A photothermal catalytic material for recycling waste polypropylene, its preparation method and application

Abstract

This invention relates to the field of photothermal catalyst technology, specifically to a photothermal catalytic material for recycling waste polypropylene, its preparation method, and its application. The photothermal catalytic material is a composite of rare earth metals and a first metal. The rare earth metals include cerium, and the first metal includes copper, gallium, cadmium, and ruthenium. The five-element synergistic introduction of CeCuCdGaRu into the photothermal catalytic material forms abundant surface active sites and electronic structures. The coupling effect between the metals in terms of redox activity, electron transfer capability, and photothermal response capability gives the photothermal catalytic material a broad spectrum of absorption capability and excellent thermal stability. It can efficiently absorb sunlight or near-infrared radiation and rapidly convert it into heat energy, causing the local temperature to rise rapidly to the critical temperature range required for polypropylene pyrolysis. This causes the surface of the waste polypropylene to melt and fully contact the catalytic surface. At the same time, light irradiation excites the polymer chains to generate free radicals, accelerating their breakage and transformation, providing a new technical path for the high-value recycling of waste plastics.

Description

Technical Field

[0001] This invention relates to the field of photothermal catalyst technology, and in particular to a photothermal catalytic material for recycling waste polypropylene, its preparation method, and its application. Background Technology

[0002] With the widespread use of polymer materials such as polypropylene (PP) in packaging, medical, and automotive fields, the increasing consumption of plastics has led to urgent problems related to solid waste disposal and environmental pollution. Traditional PP waste disposal mainly relies on two methods: mechanical recycling and incineration. While mechanical recycling has lower energy consumption, it can easily result in recycled products that do not meet application requirements. Incineration, on the other hand, produces large amounts of toxic gases such as dioxins, posing a serious threat to the environment and human health.

[0003] In recent years, chemical recycling technology has become an important way to solve the dual bottlenecks of "plastic pollution" and material value of PP waste. Common chemical recycling methods include pyrolysis, catalytic cracking, and hydrocracking. Among them, catalytic cracking technology has attracted widespread attention due to its relatively low operating temperature, controllable product distribution, and high reaction selectivity. Traditional catalytic cracking often uses solid acid catalysts (such as HZSM-5) or noble metal catalysts (such as Pt and Pd), but these catalysts often suffer from problems such as activity decay, sintering and agglomeration, and low energy transfer efficiency under high-temperature cracking conditions, resulting in complex composition of PP photothermal degradation products that are difficult to recycle.

[0004] Photothermal catalysis, as a novel green treatment method combining the advantages of photocatalysis and thermocatalysis, is increasingly being applied to the efficient degradation and resource utilization of waste polymer materials. Photothermal catalysis combines the dual driving forces of light irradiation and thermal excitation. It uses light-absorbing materials to convert light energy into heat energy, rapidly heating the catalyst to the temperature range required for thermocatalysis under light irradiation. The photothermal catalysis mechanism combines the advantages of traditional thermocatalysis and photocatalysis: on the one hand, it utilizes renewable energy sources such as solar energy or visible light to heat the reaction system, reducing dependence on external heating; on the other hand, light irradiation can excite photogenerated carriers to participate in chemical transformation on the catalyst surface, improving selectivity and reaction rate. In the process of plastic pyrolysis, the photothermal catalyst can be photoexcited and heated to high temperatures, accelerating the melting and diffusion of polymer segments, thereby increasing the contact probability between the polymer and the catalyst. Furthermore, light irradiation can induce the generation of active free radicals in polymer molecules, providing new reaction pathways for the breaking of C–C and C–H bonds.

[0005] Currently, photothermal catalytic materials mainly include noble metal nanoparticles (such as Au and Ag), semiconductor nanostructures (such as TiO2 and MoS2), and composite multi-metal systems. However, single noble metals are costly and prone to aggregation, semiconductor materials have narrow light absorption ranges and low photo-thermal conversion efficiency, and existing multi-metal composite systems are still immature in terms of component ratios and interfacial synergistic effects design, making it difficult to balance high photo-thermal conversion efficiency and long-term stability, and difficult to fully utilize solar energy. This limits their application in the high-value recycling of waste plastics. Achieving efficient pyrolysis at relatively low temperatures (200-300°C) remains a key challenge in the chemical recycling of waste plastics. Therefore, there is an urgent need to develop photothermal catalytic materials with broad-spectrum absorption capabilities and excellent photothermal conversion capabilities. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing photothermal catalytic systems, which typically require high temperatures to pyrolyze PP and have poor product selectivity, high energy consumption, and low thermal efficiency, and to provide a photothermal catalytic material for recycling waste polypropylene, its preparation method, and its application.

[0007] In a first aspect, the present invention provides a photothermal catalytic material for recycling waste polypropylene, the photothermal catalytic material being a composite of a rare earth metal and a first metal, the rare earth metal including cerium (Ce), and the first metal including copper (Cu), gallium (Ga), cadmium (Cd), and ruthenium (Ru).

[0008] In a preferred embodiment of the present invention, the particle size of the photothermal catalytic material is 5-100 nm. More preferably, the particle size of the photothermal catalytic material is 10-30 nm.

[0009] As a preferred embodiment of the present invention, in the photothermal catalytic material, based on 100% by weight of the photothermal catalytic material, the mass fraction of cerium is 22-42%, the mass fraction of copper is 15-19%, the mass fraction of gallium is 16-33%, the mass fraction of cadmium is 15-30%, and the mass fraction of ruthenium is 14-16%.

[0010] As a preferred embodiment of the present invention, the molar ratio of cerium, copper, gallium, cadmium and ruthenium is 1:1:1:1:1.

[0011] In a second aspect, the present invention provides a method for preparing photothermal catalytic materials for recycling waste polypropylene, comprising the following steps:

[0012] S1. Distribute the rare earth metal precursor and different first metal precursors to prepare solution A and solution B respectively;

[0013] S2. Add solution A dropwise to solution B and continue mixing for 1 to 4 hours to form a mixed solution;

[0014] S3. The mixed solution is transferred to a hydrothermal reactor and reacted at 150-250°C for 4-20 hours. After cooling, it is filtered and dried to obtain the photothermal catalytic material.

[0015] As a preferred embodiment of the present invention, the total amount of the rare earth metal precursor is divided into a first cerium source precursor and a second cerium source precursor. The first cerium source precursor, copper source precursor, and gallium source precursor are dispersed in a first solvent and a first reducing agent and stirred evenly to form solution A. The second cerium source precursor, cadmium source precursor, and ruthenium source precursor are dispersed in a second solvent and a second reducing agent and stirred evenly to form solution B.

[0016] Preferably, the first cerium source precursor is at least one of cerium chloride, cerium nitrate, cerium oxalate, cerium carbonate, cerium acetate, and cerium sulfate; the second cerium source precursor is at least one of cerium chloride, cerium nitrate, cerium oxalate, cerium carbonate, cerium acetate, and cerium sulfate; the materials of the first cerium source precursor and the second cerium source precursor may be the same or different, and the amounts of the first cerium source precursor and the second cerium source precursor may be the same or different.

[0017] Preferably, the copper source precursor includes at least one of copper chloride, copper nitrate, copper oxalate, copper carbonate, copper acetate, and copper sulfate; the gallium source precursor includes at least one of gallium chloride, gallium nitrate, gallium oxalate, gallium carbonate, gallium acetate, and gallium hydroxide; the cadmium source precursor includes at least one of cadmium chloride, cadmium nitrate, cadmium oxalate, cadmium carbonate, cadmium acetate, and cadmium sulfate; and the ruthenium source precursor includes at least one of ruthenium chloride, ruthenium nitrate, ruthenium oxalate, ruthenium carbonate, ruthenium acetate, and ruthenium sulfate.

[0018] As a preferred embodiment of the present invention, the molar ratio of the first cerium source precursor, the copper source precursor, and the gallium source precursor is 0.5–2:1:1–2. More preferably, the molar ratio of the first cerium source precursor, the copper source precursor, and the gallium source precursor is 0.5:1:1.

[0019] As a preferred embodiment of the present invention, the molar ratio of the second cerium source precursor, the cadmium source precursor, and the ruthenium source precursor is 0.5–2:1–2:1. More preferably, the molar ratio of the second cerium source precursor, the cadmium source precursor, and the ruthenium source precursor is 0.5:1:1.

[0020] As a preferred embodiment of the present invention, the first solvent includes water and / or an organic solvent, and the second solvent includes water and / or an organic solvent, wherein the organic solvent includes at least one of ethanol, ethylene glycol, and acetic acid.

[0021] As a preferred embodiment of the present invention, the first reducing agent is at least one of ethylene glycol (EG) and polyethylene glycol (PEG), and the second reducing agent is at least one of ethylene glycol (EG) and polyethylene glycol (PEG). The first reducing agent and the second reducing agent may be the same or different.

[0022] As a preferred embodiment of the present invention, during the preparation of solution A, stirring is carried out at room temperature for 12 to 24 hours to form a homogeneous mixed solution A.

[0023] As a preferred embodiment of the present invention, during the preparation of the B solution, stirring is carried out at room temperature for 12 to 24 hours to form a homogeneous mixed B solution.

[0024] The present invention also provides a method for recycling waste polypropylene, wherein the recycling method involves reacting the waste polypropylene in a photothermal catalytic material for recycling waste polypropylene, waste polypropylene, water, and oxygen under photothermal conditions.

[0025] The above-mentioned technical solution applies CeCuCdGaRu photothermal catalytic material to polypropylene recycling. The photothermal catalytic material constructs a composite photothermal catalytic material with multifunctional surface active sites and synergistic electronic structure regulation, successfully realizing the conversion of waste polypropylene into CH4 under photothermal conditions, providing a new path for low-carbon, high-value, and highly selective polypropylene conversion based on sunlight.

[0026] As a preferred embodiment of the present invention, the mass ratio of the photothermal catalytic material to the waste polypropylene is 1-10:1-10.

[0027] As a preferred embodiment of the present invention, the mass ratio of the water to the waste polypropylene is 10 to 100:1, and the oxygen pressure is 10 to 100 kPa.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention provides a photothermal catalytic material for recycling waste polypropylene. The photothermal catalytic material is a composite of rare earth metals and a first metal. The rare earth metals include cerium, and the first metal includes copper, gallium, cadmium, and ruthenium. The five-element photothermal catalytic material CeCuCdGaRu is synergistically introduced into the same photothermal catalytic system to form abundant surface active sites and electronic structures. The metals form a coupling effect in terms of redox activity, electron transfer capability, and photothermal response capability, which significantly improves the catalytic selectivity and stability in the cracking reaction, giving the CeCuCdGaRu photothermal catalytic material a broad spectrum absorption capability and excellent thermal stability.

[0030] 2. This invention provides the application of photothermal catalytic materials in the recycling of waste polypropylene. The photothermal catalytic materials have broad-spectrum light absorption capabilities and efficient light-to-heat energy conversion. They can efficiently absorb sunlight or near-infrared radiation and rapidly convert it into heat energy, causing the local temperature to rise rapidly to the critical temperature range (approximately 200–300°C) required for polypropylene pyrolysis. This causes the PP polymer surface to melt and fully contact the catalytic surface. At the same time, light irradiation excites the polymer chains to generate free radicals, rapidly driving the polypropylene pyrolysis reaction and accelerating its breakage and transformation. This provides a new technical path for the high-value-added recycling of waste plastics.

[0031] 3. The photothermal catalytic material provided by this invention can complete the photothermal decomposition of PP into CH4 and CH3COOH without additional external heating. The conditions are mild and suitable for industrial scale-up, and can be extended to the degradation and recycling processes of other polyolefin plastics such as PE and PP. Attached Figure Description

[0032] Figure 1 Transmission electron microscopy image of the CeCuCdGaRu photothermal catalytic material prepared in Example 1;

[0033] Figure 2 X-ray diffraction pattern of the CeCuCdGaRu photothermal catalytic material prepared in Example 1;

[0034] Figure 3 The XPS full spectrum of the CeCuCdGaRu photothermal catalytic material prepared in Example 1 is shown below.

[0035] Figure 4 The image shows a superimposed UV–Vis–NIR diffuse reflectance spectrum of the CeCuCdGaRu photothermal catalytic material prepared in Example 1 and a standard AM1.5G solar spectrum.

[0036] Figure 5 The graph shows the surface temperature change of the CeCuCdGaRu photothermal catalytic material prepared in Example 1 under natural light conditions.

[0037] Figure 6 The image shows data on the pyrolysis of polypropylene under simulated natural light conditions using the CeCuCdGaRu photothermal catalytic material prepared in Example 1. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0039] Example 1

[0040] This embodiment provides a photothermal catalytic material for recycling waste polypropylene. The photothermal catalytic material is a composite of rare earth metals and a first metal. The rare earth metals include cerium, and the first metal includes copper (Cu), gallium (Ga), cadmium (Cd), and ruthenium (Ru).

[0041] In this embodiment, the cerium source precursors are cerium nitrate (Ce(NO3)4·6H2O) and cerium trichloride (CeCl3), with the first cerium source precursor being Ce(NO3)4·6H2O and the second cerium source precursor being CeCl3; the copper source precursor is copper nitrate (Cu(NO3)2·3H2O), the gallium source precursor is gallium nitrate (Ga(NO3)3·xH2O), the cadmium source precursor is cadmium dichloride (CdCl2·2.5H2O), and the ruthenium source precursor is ruthenium trichloride (RuCl3). Based on the weight of the photothermal catalytic material as 100%, the mass fraction of cerium is 27%, the mass fraction of copper is 19%, the mass fraction of gallium is 20%, the mass fraction of cadmium is 18%, and the mass fraction of ruthenium is 16%. The preparation method of the photothermal catalytic material is as follows:

[0042] S1. Ce(NO3)4·6H2O, Cu(NO3)2·3H2O and Ga(NO3)3·xH2O were dispersed in 30 mL of ethylene glycol. The molar ratio of Ce(NO3)4·6H2O:Cu(NO3)2·3H2O:Ga(NO3)3·xH2O was 0.5:1:1. The mixture was stirred at room temperature for 16 h to form a homogeneous solution A.

[0043] Cd(NO3)2·2.5H2O, CeCl3 and RuCl3 were dispersed in 30 mL of ethylene glycol, with Cd(NO3)2·2.5H2O:CeCl3:RuCl3 = 1:0.5:1. The mixture was stirred at room temperature for 16 h to form a homogeneous solution B. In this example, ethylene glycol was used as both a solvent and a reducing agent.

[0044] S2. Add solution A dropwise to solution B and stir continuously at room temperature for 3 hours to form a homogeneous mixed solution;

[0045] S3. Transfer the mixed solution to a Teflon-lined hydrothermal reactor and place it in an oven. React at 200°C for 12 hours, then cool naturally, filter, and dry to obtain the photothermal catalytic material.

[0046] Figure 1 The image shows a high-resolution transmission electron microscope (TEM) image of the CeCuCdGaRu photothermal catalytic material prepared in Example 1. The image shows the morphology of the nanoparticles of the prepared material. The typical particle diameter is about 10-30 nm. The overall shape is nearly spherical or polyhedral and exhibits obvious agglomerated cluster distribution. The abundant grain boundaries provide the structural basis and active site support for the photothermal catalytic cracking of polypropylene.

[0047] Figure 2 The X-ray diffraction intensity distribution of the CeCuCdGaRu photothermal catalytic material is shown in the range of 10-90° at 2θ. The main peak appears at 2θ≈43°, corresponding to the (111) plane of the FCC structure. The diffraction peaks near 50° and 74° can be assigned to the (200) and (220) planes, respectively, indicating that the pentagonal metal (Ce-Cu-Cd-Ga-Ru) may have formed a single solid solution or a high-entropy alloy phase. The grain size of the material is estimated to be 25 nm according to the Scherrer equation, indicating that the material has a nanoscale grain size and abundant surface active sites.

[0048] Figure 3 The XPS full spectrum of the CeCuCdGaRu photothermal catalytic material is shown. It is easy to see that there are Ga2 p3, Cu2 p3, Ce3 d5, Cd3 d3 and Ru3 d3 orbitals. The successful synthesis of the CeCuCdGaRu photothermal catalytic material is confirmed by XRD and XPS.

[0049] Figure 4 This paper presents a superimposed image of the UV-Vis-NIR diffuse reflectance spectrum of CeCuCdGaRu material and the standard AM1.5G solar spectrum. It clearly shows that the material exhibits sustained and strong absorption in the 200-2200 nm range, with its absorption intensity highly overlapping with the high-intensity region of the solar spectrum, indicating its excellent broadband light-harvesting capability. Particularly noteworthy is the fact that the absorption edge of this material extends to approximately 2200 nm, enabling efficient utilization of energy in the near-infrared region of sunlight for photothermal conversion. This characteristic is difficult to achieve in conventional semiconductor materials (whose absorption cutoff wavelength is typically below 1100 nm). Therefore, this material has significant advantages in the fields of efficient solar energy utilization and low-energy-consumption polypropylene cracking. Figure 5 The photothermal properties of the material were further verified. Under simulated natural light conditions, the surface temperature of the material could rapidly rise to approximately 190℃, thus entering the critical pyrolysis range (180-300℃) required for polypropylene decomposition. This demonstrates that the material can efficiently convert solar radiation energy into heat energy, exhibiting excellent photothermal conversion efficiency. This experimental result provides a solid experimental foundation and feasibility support for its application in the field of photothermal catalytic decomposition of waste plastics.

[0050] This invention provides a photothermal catalytic material for the recycling of waste polypropylene. The synergistic active centers formed by elements such as Ce, Cu, and Ru on the catalyst surface not only accelerate the thermally induced depolymerization process but may also participate in C–H activation, thereby further promoting the formation of small molecule products. Figure 4 and Figure 5The results further verify that CeCuCdGaRu material not only has high energy conversion capability in photothermal coupling reaction, but also has strong catalytic activity, and is expected to be used to achieve low-carbon and controllable degradation and conversion of industrial-grade polyolefin waste.

[0051] Example 2

[0052] This embodiment provides a photothermal catalytic material for recycling waste polypropylene, similar to Embodiment 1, except that the molar ratio of cerium, copper, gallium, cadmium, and ruthenium is 2:1:1:1:1. The cerium source precursors are cerium nitrate (Ce(NO3)4·6H2O) and cerium oxalate, with the first cerium source precursor being Ce(NO3)4·6H2O and the second cerium source precursor being cerium oxalate. The copper source precursor is copper nitrate (Cu(NO3)2·3H2O), the gallium source precursor is gallium hydroxide, the cadmium source precursor is cadmium dichloride (CdCl2·2.5H2O), and the ruthenium source precursor is ruthenium acetate. The preparation method of the photothermal catalytic material is as follows:

[0053] S1. Disperse the cerium source precursor, copper source precursor and gallium source precursor in 30 mL of ethylene glycol. The molar ratio of cerium source precursor: copper source precursor: gallium source precursor is 1:1:1. Stir at room temperature for 16 h to form a homogeneous solution A.

[0054] The cadmium source precursor, cerium source precursor and ruthenium source precursor were dispersed in 30 mL of ethylene glycol, with the ratio of cadmium source precursor: cerium source precursor: ruthenium source precursor = 1:1:1. The mixture was stirred at room temperature for 16 h to form a homogeneous solution B. In this example, ethylene glycol was used as both a solvent and a reducing agent.

[0055] S2. Add solution A dropwise to solution B and stir continuously at room temperature for 4 hours to form a homogeneous mixed solution;

[0056] S3. Transfer the mixed solution to a Teflon-lined hydrothermal reactor and place it in an oven. React at 180°C for 15 hours, then cool naturally, filter, and dry to obtain the photothermal catalytic material.

[0057] Example 3

[0058] This embodiment provides a photothermal catalytic material for recycling waste polypropylene. Similar to Embodiment 1, the difference lies in the amount of each element. Based on the weight of the photothermal catalytic material as 100%, the mass fraction of cerium is 22%, copper is 16%, gallium is 17%, cadmium is 30%, and ruthenium is 14%. In this embodiment, the cerium source precursors are cerium nitrate (Ce(NO3)4·6H2O) and cerium trichloride (CeCl3), with the first cerium source precursor being Ce(NO3)4·6H2O and the second cerium source precursor being CeCl3; the copper source precursor is copper nitrate (Cu(NO3)2·3H2O), the gallium source precursor is gallium nitrate (Ga(NO3)3·xH2O), the cadmium source precursor is cadmium dichloride (Cd(Cl2·2.5H2O), and the ruthenium source precursor is ruthenium trichloride (RuCl3). The preparation method of the photothermal catalytic material is as follows:

[0059] S1. Disperse the cerium source precursor, copper source precursor and gallium source precursor in 30 mL of ethylene glycol. The molar ratio of cerium source precursor: copper source precursor: gallium source precursor is 0.5:1:1. Stir at room temperature for 16 h to form a homogeneous solution A.

[0060] The cadmium source precursor, cerium source precursor and ruthenium source precursor were dispersed in 30 mL of ethylene glycol, with the ratio of cadmium source precursor: cerium source precursor: ruthenium source precursor = 2:1:1. The mixture was stirred at room temperature for 16 h to form a homogeneous solution B. In this example, ethylene glycol was used as both a solvent and a reducing agent.

[0061] S2. Add solution A dropwise to solution B and stir continuously at room temperature for 3 hours to form a homogeneous mixed solution;

[0062] S3. Transfer the mixed solution to a Teflon-lined hydrothermal reactor and place it in an oven. React at 200°C for 12 hours, then cool naturally, filter, and dry to obtain the photothermal catalytic material.

[0063] Example 4

[0064] This embodiment provides a photothermal catalytic material for recycling waste polypropylene. Similar to Embodiment 1, the difference lies in the amount of each element. Based on the weight of the photothermal catalytic material as 100%, the mass fraction of cerium is 22%, copper is 16%, gallium is 33%, cadmium is 15%, and ruthenium is 14%. In this embodiment, the cerium source precursors are cerium nitrate (Ce(NO3)4·6H2O) and cerium trichloride (CeCl3), with the first cerium source precursor being Ce(NO3)4·6H2O and the second cerium source precursor being CeCl3; the copper source precursor is copper nitrate (Cu(NO3)2·3H2O), the gallium source precursor is gallium nitrate (Ga(NO3)3·xH2O), the cadmium source precursor is cadmium dichloride (Cd(NO3)2·2.5H2O), and the ruthenium source precursor is ruthenium trichloride (RuCl3). The preparation method of the photothermal catalytic material is as follows:

[0065] S1. Disperse the cerium source precursor, copper source precursor and gallium source precursor in 30 mL of ethylene glycol. The molar ratio of cerium source precursor: copper source precursor: gallium source precursor is 0.5:1:2. Stir at room temperature for 16 h to form a homogeneous solution A.

[0066] The cadmium source precursor, cerium source precursor and ruthenium source precursor were dispersed in 30 mL of ethylene glycol, with the ratio of cadmium source precursor: cerium source precursor: ruthenium source precursor = 0.5:1:1. The mixture was stirred at room temperature for 16 h to form a homogeneous solution B. In this example, ethylene glycol was used as both a solvent and a reducing agent.

[0067] S2. Add solution A dropwise to solution B and stir continuously at room temperature for 3 hours to form a homogeneous mixed solution;

[0068] S3. Transfer the mixed solution to a Teflon-lined hydrothermal reactor and place it in an oven. React at 200°C for 12 hours, then cool naturally, filter, and dry to obtain the photothermal catalytic material.

[0069] Comparative Example 1

[0070] This comparative example is similar to Example 1, except that the photothermal catalytic material does not contain the first metal, copper. The photothermal catalytic material of this comparative example was prepared using the method of Example 1.

[0071] Comparative Example 2

[0072] This comparative example is similar to Example 1, except that the photothermal catalytic material does not contain gallium. The photothermal catalytic material of this comparative example was prepared using the method of Example 1.

[0073] Comparative Example 3

[0074] This comparative example is similar to Example 1, except that the photothermal catalytic material does not contain the first metal cadmium. The photothermal catalytic material of this comparative example was prepared using the method of Example 1.

[0075] Comparative Example 4

[0076] This comparative example is similar to Example 1, except that the photothermal catalytic material does not contain the first metal, ruthenium. The photothermal catalytic material of this comparative example was prepared using the method of Example 1.

[0077] Application Example 1

[0078] This embodiment provides a method for recycling waste polypropylene. The recycling method involves reacting waste polypropylene, water, and oxygen in a photothermal environment containing the photothermal catalytic material of the above embodiment or comparative example.

[0079] Specifically, a quartz reactor was used to thoroughly grind and mix waste polypropylene powder (particle size 100~1000μm) and photothermal catalytic material at a mass ratio of 1:1 using an agate mortar to obtain solid powder A. Solid powder A was then transferred to a photoreactor, where deionized water and oxygen with a purity of 99.999% were added until the chamber pressure reached 80kPa and the deionization volume was 4mL. Simulated sunlight was then applied, and the total reaction time under the same illumination conditions was 8h. The average CH4 generation rate was tested at 4h and 8h, and the test data are shown in Table 1 below.

[0080] Table 1 Test data of Examples 1-4 and Comparative Examples 1-4

[0081]

[0082] As can be seen from the data above, Example 1 (Ce:Cu:Cd:Ga:Ru=1:1:1:1:1) exhibited the highest average CH4 formation rate, reaching 1777 μmol·g⁻¹ after 4 hours of reaction. -1 ·h -1 It remained at 1723 μmol·g at 8 hours. -1 ·h -1 , Figure 6 The data for the pyrolysis of polypropylene using the CeCuCdGaRu photothermal catalytic material in Example 1 at different reaction times are shown. The product of polypropylene photothermal pyrolysis is methane, indicating that the CC backbone breaks down and transforms into small molecule hydrocarbons. Notably, the average methane formation rate remained stable at 1723–1777 μmol·g⁻¹ during 8 hours of continuous light irradiation. -1 ·h -1The results demonstrate the high catalytic activity and stability of this catalyst, indicating that the multi-metal synergistic effect plays a key role in promoting C / C bond breaking and selective methane formation, and that it possesses excellent photothermal catalytic activity and reaction stability. The stable rate of methane production from the photothermal degradation of polyolefins indicates that the catalyst structure did not undergo significant deactivation or aggregation under prolonged light irradiation, and the surface active sites continued to participate in the reaction. In contrast, in Example 2, increasing the Ce content by two times significantly reduced the methane formation rate to 759.7 μmol·g. -1 ·h -1 This indicates that excessive Ce leads to an excessively high concentration of oxygen vacancies on the support surface, thereby weakening the electronic coupling effect at the metal-support interface and hindering the formation of reactive centers. Example 3 (Cd ratio 2) showed a formation rate of approximately 764.2 μmol·g⁻¹. -1 ·h -1 The methane rate was higher than in Example 2, indicating that an appropriate amount of Cd helps to form an electron-rich interface structure, but excessive doping causes band distortion and reduces the migration rate of photogenerated carriers. In Example 4, when the Ga ratio was doubled, the methane rate decreased to 336.7 μmol·g. -1 ·h -1 This indicates that an excessive increase in Ga content will inhibit the dispersion of metal particles and weaken the photothermal response induced by surface plasmon resonance (LSPR).

[0083] In the four comparative examples, the absence of different elements had varying degrees of impact on catalytic performance. The CH4 formation rates of Comparative Example 1 (Cu-free) and Comparative Example 2 (Ce-free) were significantly lower than those of Example 1, at approximately 80.9 and 60.5 μmol·g, respectively. -1 ·h -1 (4h) and 52.5 and 48.9 μmol·g -1 ·h -1 (8h) only 3%–4% of the pentagonal system. This indicates that both Cu and Ce play crucial roles in the photothermal process: Cu can form a multiphase metal interface with Ru, accelerating the separation of electron-hole pairs; the introduction of Ga can adjust the band structure and oxygen vacancy concentration of CeO2, enhancing light absorption and surface reducibility. The synergistic effect of both is essential for the formation and stabilization of active centers. Comparative Example 3 (without Cd) still maintains a certain catalytic activity, but its CH4 formation rate is significantly reduced to only 375.2 μmol·g⁻¹. -1 ·h -1 (4h) and 345.1 μmol·g -1 ·h -1(8h), approximately 20% of that in Example 1. This result indicates that Cd mainly plays a role in regulating the electron density at the Ce–Cu interface and forming structural distortions in the system, thereby promoting the generation of oxygen vacancies and improving the adsorption and activation of reactant molecules on the surface. When Cd is absent, the localization of surface electrons decreases, the number of active centers for the catalytic reaction decreases, and the gas production rate decreases significantly. The methane production rate of Comparative Example 4 (without Ru) is significantly reduced, indicating that Ru is an indispensable key active center in this system. Ru not only possesses excellent hydrogenation and C–C cleavage activity, but can also induce oxygen vacancies and carrier transfer through strong interactions with the CeO2 interface, promoting the stable formation of reaction intermediates.

[0084] In summary, this invention provides a photothermal catalytic material for the recycling of waste polypropylene. The synergistic effect of the five elements Ce, Cu, Cd, Ga, and Ru significantly enhances photothermal coupling, electron migration, and active site formation, thereby achieving efficient photothermal conversion of waste polyolefins. Changes in the content or absence of any single element disrupt the balance of electronic structure and interfacial energy levels in the system, leading to a significant decrease in activity. Therefore, the CeCuCdGaRu multi-element synergistic doping system designed in this invention has significant advantages in the photothermal catalytic conversion of waste plastics.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling waste polypropylene, characterized by, The recycling method is carried out under the photothermal condition in a system containing a photothermal catalytic material, waste polypropylene, water and oxygen, so as to convert the waste polypropylene into CH4 under the photothermal condition, wherein the photothermal catalytic material is a composite of a rare earth metal and a first metal, the rare earth metal comprises cerium, and the first metal comprises copper, gallium, cadmium and ruthenium; the photothermal catalytic material is a single solid solution or a high-entropy alloy phase. The preparation method of the photothermal catalytic material comprises the following steps: S1, distributing a rare earth metal precursor and different first metal precursors to prepare A solution and B solution, respectively; the A solution comprises a first solvent, and the first solvent comprises water and / or an organic solvent; the B solution comprises a second solvent, and the second solvent comprises water and / or an organic solvent; S2, continuously mixing the A solution into the B solution for 1-4 hours to form a mixed solution; S3, transferring the mixed solution into a hydrothermal reaction kettle and reacting at 150-250 DEG C for 4-20 hours, and then filtering and drying after cooling to obtain the photothermal catalytic material.

2. The method of claim 1, wherein the waste polypropylene is a waste polypropylene film. The particle size of the photothermal catalytic material is 5-100 nm. ​ 3. The method of claim 1, wherein the waste polypropylene is a waste polypropylene film. The molar ratio of cerium, copper, gallium, cadmium and ruthenium is 1:1:1:1:

1. ​ 4. The method of claim 1, wherein the waste polypropylene is a post-consumer waste polypropylene. The total amount of the rare earth metal precursor is divided into a first cerium source precursor and a second cerium source precursor, the first cerium source precursor, a copper source precursor and a gallium source precursor are dispersed in a first solvent and a first reducing agent to uniformly stir to form the A solution; the second cerium source precursor, a cadmium source precursor and a ruthenium source precursor are dispersed in a second solvent and a second reducing agent to uniformly stir to form the B solution; the first reducing agent is at least one of ethylene glycol and polyethylene glycol, and the second reducing agent is at least one of ethylene glycol and polyethylene glycol.

5. The method of claim 4, wherein the waste polypropylene is a post-consumer waste polypropylene. The rare earth metal precursor comprises at least one of cerium chloride, cerium nitrate, cerium oxalate, cerium carbonate, cerium acetate and cerium sulfate; the copper source precursor comprises at least one of copper chloride, copper nitrate, copper oxalate, copper carbonate, copper acetate and copper sulfate; the gallium source precursor comprises at least one of gallium chloride, gallium nitrate, gallium oxalate, gallium carbonate, gallium acetate and gallium hydroxide; the cadmium source precursor comprises at least one of cadmium chloride, cadmium nitrate, cadmium oxalate, cadmium carbonate, cadmium acetate and cadmium sulfate; and the ruthenium source precursor comprises at least one of ruthenium chloride, ruthenium nitrate, ruthenium oxalate, ruthenium carbonate, ruthenium acetate and ruthenium sulfate. The organic solvent comprises at least one of ethanol, ethylene glycol and acetic acid.

6. The method of claim 4-5, wherein the waste polypropylene is a waste polypropylene film. 6 The feeding molar ratio of the first cerium source precursor, the copper source precursor and the gallium source precursor is 0.5-2:1:1-2; and the feeding molar ratio of the second cerium source precursor, the cadmium source precursor and the ruthenium source precursor is 0.5-2:1-2:

1.

7. The method of claim 1, wherein the waste polypropylene is a post-consumer waste polypropylene. The mass ratio of the amount of the photothermal catalytic material to the amount of the waste polypropylene is 1-10:1-10; The mass ratio of the amount of the water to the amount of the waste polypropylene is 10-100:1, and the oxygen pressure is 10-100 kPa.

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