Method for promoting photodegradation of coexisting ciprofloxacin and reducing ecological toxicity of coexisting ciprofloxacin through active oxygen generated by photoaging polystyrene microplastics

Abstract

The invention discloses a method for promoting photodegradation of coexisting ciprofloxacin and reducing ecological toxicity of the coexisting ciprofloxacin by active oxygen generated by photoaging polystyrene microplastics. The polystyrene micro-plastic PS-MPs is subjected to light irradiation to be aged to a certain degree, and surface physicochemical property changes of the PS micro-plastic PS-MPs are represented through SEM, FTIR and XPS. Especially in the coexistence of aged PS, the degradation rate (67%) of CIP is almost three times of the degradation rate (21%) of CIP in the presence of original PS. Quenching experiments and steady-state concentration experiments prove that the enhancement of CIP photodegradation by aged PS-MPs is related to reactive oxygen species (ROS) generated on the surfaces of the aged PS-MPs, and < 1 > O2 plays a leading role in the photodegradation process of CIP. Bacteria inhibition experiments prove that in the presence of aged PS, the biotoxicity of CIP is weakened. The method also shows a relatively strong application effect in actual water bodies.

Description

Technical Field

[0001] The invention relates to the field of pollutant degradation, and in particular to a method in which photo-aged polystyrene microplastics generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity. Background Art

[0002] In recent years, microplastics (MPs) have been detected in large quantities in aquatic environments as a new type of pollutant, posing a potential threat to ecosystems and biological health, and have attracted great attention from the international community. More importantly, MPs not only pollute the environment, but also adsorb other pollutants in the environment, become carriers of pollutants, and promote the transfer of pollutants. Studies have found that MPs are ubiquitous in aquatic organisms such as fish and shellfish. When MPs are ingested by organisms, the adsorbed pollutants accumulate in the organisms and enter the human body through biomagnification, becoming part of the food chain. Therefore, synergistic or cumulative toxicity may occur to the human body, leading to potential health hazards.

[0003] MPs exposed to the environment are susceptible to various environmental factors and undergo varying degrees of aging, such as thermal degradation, biodegradation, ultraviolet radiation, mechanical wear, and chemical oxidation. Compared with pristine MPs, aged MPs exhibit different environmental behaviors, including changes in surface charge, hydrophilicity, pollutant adsorption capacity, and ecotoxicity. Recently published studies have shown that aged MPs can act as light shielding agents and photosensitizers to affect the migration and transformation of coexisting pollutants. On the one hand, aged MPs produce more oxygen-containing functional groups, resulting in an increase in their absorbance in the ultraviolet region, thereby competing with coexisting pollutants for photon absorption, resulting in a decrease in the degradation of pollutants under the same irradiation conditions. On the other hand, studies have shown that under simulated sunlight irradiation, MPs mainly produce environmental persistent free radicals (EPFRs) through chemical bond cleavage, which further induces the generation of ROS, which may affect the phototransformation of coexisting pollutants. Aged MPs may have stronger photoactivity than pristine MPs because they produce more chromophores (such as oxidized groups such as carbonyl groups).

[0004] Ciprofloxacin (CIP) is a third-generation fluoroquinolone antibiotic that is widely used in veterinary medicine and humans due to its potent antimicrobial activity and good oral properties. However, most antibiotics are not completely biodegradable in humans or animals, and their residues are excreted into the environment, resulting in high antibiotic concentrations in the environment, even reaching ng / mg / L. Considering the widespread coexistence of MPs and antibiotics in natural water bodies, several studies have shown that polystyrene (PS) adsorbs CIP in the environment, however, the effect of MPs on CIP photodegradation is still unclear. This study expands the current understanding of the relationship between two emerging pollutants, MPs and antibiotics, in aquatic environments and provides important evidence to demonstrate the role of PS in the degradation of CIP. Summary of the invention

[0005] In view of the joint pollution caused by the coexistence of existing polystyrene microplastics PS-MPs and quinolone antibiotics in water environments, the present invention provides a method for promoting the photocatalytic degradation of coexisting CIP by aging PS-MPs. The present invention obtains PS with different aging degrees by irradiating PS-MPs with light for different times, and studies its influence on the photodegradation of coexisting CIP. The aged PS-MPs synthesized by the present invention can significantly promote the photodegradation of coexisting ciprofloxacin, while reducing its ecotoxicity in aquatic environments.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for photoaging polystyrene microplastics to generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity, comprising the following steps: uniformly dispersing polystyrene microplastics PS-MPs particles in deionized water, performing photoaging treatment, collecting the aged polystyrene microplastic powder by suction filtration, adding the powder to an aqueous solution containing ciprofloxacin CIP, not adjusting the solution pH to avoid the influence of ion factors, and then performing a photocatalytic reaction to promote the degradation of ciprofloxacin and reduce its ecotoxicity.

[0007] Furthermore, the photoaging treatment time was 6 h, 12 h, 36 h and 72 h, the reaction temperature was about 25 °C, and the irradiation intensity was 19.17 mw / cm 2 .

[0008] Furthermore, when the aged polystyrene microplastics were mixed with an aqueous solution containing ciprofloxacin CIP, the concentration of the aged polystyrene microplastics was 1 g / L and the concentration of ciprofloxacin was 10 mg / L.

[0009] Furthermore, the photocatalytic reaction was carried out by irradiation with a 500 W xenon lamp for 5 h.

[0010] The present invention also provides an application of a method for generating active oxygen from photo-aged polystyrene microplastics to promote the photodegradation of co-existing ciprofloxacin and reduce its ecotoxicity.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The aged PS-MPs used in the present invention can significantly enhance the photoconversion process of the commonly used antibiotic CIP. This enhancement is due to the active substances produced on the aged PS surface. FTIR and XPS confirmed the increase of oxygen-containing functional groups on the aged PS surface, which is an important reason for the generation of active substances. In addition, quenching experiments and steady-state concentration experiments confirmed 1 O 2 As the leading active substance that promotes the photodegradation of CIP. And through antibacterial experiments, it is confirmed that the toxicity of CIP to Escherichia coli after degradation by aged PS is greatly reduced. Therefore, when microplastics and pollutants coexist in the water environment, they can affect the photoconversion behavior of aquatic pollutants and reduce the ecotoxicity of pollutants.

[0012] 2. The present invention utilizes aged PS-MPs to generate 1 O 2 The photodegradation of coexisting CIP is promoted without adding any exogenous catalysts, and the coexisting antibiotics can be effectively degraded under light irradiation to reduce their ecotoxicity.

[0013] 3. The method of using MPs to degrade pollutants provided by the present invention not only realizes the recycling of resources to a certain extent, but can also be directly applied to the problem of antibiotic pollution in natural water environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 (a) SEM image and photograph of PS used in the present invention; (b) size distribution diagram; (c) average particle size diagram; Figure 2 FTIR and XPS graphs of PS in the present invention; Figure 3 is a graph showing the degradation of CIP in the presence of PS in the present invention; Figure 4 It is a diagram of the quenching experiment of CIP in the present invention; Figure 5 The PS in the present invention generates 1 O 2 and 3 Steady-state concentration diagram of PS*; Figure 6 is a comparative diagram of the toxicity of CIP after degradation of aged PS in the present invention; Figure 7 It is a diagram showing the degradation effect of the aged PS synthesized in the present invention on pollutants in actual water bodies. DETAILED DESCRIPTION

[0015] Example 1: Photoaging of polystyrene microplastics (PS-MPs) and their degradation of coexisting pollutants ciprofloxacin (CIP) 0.2 g of pristine PS-MPs was mixed evenly with 40 mL of deionized water and then placed in a photochemical reactor equipped with a 500 W mercury lamp. The quartz tube was taken out at 0, 6, 12, 36, and 72 h, respectively. After filtration and drying, the PS was collected for subsequent characterization and experiments, and labeled as Virgin-PS, PS-6 h, PS-12 h, PS-36 h, and PS-72 h, respectively.

[0016] 50 mg of PS-MPs with different aging degrees were added to a quartz tube containing 50 mL of 10 mg / L CIP solution, and magnetic stirring was maintained to obtain a suspension. A photoreactor equipped with a 500 W xenon lamp simulated sunlight irradiation was used for 5 hours. During the reaction, 1 mL of the solution was taken out at predetermined time intervals, and the solubility of CIP was detected by high performance liquid chromatography.

[0017] The morphology of PS was characterized using a field emission scanning electron microscope (FESEM, SU8010) with an accelerating voltage of 10.00 kV. Due to the poor conductivity of microplastics, the samples were gold-sprayed before analysis to improve their conductivity. The size distribution information of PS was collected by analyzing the corresponding SEM images using ImageJ software. SEM images are shown in Figure 1 As shown in a, the surface of the original PS is smooth, while the surface of the aged PS is rough, and even cracks and holes appear. Figure 2 bc reflects that the average particle size of PS gradually decreases with aging. The color change corresponding to PS aging is from the initial white to light yellow or even dark yellow ( Figure 1 a ).

[0018] Figure 2 a shows the FTIR spectrum of PS. - 1 The absorption peaks at 1494 and 1601 cm -1 The peaks at 3445 cm are due to CH deformation and skeleton vibration. As the aging time increases, the peaks at these positions gradually decrease, which means that aromatic ring deformation and chain scission may have occurred in PS during UV irradiation. -1 、1746 cm -1 、1725 cm -1 、1367 cm -1 and 1034 cm -1The peaks at 1601 cm -1 The absorption peak at 1725 cm -1 (C=O), 1367 cm -1 (C-OH) and 3445 cm -1 The -OH absorption peak at 1034 cm -1 The CO absorption peak at 1725 cm is also relatively strong, which means the accumulation of oxygen-containing functional groups on the surface of aged PS. -1 The absorption peak at 3445 cm-1 is enhanced, which means that new functional groups appear, mainly the stretching vibration of C=O. We also observed that with the extension of light aging time, the absorption peak at 3445 cm-1 increases. -1 The intensity of the absorption peak (-OH) near the ions increases, while the C=O oscillation becomes more and more obvious, which indicates that a large amount of C=O is formed on the surface of PS after photo-oxidation.

[0019] The surface chemical bonds of PS were determined by XPS spectroscopy. As shown in Figure 2c–d, in the C 1s spectra of Virgin-PS and PS-6 h, there are only three C 1s peaks with binding energies of 284.7, 285.1, and 284.7 eV and 291.5 eV, corresponding to aromatic CH, aliphatic CH, and π–π* vibrations, respectively. Figure 2 c shows that the peak at 291.5 eV (π-π*) gradually decreases and disappears during the aging process of PS-72 h. The decrease in the ratio of aromatic CH to aliphatic CH means the rupture of the aromatic ring on PS. Figure 2 It can be seen from the O 1s spectrum of d that the proportion of CO gradually increases with the aging of PS. After UV irradiation, the peak with a binding energy of 284.7 eV decreases, indicating that the carbon content of PS decreases after aging. The XPS findings of PS further show that the proportion of carbon on the PS surface decreases after light irradiation, first forming CO bonds, and with aging, some carbon bonds are converted to C=O bonds. Finally, a small part is converted to OC=O bonds. Figure 2 The full spectrum in b also shows that with aging, the content of C element gradually decreases and the content of O gradually increases, which indicates that dehydrogenation and oxidation occur in PS during the aging process, which is consistent with the results of FTIR.

[0020] Figure 3The degradation diagram of CIP in the presence of PS is shown. The photodegradation kinetics of CIP in the presence of PS with different aging degrees was studied, and a control group with only pollutants was set up to describe the direct photodegradation of CIP. Figure 3 As shown in a and b, the photodegradation of CIP conforms to the pseudo-first-order kinetic model, and the coexistence of PS promotes the photodegradation of CIP. The degradation rate and degradation rate constant of the control group are 10.02% and 0.0276 h, respectively. -1 However, after adding PS, the degradation rates of CIP increased to 21.14% (Virgin-PS) and 66.65% (PS-72 h), and the related rate constants increased to 0.0484 h -1 and 0.2079 h -1 , which is equivalent to an increase of 2 and 3.3 times, respectively. The above results show that PS inevitably coexists with antibiotics and has a significant impact on the photodegradation of antibiotics.

[0021] Example 2: Quenching experiment of PS and CIP coexistence system We demonstrated the function of each ROS by quenching experiments, adding isopropyl alcohol (IPA), furfuryl alcohol (FFA), and superoxide dismutase (SOD) to scavenge the ·OH, 1 O 2 and O 2 ·- Virgin-PS, PS-36 h and PS-72 h were selected as representative coexisting PS in the free radical quenching experiment. Figure 4 As shown in Figures ac, the added free radical scavengers basically inhibited the photodegradation of CIP to varying degrees, indicating that the indirect photolysis of CIP by ROS is more significant. Among them, the inhibitory effect of adding IPA and SOD on the degradation of CIP is relatively weak. On the contrary, whether it is Virgin-PS, PS-36 h or PS-72h, the addition of FFA can significantly inhibit the degradation of CIP. For example, as reflected in k obs The inhibition values ​​of Virgin-PS were as follows: -1 Down to 0.0363 h -1 , PS-72 h from 0.1820 h -1 Down to 0.0743 h -1 , with a decrease of about 2 times. These results indicate that there are differences in the effects of pristine and aged PS on CIP degradation, which may be related to the physicochemical properties of PS with different degrees of aging, and therefore the amount of ROS generated is also different. Figure 4 df shows that by comparing the degradation rates before and after adding the scavenger, the contribution of the three free radicals can be quantified. 1 O2 and O 2 ·- The contribution rates of PS-72 h were 8.63%, 30.87% and 6.70%, respectively, indicating that 1 O 2 It is the main free radical that plays a major role in the reaction system.

[0022] Example 3: PS production 1 O 2 Steady-state concentration experiment The above quenching experiments revealed that the key role of ROS in the coexistence system can be attributed to 1 O 2 Studies have shown that aged PS containing carbonyl structures extracts light energy and is excited into triplet PS ( 3 PS*), and then transfers the energy to dissolved O 2 ,produce 1 O 2 Therefore, by using 5 mM FFA and 0.1 mM TMP as 1 O 2 and 3 The probe compound of PS* was added into the system to detect the generation of different aged PS (1 g / L) 1 O 2 and 3 The concentration of PS* further clarified 1 O 2 In order to avoid competitive interference of pollutants on free radicals, the reaction was carried out in a system without coexisting pollutants and extended to 12 hours to observe more obvious phenomena. Figure 5 As shown in a and b, PS release 1 O 2 and 3 The concentration of PS* is expressed as the amount of FFA and TMP loss, respectively. The photoconversion rate constant k of FFA obs From the original PS 0.0516 h -1 It jumped to 0.3008-0.3254 h of aged PS -1 .from Figure 5 In c, we can observe the PS produced 1 O 2 and 3 The obvious difference between PS*, more 1 O 2 and 3 PS* is generated by aged PS, and higher 1 O 2 and 3The PS* concentration corresponds to the photodegradation rate of CIP. 1 O 2 and 3 The formation of PS* may be related to the high absorbance of aged PS in the near-UV to visible light region. Figure 5 As can be seen in d, TMP was used as a probe to capture the PS-72h and CIP coexistence system. 3 After PS*, it was observed that the degradation rate of CIP was significantly reduced. 2 It also inhibits the degradation of CIP. Therefore, it can be inferred that 3 PS* is generated by reaction with oxygen via energy transfer 1 O 2 Considering 1 O 2 High reactivity with CIP, 1 O 2 It can react effectively with CIP as an electrophile, resulting in the cleavage of the piperazine ring. This suggests that aged PS plays an important role in the photoconversion of coexisting pollutants, among which 1 O 2 Play a leading role.

[0023] Example 4: Toxicity analysis and actual water application We detected Escherichia coli DH5α ( E. coli The growth of DH5α was evaluated in the presence of PS-72h after 5 h of simulated light exposure. The experiment was divided into four groups: (1) blank group: 5 mL Luria-Bertani (LB) medium and 5 mL sterile water; (2) control group: 5 mL LB, 5 mL sterile water and 1 mL Escherichia coli suspension; (3) CIP: 5 mL LB, 5 mL CIP solution (10 mg / L) and 1 mL Escherichia coli suspension; (4) PS-72h: 5 mL LB, 5 mL CIP supernatant after 5 h of photodegradation in the presence of PS-72h and 1 mL Escherichia coli suspension. Three parallel samples were set up for each group and cultured at 37℃ for 24 h. Finally, the optical density 600 value (OD600) of DH5α was measured at 600 nm by UV-visible spectrophotometry to quantify it. Figure 6 It showed that the activity of DH5α cultured with CIP stock solution was significantly inhibited, while the growth of DH5α in CIP solution after photodegradation by PS-72 h was comparable to that of the control group, indicating that the ecotoxicity of CIP was significantly reduced after photocatalytic degradation by aged PS.

[0024] PS and CIP are two major pollutants coexisting in natural water bodies, so it is crucial to evaluate the interaction between PS and CIP in real water environments. Therefore, we collected water from Weihe River in Xinxiang City, Henan Province, and studied the degradation efficiency of PS to CIP in different water matrices (represented by PS-72 h) under simulated sunlight. Figure 7 a shows that in the three different water environments, CIP can achieve relatively good degradation effects in the presence of PS-72 h. As shown in Figure 7b, without the addition of PS-72 h, the self-degradation rates of CIP in the three water bodies were all around 10%. After adding PS-72 h, the degradation rates of CIP were tap water (45%) > Weihe River water (44%) > deionized water (38%). The reason why the degradation rate of CIP in the actual water sample is slightly higher than that of deionized water may be that there are more ions and humus in natural water bodies that affect the reaction. This shows that the coexistence of MPs also has an important influence on the photodegradation of CIP in actual water bodies.

Claims

1. A method for photoaging polystyrene microplastics to generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity, characterized in that: The following steps are involved: Polystyrene microplastic PS-MPs particles were evenly dispersed in deionized water and subjected to photoaging treatment. The aged polystyrene microplastic powder was collected by filtration and added to an aqueous solution containing ciprofloxacin CIP. To avoid the influence of ionic factors, the pH of the solution was not adjusted. Then a photocatalytic reaction was carried out to promote the degradation of ciprofloxacin and reduce its ecotoxicity.

2. The method of claim 1, wherein the photo-aged polystyrene microplastics generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity, characterized in that: The photoaging treatment time was 6 h, 12 h, 36 h and 72 h, the reaction temperature was about 25 °C, and the irradiation intensity was 19.17 mw / cm 2 .

3. The method of claim 2, wherein the photo-aged polystyrene microplastics generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity, characterized in that: When the aged polystyrene microplastics were mixed with an aqueous solution containing ciprofloxacin CIP, the concentration of the aged polystyrene microplastics was 1 g / L and the concentration of ciprofloxacin was 10 mg / L.

4. The method of claim 3, wherein the photo-aged polystyrene microplastics generate active oxygen to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity, The photocatalytic reaction was carried out by irradiation with a 500 W xenon lamp for 5 h.

5. Use of the method as described in any one of claims 1 to 4 for generating reactive oxygen species from photoaged polystyrene microplastics to promote the photodegradation of coexisting ciprofloxacin and reduce its ecotoxicity.

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