Method for accelerating aging of microplastics by promoting polystyrene microplastics to generate H2O2 through environmental factors

Abstract

The invention discloses a method for promoting polystyrene micro-plastics to generate H2O2 to accelerate aging of the micro-plastics by environmental factors, the polystyrene micro-plastics promote H2O2 generated in the light aging process to be converted into reactive oxygen species (ROS) under the combined action of humic acid (HA) and ionic strength through the action of optical radiation, so that the light aging of the micro-plastics is accelerated. In the presence of HA and salinity, the light aging of micro-plastics in a water environment becomes more complicated, and subsequent products influence the ecological toxicity of pollutants. HA and ionic strength adopted in the method can promote H2O2 to be converted into ROS, the photoaging effect of PS is finally promoted, H2O2 determination proves that H2O2 is consumed in an HA and salinity system, and XPS and FTIR determination proves that oxygen-containing functional groups on the surface of the micro-plastic are increased. In addition, electron paramagnetic resonance and quenching experiments prove that. OH is used as a dominant active substance for photoaging of micro-plastics.

Description

Technical Field

[0001] The invention belongs to the field of microplastic degradation, and specifically relates to a method in which environmental factors promote polystyrene microplastics to produce H2O2 to accelerate the aging of microplastics. Background Art

[0002] Microplastics are commonly found in rivers, lakes and seawater. Their aging is often affected by environmental factors, and the dissolved organic matter (DOM) and ionic strength in the water body will affect the aging process of microplastics. Photolysis is the most important process in the aging of MPs, and photolysis is divided into direct photolysis and indirect photolysis. Direct photolysis is the direct destruction of the chemical bonds of MPs by ultraviolet light, while indirect photolysis promotes the aging of MPs through active intermediates produced during the light-induced reaction. The generation of free radicals or active substances under light conditions accelerates the aging of PS, which may accelerate the transfer of electrons and accelerate O2 ·− and H2O2 as intermediates to ·OH, thereby increasing the content of ·OH and accelerating the aging of PS.

[0003] This study preliminarily explored the effect of the coexistence of DOM and ionic strength on MPs aging. Humic acid (HA) is one of the main components of DOM in water and has received widespread attention, so they were selected as representative dissolved organic matter. + It is the most common salinity ion in rivers, lakes and oceans, so we chose NaCl as an environmental factor to simulate natural water bodies. Due to the wide application of polystyrene (PS) microplastics, we chose PS microplastics as the research object. By detecting the changes in reactive oxygen species, functional groups and oxygen content, we explained the method of promoting the conversion of H2O2 into ROS to accelerate the photoaging of microplastics. Summary of the invention

[0004] In order to overcome the defects of the prior art, the present invention provides a method for accelerating the photoaging of polystyrene microplastics by promoting the conversion of H2O2 generated during photoaging into reactive oxygen species (ROS) under the combined action of humic acid (HA) and ionic strength through light radiation.

[0005] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for promoting polystyrene microplastics to produce H2O2 to accelerate the aging of microplastics, comprising the following steps: (1) first preparing a NaCl solution of a certain concentration to simulate the actual level of the transition of ionic strength from fresh water to seawater in the environment; (2) uniformly mixing a certain amount of original polystyrene microplastics and humic acid HA, and adding the mixture to the solution formed in step (1); and (3) performing a light radiation reaction.

[0006] Furthermore, the concentrations of NaCl solution were 0.05%, 2%, and 3.5%, and the concentration of humic acid HA was 10 mg / L.

[0007] Furthermore, the conditions for the photoirradiation reaction were irradiation with a 500 W mercury lamp.

[0008] Furthermore, the method specifically includes the following steps: 0.4 g of original polystyrene microplastics is uniformly mixed with 40 mL of 10 mg / L HA, and then 0 g, 0.02 g, 0.8 g, and 1.4 g of NaCl are respectively added into a quartz tube, and placed in a photochemical reactor equipped with a 500 W mercury lamp. The quartz tube is taken out after aging for 1, 3, 5, and 7 days. After the reaction is completed, the filtrate is filtered out through a 0.22 μm filter membrane and retained for subsequent characterization; and the suspension after the reaction is filtered, and repeatedly rinsed with deionized water for 3-5 times, and the aged PS is collected for subsequent testing and analysis.

[0009] The present invention also provides an application of the above-mentioned method for promoting polystyrene microplastics to produce H2O2 and accelerate the aging of microplastics.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) The HA and ionic strength used in the present invention can promote the conversion of H2O2 to ROS, and ultimately promote the photoaging of PS. This promotion is due to the conversion of HA to an excited state under light radiation, Cl - Converted to Cl2 ·- , accelerating the generation and consumption of ROS. Through the determination of H2O2, it was proved that H2O2 was consumed under the HA and salinity system, and the increase of oxygen-containing functional groups on the surface of microplastics was confirmed by XPS and FTIR. In addition, electron paramagnetic resonance and quenching experiments confirmed ·OH as the dominant active substance in the photoaging of microplastics. Therefore, in the presence of HA and salinity, the photoaging of microplastics in water environments becomes more complicated, and the subsequent products affect the ecotoxicity of pollutants.

[0011] (2) The present invention utilizes environmental factors to promote the photoaging of polystyrene microplastics without adding any exogenous catalysts.

[0012] (3) The method for accelerating the aging of microplastics provided by the present invention can also be directly applied in natural water environments, and is expected to promote the H2O2 generated during the aging process to degrade other pollutants in the water. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a particle size distribution diagram and an average particle size diagram of aged polystyrene microplastics in the present invention; Figure 2is the FTIR graph and CI value of the aged polystyrene microplastics in the present invention; Figure 3 is the XPS graph of aged polystyrene microplastics in the present invention; Figure 4 is a ROS graph of aged polystyrene microplastics of the present invention; Figure 5 It is a diagram of the generation of H2O2 in the present invention; Figure 6 This is a diagram of H2O2 production after quenching ·OH in the present invention. DETAILED DESCRIPTION

[0014] Example 1: 0.4 g of original PS-MPs was mixed with 40 mL of 10 mg / L HA, and then 0 g, 0.02 g, 0.8 g, and 1.4 g of NaCl were added to a quartz tube, respectively, and placed in a photochemical reactor equipped with a 500 W mercury lamp. The quartz tube was taken out after aging for 1, 3, 5, and 7 days. After the reaction was completed, the filtrate was filtered through a 0.22 μm filter membrane and kept for subsequent characterization. The suspension after the reaction was filtered and rinsed repeatedly with deionized water for 3-5 times, and the aged PS was collected for subsequent test analysis.

[0015] Figure 1 The morphological changes of the PS surface were observed using a SU8010 scanning electron microscope, and the changes in the average particle size of PS were obtained using the nano-measurement software of the SEM images. Figure 1 As shown in the figure, 79% of the unaged PS particle size is larger than 40 μm, the main particle size is 40-70 μm, and the average particle size is 54.12 μm. In the HA-NaCl system, with the increase of ionic strength, the main particle size of PS continues to decrease, and the average particle size of PS also gradually decreases with the increase of ionic strength.

[0016] Figure 2 The FTIR graph and CI value of the aged polystyrene microplastics in the present invention are shown in Figure 2. The functional groups of PS were analyzed using FT-IR. It was found that PS has a peak concentration of 1650-1800 cm –1 There is a carbonyl absorption band at 1734 cm. The carbonyl signal is generated by the overlapping absorption bands of aldehydes, ketones and carboxylic acid groups generated during the aging process. The carbonyl index (CI) is often used to indicate the aging degree of plastics. This patent uses 1734 cm -1 and 1450 cm -1The CI value was measured by the ratio of the absorbance of the PS to the light. After seven days of photoaging, the CI value increased significantly. In the HA-NaCl system, the CI value increased with the increase of ionic strength, indicating that the presence of HA promoted the photoaging of PS. Photoaging increases oxygen-containing groups such as carbonyl or hydroxyl groups, indicating that the presence of HA and ionic strength promotes the surface oxidation of PS, which may be due to the oxidation of the CH bond in PS to a C=O bond. This process increases the surface polarity of the microplastics, thereby increasing the hydrophilicity of water on the surface of the material.

[0017] Figure 3 This is the XPS graph of aged polystyrene microplastics in the present invention. A new O1s peak appeared in the aged PS, indicating the generation of oxygen-containing functional groups such as carboxyl and carbonyl. In order to explore the changes in the surface chemical composition of PS with different aging degrees, we quantitatively described the degree of oxidation of PS by calculating the oxygen-carbon ratio (O / C) of PS. The O / C ratio of the original PS is 0.018, and the oxygen-carbon ratios in the HA-NaCl system are 0.268, 0.284, 0.318, and 0.291, respectively. O / C is positively correlated with ionic strength, indicating that the presence of HA and ionic strength accelerates the aging of PS.

[0018] Figure 4 This is a diagram of ROS generation of aged polystyrene microplastics of the present invention. Four characteristic peak signals with intensities of 1:2:2:1 in TEMPO spin adducts, three characteristic peak signals with intensities of 1:1:1 in DMPO spin adducts, and EPR signals of DMPO-OOH adducts were detected, indicating that ·OH, 1 O2 and O2 ·− . And the signal intensity of the characteristic peak increases with the increase of ionic strength. In the solution without adding PS, ·OH was not detected in the solution. DOM can promote the generation of a large amount of ROS. We speculate that ionic strength may also promote the generation of a large amount of ROS, thereby accelerating the aging of PS.

[0019] Figure 5 HA can be converted into excited state HA ( 3 HA*), and further reacts with dissolved oxygen to generate H2O2, O2 ·− 、·OH、 1 O2. PS photoaging in water is classified as a free radical-related polymer chain reaction process, which is mainly affected by OH, 1 O2 and O2 ·− Under light irradiation, the original PS easily absorbs light energy and induces the formation of excited triplet states. 3 PS*, 3 PS* reacts easily and can transfer energy to dissolved oxygen and form 1O2. In addition, Cl - It may also be related to 3 PS* reacts to generate Cl2 with high reactivity and selectivity ·— The dissolved oxygen reacts with the electrons to generate superoxide radicals, which then react with H + The reaction can generate H2O2. The generated H2O2 can easily react with excess electrons as an electron acceptor and be converted into ·OH. ·OH is a non-selective free radical and the most important free radical that causes light aging of plastics. Due to the strong oxidizing and electrophilic properties of hydroxyl groups, ·OH undergoes a non-selective oxidation reaction almost instantly, and can attack coexisting organic matter through single-electron oxidation, H-abstraction, and addition of unsaturated CC bonds. With the increase of aging, the production of H2O2 gradually increases, but decreases with the increase of ionic strength. In the HA-NaCl system, we found that the generated H2O2 was almost consumed. Therefore, under the promotion of HA and NaCl, this part of H2O2 may be converted into ·OH, thereby accelerating the aging of PS, resulting in an increase in the oxygen-carbon ratio and CI value of PS, proving that the aging degree of PS is higher than that of the pure water system.

[0020] Figure 6 This is a graph of H2O2 production after quenching ·OH in the present invention. After adding the quencher, H2O2 is almost no longer produced, probably because the process of ·OH and H2O2 conversion is destroyed, H2O2 is continuously converted to ·OH, but due to the quenching effect of ·OH, H2O2 is excessively consumed. Compared with the system without adding the quencher, the CI value is significantly reduced, and it shows that in the HA-NaCl system, ·OH plays an important role in the aging process of PS.

Claims

1. A method for accelerating the aging of polystyrene microplastics by promoting the production of H2O2 by environmental factors, characterized in that: The following steps are involved: (1) First, prepare a NaCl solution of a certain concentration to simulate the actual level of ionic strength transition from fresh water to sea water in the environment; (2) Mix a certain amount of original polystyrene microplastics and humic acid HA evenly and add them to the solution formed in step (1); (3) Perform a light radiation reaction.

2. The method of accelerating the aging of polystyrene microplastics by promoting the production of H2O2 by environmental factors as claimed in claim 1, characterized in that: The concentrations of NaCl solution were 0.05%, 2% and 3.5%, and the concentration of humic acid HA was 10 mg / L.

3. The method of accelerating the aging of polystyrene microplastics by promoting the production of H2O2 by environmental factors as claimed in claim 2, characterized in that: The photoirradiation reaction was carried out under the conditions of irradiation with a 500 W mercury lamp.

4. The method of accelerating the aging of polystyrene microplastics by promoting the production of H2O2 by environmental factors as claimed in claim 3, characterized in that: The specific steps include: 0.4 g of original polystyrene microplastics was mixed evenly with 40 mL of 10 mg / L HA, and then 0 g, 0.02 g, 0.8 g, and 1.4 g of NaCl were added to a quartz tube, respectively, and placed in a photochemical reactor equipped with a 500 W mercury lamp. The quartz tube was taken out after aging for 1, 3, 5, and 7 days. After the reaction, the filtrate was filtered out through a 0.22 μm filter membrane and kept for subsequent characterization; and the suspension after the reaction was filtered and rinsed repeatedly with deionized water 3-5 times, and the aged PS was collected for subsequent testing and analysis.

5. An environmental factor as described in any one of claims 1 to 3 promotes the production of H by polystyrene microplastics 2 O 2 Accelerating microplastics Application of aging methods.

Images