Photo-thermal regulation and control catalyst for selective depolymerization of mixed waste polyester as well as preparation method and application of photo-thermal regulation and control catalyst

Abstract

The invention relates to a photo-thermal regulation and control catalyst for selective depolymerization of mixed waste polyester as well as a preparation method and application of the photo-thermal regulation and control catalyst. The catalyst (Zn / Co-ZIF-C) is prepared by pyrolyzing a Zn / Co-ZIF precursor, and is structurally characterized in that zinc oxide nanoparticles, metal cobalt nanoparticles and cobalt-nitrogen coordination active sites (Co-Nx) are uniformly distributed in a nitrogen-doped carbon skeleton. During application, the illumination intensity is increased in a programmed stepped manner in a single reactor, and efficient depolymerization of different polyesters (such as PET, PC and PLA) under specific light intensity can be triggered in sequence, so that separation of each component and recovery of corresponding monomers are realized. The catalyst has broadband light absorption, high photothermal conversion efficiency, excellent catalytic activity and magnetic responsiveness, is convenient to recycle, and can synchronously realize decoloration of colored plastic. The invention provides an innovative scheme with low energy consumption, high selectivity and high efficiency for the treatment of complex mixed plastic wastes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer chemistry and catalysis technology, and particularly relates to a photo-thermal regulation catalyst for selective depolymerization of mixed waste polyesters, a preparation method and application thereof. BACKGROUND

[0002] The rapid accumulation of plastic waste has become a global environmental challenge. Polyesters such as polyethylene terephthalate (PET), polycarbonate (PC) and polylactic acid (PLA) are widely used due to their excellent properties, but their waste constitutes an important part of environmental pollution. Depolymerization of polyesters into monomers through chemical methods (such as alcoholysis) is an ideal way to achieve high-value recycling, i.e. "closed-loop recycling". However, the existing technology has the following main defects: (1) high energy consumption: traditional chemical recycling processes usually rely on external high-temperature heating (thermal catalysis), which requires a large amount of fossil fuels, resulting in low energy efficiency and high carbon emissions; (2) difficulty in processing mixed plastics: plastic waste in the real world is usually a complex mixture of multiple polymers, and most existing technologies are aimed at a single type of polyester, lacking a method that can effectively distinguish and selectively convert different polyester components in a mixed system. If not separated, direct processing will result in a useless low-value monomer mixture, greatly reducing the economic efficiency of recycling; (3) high separation cost: the cost of physical separation of mixed plastics is high and the efficiency is low, which is the main bottleneck restricting the large-scale application of chemical recycling; (4) catalyst recovery and stability problems: many catalysts are difficult to recover after reaction, or their catalytic activity decreases significantly after multiple uses, increasing process costs; (5) decolorization problem of colored plastics: dyes and pigments contained in waste plastics will contaminate the depolymerization products, requiring additional purification steps, increasing the complexity and cost of the process. Therefore, it is urgent to develop a catalytic system that can operate under mild and energy-efficient conditions and can sequentially convert mixed polyesters, while solving practical application problems such as catalyst recovery and product purification, to promote the development of waste polyester chemical recycling technology. SUMMARY

[0003] The first technical problem to be solved by the present application is to provide a photo-thermal regulation catalyst for selective depolymerization of mixed waste polyesters to solve the technical problems of high energy consumption, high cost and complex process in the existing mixed waste polyester recycling process.

[0004] The second technical problem to be solved by the present application is to provide a preparation method of the photo-thermal regulation catalyst for selective depolymerization of mixed waste polyesters.

[0005] The third technical problem to be solved by the present application is to provide an application of the photo-thermal regulation catalyst for selective depolymerization of mixed waste polyesters.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing a photothermal controlled catalyst for the selective depolymerization of mixed waste polyester includes the following steps:

[0008] (1) Dissolve Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole in organic solvents to obtain a first solution, a second solution and a third solution;

[0009] (2) The first solution is added to the third solution and stirred evenly. Then the second solution is added and stirred. A hydrothermal reaction is carried out. After solid-liquid separation, the solution is washed and dried to obtain the Zn / Co-ZIF precursor.

[0010] (3) Under a nitrogen atmosphere, the Zn / Co-ZIF precursor obtained in step (2) is calcined to obtain the product.

[0011] In some embodiments, in step (1), the organic solvent is methanol; the molar ratio of Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole is 1:1:1~5.

[0012] In some embodiments, in step (2), the stirring time is 10 min to 20 min (preferably 10 min) and the temperature is room temperature; and / or, the hydrothermal reaction is at a temperature of 100 to 150 ℃ (preferably 120 ℃) ​​and a time of 2 to 6 h (preferably 4 h); and / or, the washing is performed using methanol; and / or, the drying is at a temperature of 100 to 150 ℃ (preferably 150 ℃) and a time of 12 to 72 h (preferably 24 h).

[0013] In some embodiments, in step (3), the calcination is carried out at a temperature of 500-700 ℃ (preferably 600 ℃) for a time of 2-3 h (preferably 2 h).

[0014] The photothermal controlled catalyst for selective depolymerization of mixed waste polyester prepared by the above preparation method is also within the scope of protection of this invention; preferably, the photothermal controlled catalyst has magnetic responsiveness and broadband light absorption characteristics in the spectral range of 200-2500 nm.

[0015] The photothermal controlled catalyst for selective depolymerization of mixed waste polyester comprises: a nitrogen-doped carbon framework matrix; zinc oxide (ZnO) nanoparticles supported on the carbon framework matrix; and metallic cobalt (Co) supported on the carbon framework matrix. 0 Nanoparticles and / or Co-N xActive site.

[0016] The above-mentioned photothermal controlled catalyst for selective depolymerization of mixed waste polyester is applied in the chemical depolymerization of single or mixed waste polyester; preferably, the photothermal controlled catalyst can perform decolorization treatment while catalyzing the depolymerization of colored waste polyester.

[0017] In some embodiments, the chemical depolymerization includes the following steps:

[0018] (I) The waste polyester, the alcoholysis agent, and the photothermal controlled catalyst for selective depolymerization of the mixed waste polyester are mixed to obtain a mixture;

[0019] (II) The mixture obtained in step (I) is subjected to light irradiation to depolymerize.

[0020] In some embodiments, in step (I), the waste polyester is any one or more of polycarbonate, polylactic acid, or polyethylene terephthalate; the alcoholysis agent is ethylene glycol; the amount of photothermal controlled catalyst added is calculated as 0.5-5% (preferably 1%) of the mass of the waste polyester; and the amount of alcoholysis agent added is calculated as 2 to 4 times (preferably 4 times) of the mass of the waste polyester.

[0021] In some embodiments, in step (II), the light irradiation depolymerization is performed using one or a combination of the following operations:

[0022] Operation 1: When the waste polyester is polycarbonate, apply a low light intensity of 400~490 mW / cm² (preferably 420 mW / cm²) to raise the system temperature to the first predetermined temperature of 120-150℃ (preferably 140℃), and then stir the reaction for 60~120 min to achieve selective depolymerization of polycarbonate.

[0023] Operation 2: When the waste polyester is polylactic acid, apply a medium light intensity of 500~600 mW / cm² (preferably 520 mW / cm²) to raise the system temperature to the second predetermined temperature of 151-170℃ (preferably 160℃), and then stir the reaction for 60~120 min to achieve selective depolymerization of polylactic acid.

[0024] Operation 3: When the waste polyester is polyethylene terephthalate, apply a high light intensity of 610-700 mW / cm² (preferably 650 mW / cm²) to raise the system temperature to the third predetermined temperature of 171-200℃ (preferably 180-190℃), and then stir the reaction for 60-120 minutes to achieve selective depolymerization of polyethylene terephthalate.

[0025] In some embodiments, when the waste polyester is a mixture of polycarbonate, polylactic acid and polyethylene terephthalate, it is processed sequentially according to Operation 1, Operation 2 and Operation 3 to achieve selective depolymerization of polycarbonate, polylactic acid and polyethylene terephthalate.

[0026] Alternatively, when the waste polyester is a mixture of polycarbonate and polylactic acid, it is processed sequentially according to operation one and operation two to achieve selective depolymerization of polycarbonate and polylactic acid.

[0027] Alternatively, when the waste polyester is a mixture of polycarbonate and polyethylene terephthalate, it is processed sequentially according to operation one and operation three to achieve selective depolymerization of polycarbonate and polyethylene terephthalate.

[0028] Alternatively, when the waste polyester is a mixture of polylactic acid and polyethylene terephthalate, it is processed sequentially according to operation two and operation three to achieve selective depolymerization of polylactic acid and polyethylene terephthalate.

[0029] Beneficial effects:

[0030] (1) This invention achieves highly selective chemical recycling of mixed polyester systems. By innovatively using programmed control of light intensity, the depolymerization reactions of different polyesters can be triggered sequentially in a single reactor, thereby achieving gradient selective conversion of polycarbonate (PC), polylactic acid (PLA) and polyethylene terephthalate (PET). This method eliminates the need for complex physical sorting operations, significantly reduces the cost of mixed plastic processing, and simplifies the process flow.

[0031] (2) This invention uses light energy as the main driving force and relies on the excellent photothermal conversion capability of the catalyst to achieve efficient energy utilization in the reaction system. The catalyst exhibits broadband absorption characteristics in both the visible and near-infrared regions, and can quickly convert light energy into heat energy, achieving precise temperature control and rapid response, thereby significantly reducing dependence on external heating and achieving a low-energy-consumption, environmentally friendly green plastic depolymerization effect.

[0032] (3) The catalyst of this invention has both structural and functional advantages. The catalyst surface simultaneously contains ZnO Lewis acid sites and Co–N xThe active center synergistically promotes the breaking and alcoholysis of polyester bonds, exhibiting high activity and excellent stability. Its magnetic response characteristics allow for rapid separation and reuse after the reaction using an external magnetic field, maintaining a conversion rate of over 95% even after five cycles, demonstrating good sustainability. Simultaneously, the porous carbon framework structure of this catalyst endows it with excellent adsorption properties, enabling the simultaneous removal of dye molecules during the depolymerization process when treating colored plastic waste. As shown in Example 11, the color of the product after the reaction is significantly removed, indicating that the catalyst of this invention has a significant decolorizing effect on the system, thereby simplifying subsequent product purification steps and improving the quality and purity of the recovered monomers.

[0033] (4) The technical solution adopted in this invention is also applicable to real waste polyester systems. For waste plastic samples of different sources and colors, efficient depolymerization and high-yield product recovery can be achieved under their respective light intensity conditions, which fully demonstrates the universality and industrialization potential of this technology in complex waste plastic systems. It provides a low-energy, high-selectivity and sustainable solution for the selective recycling of mixed waste polyester, and provides a new technical path for the development of plastic recycling and green chemical processes.

[0034] (5) This invention provides a magnetic composite catalyst for selective, programmed, and gradient depolymerization of mixed waste polyesters (such as PET, PC, PLA) by controlling the intensity of light, as well as its preparation method and its application in plastic upgrading and recycling. Attached Figure Description

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0036] Figure 1 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the Zn / Co-ZIF-C catalyst of this invention.

[0037] Figure 2 The X-ray diffraction (XRD) pattern of the Zn / Co-ZIF-C catalyst of this invention is shown below.

[0038] Figure 3 The catalyst Zn / Co-ZIF-C of this invention is shown to have catalytic and decolorizing effects on a real waste polyester system. Detailed Implementation

[0039] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0040] In this embodiment of the invention, the experimental methods described are conventional methods unless otherwise specified; the reagents described are commercially available unless otherwise specified.

[0041] Example 1 illustrates the catalyst preparation process; Examples 2-4 verify the effect of different light intensities on the photothermal catalytic performance of single polyesters (PET, PLA, PC); Examples 5-7 investigate the catalytic performance of mixed polyester systems under different light intensities; Example 8 verifies the programmable effect of light gradient regulation in the selective depolymerization of mixed polyesters; Examples 9 and 10 investigate the catalyst's recovery performance and its catalytic effect in real waste polyester systems; Example 11 demonstrates that the catalyst can simultaneously depolymerize the polyester system and perform decolorization. In the mixed polyester reaction, the reactants are all granules (solid particulate form). After one substance reacts, the monomer dissolves in the solution, while the remaining substances remain in particulate form. The depolymerization products of the polyester system obtained by catalyst catalysis in this invention are all obtained by centrifugation.

[0042] Example 1: Preparation of Zn / Co-ZIF-C catalyst

[0043] (1) Synthesis of Zn / Co-ZIF precursor: Co(NO3)2·6H2O (1.098 g, 3.7 mmol) was dissolved in 15 mL of methanol, Zn(NO3)2·6H2O (1.116 g, 3.7 mmol) was dissolved in 15 mL of methanol, and 2-methylimidazole (1.232 g, 15 mmol) was dissolved in 30 mL of methanol. At room temperature, the Co salt solution was added dropwise to the 2-methylimidazole solution and stirred for 10 minutes. Then, the Zn salt solution was slowly added and stirred for another 10 minutes. The mixed suspension was transferred to a reaction vessel and hydrothermally reacted at 120 °C for 4 hours. After cooling, the product was collected by centrifugation (5000 rpm, 10 min), washed with methanol, and dried at 150 °C for 24 h to obtain the Zn / Co-ZIF precursor.

[0044] (2) Preparation of Zn / Co-ZIF-C: Take 0.5 g of the above precursor powder and place it in a tube furnace. Under a nitrogen atmosphere, heat the powder to 600°C at a rate of 5°C / min and calcine it at this temperature for 2 hours. After natural cooling, collect the black powder, which is the Zn / Co-ZIF-C catalyst.

[0045] The catalyst was characterized by SEM, TEM, and XRD (results are shown in the figure). Figure 1 and 2 (As shown)

[0046] SEM characterization revealed that the pyrolyzed material exhibited partial structural collapse and surface roughening, but still largely retained the geometric features of the precursor MOF. High-resolution TEM further confirmed the embedded nanoparticles in the material, with lattice spacings of 0.210 nm and 0.237 nm, corresponding to the metallic Co. 0 The (111) crystal plane of the precursor and the (101) crystal plane of ZnO. XRD analysis also revealed the structural transformation of the material: the sharp crystal diffraction peaks in the precursor disappeared, replaced by a broad and diffuse signal of amorphous carbon, and the corresponding Co. 0 Weak diffraction peaks were observed in ZnO nanocrystals (JCPDS 15-0806) and (JCPDS 36-1451). This confirms that the obtained catalyst has ZnO and Co uniformly distributed on a nitrogen-doped carbon framework. 0 The composite material of nanoparticles has excellent photothermal conversion performance.

[0047] Example 2: High-intensity photothermal depolymerization of single PET waste

[0048] This embodiment aims to verify the catalyst's ability to perform photothermal depolymerization of PET waste under high light intensity conditions.

[0049] (1) In a 50 mL sealed reactor, add 1.0 g of PET powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (1 wt% of the mass of PET).

[0050] (2) The light source is a xenon lamp with a light intensity of 650 mW / cm². After the system temperature stabilizes at 180℃, the reaction is carried out for 60 minutes under these conditions with a stirring rate of 500 rpm.

[0051] (3) After the reaction was completed and cooled, the product was analyzed by HPLC and the conversion rate of PET was 96%. The main product was bis(2-hydroxyethyl) terephthalate (BHET) with a yield of 93%.

[0052] Example 3: Medium-intensity photothermal depolymerization of single PLA

[0053] This embodiment aims to verify the catalyst's ability to depolymerize PLA waste under moderate light intensity.

[0054] (1) In a 50 mL sealed reactor, add 1.0 g of PLA powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (1 wt% of PLA mass).

[0055] (2) The light source is a xenon lamp with a light intensity of 520 mW / cm². After the system temperature stabilizes at 160℃, the reaction is carried out for 90 minutes under these conditions with a stirring rate of 500 rpm.

[0056] (3) After the reaction was completed and cooled, GC analysis showed that the PLA conversion rate was 92%, the main product was ethylene lactate (LA-EG), the product purity was high and the solution showed no obvious color change.

[0057] Example 4: Low-intensity photothermal depolymerization of single PC waste

[0058] This embodiment aims to verify the catalyst's efficient low-temperature depolymerization capability for PC.

[0059] (1) In a 50 mL sealed reactor, add 1.0 g of PC powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (1 wt% of the mass of PC).

[0060] (2) The light source is a xenon lamp with a light intensity of 420 mW / cm². After the system temperature stabilizes at 140℃, the reaction is carried out for 60 minutes under these conditions with a stirring rate of 500 rpm.

[0061] (3) After the reaction was completed and cooled, GC analysis showed that the PC conversion rate reached >98% and the bisphenol A (BPA) yield reached 92.31%.

[0062] Example 5: Low-intensity photothermal catalytic depolymerization of a mixed polyester system

[0063] This embodiment aims to verify the photothermal depolymerization performance of the catalyst on a blended polyester system under low light intensity conditions.

[0064] (1) In a 50 mL sealed reactor, add 0.384 g of PET powder, 0.144 g of PLA powder, 0.508 g of PC powder, 4.0 g of ethylene glycol, and 0.01 g of Zn / Co-ZIF-C catalyst (accounting for 1 wt% of the total mass of polyester).

[0065] (2) The light source is a xenon lamp with a light intensity of 420 mW / cm². After the temperature of the reaction system stabilizes at 140℃, the reaction is maintained for 120 minutes with a stirring rate of 500 rpm.

[0066] (3) After the reaction was completed and cooled, GC and HPLC analysis showed that only the PC component underwent significant depolymerization, with a bisphenol A (BPA) yield of 91.2%, while the PLA and PET components were basically unreacted. The results indicate that the catalyst can selectively activate the PC component under low light intensity conditions, achieving a preliminary reaction fractionation effect.

[0067] Example 6: Medium-intensity photothermal catalytic depolymerization of a mixed polyester system

[0068] This embodiment aims to verify the photothermal depolymerization performance of the catalyst on a blended polyester system under moderate light intensity conditions.

[0069] (1) In a 50 mL sealed reactor, add 0.384 g of PET powder, 0.144 g of PLA powder, 0.508 g of PC powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (accounting for 1 wt% of the total mass of polyester).

[0070] (2) The light source is a xenon lamp with a light intensity of 520 mW / cm². After the reaction temperature is stabilized at 160℃, the reaction is carried out for 120 minutes under these conditions with a stirring rate of 500 rpm.

[0071] (3) After the reaction, analysis showed that PC was completely converted, PLA conversion rate reached 94.6%, producing ethylene lactate glycol ester (LA-EG), while PET was basically retained. The results indicate that the catalyst can selectively promote PLA depolymerization under medium light intensity conditions and achieve reaction differentiation from PC, laying the foundation for light intensity programmable depolymerization.

[0072] Example 7: High-intensity photothermal catalytic depolymerization of a hybrid polyester system

[0073] This embodiment aims to verify the catalyst's ability to comprehensively depolymerize a mixed polyester system under high light intensity conditions.

[0074] (1) In a 50 mL sealed reactor, add 0.384 g of PET powder, 0.144 g of PLA powder, 0.508 g of PC powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (accounting for 1 wt% of the total mass of polyester).

[0075] (2) The light source is a xenon lamp with a light intensity of 650 mW / cm². After the system temperature is stabilized at 190℃, the reaction is carried out for 90 minutes under these conditions with a stirring rate of 500 rpm.

[0076] (3) After the reaction, the mixed plastic sample was completely dissolved. HPLC analysis showed that the PET conversion rate was 96.4%, the BHET yield was 92.8%, and the PLA and PC products were LA-EG and BPA, respectively. The results indicate that the catalyst can achieve efficient and complete depolymerization of the mixed polyester system under high light intensity conditions.

[0077] Example 8: Selective depolymerization in blended polyesters controlled by light gradient

[0078] This embodiment aims to verify the programmable effect of illumination gradient control in the selective depolymerization of blended polyesters.

[0079] (1) In a 50 mL sealed reactor, add 0.384 g of PET powder, 0.144 g of PLA powder, 0.508 g of PC powder, 4.0 g of ethylene glycol, and 0.01 g of Zn / Co-ZIF-C catalyst (accounting for 1 wt% of the total mass of polyester).

[0080] (2) The light source is a xenon lamp, and the light intensity is gradually increased in a stepped manner:

[0081] Stage 1 (Low Light Intensity): The light intensity was set at 420 mW / cm², and after the system temperature stabilized at 140℃, the reaction was carried out for 120 minutes with a stirring rate of 500 rpm. This stage mainly achieved selective depolymerization of PC. GC analysis showed that the PC conversion rate reached 96.5%.

[0082] Second stage (medium light intensity): The light intensity was increased to 520 mW / cm², and after the system temperature stabilized at 160℃, the reaction continued for 120 minutes with a stirring rate of 500 rpm. In this stage, PLA was completely converted to ethylene lactate (LA-EG), with a conversion rate of 92%, while PET underwent only a small amount of conversion (<5%).

[0083] The third stage (high light intensity): The light intensity was further increased to 650 mW / cm², and after the system temperature stabilized at 190℃, the reaction continued for 90 minutes with a stirring rate of 500 rpm. During this stage, PET completely depolymerized, and HPLC analysis showed that the BHET yield was 95.4%.

[0084] After the reaction, all polyester components were effectively decomposed. Separation analysis of the resulting solution showed that the three products were generated progressively in their respective stages without interference. The results indicate that the catalytic system can achieve sequential selective depolymerization of different polyester components through programmed control of light intensity, demonstrating excellent programmable reaction characteristics.

[0085] Example 9: Catalyst recovery and recycling performance

[0086] This embodiment aims to verify the recovery performance and stability of the Zn / Co-ZIF-C catalyst during multiple cycles of use.

[0087] (1) In a 50 mL sealed reactor, add 1.0 g of PET powder, 4.0 g of ethylene glycol and 0.01 g of Zn / Co-ZIF-C catalyst (1 wt% of the mass of PET).

[0088] (2) The light source is a xenon lamp with a light intensity of 650 mW / cm². After the system temperature is stabilized at 190℃, the reaction is carried out for 60 minutes with a stirring rate of 500 rpm.

[0089] (3) After the reaction is complete, stop stirring and bring a strong magnet close to the outer wall of the reactor. The catalyst is quickly adsorbed and separated from the reaction liquid. The adsorbed catalyst is ultrasonically washed three times with ethanol, dried under vacuum at 70°C and 100 mbar for 24 h, and then used directly in the next round of reaction.

[0090] Five cycles of the above operation were repeated. The results showed that the PET conversion rate remained above 95%, and the BHET yield remained at approximately 90%, with no significant decrease observed. These results indicate that the catalyst possesses excellent magnetic responsiveness and structural stability, enabling rapid and efficient recovery and reuse, and exhibits good cycle durability, providing a reliable basis for its application in industrial continuous photothermal depolymerization systems.

[0091] Example 10: Catalytic effect of photothermal catalysis system in real waste polyester system

[0092] This embodiment aims to verify the photothermal catalytic depolymerization performance of the Zn / Co-ZIF-C catalyst in a real post-consumer waste polyester system.

[0093] Nine typical waste polyester products from daily life were selected, including: five polyethylene terephthalate (PET) products (transparent beverage bottles, green beverage bottles, blue bottles, pink curtain sheets, and black packaging boxes), two polycarbonate (PC) products (yellow plastic sheets and transparent lenses), and two polylactic acid (PLA) products (white tableware and transparent cups). These waste materials were washed, shredded, and used directly in the reaction without pre-sorting or grinding.

[0094] In each experiment, 1.0 g of waste polyester sample, 4.0 g of ethylene glycol, and 0.01 g of Zn / Co-ZIF-C catalyst (accounting for 1 wt% of the polyester mass) were weighed and added to a 50 mL sealed reactor.

[0095] According to different polyester types, the light intensity is adjusted as follows: (1) PC reaction light intensity is 420 mW / cm² (about 140℃), reaction time is 60 minutes; (2) PLA reaction light intensity is 520 mW / cm² (about 160℃), reaction time is 90 minutes; (3) PET reaction light intensity is 650 mW / cm² (about 190℃), reaction time is 90 minutes;

[0096] After the reaction, GC or HPLC analysis showed that all polyesters achieved efficient depolymerization. PC samples achieved a conversion rate exceeding 95%, with a bisphenol A (BPA) yield of over 90%; PLA samples achieved a conversion rate exceeding 90%, producing ethylene glycol lactate (LA-EG); PET samples maintained a conversion rate of around 95%, with a bis-2-hydroxyethyl terephthalate (BHET) yield of approximately 88%–93%. Plastic samples of different colors and additive types all achieved efficient depolymerization under their respective optimal light intensity conditions, demonstrating that the catalyst maintains excellent activity and selectivity in complex real-world plastic waste.

[0097] Example 11: Catalytic and decolorizing effects of photothermal catalysis system in real waste polyester system

[0098] This embodiment verifies the performance of the Zn / Co-ZIF-C catalyst in photothermal catalytic depolymerization and decolorization of waste polyester systems. A green beverage bottle was selected as the catalyst. The waste material was washed, shredded, and directly used in the reaction without pre-sorting or grinding. Compared with a commonly used commercial catalyst, zinc acetate (which uses a traditional thermocatalytic reaction for depolymerization), as shown in Figure 3, the BHET product obtained using Zn(OAc)₂ still exhibits a distinct green color. However, under the catalysis of Zn / Co-ZIF-C, the decolorization performance of the obtained product is particularly outstanding. This phenomenon indicates the excellent adsorption capacity of the porous carbon framework for dye molecules during depolymerization. Further testing showed that no significant byproducts were generated in the reaction system, and the obtained product could be purified by simple precipitation and distillation. The catalyst can still be rapidly separated and reused by a magnetic field after the reaction, maintaining stable performance.

[0099] The results show that this catalytic system is not only suitable for single-component or artificially mixed systems under laboratory conditions, but can also be directly applied to real multi-component plastic waste containing impurities to achieve efficient and selective photothermal catalytic chemical recovery, and has practical industrial application potential.

[0100] This invention provides a photothermal controlled catalyst for the selective depolymerization of mixed waste polyester, its preparation method, and its application. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a photothermal controlled catalyst for the selective depolymerization of mixed waste polyester, characterized in that, Includes the following steps: (1) Dissolve Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole in organic solvents to obtain a first solution, a second solution and a third solution; (2) The first solution is added to the third solution and stirred evenly. Then the second solution is added and stirred. A hydrothermal reaction is carried out. After solid-liquid separation, the solution is washed and dried to obtain the Zn / Co-ZIF precursor. (3) Under a nitrogen atmosphere, the Zn / Co-ZIF precursor obtained in step (2) is calcined to obtain the product.

2. The preparation method according to claim 1, characterized in that, In step (1), the organic solvent is methanol; the molar ratio of Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole is 1:1:1~5.

3. The preparation method according to claim 1, characterized in that, In step (2), the stirring time is 10 min to 20 min and the temperature is room temperature; and / or the hydrothermal reaction is 100 to 150 ℃ and the time is 2 to 6 h; and / or the washing is carried out with methanol; and / or the drying is 100 to 150 ℃ and the time is 12 to 72 h.

4. The preparation method according to claim 1, characterized in that, In step (3), the calcination is carried out at a temperature of 500-700 ℃ for 2-3 hours.

5. A photothermal controlled catalyst for selective depolymerization of mixed waste polyester prepared by the preparation method according to any one of claims 1 to 4; preferably, the catalyst has magnetic responsiveness.

6. The application of the photothermal controlled catalyst for selective depolymerization of mixed waste polyester as described in claim 5 in the chemical depolymerization of single or mixed waste polyester; preferably, the photothermal controlled catalyst can perform decolorization treatment while catalyzing the depolymerization of colored waste polyester.

7. The application according to claim 6, characterized in that, The chemical depolymerization includes the following steps: (I) The waste polyester, the alcoholysis agent, and the photothermal controlled catalyst for selective depolymerization of the mixed waste polyester are mixed to obtain a mixture; (II) The mixture obtained in step (I) is subjected to light irradiation to depolymerize.

8. The application according to claim 7, characterized in that, In step (I), the waste polyester is any one or more of polycarbonate, polylactic acid, or polyethylene terephthalate; and / or, the alcoholysis agent is ethylene glycol; and / or, the amount of photothermal controlled catalyst added is calculated as 0.5-5% of the mass of the waste polyester; and / or, the amount of alcoholysis agent added is calculated as 2 to 4 times the mass of the waste polyester.

9. The application according to claim 7, characterized in that, In step (II), the light irradiation depolymerization is performed using one of the following operations or a combination of the following operations: Operation 1: When the waste polyester is polycarbonate, apply a low light intensity of 400~490 mW / cm² to raise the system temperature to the first predetermined temperature of 120-150℃, and then stir the reaction for 60~120 minutes to achieve selective depolymerization of polycarbonate. Operation 2: When the waste polyester is polylactic acid, apply a medium light intensity of 500~600 mW / cm² to raise the system temperature to the second predetermined temperature of 151-170℃, and then stir the reaction for 60~120 minutes to achieve selective depolymerization of polylactic acid. Operation 3: When the waste polyester is polyethylene terephthalate, apply a high light intensity of 610-700 mW / cm² to raise the system temperature to the third predetermined temperature of 171-200℃, and then stir the reaction for 60-120 minutes to achieve selective depolymerization of polyethylene terephthalate.

10. The application according to claim 9, characterized in that, When the waste polyester is a mixture of polycarbonate, polylactic acid and polyethylene terephthalate, it is processed in sequence according to operation one, operation two and operation three to achieve selective depolymerization of polycarbonate, polylactic acid and polyethylene terephthalate. Alternatively, when the waste polyester is a mixture of polycarbonate and polylactic acid, it is processed sequentially according to operation one and operation two to achieve selective depolymerization of polycarbonate and polylactic acid. Alternatively, when the waste polyester is a mixture of polycarbonate and polyethylene terephthalate, it is processed sequentially according to operation one and operation three to achieve selective depolymerization of polycarbonate and polyethylene terephthalate. Alternatively, when the waste polyester is a mixture of polylactic acid and polyethylene terephthalate, it is processed sequentially according to operation two and operation three to achieve selective depolymerization of polylactic acid and polyethylene terephthalate.

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