Method for researching air floatation action mechanism of natural organic matters on micro-plastics

Abstract

The invention provides a method for researching an air floatation action mechanism of a natural organic matter on micro-plastic. The method comprises the following steps: preparing a micro-plastic probe loaded with the natural organic matter, testing nano-mechanical data of the micro-plastic probe and bubbles, and analyzing the nano-mechanical data. According to the invention, a colloid probe AFM technology and SRYL theoretical simulation are combined for the first time, and the method is applied to research on a micro-plastic air floatation action mechanism by natural organic matters. The method comprises the following steps: preparing a micro-plastic probe loaded with natural organic matters, detecting the interaction between the micro-plastic probe and micron-sized bubbles in a water-phase system, substituting nano-mechanical data into an SRYL theoretical model, quantifying contributions and key parameters of different separation pressures, and carrying out visual analysis on the deformation condition of the surfaces of the bubbles. According to the research method, the research period can be greatly shortened, the interaction between the micro-plastic and the bubbles and the influence mechanism of the natural organic matter can be rapidly predicted by flexibly changing the simulation environment conditions, and theoretical support and guidance can be provided for micro-plastic air flotation research.

Description

Technical Field

[0001] The present invention belongs to the technical field of microplastic air flotation, and particularly relates to a research method for the mechanism of the effect of natural organic matter on microplastic air flotation. Background Art

[0002] Microplastics are called "marine PM2.5". Due to their small size, they can form a stable colloidal system in water, posing a great threat to the ecological environment and human health. Air flotation is one of the methods for removing microplastics. By stirring in water to generate highly dispersed micron-sized bubbles, hydrophobic solid particles in the surrounding can be adsorbed, forming flocs with an apparent density less than that of water, which can float to the liquid surface to form foam scum and then be scraped off. However, due to the large specific surface area of microplastics, they are extremely likely to adsorb various substances in the surrounding environment, thus increasing the difficulty of microplastic air flotation. Among them, various natural organic matters are contained in environments such as the ocean, lakes, and soil. These substances are extremely likely to adsorb on the surface of microplastics and form an "ecological corona", thereby changing the surface physical and chemical properties of microplastics and their air flotation effect. Since microplastic air flotation is affected by various complex factors, such as the properties of the aqueous solution, the properties of microplastics, the collision speed, etc., the mechanism of the effect of natural organic matter on microplastic air flotation is not yet clear. Therefore, establishing a research method for the mechanism of the effect of natural organic matter on microplastic air flotation has important scientific significance for improving the efficiency of microplastic air flotation and alleviating the problem of microplastic pollution.

[0003] Atomic force microscopy (AFM) technology is a nano-mechanical detection technology. By constructing micron-sized spherical particles at the end of the probe cantilever beam, it can be used to detect the interaction force between microplastics and bubbles in the microplastic air flotation system. However, previous research on the interaction force between microplastics and bubbles has remained at the description of the overall resultant force, and has not carried out precise quantitative analysis on the various surface and interface interaction forces contained therein. The main difficulty lies in that the bubble will deform when subjected to an external force, causing great difficulties in accurately calculating the absolute distance between the colloidal probe and the bubble and quantifying the nano-mechanical data. Professor Derek Y.C Chan established a Stokes-Reynold-Young-Laplace (SRYL) simulation calculation model. Combining with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the nano-mechanical data between the bubble and the solid plane was fitted, and the force-distance function relationship of various surface forces was determined. However, there has been no relevant report on the nano-mechanical analysis between solid particles and bubbles. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The present invention proposes a research method for the mechanism of the effect of natural organic matter on microplastic air flotation to solve the technical problem of how to perform nano-mechanical analysis between solid particles loaded with natural organic matter and bubbles.

[0006] (2) Technical solution

[0007] To solve the above technical problems, the present invention proposes a research method for the mechanism of the air flotation effect of natural organic matter on microplastics, and the research method includes the following steps:

[0008] S1. Prepare a microplastic probe loaded with natural organic matter;

[0009] S2. Test the nanomechanical data of the microplastic probe and the bubble

[0010] S2-1. Hydrophobically treat the glass slide at the bottom of the liquid cell for AFM testing, and then slowly inject air into the bottom of the liquid cell containing the aqueous solution through an ultra-fine glass pipette to generate bubbles and reach a stable state where the bubbles can stably adsorb at the bottom of the liquid cell and do not shake with the liquid;

[0011] S2-2. Immerse the microplastic probe loaded with natural organic matter in the aqueous solution of the liquid cell and move it above the bubble. Under a constant force load, control the microplastic probe to approach the bubble and then withdraw it to complete the acquisition of a set of nanomechanical data;

[0012] S3. Nanomechanical data analysis

[0013] Analyze the nanomechanical interaction between the microplastic probe loaded with natural organic matter and the bubble based on the SRYL theoretical model, including calculating the relationship between the separation distance between the microplastic probe and the bubble and time through the Stoke-Reynolds equation shown in Equation (1), analyzing the deformation of the water film between the microplastic probe and the bubble, calculating the relationship between the degree of water film deformation and the external force and Laplace force through the Young-Laplace equation shown in Equation (2), and analyzing the influence of hydrodynamic pressure and separation pressure on bubble deformation:

[0014]

[0015]

[0016] where h(r,t) is the separation distance between the microplastic probe and the bubble; μ is the viscosity of the aqueous solution; r is the distance in the direction connecting the centers of the bubble and the microplastic probe. When the microplastic probe contacts the bubble, the value of r is defined as 0; t is time; p(r,t) is the excess hydrodynamic pressure in the water film relative to the bulk solution; γ is the surface tension of the aqueous solution, R b , R pLet \(r\) be the radius of the bubble and the microplastic probe, and \(\Pi[h(r,t)]\) be the total separation pressure between the microplastic probe and the bubble, that is, the interaction force per unit area between the microplastic probe and the bubble in the aqueous solution, including van der Waals force, double-layer force, and hydrophobic force; \(\Pi[h(r,t)]\) is an unknown quantity, and the others are known quantities.

[0017] Further, step S1 specifically includes the following steps:

[0018] S1-1. Immerse the plastic microspheres in the natural organic matter solution, and then obtain the plastic microspheres with natural organic matter loaded on the surface through centrifugation and drying.

[0019] S1-2. Redisperse the plastic microspheres with natural organic matter loaded in the solvent to obtain a dispersion. Use a dropper to suck the dispersion and transfer it onto a glass slide, and naturally dry to remove the solvent to obtain a glass slide with plastic microspheres loaded.

[0020] S1-3. Under the AFM integrated optical microscope, manipulate the tip-less probe cantilever to make the probe cantilever approach the glass slide coated with the adhesive, and dip a small amount of adhesive at the end of the cantilever.

[0021] S1-4. Replace the glass slide coated with the adhesive with the glass slide with plastic microspheres loaded, manipulate the end of the cantilever to pick up a plastic microsphere, and dry it to make a microplastic probe loaded with natural organic matter.

[0022] Further, in step S1-1, the plastic microsphere materials include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, and derivatives of the above polymers.

[0023] Further, in step S1-2, the natural organic matter solution includes humic acid, alginic acid, tannic acid, and protein solution.

[0024] Further, in step S1-2, immerse the plastic microspheres in the natural organic matter solution for 0.5 to 48 hours.

[0025] Further, in step S1-4, dry for at least 24 hours.

[0026] Further, in step S2-2, each test is repeated at least 5 times.

[0027] (III) Beneficial effects

[0028] The present invention provides a research method for the mechanism of the air flotation of microplastics by natural organic matter, including preparing microplastic probes loaded with natural organic matter, testing the nano-mechanical data of the interaction between the microplastic probes and bubbles, and analyzing the nano-mechanical data. The present invention combines the colloidal probe AFM technology with the SRYL theoretical simulation for the first time and applies it to the research on the mechanism of the air flotation of microplastics by natural organic matter. By preparing microplastic probes loaded with natural organic matter, detecting their interaction with micron-sized bubbles in the aqueous phase system, substituting the nano-mechanical data into the SRYL theoretical model, quantifying the contributions of different separation pressures and their key parameters, and visually analyzing the deformation of the bubble surface.

[0029] The method of the present invention can detect the interaction mechanism between microplastics adsorbed with natural organic matter and bubbles at the nano-scale, accurately quantify the respective contributions of different separation pressures, such as van der Waals force, double-layer force and hydrophobic force, and provide a visual analysis of the deformation of bubbles during the air flotation process. Due to the wide variety of microplastic specifications and natural organic matter types, and the different water body conditions in different regions, it greatly increases the difficulty of the research on microplastic air flotation technology. Conventional air flotation experiments require a large amount of raw materials and take a long time. The research method of the present invention can greatly shorten the research cycle. By flexibly changing the simulated environmental conditions, it can quickly predict the interaction between microplastics and bubbles and the influence mechanism of natural organic matter, and can provide theoretical support and guidance for the research on microplastic air flotation. Brief Description of the Drawings

[0030] Figure 1 is the research model of the air flotation of microplastics by natural organic matter of the present invention;

[0031] Figure 2 is the visual analysis of the nano-mechanical interaction between the simulated polyethylene microplastic probe adsorbed with humic acid and bubbles, the contributions of each separation pressure, and the deformation of bubbles in Example 1;

[0032] Figure 3 is the visual analysis of the nano-mechanical interaction between polyvinyl chloride and polymethyl methacrylate microplastics adsorbed with alginic acid and bubbles in Example 2;

[0033] Figure 4 is the change in the air flotation transport rate of different microplastics before and after adsorbing natural organic matter. Detailed Description of the Embodiments

[0034] To make the objectives, contents and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention with reference to the drawings and embodiments.

[0035] The present invention provides a research method for the mechanism of the air flotation of microplastics by natural organic matter, and its research model is as Figure 1 shown. The specific steps of this research method are as follows:

[0036] S1. Prepare microplastic probes loaded with natural organic matter

[0037] Specifically, it includes the following steps:

[0038] S1-1. Immerse plastic microspheres in a natural organic matter solution for 0.5 to 48 hours, and then obtain plastic microspheres with natural organic matter loaded on the surface through centrifugal drying;

[0039] The plastic microsphere materials include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, and derivatives of the above polymers; the natural organic matter solutions include humic acid, alginic acid, tannic acid, protein solutions, etc.

[0040] S1-2. Redisperse the plastic microspheres loaded with natural organic matter in a solvent to obtain a dispersion. Use a dropper to suck the dispersion and transfer it onto a glass slide, and naturally dry to remove the solvent to obtain a glass slide with plastic microspheres loaded;

[0041] S1-3. Under an AFM integrated optical microscope, control the tip-less probe cantilever to make the probe cantilever approach the glass slide coated with an adhesive, and dip a small amount of adhesive at the end of the cantilever;

[0042] S1-4. Replace the glass slide coated with the adhesive with the glass slide loaded with plastic microspheres, control the end of the cantilever to pick up a plastic microsphere, and dry for at least 24 hours to make a microplastic probe loaded with natural organic matter.

[0043] S2. Test the nanomechanical data of the microplastic probe and the bubble

[0044] S2-1. Hydrophobically treat the glass slide at the bottom of the liquid cell for AFM testing, and then slowly inject air into the bottom of the liquid cell containing an aqueous solution through an ultra-fine glass pipette to generate bubbles and reach a stable state where the bubbles can be stably adsorbed at the bottom of the liquid cell and do not shake with the liquid;

[0045] S2-2. Immerse the microplastic probe loaded with natural organic matter in the aqueous solution of the liquid cell, and move it above the bubble. Under a constant force load, control the microplastic probe to approach the bubble and then withdraw to complete the acquisition of a set of nanomechanical data. Each test is repeated at least 5 times.

[0046] The interaction mechanism between the microplastic probe and the bubble can be judged by analyzing the characteristics of the force curve. Among them, there is a water film between the microplastic probe and the bubble during the process of the microplastic probe approaching the bubble. Before reaching the constant load force, the microplastic probe will penetrate the water film. When the microplastic probe penetrates the water film and adheres to the bubble, the water film undergoes a process of being squeezed and drained, thereby obtaining the force curve when the microplastic probe approaches. When the microplastic probe penetrates the water film but does not adhere to the bubble, the water film undergoes a process of re-filling with water when the microplastic probe withdraws, thereby obtaining two force curves when the microplastic probe approaches and withdraws.

[0047] S3. Nano-mechanical data analysis

[0048] Based on the SRYL theoretical model, analyze the nano-mechanical interaction between the microplastic probe loaded with natural organic matter and the bubble, including calculating the relationship between the separation distance between the microplastic probe and the bubble (i.e., the thickness of the water film between the two) and time through the Stoke-Reynolds equation shown in Equation (1), analyzing the deformation of the water film between the microplastic probe and the bubble, and calculating the relationship between the degree of water film deformation and the external force and Laplace force through the Young-Laplace equation shown in Equation (2), and analyzing the influence of hydrodynamic pressure and separation pressure on bubble deformation:

[0049]

[0050] Among them, h(r,t) is the separation distance between the microplastic probe and the bubble; μ is the viscosity of the aqueous solution; r is the distance in the direction connecting the centers of the bubble and the microplastic probe. When the microplastic probe contacts the bubble, the r value is defined as 0; t is the time; p(r,t) is the excess hydrodynamic pressure in the water film relative to the bulk solution; γ is the surface tension of the aqueous solution, R b ,R p and R VDW are the radii of the bubble and the microplastic probe, Π[h(r,t)] is the total separation pressure between the microplastic probe and the bubble, that is, the mutual force per unit area between the microplastic probe and the bubble in the aqueous solution, including van der Waals force (Π EDL ), double-layer electric force (Π HB ) and hydrophobic force (Π

[0051] Based on the SRYL theoretical model of the present invention, the contributions of each separation pressure and the bubble deformation can be fitted. By changing factors such as the type of natural organic matter, the specifications of microplastics (composition, size, etc.), the ratio of the aqueous solution (salt concentration, salt valence, pH value, etc.), and the speed of the microplastic probe approaching the bubble (simulating the influence of water flow dynamics), the action mechanism of natural organic matter on microplastic flotation in different environments can be simulated and analyzed.

[0052] Example 1

[0053] S1. Preparation of polyethylene microplastic probes loaded with humic acid

[0054] S1-1. The polyethylene (PS) microspheres were immersed in a 30 mg / L humic acid (HA) solution for 12 hours and dried by centrifugation to obtain polyethylene (HA@PS) microspheres loaded with humic acid on the surface;

[0055] S1-2. Re-disperse the HA@PS microspheres in ethanol, transfer a small amount of the dispersion to a glass slide with a dropper, and dry naturally to remove the solvent;

[0056] S1-3. Manipulate the tipless triangular probe cantilever under the AFM integrated optical microscope, bring it close to the glass sheet coated with AB glue, and dip a small amount of adhesive at the end of the cantilever;

[0057] S1-4. Replace the glass sheet coated with AB glue with a glass sheet loaded with HA@PS microspheres, manipulate the AFM probe so that the end of its cantilever beam sticks to a HA@PS microsphere, and dry it for 24 hours to make a HA@PS microplastic probe.

[0058] S2. Nanomechanical data of microplastic probes and bubbles

[0059] S2-1. The glass sheet at the bottom of the liquid pool for AFM testing is hydrophobicized, and then air is slowly injected into the bottom of the liquid pool containing the aqueous solution through an ultra-fine glass pipette to generate bubbles and wait for them to stabilize;

[0060] S2-2. Immerse the HA@PS microplastic probe in the aqueous solution of the liquid pool and move it above the bubble. Under a constant force load, manipulate the microplastic probe to approach the bubble and then withdraw it to complete the collection of nanomechanical data. To ensure data reliability, each test was repeated at least 5 times.

[0061] S3. Nanomechanical Data Analysis

[0062] The nanomechanical interaction between the HA@PS microplastic probe and the bubble is analyzed based on the SRYL theoretical model, including calculating the relationship between the separation distance between the microplastic probe and the bubble (i.e., the thickness of the water film between the two) and time through the Stoke-Reynolds equation shown in equation (1), analyzing the deformation of the water film between the microplastic probe and the bubble, calculating the relationship between the degree of water film deformation and the external force and Laplace force through the Young-Laplace equation shown in equation (2), and analyzing the influence of hydrodynamic pressure and separation pressure on bubble deformation.

[0063] Based on the SRYL theoretical model, the contribution of each separation pressure and bubble deformation can be fitted. The corresponding nanomechanical test data and its fitting data are shown in Figure 2As shown. A large repulsive force of ~9.0 nN was generated when the HA@PS microplastic probe approached the bubble, and obvious concave deformation occurred to the bubble ( Figure 2 inner inset A in 0 ). The decay length D of the hydrophobic interaction between the bubble and the HA@PS MP was

[0064] Example 2

[0065] S1. Prepare microplastic probes loaded with alginic acid

[0066] S1-1. Immerse polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) microspheres in 50 mg / L alginic acid (SA) solution for 24 hours respectively, and obtain polyvinyl chloride (SA@PVC) and polymethyl methacrylate (SA@PMMA) microspheres with alginic acid loaded on the surface by centrifugal drying;

[0067] S1-2. Redisperse SA@PVC microspheres and SA@PMMA microspheres in ethanol respectively, suck a small amount of the dispersion with a dropper and transfer it to a glass slide, and remove the solvent by natural drying;

[0068] S1-3. Under an AFM integrated optical microscope, control the needleless diving board type probe cantilever to make it approach the glass slide coated with epoxy glue, and dip a small amount of adhesive at the end of the cantilever;

[0069] S1-4. Replace the glass slide coated with epoxy glue with the glass slide carrying SA@PVC microspheres or SA@PMMA microspheres, control the AFM probe to make the end of its cantilever pick up a microsphere, and dry for 48 hours to make two kinds of microplastic probes, SA@PVC and SA@PMMA.

[0070] S2. Test the nanomechanical data of the microplastic probe and the bubble

[0071] S2-1. Hydrophobically treat the glass slide at the bottom of the liquid cell for AFM testing, and then slowly inject air into the bottom of the liquid cell containing the aqueous solution through an ultra-fine glass pipette to generate bubbles and wait for them to stabilize;

[0072] S2-2. Immerse the SA@PVC or SA@PMMA microplastic probe in the aqueous solution of the liquid cell, and move it above the bubble. Under a constant force load, control the microplastic probe to approach the bubble and then withdraw it to complete the acquisition of a set of nanomechanical data; to ensure the reliability of the data, each test is repeated at least 5 times.

[0073] S3. Nanomechanical data analysis

[0074] The analysis method is the same as that in Example 1, and the corresponding nano-mechanical test data and their fitting data are as Figure 3 shown.

[0075] The results show that the loading of SA has a slight inhibitory effect on the attachment of microplastics to the bubble surface. The decay lengths D of the hydrophobic force between the bubble and SA@PVC and SA@PVC are 0 0.39±0.02 nm and 0.38±0.02 nm respectively, the bubble deformation is small, and the minimum separation distances are 3.9 nm and 3.8 nm respectively. Compared with the results of HA@PS, the total repulsive separation pressure before the bubble attachment triggered by SA@PVC and SA@PMMA is smaller, indicating that the latter two are more likely to occur flotation. The results of these forces are in good agreement with the macroscopic flotation experiment results, as Figure 4 shown. The transport rates of the original PS microplastics and PVC microplastics are as high as 98.1% and 96.8% respectively, while the transport rate of PMMA microplastics is relatively low, only 86.9%. After the loading of humic acid, the transport rates of HA@PS and HA@PVC decreased significantly to 76.8% and 58.8% respectively, while the transport rate of HA@PMMA only decreased slightly to 83.4%. In contrast, the influence of alginic acid loading on the transport rates of the three microplastics is relatively small. The above macroscopic results are consistent with the nano-mechanical test results, thus verifying the effectiveness of the research method for the mechanism of natural organic matter on the flotation of microplastics proposed by the present invention.

[0076] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A method for studying the mechanism of natural organic matter flotation on microplastics, characterized in that: The research method comprises the following steps: S1. Preparation of microplastic probes loaded with natural organic matter; S2. Nanomechanical data of microplastic probes and bubbles S2-1. The glass sheet at the bottom of the liquid pool for AFM testing is treated with hydrophobicity, and then air is slowly injected into the bottom of the liquid pool containing the aqueous solution through an ultra-fine glass pipette to generate bubbles and reach a stable state in which the bubbles can be stably adsorbed at the bottom of the liquid pool and do not sway with the liquid; S2-2. Immerse the microplastic probe loaded with natural organic matter in the aqueous solution of the liquid pool and move it above the bubble. Under a constant force load, manipulate the microplastic probe to approach the bubble and then withdraw it to complete the collection of nanomechanical data; S3. Nanomechanical Data Analysis Based on the SRYL theoretical model, the nanomechanical interaction between the microplastic probe loaded with natural organic matter and the bubble is analyzed, including calculating the relationship between the separation distance between the microplastic probe and the bubble and time through the Stoke-Reynolds equation shown in equation (1), analyzing the deformation of the water film between the microplastic probe and the bubble, calculating the relationship between the deformation degree of the water film and the external force and Laplace force through the Young-Laplace equation shown in equation (2), and analyzing the influence of hydrodynamic pressure and separation pressure on bubble deformation: Wherein, h(r,t) is the separation distance between the microplastic probe and the bubble; μ is the viscosity of the aqueous solution; r is the distance between the center of the bubble and the microplastic probe. When the microplastic probe contacts the bubble, the r value is defined as 0; t is the time; p(r,t) is the excess hydrodynamic pressure in the water film relative to the bulk solution; γ is the surface tension of the aqueous solution, R b , R p is the radius of the bubble and the microplastic probe, Π[h(r,t)] is the total separation pressure between the microplastic probe and the bubble, that is, the interaction force per unit area between the microplastic probe and the bubble in the aqueous solution, including van der Waals force, double layer force and hydrophobic force; Π[h(r,t)] is an unknown quantity, and the others are known quantities.

2. The method for studying the mechanism of natural organic matter flotation on microplastics according to claim 1, characterized in that: Step S1 specifically includes the following steps: S1-1. After the plastic microspheres are immersed in a natural organic solution, they are dried by centrifugation to obtain plastic microspheres with natural organic matter on the surface; S1-2. The plastic microspheres loaded with natural organic matter are redispersed in a solvent to obtain a dispersion, the dispersion is transferred to a glass sheet using a dropper, and the solvent is naturally dried to obtain a glass sheet loaded with plastic microspheres; S1-3. Manipulate the tipless probe cantilever under the AFM integrated optical microscope, bring the probe cantilever close to the glass sheet coated with adhesive, and dip a small amount of adhesive at the end of the cantilever; S1-4. Replace the glass sheet coated with adhesive with a glass sheet loaded with plastic microspheres, manipulate the end of the cantilever beam to stick a plastic microsphere, dry it, and make a microplastic probe loaded with natural organic matter.

3. The method for studying the mechanism of natural organic matter on microplastic flotation as claimed in claim 2, characterized in that: In step S1-1, the plastic microsphere material includes polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, and derivatives of the above polymers.

4. The method for studying the mechanism of natural organic matter flotation on microplastics as claimed in claim 2, characterized in that: In step S1-2, the natural organic matter solution includes humic acid, alginic acid, tannic acid, and protein solution.

5. The method for studying the mechanism of natural organic matter flotation on microplastics as claimed in claim 2, characterized in that: In step S1-2, the plastic microspheres are immersed in the natural organic matter solution for 0.5 to 48 hours.

6. The method for studying the mechanism of natural organic matter flotation on microplastics as claimed in claim 2, characterized in that: In step S1-4, drying is performed for at least 24 hours.

7. The method for studying the mechanism of natural organic matter flotation on microplastics as claimed in claim 2, characterized in that: In step S2-2, each test is repeated at least 5 times.

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