MIL-53(Al) material by ball milling-aqueous solution reflux degradation of waste PET, which is characterized by comprising the following steps:

[0007] (1) Mix waste PET and solid strong base compound evenly and carry out ball milling to obtain a ball-milled product; then, dissolve the ball-milled product in deionized water to obtain a mixed solution of terephthalate and ethylene glycol;

[0008] (2) Mix the mixed solution obtained in step (1) with an aluminum salt solution, and carry out reflux heating and stirring reaction to generate MIL-53(Al) material.

[0009] As a further preference of the present invention, in step (2), the reaction temperature of the reflux heating and stirring reaction is 60-100 °C, and the reaction time is 6-24 h.

[0010] As a further preference of the present invention, in step (1), the solid strong base compound is selected from sodium hydroxide and potassium hydroxide.

[0011] As a further preference of the present invention, in step (1), the ball milling time is 2-5 h, and the rotation speed is 200-600 r / min.

[0012] As a further preference of the present invention, in the mixed solution obtained in step (1), the concentration of the mixed solution of terephthalate and ethylene glycol is 51.3-124.5 mg / mL.

[0013] As a further preference of the present invention, in step (2), the mixed solution obtained in step (1) and the aluminum salt solution are mixed according to the mass ratio of the aluminum salt in the aluminum salt solution to the terephthalic acid ligand contained in the terephthalate in the mixed solution being 0.33-1.

[0014] As a further preference of the present invention, in step (2), the aluminum salt is at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate.

[0015] As a further preference of the present invention, the specific surface area of the MIL-53(Al) material generated in step (2) is 801-894 m2 / g.

[0016] As a further preference of the present invention, the MIL-53(Al) material is obtained by centrifuging the reacted system to obtain a solid, and then washing and drying the solid.

[0017] Through the above technical solution conceived by the present invention, compared with the prior art, the method of the present invention combines ball milling treatment with aqueous solution reflux reaction. First, in a strong alkaline environment, waste polyethylene terephthalate (PET) is degraded into terephthalate and ethylene glycol through mechanochemical action. Then, the degradation products react with an aluminum salt aqueous solution through solution reflux to promote the coordination synthesis of high specific surface area MIL-53(Al) between terephthalate and aluminum salt. In the method of the present invention, waste PET is first mixed with a solid strong base compound and then ball milled. The strong base compound reacts with waste PET, and the solid-phase depolymerization of PET generates degradation products terephthalate and ethylene glycol. Subsequently, the degradation products are mixed with an aluminum salt solution, refluxed, heated and stirred, and terephthalic acid ions coordinate with aluminum ions to form MIL-53(Al). The aqueous solution reflux method continuously heats and condenses to keep the reaction system at a stable temperature, which is beneficial to the uniform growth of MOF crystals, improves the crystallinity and specific surface area of MOF. Moreover, during the process, impurities and by-products in the system can be effectively removed to avoid blocking the pores, further improving the specific surface area of MOF.

[0018] The hydroxyl groups in the ethylene glycol structure obtained by the ball milling method can form hydrogen bonds with water molecules, so that ethylene glycol has a synergistic effect with the aqueous solution reflux method: First, ethylene glycol can adjust the polarity of the mixed solution of degradation products and aluminum salt, ensure sufficient contact between aluminum ions and terephthalic acid ions, promote the dispersion of aluminum ions and their coordination with terephthalic acid ions, and accelerate lattice formation and stable crystal nucleus sites. Second, ethylene glycol increases the boiling point of water, which is beneficial to maintaining the temperature of the reaction system, uniformly transferring heat, avoiding uneven heating, keeping the system stable, promoting the rapid growth of crystals, improving the MOF yield, and regulating the MOF size.

[0019] Specifically, the present invention can achieve the following beneficial effects:

[0020] (1) Compared with traditional PET upgrading chemical recycling methods, such as the solventolysis method that consumes excessive organic solvents and has a long reaction time, the pyrolysis method that has high energy consumption and complex product components, and the catalytic hydrogenolysis method that relies on an H2 atmosphere, the method of the present invention first realizes the green and controllable degradation of waste PET in a normal temperature and pressure air atmosphere by ball milling treatment, and then uses an aqueous solution reflux reaction to upgrade and recycle it into a MOF material with a high specific surface area in a low temperature and pressure air atmosphere. For another example, traditional PET upgrading recycling methods degrade waste PET into products such as terephthalic acid, ethylene glycol, xylene, and unsaturated hydrocarbons, and the scope of reuse of the products is narrow. The present invention realizes the green and controllable degradation of waste PET and its upgrading and recycling into a MOF material with a high specific surface area, with efficient reaction, easy to scale up, and the product having unique advantages in the fields of gas storage and separation, catalysis, drug delivery, chemical / biological sensing, etc.

[0021] (2) Compared with the traditional solvothermal method for preparing MOF, the ball milling-aqueous solution reflux method of the present invention has significant advantages. First, no organic solvents are used throughout the process, greatly reducing resource consumption and avoiding the generation of secondary pollution. Second, the reaction is carried out in a low temperature and pressure air atmosphere, and the operation process is simple and controllable, safe and environmentally friendly. Third, the reaction is efficient, the post-treatment is simple, and it is easy to mass-produce MOF. The present invention provides a new solution for the large-scale upgrading chemical recycling of waste PET into MOF, and is expected to realize the industrialization of waste PET recycling and utilization and make it move towards circular economy.

[0022] (3) Compared with the reported two-step ball milling method, the two-step ball milling method assisted by trace organic solvents, the ball milling-constant temperature aqueous solution stirring method, and the ball milling-electrochemical degradation method, the ball milling-aqueous solution reflux method of the present invention has significant advantages. First, the ball milling-aqueous solution reflux method avoids the problems of the destruction of the MOF crystal structure and the low purity of MOF caused by a large amount of insoluble impurities such as iron filings and incompletely degraded PET powder in the products of the two-step ball milling method. Second, the MOF prepared by the ball milling-aqueous solution reflux method has a high specific surface area (801 - 894m 2 / g), which is significantly higher than all previous methods. For example, the specific surface area of the MOF prepared by the two-step ball milling method or the ball milling-constant temperature aqueous solution stirring method is less than 150m 2 / g, the specific surface area of the MOF prepared by the two-step ball milling method assisted by trace organic solvents is 539 - 605m 2 / g, and the specific surface area of the MOF prepared by the ball milling-electrochemical degradation method is 369m 2 / g. This is because in the ball milling-aqueous solution reflux method, the aqueous solution reflux method continuously heats and condenses, keeping the reaction system at a stable temperature, which is beneficial to the uniform growth of MOF crystals, improving the crystallinity and specific surface area of MOF. Moreover, during the process, impurities and by-products in the system can be effectively removed, avoiding clogging of the pores and further increasing the specific surface area of MOF. As analyzed above, ethylene glycol and the aqueous solution reflux method also have a synergistic effect, which can further promote the rapid growth of crystals, increase the yield of MOF, regulate the size of MOF, and ensure the specific surface area of the product MOF.

[0023] In summary, the method of the present invention can convert waste PET into MOF materials (especially MOF materials with a specific surface area of 801-894 m 2 / g) under normal pressure air conditions, providing a new idea for the large-scale, continuous and controllable degradation of waste PET into MOF with a high specific surface area. MOF products with stable crystal structures, high purity and specific surface area also have broad application prospects. The present invention uses the ball milling-aqueous solution reflux method to greenly and controllably degrade and upgrade and recycle waste PET into MOF with a high specific surface area. This method is low-cost, green and environmentally friendly, does not use organic solvents, has a high yield, is easy to scale up production, and the whole process is carried out under normal pressure air atmosphere. The present invention provides a new way for the green and controllable degradation and large-scale upgrade and recycling of waste PET, and also provides a new method for the industrial preparation of MOF materials with a high specific surface area, promising to realize the industrialization of waste PET recycling and utilization and make it move towards circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 1 is the X-ray powder diffraction pattern, infrared spectrum, nitrogen adsorption-desorption curve and pore size distribution diagram of MIL-53(Al) in Example 1; wherein, Figure 1 a in FIG. 1 is the X-ray powder diffraction pattern, Figure 1 b in FIG. 1 is the infrared spectrum, Figure 1 c in FIG. 1 is the nitrogen adsorption-desorption curve, Figure 1 d in FIG. 1 is the pore size distribution diagram.

[0025] Figure 2 FIG. 2 is the X-ray powder diffraction pattern and scanning electron microscope image of MIL-53(Al) in Example 2; wherein, Figure 2 a in FIG. 2 is the X-ray powder diffraction pattern, Figure 2 b in FIG. 2 is the scanning electron microscope image.

[0026] Figure 3 FIG. 3 is the X-ray powder diffraction pattern, infrared spectrum and scanning electron microscope image of MIL-53(Al) in Example 3; wherein, Figure 3 a in FIG. 3 is the X-ray powder diffraction pattern, Figure 3 b in FIG. 3 is the infrared spectrum,Figure 3 c in Figure 3 and d in

[0027] Figure 4 are the X-ray powder diffraction pattern, infrared spectrum and scanning electron microscope images of MIL-53(Al) in Example 4; among them, Figure 4 a in Figure 4 is the X-ray powder diffraction pattern, Figure 4 b in Figure 4 is the infrared spectrum,

[0028] Figure 5 are the X-ray powder diffraction pattern and scanning electron microscope images of MIL-53(Al) in Example 5; among them, Figure 5 a in Figure 5 is the X-ray powder diffraction pattern,

[0029] Figure 6 are the X-ray powder diffraction pattern, infrared spectrum and scanning electron microscope images of MIL-53(Al) in Example 6; among them, Figure 6 a in Figure 6 is the X-ray powder diffraction pattern, Figure 6 b in Figure 6 is the infrared spectrum,

[0030] Figure 7 are the X-ray powder diffraction pattern, infrared spectrum and scanning electron microscope images of MIL-53(Al) in Example 7; among them, Figure 7 a in Figure 7 is the X-ray powder diffraction pattern, Figure 7 b in Figure 7 is the infrared spectrum,

[0031] Figure 8 are the X-ray powder diffraction pattern and scanning electron microscope images of Al-MOF in Comparative Example 1; among them, Figure 8 a in Figure 8 is the X-ray powder diffraction pattern,

[0032] Figure 9 are the X-ray powder diffraction pattern and scanning electron microscope images of MIL-53(Al) in Comparative Example 2; among them, Figure 9 a in Figure 9 is the X-ray powder diffraction pattern, Detailed implementation mode

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Generally speaking, the method for preparing MIL-53(Al) material by ball milling-aqueous solution reflux degradation of waste PET in the present invention is to first put waste PET and solid strong base compound into a ball milling tank for ball milling. PET is degraded into terephthalate and ethylene glycol (the mechanochemical action of ball milling has been reported by the inventor in many previous reports, such as ZL202211401069.6, CN202410847823.1, etc., which will not be elaborated in the present invention); then, the degradation product is mixed with aluminum salt solution, and refluxed, heated and stirred. Terephthalate coordinates with aluminum salt to form MIL-53(Al). The product can be obtained by centrifugation, washing and drying.

[0035] The following are specific examples (the reflux heating reaction in each of the following examples is similar to the common reflux heating and is carried out under the condition of normal pressure air atmosphere):

[0036] Example 1

[0037] (1) Add 12 g of waste PET and 5 g of sodium hydroxide into a ball milling tank, with a ball milling speed of 500 r / min and a ball milling time of 3.5 h to obtain a white product.

[0038] (2) Dissolve the white product in (1) in 190 mL of deionized water, and filter it by suction to obtain a PET degradation solution with a concentration of 51.3 mg / mL (the concentration of the PET degradation solution is obtained by taking 1 mL of the PET degradation solution in a petri dish, drying it in an oven at 90 °C for 2 h, and weighing and calculating; the same below).

[0039] (3) Weigh 3.0 g of aluminum chloride hexahydrate and dissolve it in 5.8 mL of deionized water solution. After mixing the above solution with 60 mL of PET degradation solution by stirring, reflux and stir at 60 °C for 24 h, centrifuge, wash and dry the product to obtain MIL-53(Al) material, with a yield of 99% and a specific surface area of 894 m 2 / g.

[0040] Figure 1 where a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 1In this, b is the infrared spectrum of MIL-53(Al). From the X-ray powder diffraction pattern, it can be seen that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The infrared spectrum shows that MIL-53(Al) has significant infrared characteristic absorption peaks, also indicating the successful synthesis of MIL-53(Al). The nitrogen adsorption and desorption isotherm curve shows that MIL-53(Al) has an obvious adsorption and desorption hysteresis loop. The pore size distribution diagram shows that there are a large number of micropores (<2 nm), and the specific surface area is 894 m 2 / g.

[0041] Example 2

[0042] (1) Add 12 g of waste PET and 7 g of potassium hydroxide into the ball milling tank, with a ball milling speed of 300 r / min and a ball milling time of 3.5 h to obtain a white product.

[0043] (2) Dissolve the white product in (1) in 190 mL of deionized water, and filter by suction to obtain a PET degradation solution with a concentration of 51.3 mg / mL.

[0044] (3) Weigh 13.1 g of aluminum sulfate octadecahydrate and dissolve it in 25.1 mL of deionized water solution. After mixing the above solution with 60 mL of PET degradation solution by stirring, reflux and stir at 100 °C for 6 h, and centrifuge, wash, and dry the product to obtain MIL-53(Al) material. The yield is 88%, and the specific surface area is 831 m 2 / g.

[0045] Figure 2 In this, a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 2 In this, b is the scanning electron microscope image of MIL-53(Al). From the X-ray powder diffraction pattern, it can be seen that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The scanning electron microscope image shows that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 70 nm (measured by Nano Measurer software, the same below).

[0046] Example 3

[0047] (1) Add 12 g of waste PET and 7 g of potassium hydroxide into the ball milling tank, with a ball milling speed of 400 r / min and a ball milling time of 2 h to obtain a white product.

[0048] (2) Dissolve the white product in (1) in 100 mL of deionized water, and filter by suction to obtain a PET degradation solution with a concentration of 100.8 mg / mL.

[0049] (3) Weigh 2.9 g of aluminum chloride hexahydrate and dissolve it in 5.6 mL of deionized water. After stirring and mixing the above solution with 50 mL of PET degradation solution, reflux and stir at 100 °C for 24 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 83% and a specific surface area of 875 m 2 / g.

[0050] Figure 3 In Figure 3 , a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 3 In Figure 3 , b is the infrared spectrum of MIL-53(Al), Figure 3 In , c and d are the scanning electron microscope images of MIL-53(Al). It can be seen from the X-ray powder diffraction pattern that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The infrared spectrum shows that MIL-53(Al) has significant infrared characteristic absorption peaks, also indicating the successful synthesis of MIL-53(Al). The scanning electron microscope images show that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 100 nm.

[0051] Example 4

[0052] (1) Add 12 g of waste PET and 5 g of sodium hydroxide into the ball milling tank, with a ball milling speed of 400 r / min and a ball milling time of 3.5 h to obtain a white product.

[0053] (2) Dissolve the white product in (1) in 180 mL of deionized water and filter by suction to obtain a PET degradation solution with a concentration of 53.5 mg / mL.

[0054] (3) Weigh 7.6 g of aluminum nitrate nonahydrate and dissolve it in 14.7 mL of deionized water. After stirring and mixing the above solution with 40 mL of PET degradation solution, reflux and stir at 80 °C for 12 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 91% and a specific surface area of 803 m 2 / g.

[0055] Figure 4 In Figure 4 , a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 4 In Figure 4 , b is the infrared spectrum of MIL-53(Al), Figure 4Figures c and d are the scanning electron microscope images of MIL-53(Al). From the X-ray powder diffraction pattern, it can be seen that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The infrared spectrum shows that MIL-53(Al) has significant infrared characteristic absorption peaks, also indicating the successful synthesis of MIL-53(Al). The scanning electron microscope image shows that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 60 nm.

[0056] Example 5

[0057] (1) Add 12 g of waste PET and 5 g of sodium hydroxide into a ball milling jar, with a ball milling speed of 600 r / min and a ball milling time of 3 h to obtain a white product.

[0058] (2) Dissolve the white product in (1) in 80 mL of deionized water, and filter by suction to obtain a PET degradation solution with a concentration of 124.5 mg / mL.

[0059] (3) Weigh 2.7 g of aluminum chloride hexahydrate and dissolve it in 5.2 mL of deionized water solution. After stirring and mixing the above solution with 30 mL of PET degradation solution, reflux and stir at 70 °C for 18 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 90% and a specific surface area of 801 m 2 / g.

[0060] Figure 5 Figure a in is the X-ray powder diffraction pattern of MIL-53(Al), Figure 5 Figure b in is the scanning electron microscope image of MIL-53(Al). From the X-ray powder diffraction pattern, it can be seen that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The scanning electron microscope image shows that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 50 nm.

[0061] Example 6

[0062] (1) Add 12 g of waste PET and 5 g of sodium hydroxide into a ball milling jar, with a ball milling speed of 500 r / min and a ball milling time of 4.5 h to obtain a white product.

[0063] (2) Dissolve the white product in (1) in 180 mL of deionized water, and filter by suction to obtain a PET degradation solution with a concentration of 53.5 mg / mL.

[0064] (3) Weigh 20.4 g of aluminum sulfate octadecahydrate and dissolve it in 39.2 mL of deionized water solution. After stirring and mixing the above solution with 40 mL of PET degradation solution, reflux and stir at 90 °C for 18 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 83% and a specific surface area of 811 m 2 / g.

[0065] Figure 6 In [a certain figure], a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 6 In [a certain figure], b is the infrared spectrum of MIL-53(Al), Figure 6 In [a certain figure], c and d are the scanning electron microscope images of MIL-53(Al). It can be seen from the X-ray powder diffraction pattern that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The infrared spectrum shows that MIL-53(Al) has significant infrared characteristic absorption peaks, also indicating the successful synthesis of MIL-53(Al). The scanning electron microscope images show that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 80 nm.

[0066] Example 7

[0067] (1) Add 12 g of waste PET and 7 g of potassium hydroxide into the ball milling tank, with a ball milling speed of 200 r / min and a ball milling time of 5 h to obtain a white product.

[0068] (2) Dissolve the white product in (1) in 100 mL of deionized water and filter by suction to obtain a PET degradation solution with a concentration of 100.8 mg / mL.

[0069] (3) Weigh 21.6 g of aluminum nitrate nonahydrate and dissolve it in 41.5 mL of deionized water solution. After stirring and mixing the above solution with 40 mL of PET degradation solution, reflux and stir at 100 °C for 12 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 73% and a specific surface area of 857 m 2 / g.

[0070] Figure 7 In [a certain figure], a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 7 In [a certain figure], b is the infrared spectrum of MIL-53(Al), Figure 7Figures c and d are the scanning electron microscope images of MIL-53(Al). From the X-ray powder diffraction pattern, it can be seen that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The infrared spectrum shows that MIL-53(Al) has significant infrared characteristic absorption peaks, also indicating the successful synthesis of MIL-53(Al). The scanning electron microscope image shows that the morphology of MIL-53(Al) is irregular nanoparticles with a size of 20 - 100 nm.

[0071] Comparative Example 1 (In this comparative example, the ball milling - stirring method in aqueous solution at room temperature was used)

[0072] (1) Add 12 g of waste PET and 7 g of potassium hydroxide into the ball milling jar, with a ball milling speed of 400 r / min and a ball milling time of 3 h to obtain a white product.

[0073] (2) Dissolve the white product in (1) in 90 mL of deionized water, and filter by suction to obtain a PET degradation solution with a concentration of 105.1 mg / mL.

[0074] (3) Weigh 6.1 g of aluminum chloride hexahydrate and dissolve it in 11.7 mL of deionized water solution. After stirring and mixing the above solution with 40 mL of PET degradation solution, stir at room temperature for 24 h, and centrifuge, wash, and dry the product to obtain an Al-MOF material with a yield of 80%, and the specific surface area is only 89 m 2 / g, which is significantly lower than the specific surface area (801 - 894 m 2 / g) of the MOF synthesized by the ball milling - aqueous solution reflux method in the above examples.

[0075] Regarding the Al-MOF material prepared in Comparative Example 1, Figure 8 Figure a is the X-ray powder diffraction pattern of Al-MOF, Figure 8 Figure b is the scanning electron microscope image of Al-MOF. From the X-ray powder diffraction pattern, it can be seen that the characteristic diffraction peaks of Al-MOF partially coincide with those of MIL-53(Al), indicating that the crystal structure of the Al-MOF synthesized by the ball milling - stirring method in aqueous solution at room temperature is imperfect, and the coordination of aluminum ions with organic ligands is incomplete. This is because the formation of MOF involves a complex self-assembly process. At room temperature, the molecular motion is slow, and it is difficult to overcome the kinetic barrier. Moreover, the reaction rate at room temperature is low, and it is difficult to effectively form the metal - ligand bonds required for MOF, resulting in a slow or incomplete crystallization process. The scanning electron microscope image shows that the morphology of Al-MOF is irregular stacked nanoparticles with a size of 40 - 200 nm.

[0076] Comparative Example 2 (In this comparative example, ball milling was not used, but a disodium terephthalate solution was directly prepared, and ethylene glycol was not added)

[0077] (1) Weigh 1.6 g of sodium hydroxide and 3.3 g of terephthalic acid, and ultrasonically dissolve them in 28.8 mL of deionized water solution to obtain a disodium terephthalate solution with a concentration of 105.1 mg / mL.

[0078] (2) Weigh 6.1 g of aluminum chloride hexahydrate and dissolve it in 11.7 mL of deionized water solution. After stirring and mixing the above solution with the disodium terephthalate solution, reflux and stir at 90 °C for 24 h. Centrifuge, wash, and dry the product to obtain MIL-53(Al) material with a yield of 78% and a specific surface area of 439 m 2 / g, which is significantly lower than the specific surface area of the MOF synthesized by ball milling-aqueous solution reflux in the above examples (801 - 894 m 2 / g).

[0079] Regarding the MIL-53(Al) material prepared in Comparative Example 2, Figure 9 where a is the X-ray powder diffraction pattern of MIL-53(Al), Figure 9 and b is the scanning electron microscope image of MIL-53(Al). It can be seen from the X-ray powder diffraction pattern that MIL-53(Al) has significant characteristic diffraction peaks, indicating the successful synthesis of MIL-53(Al). The scanning electron microscope image shows that the morphology of MIL-53(Al) is irregular nanorods, which is significantly different from the nanoparticles prepared in Examples 1 - 7. At the same time, the size of the MIL-53(Al) material prepared in Comparative Example 2 is 60 - 400 nm, which is larger than the nanoparticles in Examples 1 - 7. From the comparison between Examples 1 - 7 and Comparative Example 2, it can be seen that ethylene glycol in the PET degradation liquid and aqueous solution reflux have a synergistic effect (different from the ball milling in Comparative Example 1 followed by stirring with normal temperature aqueous solution, which cannot produce a synergistic effect). Under reflux conditions, the hydroxyl group of ethylene glycol can form hydrogen bonds with water molecules, adjust the polarity and boiling point of the reaction solution, contribute to the dispersion of aluminum ions and their coordination with terephthalic acid ions, regulate the size of the MOF, and generate MIL-53(Al) with smaller size, higher yield and specific surface area.

[0080] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing MIL-53 (Al) material by ball milling-water solution reflux degradation of waste PET, characterized in that: The following steps are involved: (1) mixing waste PET and a solid strong base compound uniformly and ball-milling to obtain a ball-milled product; then, dissolving the ball-milled product in deionized water to obtain a mixed solution of terephthalate and ethylene glycol; (2) The mixed solution obtained in step (1) is mixed with an aluminum salt solution, and the mixture is refluxed, heated, stirred, and reacted to produce a MIL-53 (Al) material.

2. The method according to claim 1, characterized in that: In step (2), the reaction temperature of the reflux heating and stirring reaction is 60 to 100° C., and the reaction time is 6 to 24 hours.

3. The method according to claim 1, characterized in that: In step (1), the solid strong base compound is selected from sodium hydroxide and potassium hydroxide.

4. The method according to claim 1, characterized in that: In step (1), the ball milling time is 2 to 5 hours and the rotation speed is 200 to 600 r / min.

5. The method according to claim 1, characterized in that: In the mixed solution obtained in step (1), the concentration of the mixed solution of terephthalate and ethylene glycol is 51.3 to 124.5 mg / mL.

6. The method according to claim 1, characterized in that: In step (2), the mixed solution obtained in step (1) and the aluminum salt solution are mixed in a mass ratio of 0.33 to 1 between the aluminum salt in the aluminum salt solution and the terephthalic acid ligand contained in the terephthalate in the mixed solution.

7. The method according to claim 1, characterized in that: In step (2), the aluminum salt is at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate.

8. The method according to claim 1, characterized in that: The specific surface area of ​​the MIL-53 (Al) material produced in step (2) is 801 to 894 m 2 / g.

9. The method according to claim 1, characterized in that: The MIL-53 (Al) material is obtained by centrifuging the system after the reaction to obtain a solid, and then washing and drying the solid.

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