A biochar-mediated polyethylene microplastic photoaging method

Abstract

The application discloses a biochar-mediated polyethylene microplastic photoaging method, and belongs to the technical field of microplastic degradation. The method comprises the following steps: taking biochar as an aging medium, degrading and aging polyethylene microplastics through a photoaging light source, and the mass ratio of the biochar to the polyethylene microplastics is 1:1.5-2.5. The method can effectively improve the aging effect of the polyethylene microplastics.

Description

Technical Field

[0001] This invention relates to the field of microplastic degradation technology, and more specifically to a biochar-mediated photoaging method for polyethylene microplastics. Background Technology

[0002] Plastics are a technologically mature, easy-to-manufacture, widely used, low-cost, and stable material, possessing immense economic and social value compared to natural materials. While the use of plastics has ushered in an era of disposable living, it has also brought serious environmental pollution problems. Plastics entering the environment gradually break down under the influence of light, mechanical wear, and biological processes. This breakdown process does not completely decompose the plastics but transforms them into countless smaller plastic particles, known as microplastics. Microplastics (MPs) refer to plastic fragments or particles with a particle size ≤ 5 mm. They are characterized by their small size, large specific surface area, and strong hydrophobicity, making them ideal carriers for many hydrophobic organic pollutants and heavy metals in the environment. MPs released into the environment can directly toxicize organisms in water and soil and can also expose humans through various pathways, posing potential health risks. MPs entering the environment inevitably undergo a series of biological and abiotic aging processes under the combined influence of various environmental factors, altering their surface morphology, crystallinity, roughness, surface area, functional groups, particle size, and other properties, thereby changing their environmental behavior and ecological risks.

[0003] Currently, common aging methods for polymer materials (MPs) mainly fall into three categories: physical, chemical, and biological. Physical aging methods primarily include weathering and physical abrasion: weathering degradation leads to surface embrittlement and microcracks, with the breaking of chemical bonds causing them to decompose into smaller fragments, achieving the aging effect. Chemical aging methods include acid and alkali corrosion, photoaging, and high-temperature oxidation: after acid and alkali corrosion, the surface of MPs becomes rough, wrinkled, and contains debris. Furthermore, under strong oxidizing agents or exposure to visible light sources, MPs undergo polymer chain reactions and chain breakage, resulting in changes in surface morphology and an increase in oxygen-containing functional groups, among other aging phenomena. Biological aging methods include microbial aging: microorganisms can use MPs as a carbon source, decomposing them through intestinal flora or hydrolytic enzymes produced by microorganisms. However, under natural conditions, MP aging is primarily photoaging, involving the participation of free radicals. Therefore, under light conditions, materials capable of generating a large number of free radicals can be used to age MPs, adjusting the light source and its proportion to achieve the best degradation or aging effect.

[0004] In the laboratory, aging pathways for microplastics (MPs) include mechanical abrasion through sand mixing and vibration, photoaging, acid and alkali corrosion, high-temperature oxidation with strong oxidants, and microbial degradation. However, these methods have drawbacks such as poor aging effect, high cost, and the potential generation of new pollutants. Furthermore, because MPs are widely distributed and have low abundance in natural environments, and current MP aging methods are not suitable for complex soil environments, this is one area where research needs improvement. Moreover, existing MP aging methods are not applicable to natural environmental conditions, resulting in poor MP aging efficiency and low MP removal efficiency. Summary of the Invention

[0005] To address the above problems, this invention provides a biochar-mediated photoaging method for polyethylene microplastics, which can effectively improve the aging effect of polyethylene microplastics.

[0006] The present invention aims to provide a biochar-mediated photoaging method for polyethylene microplastics, comprising the following steps:

[0007] Biochar was used as an aging medium to degrade and age polyethylene microplastics using a photo-aging light source; the mass ratio of biochar to polyethylene microplastics was 1:1.5-2.5.

[0008] In a preferred embodiment, biochar and polyethylene microplastics are mixed evenly and then irradiated with a photoaging light source. During the irradiation process, the mixture is stirred daily to ensure uniform light exposure.

[0009] In a preferred embodiment, the light aging source is ultraviolet light or blue light.

[0010] In a preferred embodiment, the ultraviolet light is UVA or UVB.

[0011] In a preferred embodiment, the power of the photoaging light source is 180W.

[0012] In a preferred embodiment, the mass ratio of biochar to polyethylene microplastics is 1:2.

[0013] In a preferred embodiment, the degradation time is 7-90 days.

[0014] In a preferred embodiment, the degradation temperature is 25°C.

[0015] In a preferred embodiment, the biochar is obtained by pyrolyzing apple wood at 450°C.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] Biochar is a good medium for degrading polyethylene microplastics (PE-MPs), but its degradation effect varies due to complex environmental conditions. Therefore, this invention uses fruitwood biochar to photo-age PE-MPs under UVB light. This process is not only simple and easy to operate, but also generates more free radicals, improving the aging effect on PE-MPs and other microplastics in the environment. This demonstrates good research value and application prospects in the field of soil microplastic degradation. Attached Figure Description

[0018] Figure 1 Flowchart of photoaging process for PE-MPs;

[0019] Figure 2 The photoaging mechanism of PE-MPs;

[0020] Figure 3 The images show the scanning images of pure polyethylene plastic under UVA aging conditions. Image a is the scanning image with a scale of 100 μm after 7 days of aging, image b is the scanning image with a scale of 50 μm after 7 days of aging, image c is the scanning image with a scale of 100 μm after 90 days of aging, and image d is the scanning image with a scale of 50 μm after 90 days of aging.

[0021] Figure 4 The images show the scanning images of pure polyethylene plastic under UVB conditions. Image a is the scanning image with a scale of 100 μm after 7 days of aging, image b is the scanning image with a scale of 50 μm after 7 days of aging, image c is the scanning image with a scale of 100 μm after 90 days of aging, and image d is the scanning image with a scale of 50 μm after 90 days of aging.

[0022] Figure 5 The bar graph shows the contact angle between polyethylene microplastics with 1g and 3g of biochar added and water after aging for different days under UVB light source conditions.

[0023] Figure 6 Infrared spectra of the original untreated polyethylene microplastics and the polyethylene microplastics of Example 4 after 90 days of aging treatment.

[0024] Figure label:

[0025] 1-Biochar, 2-Polyethylene microplastics, 3-Petroleum dish, 4-Light incubator. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that PE-MPs refers to polyethylene microplastics.

[0028] To address the problems of aging MPs in existing technologies, this invention provides a biochar-mediated photoaging method for polyethylene microplastics.

[0029] The specific technical solution is as follows:

[0030] Biochar was used as an aging medium to degrade and age polyethylene microplastics using a photo-aging light source. The mass ratio of biochar to polyethylene microplastics was 1:1.5-2.5.

[0031] This invention uses apple wood biochar and polyethylene microplastics as raw materials. After uniform mixing, the polyethylene microplastics are degraded and aged by irradiation with a photoaging light source. Figure 1 As shown. Stirring the PE-MPs daily during irradiation ensures uniform light exposure, resulting in better aging performance.

[0032] The biochar used in this invention is apple wood biochar, and its preparation method is as follows:

[0033] Apple wood was placed in a tube furnace and heated from room temperature to 450°C at a rate of 10°C / min. After pyrolysis for 2 hours, the temperature was lowered to room temperature and passed through a 60-mesh sieve to obtain apple wood biochar.

[0034] Other types of biochar can also be used in this invention, and they can be obtained through commercial channels. This invention does not impose any particular limitation on them.

[0035] In some preferred embodiments, the power of the photoaging light source is 180W.

[0036] Understandably, 180W is chosen to approximate the actual ground irradiance in real-world environments.

[0037] In some preferred embodiments, the present invention uses a light incubator for light treatment, with the temperature controlled at 25°C.

[0038] In some preferred embodiments, the aging effect is best when the mass ratio of biochar to polyethylene microplastics is 1:2.

[0039] In some preferred embodiments, the light source for photoaging is ultraviolet light or blue light.

[0040] It is understandable that materials that can generate a large number of free radicals under light conditions are used to age polyethylene microplastics. Adjusting the light source and its addition ratio can optimize the degradation or aging effect of polyethylene microplastics.

[0041] This invention uses biochar to photo-age PE-MPs, and the mechanism is as follows: Figure 2 As shown. Figure 2 It can be seen that, under light conditions, PFRs generated on the surface of highly aromatic macromolecules such as biochar can induce the formation of ·OH and O2· in the system. - ROS: O2· - It originates from the oxidation reaction of O2 in the air under light, but O2· - The structure is extremely unstable, and this unstable structure can interact with H. + An addition reaction occurs to generate ·OH. ROS is highly reactive and can attack the long chains of polymers like PE-MPs, altering their surface structure and causing aging. It should be noted that ROS is reactive oxygen species, ·OH is a hydroxyl radical, and O2· - It is a superoxide free radical.

[0042] Example 1

[0043] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0044] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 7 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0045] Example 2

[0046] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0047] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 30 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0048] Example 3

[0049] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0050] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 60 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light exposure.

[0051] Example 4

[0052] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0053] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0054] Example 5

[0055] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0056] Step 2: In a light incubator, use a 180W UVA light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0057] Example 6

[0058] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.

[0059] Step 2: In a light incubator, use a 180W blue light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0060] Example 7

[0061] Step 1: Mix the apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:1.5.

[0062] Step 2: In a light incubator, use a 180W UVA light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0063] Example 8

[0064] Step 1: Mix the apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:2.5.

[0065] Step 2: In a light incubator, use a 180W UVA light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0066] Comparative Example 1

[0067] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:3.

[0068] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 7 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0069] Comparative Example 2

[0070] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:3.

[0071] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 30 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0072] Comparative Example 3

[0073] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:3.

[0074] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 60 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light exposure.

[0075] Comparative Example 4

[0076] Step 1: Mix apple wood biochar prepared at 450℃ with polyethylene microplastic powder in a petri dish at a mass ratio of 1:3.

[0077] Step 2: In a light incubator, use a 180W UVB light source to irradiate the ground for 90 days to approximate the actual ground irradiance in the real environment, and control the temperature at 25℃; stir evenly once a day to ensure uniform light irradiation.

[0078] After irradiation, the MPs were separated from the mixture using an oil-water cryo-separation method, and then washed repeatedly with anhydrous ethanol and ultrapure water until the rapeseed oil coating on the surface of the MPs was completely removed.

[0079] The oil + water cryogenic separation method is referenced in patent number ZL 202111001477.8, entitled "A Method for Separating Microplastics and Biochar." The specific operating steps are as follows:

[0080] Step 1, Aeration and Flotation: Add the irradiated sample to a 1000mL low-temperature resistant beaker, and then add ultrapure water at a ratio of 1g:1000ml to obtain a mixture of biochar and microplastics. Use an aeration pump to continuously aerate the mixture of biochar and microplastics, so that the microplastics float on the upper layer of the mixture and the biochar settles on the lower layer, thus obtaining an aerated solution.

[0081] Step 2, aggregation and freezing: rapeseed oil is added to the aeration solution obtained in Step 1, so that the microplastics aggregate in the 4cm thick oil layer formed by the rapeseed oil in the upper part of the aeration solution, while the biochar is deposited in the water layer in the lower part of the aeration solution. After standing for 30 minutes, it is frozen at -20℃ for 24 hours, so that the oil layer does not solidify but the water layer solidifies, and the freezing liquid is obtained.

[0082] Step 3, Aeration and Separation: Pour the oil layer on the upper layer of the refrigerant obtained in Step 2 into the separatory funnel of the aeration and separation equipment for separation. Then, send the separated lower layer liquid into a separator containing water, and wash the inner wall of the separatory funnel with rapeseed oil so that the residual microplastics are sent into the separator with the washing liquid. At the same time, start the aeration pump to aerate the mixture of water and lower layer liquid in the separator through the aeration disc, so that the microplastics in the lower layer liquid float on the upper layer. When the microplastics exceed the height line on the separator wall, they enter the collection cylinder through the collection hole and settle on the bottom of the collection cylinder to obtain crude microplastics.

[0083] Step 4: Vacuum Filtration and Drying: The crude microplastics obtained in Step 3 are fed into a sand core filter device via pipeline, and the vacuum filtration pump is started for filtration. The filter membrane installed in the sand core filter device is a 0.45μm organic filter membrane. During the filtration process, the microplastics are retained, and the filter residue and filtrate are collected. Then, the filter residue is repeatedly washed with a 30% H2O2 solution and anhydrous ethanol to remove organic matter and rapeseed oil from the surface of the microplastics. The washed PE-MPs are then dried at a low temperature of 30℃ to obtain the microplastics. Testing is then performed.

[0084] Figure 3 and Figure 4 The images show scanned images of polyethylene microplastics after 7 days and 90 days of aging under UVA and UVB light conditions, respectively, on pure polyethylene plastic. Figure 3 and Figure 4 It can be seen that the surface morphology of PE-MPs is affected by different light sources after aging treatment. The most obvious effect is the change in surface roughness of PE-MPs under UVB light source. The surface of PE-MPs gradually changes from relatively smooth to having more wrinkles. Therefore, it can be concluded that UVB has a better aging effect on polyethylene microplastics than UVA light source.

[0085] The following describes the characterization of polyethylene microplastics treated under UVB light source conditions.

[0086] The contact angles of the polyethylene microplastics treated in Examples 1-4 and Comparative Examples 1-4 with water were compared, such as... Figure 5 As shown in the bar chart, under UVB light source conditions, the contact angles of polyethylene microplastics with added 1g and 3g of biochar with water after aging for different numbers of days are [not shown in the bar chart]. Figure 5 It can be seen that the contact angle between the surface of polyethylene microplastics and water changed under different aging conditions. Since the surface of polyethylene microplastics has more oxygen-containing functional groups and stronger hydrophilicity after aging, the contact angle with water is smaller. Therefore, it can be concluded that the aging degree of microplastics is higher when the biochar addition is 1g.

[0087] Figure 6 The infrared spectra of the original untreated polyethylene microplastics and the polyethylene microplastics after 90 days of aging treatment in Example 4 are shown below. Figure 6 It can be seen that PE-MPs are at 715cm -1 1465cm -1 2848cm -1 and 2920cm- 1 A strong absorption peak was observed at 1740 cm⁻¹, and newly formed peaks appeared in aged PE-MPs. -1 The deformation vibration peak at -C=O and 3428-3669 cm -1 The deformation vibration peak of -OH indicates that light irradiation oxidizes PE-MPs, resulting in the formation of oxygen-containing functional groups on the PE-MPs surface. This demonstrates that under light irradiation, biochar can induce the formation of ·OH and O2· in the system. - Wait for ROS.

[0088] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0089] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A biochar-mediated photoaging method for polyethylene microplastics, characterized in that, Includes the following steps: Biochar was used as an aging medium to degrade and age polyethylene microplastics using a photo-aging light source; the mass ratio of biochar to polyethylene microplastics was 1:1.5-2.

5. Biochar is obtained by pyrolyzing apple wood at 450℃.

2. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, After the biochar and polyethylene microplastics are mixed evenly, they are irradiated with a light aging light source. During the irradiation process, the mixture is stirred every day to ensure that the light is evenly applied.

3. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, The light source for photoaging is ultraviolet light or blue light.

4. The biochar-mediated photoaging method for polyethylene microplastics according to claim 3, characterized in that, Ultraviolet light is either UVA or UVB.

5. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, The power of the light aging source is 180W.

6. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, The mass ratio of biochar to polyethylene microplastics is 1:

2.

7. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, The degradation time is 7-90 days.

8. The biochar-mediated photoaging method for polyethylene microplastics according to claim 1, characterized in that, The degradation temperature is 25℃.

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