Method for evaluating persistent free radical reaction activity difference with carbon and oxygen as centers and application

Abstract

The invention discloses a method for evaluating the reaction activity difference of persistent free radicals with carbon and oxygen as the center and application, and belongs to the technical field of environmental effect research of organic pollutants. The method comprises the following steps: screening and calcining an aluminum oxide, respectively mixing the aluminum oxide with an anthracene cyclohexane solution and a catechol cyclohexane solution, reacting under the dark room-temperature condition, mixing the prepared durable free radical model particles taking carbon and oxygen as centers with phenol pollutants, and carrying out normal-temperature dark reaction to obtain the durable free radical model particles. After methanol ultrasonic extraction, the degradation effect is analyzed by adopting high performance liquid chromatography. According to the method, the degradation difference of phenol pollutants is compared, the generation of EPFRs particle reactive oxygen species (ROS) is detected by an EPR technology, and accurate evaluation of the reaction activity difference of signal intensity of. O2 <-> and. OH generated by persistent free radicals taking carbon and oxygen as the center is realized; a directional evaluation system of the persistent free radical reaction activity difference with carbon and oxygen as the center is established for the first time, the bottleneck that the activity is reflected only by depending on the apparent concentration of persistent free radicals in traditional research is broken through, and the technical blank of accurate evaluation of the persistent free radical reaction activity is filled.

Description

Technical Field

[0001] The present invention belongs to the research field of environmental effects of organic pollutants, and relates to a method and application for evaluating the difference in the reactivity of persistent free radicals centered on carbon and oxygen. Background Art

[0002] In recent years, environmentally persistent free radicals (EPFRs), as a new type of environmental pollutant, have attracted extensive attention from researchers due to their unique properties and significant toxic effects. Compared with short-lived free radicals (such as ·OH, 10 -9 seconds), the lifespan of EPFRs under natural conditions can be as long as several minutes to several days, or even several months. It has been found that EPFRs widely exist in environmental media such as atmospheric particulate matter and soil, can cause oxidative stress to organisms, damage DNA, and trigger diseases such as lungs and cardiovascular diseases. In addition to the toxic effects of EPFRs, the transformation of organic pollutants caused by the reactivity of EPFRs has attracted extensive attention from researchers.

[0003] EPFRs are divided into carbon-centered and oxygen-centered EPFRs according to the atomic position of the single electron. Usually, they can be judged according to the g factor. Those with a g factor lower than 2.0030 are carbon-centered EPFRs, while those with a g factor higher than 2.0040 are oxygen-centered EPFRs. The type of the parent organic pollutant will determine the type of EPFRs generated, and the difference in the reactivity of different types of EPFRs (such as carbon-centered and oxygen-centered EPFRs) is also an overlooked link in the current research on the environmental effects of EPFRs.

[0004] Currently, the apparent concentration of EPFRs is usually used to describe its reactivity in the transformation of organic pollutants, but the difference in the reactivity of different types of EPFRs is ignored, which hinders the accurate assessment of the environmental effects of EFPRs. Therefore, it is of great significance to develop a method that is simple to operate, mild in conditions, and can accurately evaluate the difference in the reactivity of persistent free radicals centered on carbon and oxygen for accurately evaluating the environmental effects of EPFRs. Summary of the Invention

[0005] Aiming at the above technical problems, the purpose of the present invention is to provide a method for evaluating the difference in the reactivity of persistent free radicals centered on carbon and oxygen, which is used to solve the problem that there is a lack of systematic evaluation methods for the reactivity difference of persistent free radicals centered on carbon and oxygen in the environment; the present invention evaluates the difference in the reactivity of carbon-centered and oxygen-centered EPFRs by generating carbon-centered and oxygen-centered EPFRs particles and comparing the difference in their degradation efficiency of phenolic compounds.

[0006] To achieve the object of the present invention, the specific solution of the present invention is as follows:

[0007] (1) Pretreatment of aluminum oxide: Screen and calcine the aluminum oxide to obtain a loading material, dehydrate the surface of the aluminum oxide, and expose as many sites as possible for loading pollutants;

[0008] (2) Preparation of EPFRs: The loading material obtained in step (1) is respectively mixed with anthracene cyclohexane solution and catechol cyclohexane solution by shaking in a container with a polytetrafluoroethylene liner. The mixed solution is placed in a dark constant temperature oven for reaction, and the cyclohexane in the mixed solution is purged with a nitrogen purging instrument. After drying, carbon-centered environmentally persistent free radical particles EPFRs and oxygen-centered environmentally persistent free radical particles EPFRs are respectively obtained;

[0009] (3) Degradation of pollutants: Mix phenolic pollutants with the carbon-centered and oxygen-centered environmentally persistent free radicals in step (2), and carry out the reaction under light-shielded and normal temperature conditions;

[0010] (4) Extraction and analysis: Add methanol to the reaction system in step (3) for ultrasonic extraction. After filtration, the concentration of phenolic pollutants is detected by high performance liquid chromatography (HPLC), and the difference in the reaction activities of carbon-centered and oxygen-centered persistent free radicals is evaluated by comparing the levels of phenolic pollutant concentrations.

[0011] Preferably, the aluminum oxide in step (1) is silicon-modified aluminum oxide (a commercially available product), and the aluminum oxide is characterized by a high specific surface area, rich surface active sites and excellent chemical stability.

[0012] Preferably, in step (1), the aluminum oxide is screened to 100-200 mesh, a 100-200 mesh standard sieve is used, the calcination is carried out in a muffle furnace, the calcination temperature is 400-500 °C, and the calcination time is 3-4 h.

[0013] Preferably, in step (2), the loading material is mixed with the anthracene cyclohexane solution and the catechol cyclohexane solution at a solid-liquid ratio of 300 mg: 2 mL. The concentrations of the anthracene cyclohexane solution and the catechol cyclohexane solution are 100-400 mg / L, the reaction temperature is 20-25 °C, the reaction time is 7-9 hours, the drying temperature is 30-40 °C, and the drying time is 1-2 h.

[0014] Preferably, in step (3), the phenolic pollutants are configured into an aqueous solution with a concentration of 20 mg / L, and the solid-liquid ratio with the EPFRs particles is 100 mg: 1 mL, and the reaction time under light-shielded and normal temperature conditions is 1-3 h.

[0015] Preferably, in step (4), the C18 reversed-phase column (250 mm × 4.6 mm, 5 μm) is used as the chromatographic column for detecting the concentration of phenolic pollutants by high-performance liquid chromatography, wherein the mobile phase is methanol-water with a volume ratio of 65:35 to 80:20, the detection wavelength is 270 - 282 nm, the flow rate of the mobile phase is 1.0 mL / min, and the column temperature is 35°C.

[0016] Preferably, the application of the method of the present invention in degrading phenolic pollutants is to evaluate the environmental effects of persistent free radicals by comparing the degradation rate differences of phenolic pollutants by carbon-centered persistent free radicals and oxygen-centered persistent free radicals. The results show that the degradation efficiency and reactivity of carbon-centered free radicals are higher than those of oxygen-centered free radicals.

[0017] Compared with the prior art, what are the advantages of the present invention:

[0018] (1) By constructing a reaction system of anthracene / catechol as an organic precursor and aluminum oxide as a model material, this method optimizes the solid-liquid ratio (300 mg:2 mL) of the aluminum oxide-supported material and the anthracene / catechol precursor mother liquor and its dark reaction conditions (20 - 25°C, 7 - 9 h), significantly improving the operation convenience and experimental repeatability. At the same time, combined with methanol ultrasonic extraction and high-performance liquid chromatography (HPLC) for accurate analysis, by using EPR technology to detect the superoxide anion radical (·O2 - ) generated by EPFRs particles mediating reactive oxygen species (ROS) in the liquid-phase reaction. In addition, the environmentally friendly characteristics of aluminum oxide and the high-activity advantages of carbon-centered free radicals ensure the reliability of the degradation efficiency evaluation, providing a new strategy with both scientific value and engineering application potential for the treatment of organic pollutants and the development of environmental catalytic materials.

[0019] (2) By screening and calcining aluminum oxide for simplified pretreatment and the directional reaction of the anthracene / catechol precursor, the present invention clarifies the high-efficiency degradation characteristics of carbon-centered free radicals with the degradation rate of phenolic pollutants, and realizes the controllable preparation of carbon / oxygen-centered persistent free radicals for the first time.

[0020] (3) The method of the present invention is simple to operate and has mild conditions, and can accurately evaluate the difference in the reaction activities of persistent free radicals centered on carbon and oxygen, which is of great significance for accurately evaluating the environmental effects of EPFRs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the experimental process of the present invention.

[0022] Figure 2 It is a signal diagram of the persistent free radicals obtained in Example 3.

[0023] Figure 3It is a diagram of superoxide radicals mediated by persistent free radicals in a liquid phase environment in Example 4.

[0024] Figure 4 It is a diagram of hydroxyl radicals mediated by persistent free radicals in a liquid phase environment in Example 4.

[0025] Figure 5 It is a diagram of the degradation rate of hydroquinone by carbon and oxygen persistent free radical pairs obtained in Application Example 1.

[0026] Figure 6 It is a degradation curve diagram of hydroquinone by carbon-centered persistent free radicals obtained in Application Example 1 over time.

[0027] Figure 7 It is a mechanism diagram of the degradation of hydroquinone by carbon-centered persistent free radicals in Application Example 1. Detailed implementation manners

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0029] Example 1

[0030] A preparation method of carbon-centered environmentally persistent free radicals includes the following steps:

[0031] (1) After passing aluminum oxide through a 100-mesh sieve, it is placed in a muffle furnace and calcined at 450 °C for 4 h to obtain a loading material, achieving the purpose of dehydrating the surface of aluminum oxide and exposing as many sites as possible for pollutant loading.

[0032] (2) Anthracene is dissolved in cyclohexane to obtain a 100 mg / L anthracene-cyclohexane mother liquor.

[0033] (3) 600 mg of the loading material is mixed with 2 mL of the anthracene-cyclohexane mother liquor in a 40 mL glass bottle with a polytetrafluoroethylene-lined screw cap, and oscillated on a vortex mixer for 40 s to mix evenly.

[0034] (4) The mixed solution in step (3) is placed in a dark and dry environment at 25 °C and cultured for 7 h, and the cyclohexane in the mixed solution is purged with a nitrogen purging instrument to obtain a dry powder, which is the carbon-centered environmentally persistent free radical particles.

[0035] Example 2

[0036] A preparation method of oxygen-centered environmentally persistent free radicals includes the following steps:

[0037] (1) The aluminum oxide was sieved through a 200-mesh sieve and then calcined in a muffle furnace at 400 °C for 4 h to obtain the supported material, aiming to dehydrate the surface of the aluminum oxide and expose as many sites as possible for pollutant loading.

[0038] (2) Catechol was dissolved in cyclohexane to obtain a 400 mg / L catechol cyclohexane stock solution.

[0039] (3) 600 mg of the supported material was mixed with 2 mL of the catechol cyclohexane stock solution in a 40 mL glass bottle with a polytetrafluoroethylene-lined screw cap and shaken on a vortex mixer for 40 s to mix evenly.

[0040] (4) The mixed solution obtained in step (3) was placed in a dark and dry environment at 25 °C for 7 h, and the cyclohexane in the mixed solution was purged with a nitrogen purging instrument to obtain a dry powder, which was the oxygen-centered environmentally persistent free radical particles.

[0041] Example 3

[0042] Detection of the signal intensity of carbon- and oxygen-centered environmentally persistent free radicals (EPFRs), the operating steps are as follows;

[0043] Weighed the dry powders of the carbon- and oxygen-centered environmentally persistent free radical particles prepared in Examples 1 and 2 into quartz tubes of an electron paramagnetic resonance spectrometer (EPR) respectively, and carried out the detection of the signal intensity of environmentally persistent free radicals (EPFRs). The specific measurement parameters of the equipment were: microwave power 10 mW, magnetic field center 3518 G, scanning width 100 G, scanning time 83.97 ms, scanning times 1 time, microwave power 9.86 GHz, amplitude modulation 3 G, resolution 1024 points, receiving gain 3.17×10 4 , time constant 40.96 msm, and the test results are as Figure 2 shown.

[0044] From Figure 2 it can be seen that the g value of the EPFRs generated from catechol is 2.0043, indicating that the generated is oxygen-centered persistent free radicals; the g value of the EPFRs generated from catechol is 2.0043, indicating that the generated is oxygen-centered persistent free radicals.

[0045] Example 4

[0046] Monitoring the generation of reactive oxygen species (ROS) mediated by carbon- and oxygen-centered persistent free radical EPFRs particles in liquid-phase reactions, the operating steps include the following:

[0047] (1) Prepared 0.2 M DMPO solutions using phosphate buffer (PBS) and dimethyl sulfoxide (DMSO) as solvents respectively.

[0048] (2) Mix 20 mg of sample particles with 200 μL of freshly prepared DMPO solution in an EP tube. After oscillating for 40 s using a vortex mixer (XH-D, Jiuping Instruments), aspirate 50 μL of the mixed solution using a capillary tube for EPR spectroscopy analysis.

[0049] (3) Detect the generation of reactive oxygen species (ROS) mediated by EPFRs particles in the liquid-phase reaction through electron paramagnetic resonance (EPR) technology. The superoxide radicals generated by carbon-centered persistent free radicals in the liquid-phase environment are as Figure 3 shown, and the hydroxyl radicals generated by oxygen-centered persistent free radicals in the liquid-phase environment are as Figure 4 shown.

[0050] Using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin trap to monitor the superoxide anion radicals (·O2 - ) generated by carbon-centered persistent free radicals in the liquid-phase environment and the hydroxyl radicals (·OH) generated by oxygen-centered persistent free radicals in the liquid-phase environment, it was found that the signal intensities of the superoxide anion radicals (·O 2- ) and superoxide anion radicals (·OH) generated by carbon-centered persistent free radicals are significantly greater than those of oxygen-centered persistent free radicals.

[0051] Application Example 1

[0052] The degradation of hydroquinone by environmental persistent free radicals centered on carbon and oxygen includes the following steps:

[0053] Prepare an aqueous solution of hydroquinone at 20 mg / L and mix it with the environmental persistent free radical particles centered on carbon and oxygen prepared in Examples 1 and 2. The environmental persistent free radical particles centered on carbon and oxygen and the hydroquinone solution are mixed at a solid-liquid ratio of 100 mg:1 mL. React under dark and room temperature conditions for 3 h, then add methanol to the reaction system for ultrasonic extraction. After filtration, detect the concentration of hydroquinone by high performance liquid chromatography (HPLC). The results are as Figure 5 shown.

[0054] From Figure 5 it can be seen that carbon-centered persistent free radicals have specific degradation ability for the target pollutant hydroquinone, while oxygen-centered persistent free radicals show relatively weak degradation activity for hydroquinone, verifying that carbon-centered persistent free radicals have stronger degradation efficiency and higher reactivity for hydroquinone, which is consistent with the ROS signal intensity measured in Example 3; from Figure 6 it can be seen that the degradation rate of carbon-centered persistent free radicals for the target pollutant hydroquinone is relatively high within 3 h.

[0055] Combining Example 4 with Application Example 1, a reasonable transformation mechanism for the degradation of hydroquinone by carbon-centered environmental persistent free radicals is inferred as follows: Figure 7 As shown in the figure, in the system of hydroquinone degradation by carbon-centered persistent free radicals, the oxidation reaction of hydroquinone presents a typical multi-stage free radical chain reaction mechanism. The reaction mechanism starts with the single electron transfer of anthracene molecules induced by the surface defect site of aluminum oxide to form a carbon center, which then reacts with molecular oxygen to generate the key active species superoxide radical (·O2 - ); superoxide radicals as electron acceptors preferentially capture the π electrons of the phenolic hydroxyl group of hydroquinone to generate semiquinone free radical intermediates, which are converted into stable p-benzoquinone structures through deprotonation and intramolecular rearrangement. Finally, the quinone products react with anthracene derivatives to form naphthoquinone complexes through addition reactions. This method verifies that the present invention establishes a reaction system with anthracene / catechol as organic precursors and aluminum oxide as model materials to obtain superoxide anion free radicals (·O2 - ) is feasible for degrading phenolic pollutants, while the oxygen-centered environmental persistent free radicals are relatively weak, but it can still be used as a method to evaluate the differences in the activity of environmental persistent free radicals.

[0056] In summary, the present invention can evaluate the difference in free radical reactivity by comparing the difference in the degradation efficiency of carbon- and oxygen-centered environmental persistent free radicals on phenolic substances, thereby obtaining a method for evaluating the difference in the reactivity of carbon- and oxygen-centered persistent free radicals.

[0057] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen, characterized in that: The following steps are involved: (1) Aluminum oxide pretreatment: screening and calcining aluminum oxide to obtain supported materials; (2) Preparation of EPFRs: The supported material obtained in step (1) is mixed with anthracene cyclohexane solution and catechol cyclohexane solution respectively, and the mixed solution is placed in the dark at room temperature for reaction, and then purged with nitrogen and dried to obtain carbon- and oxygen-centered persistent free radical particles respectively; (3) Pollutant degradation: mixing the phenol pollutant solution with the carbon- and oxygen-centered persistent free radical particles in step (2) and reacting them in a dark and room temperature environment; (4) Extraction analysis: Methanol is added to the reaction system in step (3) for ultrasonic extraction, and the concentration of phenolic pollutants is detected after filtration.

2. The method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen according to claim 1, characterized in that: The aluminum oxide is silicon-modified aluminum oxide.

3. The method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen according to claim 1, characterized in that: In step (1), the aluminum oxide is sieved to 100-200 meshes, the calcination temperature is 400-500° C., and the calcination time is 3-4 hours.

4. The method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen according to claim 1, characterized in that: In step (2), the load material is mixed with anthracene cyclohexane solution and catechol cyclohexane solution at a solid-liquid ratio of 300 mg:2 mL, and the concentrations of the anthracene cyclohexane solution and catechol cyclohexane solution are 100-400 mg / L.

5. The method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen according to claim 1, characterized in that: The phenolic pollutants in step (3) are prepared into a 20 mg / L aqueous solution, and the solid-liquid ratio of the phenolic pollutant aqueous solution to the carbon- and oxygen-centered persistent free radical particles is 100 mg: 1 mL.

6. The method for evaluating the difference in reactivity of persistent free radicals centered on carbon and oxygen according to claim 1, characterized in that: The concentration of phenolic pollutants in step (4) is detected using a high performance liquid chromatography column of a C18 reverse phase column, wherein the mobile phase is a methanol-water volume ratio of 65:35 to 80:20, the detection wavelength is 270-282 nm, the mobile phase flow rate is 1.0 mL / min, and the column temperature is 35°C.

7. Application of the method according to claim 1 in degrading phenolic pollutants, characterized in that: The environmental effects of persistent free radicals were evaluated by comparing the degradation rates of phenol pollutants by carbon-centered persistent free radicals and oxygen-centered persistent free radicals. The degradation efficiency and reaction activity of carbon-centered free radicals were higher than those of oxygen-centered free radicals.

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