ZnAl-F-LDH catalyst, preparation method thereof and application of ZnAl-F-LDH catalyst in plastic degradation

Abstract

The invention discloses a ZnAl-F-LDH catalyst, a preparation method thereof and application of the ZnAl-F-LDH catalyst in plastic degradation, and belongs to the technical field of plastic chemical recovery. According to the invention, LDH is used as a template, and fluorine atoms are used for replacing part of oxygen atoms to construct the ZnAl-F-LDH catalyst with excellent performance of photo-thermal catalytic conversion of plastic PET. The ZnAl-F-LDH catalyst can realize efficient catalytic conversion of PET waste plastics at a low temperature, compared with a traditional chemical recovery technology, the method has the advantages of high catalytic efficiency, environmental protection and the like, and the ZnAl-F-LDH catalyst is easy to produce in batches and shows a wide commercial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic chemical recycling, and more specifically relates to a ZnAl-F-LDH catalyst, a preparation method thereof, and an application thereof in plastic degradation. Background Art

[0002] With the development of society, plastics have become an indispensable part of daily life. Due to many advantages such as light weight, low cost, long durability, and wide chemical uses, plastics have been widely used in fields such as agriculture, construction, and the electronics industry. However, the recycling of waste plastics is very difficult. At present, the treatment methods of waste plastics can be divided into two categories: physical recycling and chemical recycling. Among them, physical recycling mainly includes incineration, landfill, mechanical recycling, etc. However, the incineration method for treating waste plastics will release environmental pollution gases such as nitrogen oxides; the landfill method will pollute groundwater, occupy land resources, and make the soil lose fertility, directly affecting human daily life; the mechanical recycling method consumes a large amount of manpower and material resources and has a high cost, which is not conducive to popularization and operation. Compared with traditional plastic recycling strategies, chemical recycling can achieve efficient catalytic conversion of waste plastics.

[0003] In the aspect of chemical upgrading and recycling of plastic waste, significant progress has been made in various ways such as thermal catalysis, photocatalysis, electrocatalysis, and enzyme catalysis. Among them, thermal catalysis technology can depolymerize waste plastics back to monomers, and the monomers can be polymerized into plastic products again after purification. This cyclic recycling strategy can achieve resource recycling, but the pyrolysis process of plastic waste usually requires harsh reaction conditions and expensive metal catalysts. Different from pyrolysis, photocatalysis technology has received extensive attention in recent years because it does not involve high temperature and high pressure. However, low solar energy capture efficiency and the recombination of photo-generated carriers limit its catalytic performance. Photothermal catalysis emerged as a technology that combines the advantages of photocatalysis and pyrolysis by synergistically using thermal energy and light energy. Compared with energy-intensive thermal catalysis, renewable solar energy-driven photothermal catalysis provides a green and sustainable way to drive catalytic reactions. Therefore, photothermal catalysis can exhibit excellent catalytic performance even under mild conditions.

[0004] However, due to the introduction of thermal effects in the photothermal catalytic conversion of plastics, compared with photocatalysis, the selectivity of products is difficult to control, and currently, the research on the plastic conversion mechanism under the synergistic action of light and heat is in its infancy, which restricts the directional design and performance optimization of catalysts. Therefore, constructing a photothermal catalyst with high photothermal conversion ability and high product selectivity is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a ZnAl-F-LDH catalyst, a preparation method thereof, and an application thereof in plastic degradation to solve the problems existing in the above-mentioned prior art and achieve efficient photothermal catalytic conversion of waste plastics.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: Provide a preparation method of a ZnAl-F-LDH catalyst, including the following steps:

[0008] Mix a zinc source, an aluminum source and a fluorine source to obtain a mixed salt solution;

[0009] Mix the mixed salt solution, a sodium hydroxide solution and a sodium carbonate solution, and react to obtain the ZnAl-F-LDH catalyst.

[0010] Preferably, the zinc source is zinc nitrate hexahydrate; the aluminum source is aluminum nitrate nonahydrate; the fluorine source is sodium hexafluoroaluminate.

[0011] Preferably, the molar ratio of the fluorine source to the total metal ions in the mixed salt solution is 0.5-2:1.

[0012] Preferably, the volume ratio of the sodium hydroxide solution to the sodium carbonate solution is 1:1.

[0013] Preferably, the concentration of the sodium hydroxide solution is 0.1-1 mol / L; the molar ratio of carbonate ions in the sodium carbonate solution to aluminum ions in the mixed salt solution is 0.5-2:1.

[0014] Preferably, the temperature of the reaction is 60-120 °C, the pH value is 9-11, and the time is 10-24 h.

[0015] The present invention uses LDH as a template and constructs a ZnAl-F-LDH catalyst with excellent photothermal catalytic conversion of plastic PET performance by replacing part of the oxygen atoms with fluorine atoms. Due to the high electronegativity of fluorine atoms, the interaction between the catalyst and the solvent is enhanced, promoting the oxygen atoms in the solvent to be more electron-rich, which is beneficial to the occurrence of nucleophilic addition-elimination reactions, thereby enhancing the efficiency of photothermal catalytic conversion of PET.

[0016] The catalyst prepared by the present invention maintains the original skeleton structure characteristics of LDH and is in a flaky structure. Compared with conventional LDH, the separation efficiency of electron-hole pairs is improved, and the efficiency of photothermal catalytic conversion of PET is enhanced.

[0017] The second technical solution of the present invention: Provide a ZnAl-F-LDH catalyst prepared according to the above preparation method.

[0018] The third technical solution of the present invention: Provide an application of the above ZnAl-F-LDH catalyst in the photothermal catalytic conversion of plastics.

[0019] Preferably, the plastic includes PET waste plastic.

[0020] The fourth technical solution of the present invention: Provide a method for photocatalytic conversion of plastics, including the following steps:

[0021] Mix the ZnAl-F-LDH catalyst, plastic and ethylene glycol, and then carry out photocatalytic reaction to complete the photocatalytic conversion of plastics.

[0022] Preferably, the addition amount of the ZnAl-F-LDH catalyst is 0 to 100% (excluding 0) of the mass of the plastic; the photocatalytic reaction includes: using a xenon lamp with a power of 0 to 300w (excluding 0) as the light source, controlling the temperature of the photocatalytic reaction to be 130 to 170°C, and the time to be 1 to 6h.

[0023] The present invention discloses the following technical effects:

[0024] In order to design and develop a highly efficient, structurally stable and low-cost photocatalyst for the efficient and highly selective chemical recycling of plastics, the present invention constructs a fluorine-substituted ZnAl-F-LDH photocatalyst based on a ZnAl-LDH template derivative, and uses this catalyst to efficiently catalyze the conversion of waste PET plastics into BHET.

[0025] The photocatalyst constructed by the present invention improves the electron-hole separation ability compared with the simple ZnAl-LDH catalyst. And fluorine atoms have high electronegativity, which enhances the interaction between the catalyst and the solvent, promotes the oxygen atoms in the solvent to be more electron-rich, is conducive to the occurrence of nucleophilic addition-elimination reactions, and thus enhances the efficiency of photocatalytic conversion of PET. In addition, the photocatalyst prepared by the present invention can achieve the efficient catalytic conversion of waste PET plastics. Compared with traditional chemical recycling technologies, it has the advantages of simple operation, low price, high catalytic efficiency, environmental friendliness, etc., is easy to mass-produce, and shows broad commercial application value. Description of the Drawings

[0026] Figure 1 X-ray diffraction pattern of the ZnAl-F-LDH catalyst prepared in Example 1;

[0027] Figure 2 X-ray diffraction pattern of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0028] Figure 3 Scanning electron microscope image of the ZnAl-F-LDH catalyst prepared in Example 1;

[0029] Figure 4 Scanning electron microscope image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0030] Figure 5Scanning electron microscopy energy spectrum diagram of the ZnAl-F-LDH catalyst prepared in Example 1;

[0031] Figure 6 Photoelectrochemical test diagram of the ZnAl-F-LDH catalyst prepared in Example 1;

[0032] Figure 7 Photoelectrochemical test diagram of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0033] Figure 8 Infrared spectrum diagram of the ZnAl-F-LDH catalyst prepared in Example 1;

[0034] Figure 9 Infrared spectrum diagram of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0035] Figure 10 Infrared spectrum diagram of the photothermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1;

[0036] Figure 11 Infrared spectrum diagram of the photothermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0037] Figure 12 Nuclear magnetic resonance spectrum diagram of the photothermal catalytic product BHET of the ZnAl-F-LDH catalyst prepared in Example 1;

[0038] Figure 13 Nuclear magnetic resonance spectrum diagram of the photothermal catalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0039] Figure 14 Conversion performance diagram of the ZnAl-F-LDH catalyst prepared in Example 1 for photothermal catalytic conversion of PET waste plastics at different temperatures;

[0040] Figure 15 Conversion performance diagram of the ZnAl-F-LDH catalyst prepared in Example 1 for photothermal catalytic conversion of PET waste plastics at different times;

[0041] Figure 16 Conversion performance diagram of the ZnAl-LDH catalyst prepared in Comparative Example 1 for photothermal catalytic conversion of PET waste plastics at different times;

[0042] Figure 17 Catalytic conversion effect of the ZnAl-F-LDH catalyst prepared in Example 1 on different PET waste plastics. Detailed implementation mode

[0043] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0045] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0046] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0047] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0048] It should be noted that the aspects not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0049] Unless otherwise specified, the raw materials used in the following examples and comparative examples of the present invention are all commercially available products, and the sources of the commercially available products do not affect the technical effects of the present invention.

[0050] Example 1

[0051] Preparation of ZnAl-F-LDH catalyst:

[0052] Weigh 5.95 g of zinc nitrate hexahydrate, 1.875 g of aluminum nitrate nonahydrate, and 1.049 g of sodium hexafluoroaluminate and dissolve them in 100 mL of deionized water (in the mixed solution, Zn 2+ and Al 3+In a molar ratio of 2:1), the solution was mixed evenly by ultrasonic oscillation stirring; 100 mL of an aqueous sodium hydroxide solution with a concentration of 0.1 mol / L was prepared; 100 mL of an aqueous sodium carbonate solution was prepared; the mixed salt solution and the sodium hydroxide solution were simultaneously dropped into the sodium carbonate solution (the molar ratio of CO3 2- and Al 3+ is 0.5:1), and the pH value of the obtained mixed solution was controlled to be 10. ZnAl-F-LDH was synthesized by the coprecipitation method, where the reaction conditions were controlled at 80 °C and kept at a constant temperature for 12 h; finally, the obtained precipitate was washed with deionized water and dried at 60 °C for 12 h to obtain the ZnAl-F-LDH catalyst.

[0053] Figure 1 is the X-ray diffraction pattern of the ZnAl-F-LDH catalyst prepared in Example 1;

[0054] Figure 3 is the scanning electron microscope image of the ZnAl-F-LDH catalyst prepared in Example 1;

[0055] Figure 5 is the scanning electron microscope energy spectrum of the ZnAl-F-LDH catalyst prepared in Example 1;

[0056] Figure 6 is the optoelectronic test chart of the ZnAl-F-LDH catalyst prepared in Example 1;

[0057] Figure 8 is the infrared spectrum of the ZnAl-F-LDH catalyst prepared in Example 1.

[0058] It can be seen from Figure 3 that the ZnAl-F-LDH catalyst prepared in Example 1 maintained the original framework structure characteristics of LDH and showed a flaky structure. It can be seen from Figure 5 that in the present invention, using LDH as a template, the ZnAl-F-LDH catalyst was constructed by replacing some oxygen atoms with fluorine atoms.

[0059] The process of the ZnAl-F-LDH catalyst for photocatalytic degradation of waste PET plastics to produce BHET (bis(2-hydroxyethyl) terephthalate) is as follows:

[0060] The prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) were mixed evenly and placed in 30 mL of ethylene glycol. The reaction temperature was controlled at 160 °C, and a 300 W xenon lamp was used as the light source for the photocatalytic experiment to carry out the photocatalytic conversion experiment; after 6 h, the products were collected and the results were analyzed using infrared and nuclear magnetic resonance spectroscopy.

[0061] Figure 10Infrared spectrum of BHET, the photothermal catalytic product of the ZnAl-F-LDH catalyst prepared in Example 1;

[0062] Figure 12 Nuclear magnetic resonance spectrum of BHET, the photothermal catalytic product of the ZnAl-F-LDH catalyst prepared in Example 1.

[0063] From Figure 10 and Figure 12 it can be seen that the ZnAl-F-LDH catalyst prepared in Example 1 can convert PET plastic to obtain high-purity BHET.

[0064] Verify the photothermal catalytic conversion performance of the ZnAl-F-LDH catalyst prepared at different temperatures for PET waste plastics:

[0065] Mix the prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) evenly and place them in 30 mL of ethylene glycol. Control the reaction temperatures to be 130 °C, 140 °C, 150 °C, 160 °C and 170 °C respectively. Use a 300 W xenon lamp as the light source for the photothermal catalytic experiment, and conduct the photothermal catalytic conversion experiment for 6 h; analyze the conversion rate of commercial PET waste plastics, and the results are as Figure 14 shown.

[0066] Figure 14 Photothermal catalytic conversion performance diagram of the ZnAl-F-LDH catalyst prepared in Example 1 for PET waste plastics at different temperatures.

[0067] Verify the photothermal catalytic conversion performance of the ZnAl-F-LDH catalyst prepared at different times for PET waste plastics:

[0068] Mix the prepared ZnAl-F-LDH catalyst (0.5 g) and commercial PET plastic (5 g) evenly and place them in 30 mL of ethylene glycol. Control the reaction temperature to be 160 °C, use a 300 W xenon lamp as the light source for the photothermal catalytic experiment, and conduct the photothermal catalytic conversion experiment for 1 h, 2 h, 3 h, 4 h, 5 h and 6 h respectively; analyze the conversion rate of commercial PET waste plastics, and the results are as Figure 15 shown.

[0069] Figure 15 Photothermal catalytic conversion performance diagram of the ZnAl-F-LDH catalyst prepared in Example 1 for PET waste plastics at different times.

[0070] From Figure 14 and Figure 15 it can be seen that the ZnAl-F-LDH catalyst prepared in Example 1 can completely convert PET plastic to BHET within 6 h at a relatively low temperature.

[0071] Comparative Example 1

[0072] Preparation of ZnAl-LDH catalyst:

[0073] Weigh 5.95 g of zinc nitrate hexahydrate and 3.82 g of aluminum nitrate nonahydrate and dissolve them in 100 mL of deionized water (the molar ratio of Zn 2+ and Al 3+ in the mixed solution is 2:1). Mix the solution evenly by ultrasonic vibration stirring; prepare 100 mL of sodium hydroxide aqueous solution with a concentration of 0.1 mol / L; prepare 100 mL of sodium carbonate aqueous solution; drop the mixed salt solution and sodium hydroxide solution into the sodium carbonate solution simultaneously (the molar ratio of CO3 2- and Al 3+ in the mixed solution is 0.5:1), and control the pH value of the obtained mixed solution to be 10. Synthesize and prepare ZnAl-LDH by the coprecipitation method, where the reaction conditions are controlled at 80 °C and kept at a constant temperature for 12 h; finally, wash the obtained precipitate with deionized water and dry it at 60 °C for 12 h to obtain the ZnAl-LDH catalyst.

[0074] Figure 2 is the X-ray diffraction pattern of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0075] Figure 4 is the scanning electron microscope image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0076] Figure 7 is the optoelectronic test image of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0077] Figure 9 is the infrared spectrum of the ZnAl-LDH catalyst prepared in Comparative Example 1.

[0078] The process of photocatalytic degradation of PET waste plastics by ZnAl-LDH catalyst to produce BHET (bis(2-hydroxyethyl) terephthalate) is as follows:

[0079] Mix the prepared ZnAl-LDH catalyst (0.5 g) and commercial PET plastic (5 g) evenly and place them in 30 mL of ethylene glycol. Control the reaction temperature to be 160 °C, use a 300 W xenon lamp as the light source for the photocatalytic experiment, and conduct the photocatalytic conversion experiment; collect the products and analyze the results using infrared and nuclear magnetic resonance spectroscopy.

[0080] Figure 11 is the infrared spectrum of the photocatalytic product BHET of the ZnAl-LDH catalyst prepared in Comparative Example 1;

[0081] Figure 131H NMR spectrum of BHET, the product of the photothermal catalysis of the ZnAl-LDH catalyst prepared in Comparative Example 1.

[0082] Verify the photothermal catalytic conversion performance of the ZnAl-LDH catalyst prepared at different times for PET waste plastics:

[0083] Mix the prepared ZnAl-LDH catalyst (0.5 g) and commercial PET plastic (5 g) evenly and place them in 30 mL of ethylene glycol. Control the reaction temperature at 160 °C respectively, and use a 300 W xenon lamp as the light source for the photothermal catalytic experiment to conduct the photothermal catalytic conversion experiment for 1 h, 2 h, 3 h, 4 h, 5 h and 6 h respectively; analyze the conversion rate of commercial PET waste plastics, and the results are as Figure 15 shown.

[0084] Figure 16 Photothermal catalytic conversion performance diagram of the ZnAl-LDH catalyst prepared in Comparative Example 1 at different times for PET waste plastics.

[0085] Compare Figure 15 and Figure 16 According to the data, the ZnAl-F-LDH catalyst prepared in Example 1 has significantly better conversion effect on commercial PET plastics than Comparative Example 1.

[0086] Figure 17 Conversion effect of the ZnAl-F-LDH catalyst prepared in Example 1 on PET plastics in life.

[0087] From Figure 17 it can be seen that the ZnAl-F-LDH catalyst prepared in Example 1 can realize the catalytic conversion of waste plastics generated in real life and efficiently catalyze the conversion of PET waste plastics within 6 h.

[0088] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts between the various embodiments, reference can be made to each other.

[0089] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a ZnAl-F-LDH catalyst, characterized in that, It includes the following steps: Mix a zinc source, an aluminum source and a fluorine source to obtain a mixed salt solution; Mix the mixed salt solution, a sodium hydroxide solution and a sodium carbonate solution, and react to obtain the ZnAl-F-LDH catalyst.

2. The preparation method according to claim 1, characterized in that, The zinc source is zinc nitrate hexahydrate; the aluminum source is aluminum nitrate nonahydrate; the fluorine source is sodium hexafluoroaluminate.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the fluorine source to the total metal ions in the mixed salt solution is 0.5-2:

1.

4. The preparation method according to claim 1, wherein The volume ratio of the sodium hydroxide solution to the sodium carbonate solution is 1:

1.

5. The preparation method according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 0.1-1 mol / L; and / or, the molar ratio of carbonate ions in the sodium carbonate solution to aluminum ions in the mixed salt solution is 0.5-2:

1.

6. The preparation method according to claim 1, wherein The temperature of the reaction is 60-120 °C, the pH value is 9-11, and the time is 10-24 h.

7. A ZnAl-F-LDH catalyst prepared by the preparation method according to claims 1-6.

8. An application of the ZnAl-F-LDH catalyst according to claim 7 in the photothermal catalytic conversion of plastics.

9. A method for photocatalytic degradation of plastics, characterized in that, It includes the following steps: Mix the ZnAl-F-LDH catalyst, plastic and solvent and then carry out a photothermal catalytic reaction to complete the photothermal catalytic conversion of the plastic.

10. The method according to claim 9, wherein The addition amount of the ZnAl-F-LDH catalyst is 0-100% of the mass of the plastic, not including 0; the photothermal catalytic reaction includes: using a xenon lamp with 0-300 w as the light source, not including 0, controlling the temperature of the photothermal catalytic reaction to be 130-170 °C, and the time to be 1-6 h.

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