Method for promoting aging of polystyrene micro-plastic based on Fe (III) self-Fenton reaction under illumination

Abstract

The invention discloses a method for promoting aging of polystyrene micro-plastic based on Fe (III) self-Fenton reaction under illumination. Adding a FeCl3 solution into the mixed solution of the polystyrene micro-plastic and the water; and adjusting the pH value to be neutral, and irradiating in a photoreactor to promote the aging of the polystyrene micro-plastic. When the PS-MPs are exposed in a UV / Fe (III) system, the surface appearance of the PS-MPs is in a notch shape, cracks, pores and even fractures. Meanwhile, oxygen-containing functional groups are increased, and the CI value is increased along with the prolonging of the aging time. In addition, Fe (III) generates. OH in the Fenton reaction, so that the aging process of PS-MPs is accelerated. By researching the aging behavior of the MPs in the environment medium, the potential risk of the MPs in the environment can be evaluated.

Description

Technical Field

[0001] The invention belongs to the field of interaction between microplastics and environmental media, and relates to a method for promoting aging of polystyrene microplastics through Fe (III) self-Fenton reaction under light. Background Art

[0002] Waste plastic products undergo physical, chemical and biological degradation in exposed environments to produce smaller microplastics (MPs), which are more easily ingested by a variety of organisms and finally enter the food chain, posing a threat to the balance of the ecosystem and human health. Photo-aged microplastics induce neurotoxicity through oxidative stress and abnormal neurotransmission in zebrafish larvae (Danio rerio), and aged MPs cause more severe neurotoxicity compared to original MPs. Therefore, understanding the effects and mechanisms of environmental media on the aging behavior of MPs is of practical significance in assessing the potential environmental hazards of MPs in aquatic environments.

[0003] Fe is a substance that is ubiquitous in natural ecosystems and has high redox activity. Studies have shown that low concentrations of natural iron (0.3 - 0.6 mg·L -1 ), by simply adding H 2 O 2 It is sufficient to form hydroxyl radicals (·OH) by photo-Fenton reaction at an initial neutral pH to achieve the removal of organic pollutants in water. However, compared with the degradation of these pollutants, the aging of microplastics is a long process, and it is unknown whether dissolved iron (DFe) in natural aquatic environments can maintain the aging of microplastics through the Fe(III) / Fe(II) cycle. Due to the prevalence and abundance of polystyrene (PS) in water bodies, and the significant photoaging characteristics of PS, it was selected as a model of microplastic pollution in aquatic environments for study. This application is carried out without aeration or addition of chemical oxidants (such as H 2 O 2 ) to investigate the redox chemistry of Fe(III)-induced iron and the H 2 O 2 The formation and photoaging mechanism of PS-MPs. Summary of the invention

[0004] The present invention provides a method for analyzing the effect of Fe(III) in the environment on the aging of polystyrene microplastics, which helps us to deeply understand the photochemical transformation of PS-MPs under the coexistence of different natural water components.

[0005] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light, comprising the following steps: (1) adding FeCl 3 solution; (2) after adjusting the pH to neutral, place it in a photoreactor for irradiation to promote the aging of polystyrene microplastics.

[0006] Furthermore, the mass volume ratio of the polystyrene microplastic to water in step (1) is 0.4 g:80 mL.

[0007] Furthermore, in step (1), FeCl 3 The concentration of the solution was 20 μmol / L.

[0008] Furthermore, in step (2), the irradiation conditions in the photoreactor are: using a 500W ultraviolet mercury lamp, the wavelength of ultraviolet irradiation is 396nm.

[0009] Furthermore, in step (2), the irradiation time in the photoreactor is 4, 12, 24, 36, 48, 72 and 96 hours.

[0010] Further, in step (2), the Fe(II) / Fe(III) / Fe 总 , H 2 O 2 , pH, and instantaneous concentration of OH.

[0011] Furthermore, after the reaction was completed, the microplastic system was vacuum filtered, washed three times with deionized water, and dried.

[0012] The present invention also provides an application of the above-mentioned method for promoting the aging of polystyrene microplastics based on the Fe (III) self-Fenton reaction under light.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention systematically studies the method of promoting the aging of polystyrene microplastics by the self-Fenton reaction of Fe (III) under light, providing a theoretical basis for further understanding the interaction between PS-MPs and natural water components. When exposed to the UV / Fe (III) system, the surface morphology of PS-MPs has notched shapes, cracks, pores and even fractures. At the same time, the oxygen-containing functional groups increase, and the CI value increases with the extension of aging time. In addition, the generation of ·OH in the self-Fenton reaction of Fe (III) accelerates the aging process of PS-MPs. The present invention is conducive to evaluating the potential risks of MPs in the environment by studying the aging behavior of MPs in environmental media. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 PS-MPs in Fe(III) and pure H 2Scanning electron microscope (SEM) images before and after aging in O for 96 h; Figure 2 PS-MPs in Fe(III) and pure H 2 FTIR and CI results at different aging time points in O, where (a) represents the FTIR spectrum and (b) represents the CI result; Figure 3 PS-MPs in Fe(III) and pure H 2 C1s and O1s spectra before and after aging in O for 96 h, where (a) represents the C1s spectrum and (b) represents the O1s spectrum; Figure 4 PS-MPs in Fe(III) and pure H 2 Two-dimensional correlation Fourier transform infrared spectroscopy (2D-COS) (synchronous and asynchronous) plots in O; Figure 5 is the instantaneous Fe of PS-MPs at each aging time point in the Fe(Ⅲ) system. 2＋ , Fe 3＋ , Fe (total) concentration; Figure 6 PS-MPs in Fe(III) and pure H 2 H at different aging time points in O 2 O 2 instantaneous concentration; Figure 7 The original PS-MPs (untreated PS-MPs) and PS-MPs in Fe(III) and pure H 2 EPR signal of ·OH after aging in O for 96 h. DETAILED DESCRIPTION

[0015] Example 1: Photoaging test 0.4 g of polystyrene powder was added to 80 ml of aqueous solution (Fe 3+ The concentration was 20 μmol / L), and the initial pH was adjusted to 7 ± 0.3 with HCl and NaOH. The experimental group was marked as Fe (Ⅲ) system, and the control group was marked as H 2O system. Stir in the dark for 2 hours in the photochemical reactor to make the PS-MPs suspension evenly dispersed. A 500w UV high-pressure mercury lamp (wavelength 396nm) was used to simulate natural light. Due to the evaporation of water, the solution was reduced and the solution was replenished to 80ml every 4h. At the predetermined time (4, 12, 24, 36, 48, 72 and 96h), the solution was taken out and filtered through a 0.45μm filter membrane and placed in the dark for the next step. Then, the suspension was collected through a filter membrane (0.45μm) PS-MPs sample, dried (50°C, 48 hours), and stored in a bottle at room temperature away from light. All experiments (i.e. MPs aging, characterization, etc.) were repeated three times in this study.

[0016] Example 2: Characterization of PS-MPs In order to characterize the changes in the physicochemical properties of PS-MPs before and after Fe (III) treatment, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to study their surface morphology, molecular structure and chemical bonds, and elemental composition. Dynamic illumination time infrared spectra were constructed based on the infrared images, and 2D-COS analysis was performed to determine the change order of different functional groups.

[0017] Example 3: Conditions for Fe(III)-mediated self-Fenton reaction Fe(II) / Fe(III) / Fe(total) instantaneous concentration, H 2 O 2 Determination of ·OH: The instantaneous concentration of Fe(II) / Fe(III) / Fe(total) was determined by the improved 1,10-phenanthroline spectrophotometry; H 2 O 2 concentration; 50 mg of the aged sample was mixed with 500 μL of 100 mM DMPO aqueous solution and an electron paramagnetic resonance spectrometer (BrukerEMXPLUS) was used to measure ·OH in the aging of PS-MPs.

[0018] result: 1. Surface morphology of PS-MPs like Figure 1The original PS-MPs have a smooth surface with slight cracks, which may be due to slight wear or oxidation of the molecular chain ends during the production, transportation and storage of PS-MPs. These cracks are also potential aging sites. Compared with the original PS-MPs, the aged PS-MPs have many notches, cracks, pores and even fractures on the surface, especially the PS-MPs in the Fe(Ⅲ) system are severely broken, and the smooth surface morphology is completely destroyed. It shows that Fe(Ⅲ) as a photosensitive substance promotes the indirect photoaging of PS-MPs. The aging of amorphous polymers is carried out by destroying the entanglement network between polymer chains through chain scission, causing them to break into more small molecular weight organic matter, which shows that Fe(Ⅲ) affects the chain scission of PS-MPs under irradiation, thereby accelerating the photoaging of PS-MPs.

[0019] 2. Composition and changes of PS-MPs functional groups Fourier transform infrared spectroscopy (FTIR) was used to characterize the changes in functional groups of PS-MPs before and after aging. Figure 2 (a), pristine PS-MPs at 1722 cm −1 The characteristic absorption peak at is attributed to the stretching vibration peak of C=O, which may be caused by oxidation or wear of PS-MPs during preparation, transportation and storage. It occurs at the end of the molecular chain, indicating that the degree of oxidation is not deep. As aging progresses, the intensity of C=O increases with the increase of aging time, indicating that more oxygen-containing groups are introduced during the aging process of PS-MPs. This shows that Fe(Ⅲ)-treated PS-MPs can better promote the formation of carbonyl groups. We use the carbonyl index (CI) to quantitatively describe the changes in carbonyl content. The higher the CI value, the higher the content of oxygen-containing functional groups in PS-MPs. The carbonyl index is expressed by the carbonyl absorption intensity (1722 cm −1 ) and the methylene absorption intensity (1452 cm −1 ) is calculated by the ratio of Figure 2 (b) The CI value increased positively with the irradiation time and increased significantly after 96 h of illumination, from the original 0.011 to 0.502 (pure water) and 0.72 (Fe(Ⅲ) system), respectively, indicating that Fe(Ⅲ) and light accelerated the aging of PS-MPs.

[0020] XPS characterized the changes in the surface carbon, oxygen binding state and functional groups of PS-MPs before and after aging. Figure 3, C1s graph shows that CH, CO, C=O, π-π* correspond to 284.5, 286.6, 288.0 and 292.2 eV, respectively. PS-MPs showed a decrease in the relative proportion of aromatic CH, an increase in the relative proportion of aliphatic CH, an increase in CO and C=O, and a decrease in the peak intensity of π-π* after 96 h of Fe(Ⅲ) treatment, proving that the aromatic ring was broken to form oxygen-containing groups. O1s graph shows that CO, C=O and OC=O correspond to 532.3, 533.27 and 534.12 eV, respectively. Compared with the original PS-MPs, aging significantly promotes the increase in the relative proportion of OC=O with the extension of irradiation time, indicating that more carboxyl groups are generated, which may be due to the disproportionation reaction of polymer alkoxy groups. Fe(Ⅲ) system PS-MPs have the most oxidized groups formed on the surface, proving that PS-MPs are more thoroughly oxidized in the Fe(Ⅲ) environment.

[0021] In order to explore the aging mechanism of PS-MPs in Fe(III) environment, 2D-COS analysis was performed on FTIR data to determine the changing order of functional groups of PS-MPs under different environmental conditions. Figure 4 As shown in the synchronous correlation spectrum, the diagonal peaks at 748, 1217, 1376, 1494, and 1716 cm −1 There are five main peaks at 748, 1217, and 1716 cm −1 The peak intensity at is stronger, which may be due to the breakage or opening of the benzene ring in the long chain structure of PS-MPs. In addition, during the aging process of PS-MPs under different environmental conditions, all functional groups change simultaneously with the increase of time and the peak distribution is relatively consistent, indicating that the Fe (III)-mediated aging process is consistent with the self-oxidation of PS-MPs in a pure water environment.

[0022] The asynchronous correlation spectrum can reflect the order of functional group changes during the aging process of PS-MPs. The asynchronous mapping is diagonally antisymmetric. According to the Noda rule, when (Φ(x 1 , x 2 )) and (ψ(x 1 , x 2 )) is the same, indicating that x 1 Appears in x 2 Before, otherwise, the rule is the opposite. Based on this, we found that the aging order of PS-MPs in Fe (III) environment is consistent with that in pure water environment: CH>Benzene ring>C-OH>CO>C=O. The consistent reaction order indicates that PS-MPs have the same direct photolysis and indirect photolysis, and Fe (III) will not change the aging pathway of PS-MPs.

[0023] 3. Conditions for Fe(III)-mediated self-Fenton reaction Figure 5 As shown in the figure, with the extension of irradiation time, Fe(II) gradually increased, reaching a maximum value of 20.79 μM at 72h, and then decreased. Fe(III) showed a parabolic trend of first increasing, then decreasing, and then increasing again within 72h. 2 O 2 The concentration changes with aging time were monitored. Figure 6 It can be seen that when PS-MPs are photoconverted in pure water, H 2 O 2 The concentration gradually increased with time, and increased to 279-286.04 μM after 72 h. 2 O 2 The concentration first increased to 21.31-26.3 μM and then gradually decreased, indicating that H 2 O 2 Consumed as an intermediate. 2 O 2 The content of Fe(II) during the aging process is sufficient to support the self-Fenton reaction. Within the initial 24 hours of the reaction, the aging effect of Fe(III) on PS-MPs was poor, which can be proved by the CI value, and the Fe(II) in the system was lower than Fe(III). Because the Fenton method is less effective under neutral conditions. As the reaction proceeds, Fe hydrolysis plastic aging reduces the pH value of the system, thus providing good environmental conditions for the Fenton reaction. The aging of PS-MPs was improved, and the concentration of Fe(II) rose rapidly. The change of Fe(II) at the inflection point of 72h proves that the valence state of Fe was changed while the PS-MPs were aged, so that some dissolved Fe(III) remained in the system, and the level of dissolved Fe(II) was maintained by photoreduction, maintaining the continuous aging of PS. Figure 7 The EPR test results after aging for 96 h showed that the aging of PSMPs in water environment produced less ·OH, indicating that H 2 O 2 The ·OH signal is relatively strong in the Fe(Ⅲ) system, indicating that the Fe-containing environment is more conducive to H 2 O 2 The accelerated conversion of ·OH promotes the aging of PS-MPs.

Claims

1. A method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light, characterized in that: The following steps are involved: (1) Add FeCl3 solution to the mixed solution of polystyrene microplastics and water; (2) Adjust the pH to neutral and place it in a photoreactor for irradiation to promote the aging of polystyrene microplastics.

2. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light according to claim 1, characterized in that: The mass volume ratio of the polystyrene microplastic to water in step (1) is 0.4 g:80 mL.

3. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light according to claim 1, characterized in that: The concentration of the FeCl3 solution in step (1) is 20 μmol / L.

4. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light according to claim 1, characterized in that: In step (2), the irradiation conditions in the photoreactor are: using a 500W ultraviolet mercury lamp, the wavelength of ultraviolet irradiation is 396nm.

5. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light according to claim 1, characterized in that: In step (2), the irradiation time in the photoreactor is 4, 12, 24, 36, 48, 72 and 96 hours.

6. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light as claimed in claim 5, characterized in that: In step (2), the Fe(II) / Fe(III) / Fe 总 , H2O2, PH, and ·OH instantaneous concentrations.

7. The method for promoting the aging of polystyrene microplastics based on Fe (III) self-Fenton reaction under light according to claim 6, characterized in that: After the reaction, the microplastic system was vacuum filtered, washed three times with deionized water, and dried.

8. Use of the method for promoting the aging of polystyrene microplastics based on the self-Fenton reaction of Fe (III) under light as described in any one of claims 1 to 7.

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