A polyolefin plastic catalytic degradation method based on a Pt-Ir alloy nanoscale enzyme

Abstract

The application discloses a polyolefin plastic catalytic degradation method based on a Pt-Ir alloy nanoscale enzyme and belongs to the technical field of nanometer catalysis. The application discloses a synthesis method of a Pt-Ir alloy nanoscale enzyme and the activity of the Pt-Ir alloy nanoscale enzyme in catalytic degradation of polyolefin plastics. The plastic is mixed with the Pt-Ir alloy nanoscale enzyme and then placed in a hydrothermal reaction kettle to perform a catalytic degradation reaction of the plastic, so that the reaction time and the reaction temperature can be effectively reduced. The principle is that the Pt-Ir alloy nanoscale enzyme has peroxidase (POD) activity, can generate active free radicals, catalyzes the oxidative cleavage of C-C bonds in the interior of polyolefin plastic molecules, and realizes efficient and low-energy-consumption rapid degradation of the polyolefin plastic. The technology can realize efficient degradation of the polyolefin plastic and effectively reduces the cost and energy consumption. In the hydrothermal reaction kettle, the temperature is 140 DEG C, and after 12 h of degradation reaction, the degradation rate of the polyolefin plastic can reach 80%.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalysis technology, specifically a method for catalytic degradation of polyolefin plastics based on Pt-Ir alloy nanoenzymes. Background Technology

[0002] Plastic waste has evolved into a global environmental problem and a prominent public health hazard. Indiscriminate exposure to plastic-related chemicals, from embryonic development to old age, continuously increases the risk of miscarriage, premature birth, malignant tumors, asthma, and other diseases. Studies have confirmed that humans ingest approximately 0.1–5 g of microplastic particles weekly through various pathways, and their cumulative effects in the body remain largely unknown. Global plastic production has experienced explosive growth, soaring from only 2 million tons in 1950 to 475 million tons in 2022, and is projected to exceed 1.2 billion tons by 2060. The severe situation of plastic pollution urgently requires the research and application of efficient treatment technologies.

[0003] Currently, the mainstream treatment pathways for plastic waste can be summarized into three categories: 1) Physical recycling, where recycled waste plastics are pretreated by washing and drying before being extruded and granulated for recycling. However, this process leads to a significant decline in the mechanical and processing properties of plastics, greatly reducing the utilization value of recycled materials; 2) Chemical recycling, which uses thermal effects or chemical catalysts (such as solid acids and solid alkalis) to induce the breaking and degradation of C-C bonds within plastic molecules. However, such reactions require stringent high-temperature and high-pressure conditions, resulting in high energy consumption and a high risk of secondary environmental pollution; 3) Bioenzymatic degradation recycling, relying on the development of enzyme-directed evolution technology, various bioenzymes are gradually being applied to the field of plastic degradation. However, bioenzymes generally exhibit strong substrate specificity, making it difficult to achieve efficient degradation of a broad range of plastic types. Breakthroughs have been made in the bio-enzymatic degradation technology of polyethylene terephthalate (PET). The engineered leaf-branch compost cutinase (LCC) developed by V. Tournier's team can degrade 90% of pretreated post-consumer PET (pc-PET) within 10 hours at 72 ℃ and pH 8.0. However, highly active biodegradable enzymes are still lacking for polyolefin plastics. More importantly, bio-enzymes themselves suffer from complex preparation processes, poor environmental tolerance, and difficulty in secondary recycling, severely restricting the industrial-scale application of bio-enzymatic degradation technology for plastics.

[0004] Nanozymes are a class of catalytic nanomaterials exhibiting high efficiency, stability, and multifunctionality, finding wide application in biomedicine, environmental remediation, and other fields. Nanozymes are not only cheaper to prepare than biological enzymes, but also possess strong environmental adaptability, maintaining catalytic activity under harsh conditions such as high temperature, acidity, and alkalinity. Furthermore, nanozymes support recycling. Because nanozymes are constructed using biomimetic active centers, the easily adjustable nature of these centers grants them a wider range of applications. Currently, nanozymes are widely used in key areas such as biomedicine, chemical engineering, and environmental protection due to these advantages. For example, Mn3O4 nanoparticles prepared by Ge Zhiqiang et al. at Tianjin University via chemical precipitation can effectively remove the dye pollutant acridine orange from aqueous solutions; Rao Hanbing et al. at Sichuan Agricultural University synthesized Co3O4 / CoFe2O4 hollow nanocubes, which can degrade 99.24% of the toxic dye Rhodamine B within 20 minutes. In 2022, nanozymes were recognized as one of the top ten emerging technologies in the field of chemistry by IUPAC.

[0005] In summary, traditional plastic degradation technologies all suffer from significant application shortcomings. Starting from the core degradation mechanism of catalytically breaking the internal chemical bonds of plastic molecules, cost control of catalysts has become a key issue restricting the industrial application of plastic degradation technologies. The catalytic characteristics and application advantages of nanozyme technology precisely address and solve this industry pain point. Therefore, this invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a catalytic degradation technology for polyolefin plastics based on Pt-Ir alloy nanozymes. The basic principle is to utilize the peroxidase-like (POD) activity of Pt-Ir alloy nanozymes to catalyze the breaking of C-C bonds within polyolefin plastics, achieving highly efficient degradation of polyolefin plastics and significantly reducing the cost of plastic degradation. This invention also provides a method for preparing Pt-Ir alloy nanozymes and their application in the field of plastic degradation.

[0007] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0008] Step 1: Preparation of Pt-Ir alloy nanozymes

[0009] Weigh appropriate amounts of hexachloroiridic acid (H₂IrCl₆) and potassium tetrachloroplatinate (K₂PtCl₄), and place the two metal salt reagents into two separate 50 mL centrifuge tubes. Add an equal amount of deionized water to each tube, and use ultrasound to help disperse the two metal salt solutions evenly. Then mix the two metal salt solutions, and after mixing, place them at ambient temperature for later use, avoiding the introduction of impurities and solution separation.

[0010] Furthermore, the molar ratio of hexachloroiridic acid to potassium tetrachloroplatinate is (H2IrCl6:K2PtCl4 = 1:0.1-10).

[0011] Preferably, the molar ratio of the two metal salts is 1:1.

[0012] Polyvinylpyrrolidone (PVP) powder was placed in a flask, and triethanolamine (TEG) was added as a reaction solvent. The solution was heated to 200-240°C. The prepared mixed metal salt solution was then transferred to a peristaltic pump reservoir. The peristaltic pump was turned on, and the pump speed was adjusted until all the mixed metal salt solution was added to the flask. After the addition was complete, the heating temperature was maintained, and stirring was continued for 20-60 minutes. After the reaction was complete, the reaction solution was collected, the sample was centrifuged, the supernatant was discarded, and the precipitate was collected. The obtained precipitate was dried to obtain powdered Pt-Ir alloy nanozyme.

[0013] Preferably, the heating temperature is 230°C.

[0014] Furthermore, the flow rate range of the peristaltic pump is 1-5 mL / min.

[0015] Preferably, the flow rate of the peristaltic pump is 2 mL / min.

[0016] Preferably, after all the mixed metal salt solution is added to the reaction, the heating temperature is maintained and stirring is continued for 30 minutes.

[0017] Step 2: Degradation of polyolefin plastics

[0018] A measured amount of buffer solution was placed in a 50 mL hydrothermal reactor, along with the weighed microplastics. Then, the corresponding Pt-Ir alloy stock solution was added to the reactor. Finally, 0-50 mM H₂O₂ or ammonium persulfate (APS) was added, the reactor was immediately sealed, and placed in an oven for reaction.

[0019] Further, the buffer solution has a pH of 4-8, and the buffer solution may include one or more of PB buffer, PBS buffer, or Tris-HCl buffer.

[0020] Furthermore, the microplastic is polyethylene or polypropylene (PP or PE).

[0021] Preferably, the plastic is pretreated before the microplastics degrade.

[0022] The pretreatment may include granulating the plastic.

[0023] Preferably, the polyethylene or polypropylene microplastics are granulated to an average particle size of 100 mesh.

[0024] Furthermore, the mass ratio of the Pt-Ir alloy nanozyme to the microplastics used is 1:10-100.

[0025] Preferably, the concentration of the Pt-Ir alloy stock solution is 1 mg / mL.

[0026] Furthermore, the concentration of H2O2 is (200-250 mM).

[0027] Furthermore, the concentration of the APS is (5-20 mM).

[0028] Furthermore, the reaction temperature is 120℃-180℃, and the reaction time is 10-16 h.

[0029] After the reaction is complete, wait for the reactor to cool to ambient temperature, then open the reactor and remove the reaction liquid. Wash the reactor three times and recover the washing liquid for subsequent filtration and weighing.

[0030] Regarding the calculation of degradation rate: The degradation rate of plastics is calculated using the weight loss method. After the reaction is complete, the reaction solution and washing solution are collected, and then all liquids are filtered through a membrane. The filter membrane containing microplastics is dried and weighed, and the mass difference (Δm) of the filter membrane before and after filtration is calculated. The specific formula for calculating the degradation rate is as follows:

[0031] Degradation rate (%) = x 100%

[0032] Furthermore, the microporous filter membrane used in the vacuum filtration is made of cellulose acetate, with a pore size of 0.22 μm.

[0033] This invention addresses the problems of high cost, difficult storage, and poor environmental tolerance in existing plastic degradation processes by developing a plastic degradation technology based on Pt-Ir alloy nanozymes. Furthermore, it saves time and economic costs associated with the preparation of pure enzyme formulations. Under conditions that promote mass transfer, it ensures both enzyme activity and low energy consumption.

[0034] Using the method provided by this invention to degrade polyolefin plastics, under the premise of reducing the production cost of catalysts, the degradation rate of polyethylene can reach 95% after 10 hours of catalytic reaction; the degradation rate of polypropylene microplastics can reach 82% after 10 hours. Attached Figure Description

[0035] Figure 1 Example 1: Transmission electron microscope image of Pt-Ir alloy

[0036] Figure 2 The degradation rate of polyethylene plastic by Pt-Ir in Examples 2 and 4

[0037] Figure 3 The degradation rate of polypropylene plastic by Pt-Ir in Examples 3 and 5 Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0039] Example 1: Preparation of Pt-Ir alloy nanozymes:

[0040] Weigh 203.5 mg of hexachloroiridium acid (H₂IrCl₆, 0.5 mM) and 207.7 mg of potassium tetrachloroplatinate (K₂PtCl₄, 0.5 mM), and place each metal salt reagent into two separate 50 mL centrifuge tubes. Add 20 mL of deionized water to each tube and disperse the two metal salt solutions evenly using sonication. Then mix the two metal salt solutions and allow them to stand at ambient temperature for later use, taking care to avoid the introduction of impurities and solution separation.

[0041] Weigh 555 mg of polyvinylpyrrolidone (PVP) into a flask, add 150 mL of triethanolamine (TEG) as a reaction solvent, and heat the solution to 230°C. Then, transfer the previously prepared mixed metal salt solution into a peristaltic pump reservoir, turn on the peristaltic pump, and adjust the pump speed to 2 mL / min until all the mixed metal salt solution is added to the flask. After the addition is complete, maintain stirring at 230°C for 30 min. After the reaction is complete, collect the reaction solution, centrifuge the sample, discard the supernatant, collect the precipitate, and dry the precipitate to obtain powdered Pt-Ir alloy nanozyme.

[0042] Example 2: A Pt-Ir alloy nanoenzyme technology for the degradation of polyethylene plastics:

[0043] 7 mL of phosphate buffer (pH 4.0) was placed in a 50 mL hydrothermal reactor, along with 15 mg of weighed polyethylene microplastics. Then, 3 mL of Pt-Ir alloy stock solution (Pt:Ir molar ratio = 1:1, solvent: water, Pt-Ir alloy concentration: 1 mg / mL) was added to the reactor. Finally, the corresponding H₂O₂ (200 mM) was added, and the reactor was immediately sealed and placed in an oven at 140°C for 10 h. After the reaction was complete, the reactor was allowed to cool to 25°C, then opened and the reaction solution was aspirated. The reactor was washed three times, and the washing liquid was recovered for subsequent filtration and weighing.

[0044] According to the weight loss method formula, the degradation rate of the plastic in this embodiment is 95%.

[0045] Example 3: A Pt-Ir alloy nanoenzyme technology for the degradation of polyethylene plastics:

[0046] 7 mL of phosphate buffer (pH 4.0) was placed in a 50 mL hydrothermal reactor, and 15 mg of polypropylene microplastics was added. Then, 3 mL of Pt-Ir alloy stock solution (Pt:Ir molar ratio 1:1, solvent: water, Pt-Ir alloy concentration 1 mg / mL) was added to the reactor. Finally, the corresponding H₂O₂ (200 mM) was added, the reactor was immediately sealed, and placed in an oven at 140°C for 10 h. After the reaction was complete, the reactor was allowed to cool to 25°C, then opened and the reaction solution was aspirated. The reactor was washed three times, and the washing liquid was recovered for subsequent filtration and weighing.

[0047] According to the weight loss method formula, the degradation rate of the plastic in this embodiment is 82%.

[0048] Example 4: A Pt-Ir alloy nanoenzyme technology for the degradation of polyethylene plastics:

[0049] 7 mL of phosphate buffer (pH 4.0) was placed in a 50 mL hydrothermal reactor, along with 15 mg of weighed polyethylene microplastics. Then, 3 mL of Pt-Ir alloy stock solution (Pt:Ir molar ratio 1:1, solvent: water, Pt-Ir alloy concentration 1 mg / mL) was added to the reactor. Finally, granular ammonium persulfate was added (to a final concentration of 10 mM). The reactor was immediately sealed and placed in an oven at 140°C for 10 h. After the reaction was complete, the reactor was cooled to 25°C, opened, and the reaction solution was aspirated. The reactor was washed three times, and the washing liquid was recovered for subsequent filtration and weighing.

[0050] According to the weight loss method formula, the degradation rate of the plastic in this embodiment is 90%.

[0051] Example 5: A Pt-Ir alloy nanoenzyme technology for the degradation of polyethylene plastics:

[0052] 7 mL of phosphate buffer (pH 4.0) was placed in a 50 mL hydrothermal reactor, and 15 mg of polypropylene microplastics were added. Then, 3 mL of Pt-Ir alloy stock solution (Pt:Ir molar ratio 1:1, solvent: water, Pt-Ir alloy concentration 1 mg / mL) was added to the reactor. Finally, granular ammonium persulfate was added (to a final concentration of 10 mM). The reactor was immediately sealed and placed in an oven at 140°C for 10 h. After the reaction was complete, the reactor was cooled to 25°C, opened, and the reaction solution was aspirated. The reactor was washed three times, and the washing liquid was recovered for subsequent filtration and weighing.

[0053] According to the weight loss method formula, the degradation rate of the plastic in this embodiment is 80%.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0055] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for synthesizing a Pt-Ir alloy nanoszyme, characterized in that, Pt-Ir alloy nanozymes have sizes ranging from 2 to 200 nanometers. The synthesis method of Pt-Ir alloy nanozyme involves co-reducing an aqueous solution of two metal salt precursors, hexachloroiridium acid (H2IrCl6) and potassium tetrachloroplatinate (K2PtCl4), heating to 200-240℃, and stirring for 20-60 min. Alloy nanoparticles are synthesized in one step in the presence of a surfactant, wherein the Pt molar ratio of the synthesized Pt-Ir alloy is 10%-90%wt.

2. The method of claim 1, wherein, The PtIr alloy nanozymes used are modified by adding functional groups to the surface of the nanozymes; or the PtIr alloy nanozymes used are recycled and reused.

3. Pt-Ir alloy nanozyme synthesized using the synthesis method described in claim 1.

4. The method of applying the Pt-Ir alloy nanozyme as described in claim 3, characterized in that, A measured amount of buffer solution was placed in a hydrothermal reactor, and the weighed microplastics were added at the same time. Then, the corresponding Pt-Ir alloy stock solution was measured and added to the reactor. Finally, H2O2 or ammonium persulfate APS was added, the reactor was immediately sealed, and the reactor was placed in an oven for reaction. The buffer solution has a pH of 4-8, and the buffer solution includes one or more of PB buffer, PBS buffer, or Tris-HCl buffer. The microplastic is polyethylene or polypropylene; The mass ratio of the Pt-Ir alloy nanoenzyme to the microplastic used is 1:10-100; The final concentration of H2O2 is 200-250 mM; the final concentration of APS is 5-20 mM. The reaction temperature is 120℃-180℃, and the reaction time is 10-16 h; the reaction system for the catalytic degradation of polyolefin plastics is an aqueous phase, and the reaction device is a sealed container that can provide high-temperature conditions of 120-200℃.

5. The method as described in claim 1, characterized in that, The polyolefin plastic has undergone pre-granulation pretreatment.

Images