Preparation method of micro-nano plastic adsorbent in water and application thereof

Abstract

The application discloses a preparation method of a micro-nano plastic adsorbent in water and application thereof. Fe3O4@C nanoparticles are prepared first, imidazole groups are introduced to the surface of the Fe3O4@C nanoparticles through amidation, the Fe3O4@C nanoparticles with the introduced imidazole groups are dispersed in bromododecane, and the dispersion is uniformly dispersed through intense ultrasonic dispersion, then the Fe3O4@C nanoparticles are heated and magnetically stirred under N2 protection, while condensation reflux is carried out, and the heating is stopped and the Fe3O4@C nanoparticles are naturally cooled; the supernatant is removed through centrifugation, the precipitate is washed for three times, and the Fe3O4@C nanoparticles with positive electricity and alkyl chain modification are obtained through drying. The Fe3O4@C nanoparticles have a core-shell structure, the carbon shell tightly wraps the core without any gap, the carbon shell provides good protection for the Fe3O4 core, the Fe3O4@C nanoparticles have good acid resistance and superparamagnetism, have good dispersibility, can be dispersed and utilized again, and have the advantages of economy, environmental protection, durability and low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nano plastic removal in water environment, and in particular to a preparation method of a micro-nano plastic adsorbent in water and application thereof. BACKGROUND

[0002] Microplastics have become a major global environmental problem. With further research, it has been found that nano plastics can cause harm at the cellular and molecular levels, and have a great negative impact on the growth, development and reproduction of organisms. Micro-nano plastics can accumulate in the environment, adsorb and release harmful substances, endangering ecological and environmental safety, and can enter the human body through food chains and drinking water, and even break through the gastrointestinal cell barrier of the human body, enter the human body circulation, and pose a great potential harm to human health. Microplastics have been listed as new pollutants, which are widely distributed in water environments such as lakes and rivers, and are difficult to decompose, can exist in the environment for hundreds of years, and the pollution will continue to increase with time. Research has found that 81% of tap water and 93% of bottled water also contain micro-nano plastics, which can directly enter the human body. Therefore, the removal of micro-nano plastics in water has become a scientific problem that needs to be solved urgently.

[0003] As a new pollutant, there is currently a lack of targeted removal means in environmental water and tap water. The current typical microplastic treatment process in water includes traditional methods such as filtration, coagulation and biological treatment, all of which have certain deficiencies. For example, microplastics of smaller size, even nanoscale plastics, are difficult to be effectively removed by conventional filtration and coagulation in tap water plants; and the biological treatment process is harsh and costly. It has been found that most micro-nano plastics in the environment are negatively charged, so it is urgent to develop a low-cost, environmentally friendly micro-nano plastic removal technology for negatively charged micro-nano plastics in water to ensure water environment and drinking water safety and protect human health. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a preparation method of a micro-nano plastic adsorbent in water and application thereof. The adsorbent prepared by the method has a core-shell nanostructure with positive charge and alkyl chain, and superparamagnetic property, has good adsorption performance, can be used for removal and quantitative analysis of micro-nano plastics in water, has high removal rate, low cost, is green and environmentally friendly, and can be reused.

[0005] To solve the problems of the prior art, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a micro-nano plastic adsorbent in water, comprising the following steps:

[0007] Step 1, preparing Fe3O4@C nanoparticles

[0008] Fe3O4@C nanoparticles with superparamagnetic core-shell structure were obtained by dispersing ferrocene powder in acetone, stirring until uniform dispersion, adding 30% hydrogen peroxide, continuing to stir for 30 min, then transferring to a hydrothermal reactor, and placing the reactor in an oven at 210 ℃ for 48 h or more. After natural cooling, the black product was washed by centrifugation with acetone to remove excess ferrocene, and finally dried in an oven at 60 ℃ for 12 h or more.

[0009] Step 2: Surface amidation of Fe3O4@C nanoparticles to introduce imidazole groups

[0010] Fe3O4@C nanoparticles were dispersed in deionized water and ultrasonically dispersed for 2 h. Then EDC solution and NHS solution were added, and the nanoparticles were magnetically stirred for 1 h or more to activate and stabilize the carboxyl groups on the surface of the nanoparticles. Then 1-(3-aminopropyl)imidazole was added, and the mixture was heated and magnetically stirred for 2 h or more. The supernatant was removed by centrifugation, and the nanoparticles were washed with deionized water for 3 times or more and dried at 60 ℃ for 10 h to obtain Fe3O4@C nanoparticles with imidazole groups introduced.

[0011] Step 3: Fe3O4@C nanoparticles with imidazole groups were dispersed in bromododecane and ultrasonically dispersed. Then the mixture was transferred to a flask and heated at 110 ℃ under N2 protection for 18 h or more with magnetic stirring and condensation reflux. After heating, the mixture was naturally cooled. The supernatant was removed by centrifugation, and the precipitate was washed with ethanol or acetone for 3 times and dried at 60 ℃ for 10 h or more. Finally, positively charged and alkyl chain modified Fe3O4@C nanoparticles were obtained. The reaction of bromododecane with imidazole introduced dodecyl chains, which could enhance the van der Waals force between the nanoparticles and microplastic particles. When the alkyl chain was too short, the force was not obvious. When the alkyl chain was too long, the synthesis conditions were harsh and the water solubility was poor.

[0012] As an improvement, the EDC solution and NHS solution in step 2 were prepared by MES buffer (morpholine ethanesulfonic acid) with a pH of 6. The volume ratio of the EDC solution to the NHS solution was 1:1, which served as an activator to improve the activation efficiency of the surface carboxyl groups.

[0013] As an improvement, 1-(3-aminopropyl)imidazole was used to react with the surface carboxyl groups in step 3. Excessive imidazole was used to ensure sufficient reaction. This step could be carried out at 80 ℃ under heating conditions, which saved reaction time and improved reaction efficiency.

[0014] As an improvement, bromododecane was used to react with imidazole in step 3 to introduce dodecyl chains, which could enhance the van der Waals force between the nanoparticles and microplastic particles. When the alkyl chain was too short, the force was not obvious. When the alkyl chain was too long, the structure was unstable, and the synthesis conditions were harsh and the water solubility was poor.

[0015] The application of the micro-nano plastic adsorbent prepared by the method in removing micro-nano plastics in water.

[0016] The application specifically comprises the following steps:

[0017] Step 1, adding positively charged superparamagnetic nanoparticles with dodecyl chains into a container containing a solution of micro-nano plastics to be removed, and fully stirring to mix uniformly;

[0018] Step 2, placing a magnet outside the container, and the magnetic particles adsorbing the micro-nano plastics quickly gather on the inner side of the container close to the magnet, and the solution becomes clear within 3 minutes;

[0019] Step 3, keeping the adsorption of the magnet, and discharging the pure water after removing the micro-nano plastics, that is, realizing the rapid and efficient removal of micro-nano plastics in water, and repeating the adsorption operation more than twice to ensure sufficient removal.

[0020] The specific desorption method includes but is not limited to the following: placing the adsorbed material into a hydrochloric acid solution, shaking for 2 h, ultrasonicating for 1 h, and standing for more than 6 h, so that the micro-nano plastics are separated from the adsorbent particles, placing a magnet outside the solution to transfer the adsorbent particles out for reuse, and repeating the operation more than twice to ensure complete desorption.

[0021] The principle of desorption is that, under strong acidity (pH≤1), the hydrogen ion concentration is extremely high, which competes with the adsorbent for the negatively charged micro-nano plastics, the adsorption force between the adsorbent and the micro-nano plastics is weakened, and the micro-nano plastics are separated from the adsorbent; in addition, under the condition of strong acid, the zeta potential and electrical properties of the micro-nano plastics change, the electrostatic attraction is weakened, and even the electrostatic repulsion is generated, so that the micro-nano plastics are separated from the functionalized core-shell nanoparticles; since the carbon layer tightly wraps the inner core of the four-iron oxide, the acid solution does not damage the inner core structure, nor does it damage the imidazole group and alkyl chain structure on the surface, so the magnetic nanoparticles can be reused. Beneficial effects

[0022] Compared with the prior art, the preparation method of the micro-nano plastic adsorbent in water and the application thereof have obvious advantages in removing micro-nano plastics compared with the traditional filtration, flocculation and biological treatment, have high adsorption capacity and high removal efficiency, can effectively remove nano plastics, can adsorb various types of micro-nano plastics from nanometers to microns, and the one-time removal rate of 100 nm polystyrene nano plastic solution is as high as 98%, has low cost, is green and environmentally friendly, and can be reused, and the concentration of micro-nano plastics in water can be quantitatively analyzed through desorption, which provides a new direction for the removal of micro-nano plastics in water and pollution investigation. The specific advantages are as follows:

[0023] The Fe3O4@C nanoparticles prepared by the application have a core-shell structure, the inner core is ferroferric oxide, the outer layer is a carbon shell, the overall size is 150+ / -10 nm, the carbon shell has a thickness of about 15-18 nm, the carbon shell tightly wraps the inner core without any gap, the carbon shell provides good protection for the ferroferric oxide inner core, has good acid resistance (long-term use in an acidic solution with pH=1), and can be used in a complex water environment; the material has superparamagnetism, good dispersibility, can be gathered under the action of a magnet, and can be dispersed again after the magnet is removed, and can be reused; the carbon shell surface has a large number of carboxyl groups, so that the nanoparticles exhibit electronegativity, the Zeta potential is in the range of negative 22-35 mV when the pH is in the range of 5-9, and can be used for adsorbing positively charged micro-nano plastic particles; through functional modification of the surface carboxyl groups, the nanoparticles will have corresponding functional characteristics.

[0024] Most of the micro-nano plastics in water exhibit negative electronegativity, positively charged imidazole groups and alkyl chains are introduced on the surface of the material through amidation and substitution reaction, the Zeta potential of the new functional material in the aqueous solution exhibits positive 22 mV, has good dispersibility, and the molecular structure is stable, and can effectively adsorb various different sizes and different types of negatively charged micro-nano plastic particles; the material surface is connected with a dodecyl chain, which enhances the van der Waals force between molecules and improves the adsorption capacity; when in contact with nano-plastic, through electrostatic attraction and enhanced intermolecular van der Waals force, nano-plastic and adsorbent particles quickly form agglomeration and are adsorbed together; the functional material has good superparamagnetism, can be quickly gathered under the action of a magnet, and can be dispersed again after the magnet is removed, thereby ensuring that the adsorbent has the advantage of being reusable.

[0025] The adsorbent has a stable molecular structure, strong acid and alkali resistance, can adapt to the application of complex water environment, can be reused through desorption treatment, and has the advantages of economy, environmental protection, durability and low cost.

[0026] The adsorbent can also be used for quantitative analysis of micro-nano plastic, micro-nano plastic is extracted from water by the adsorbent, and then dispersed in a specific solution through desorption operation, and can be quantified by measuring the absorbance through ultraviolet-visible light spectrophotometry or by measuring the turbidity through a turbidimeter. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Fig. 1 is a structure schematic diagram of Fe3O4@C nanoparticles prepared in the embodiments of the application, (a) is 50 nm, and (b) is 0.5 microns;

[0028] Figure 2(a) Zeta potential of the Fe3O4@C nanoparticle raw material prepared in step 1, Zeta potential -35mV, (b) Zeta potential diagram of the Fe3O4@C adsorbent modified with imidazole groups and alkyl chains obtained in step 3, Zeta potential +22mV;

[0029] Figure 3 From left to right: 100 nm polystyrene dispersion, pure water, and 100 nm polystyrene dispersion after adsorption with functionalized adsorbent;

[0030] Figure 4 The working curve of different concentrations of 100 nm polystyrene solution and absorbance at 225 nm shows a good linear relationship. 2 Greater than 0.99, the concentration of polystyrene solution can be detected by absorbance;

[0031] Figure 5 The figure is a flow chart of adsorption and desorption of the micro-nano plastic adsorbent of the present invention. DETAILED DESCRIPTION

[0032] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0033] The principle of determining the removal rate and quantification by UV-visible spectrophotometry and turbidity method: Since the higher the concentration of micro-nanoplastics in water, the higher the turbidity value, and the corresponding larger the ultraviolet light absorption value, the working curve of concentration and turbidity value / absorbance can be used to detect the concentration of micro-nanoplastics, thereby determining the removal rate after adding adsorbent and realizing quantitative analysis. Example 1

[0034] 0.6 g of ferrocene powder was weighed into a beaker. 60 mL of acetone was added to the beaker and magnetically stirred for 15 minutes until uniformly dispersed. 4 mL of 30% hydrogen peroxide was then added and stirred for another 30 minutes. The mixture was then transferred to a reactor. The reactor was placed in an oven and reacted at 210°C for 48 hours before naturally cooling. The product was centrifuged to remove the supernatant and then washed several times with acetone to remove excess ferrocene. After washing, the black precipitate was placed in an oven and dried at 60°C for 12 hours to obtain Fe3O4@C nanoparticles with a superparamagnetic core-shell structure.

[0035] The obtained Fe3O4@C nanoparticles were characterized as follows: Figure 1 As shown in the figure, it can be seen that the core is ferroferric oxide and the outer layer is a carbon shell, that is, the size of the carbon-coated ferroferric oxide nanostructure is 150±10 nm. The Fe3O4@C nanoparticles have superparamagnetism, and the outer carbon shell provides protection for the core ferroferric oxide, as shown inFigure 1 As shown in the figure; wherein the carbon shell surface has a large number of carboxyl groups, resulting in Fe3O4@C nanoparticles showing electronegativity, and the Zeta potential is in the range of negative 22-35 mV at pH in the range of 5-9, which can be used to adsorb positively charged micro-nano plastic particles. Example 2

[0036] Take 50 mg of Fe3O4@C nanoparticles with superparamagnetic core-shell structure and disperse them in 50 mL of deionized water, and ultrasonic for 2 h to make the Fe3O4@C material uniformly dispersed in deionized water, and then transfer to a beaker; add one part of 30 mL EDC solution and one part of 30 mL NHS solution to the above beaker, start magnetic stirring, time 1 h, the purpose is to activate the -COOH group on the surface of Fe3O4@C; add 1 mL of 1-(3-aminopropyl) imidazole, continue to stir for a long time; centrifuge to remove the supernatant, wash with deionized water three times, and dry at 60°C for 10 h to obtain Fe3O4@C nanoparticles with imidazole groups introduced, wherein the EDC solution and the NHS solution are prepared by MES buffer (morpholine ethanesulfonic acid), the buffer pH is 6, and the volume ratio of the EDC solution and the NHS solution is 1:1, which serves as an activator to improve the activation efficiency of the surface carboxyl group. Example 3

[0037] ①Disperse the Fe3O4@C particles with imidazole groups introduced into bromododecane, ultrasonic for 20 min, then transfer to a flask, magnetic stirring under N2 protection, heating at 110°C, magnetic stirring for 18 h or more, while condensing reflux, after heating stops, natural cooling;

[0038] ②Centrifuge to remove the supernatant, wash with ethanol or acetone three times, and dry at 60°C for 10 h or more to obtain positively charged and alkyl chain modified Fe3O4@C nanoparticles.

[0039] The positively charged Fe3O4@C nanoparticles with long alkyl chains have a Zeta potential greater than 22 mv under acidic pH conditions, as shown in the figure, and can adsorb negatively charged micro-nano plastics. Figure 2 At the same time, the material has good superparamagnetism and can be reused after being adsorbed by a magnet. Example 4

[0040] Adsorption removal and quantification of micro-nano plastics in water: (1) Add the prepared positively charged and alkyl chain modified Fe3O4@C nanoparticles as adsorbent to the micro-nano plastic water, and mix well by stirring;

[0041] (2) Put the magnet outside the container, the agglomerates of micro-nano plastics and adsorbents will quickly gather to the inside of the container close to the magnet, and the solution will become clear within 3 minutes, and the adsorption effect is as Figure 3 ;

[0042] (3) Keep the adsorption effect of the magnet, and release the pure water removed of micro-nano plastics, that is, to realize the rapid and efficient removal of micro-nano plastics in water. In order to ensure complete and sufficient removal, the above operation is repeated more than twice.

[0043] (4) The content and removal rate of micro-nano plastics can be quantitatively analyzed by ultraviolet-visible spectrophotometer / turbidimeter. Taking the detection of polystyrene nanoparticles by ultraviolet spectrophotometer as an example: polystyrene nanoparticles have good absorbance of ultraviolet light at 225 nm. Based on this, the working curve of the absorbance value of 100 nm polystyrene nanoparticles at 225 nm under different concentrations is established, as Figure 4 , the abscissa is the concentration, the ordinate is the absorbance value, and the working curve equation y =0.08561 x +0.04635, R 2 >0.99, and the linear relationship is good. The concentration of polystyrene solution can be detected by the absorbance value at 225 nm of the ultraviolet spectrophotometer.

[0044] Based on the above method, 10 mg of adsorbent dry powder is added to 6 mL of 100 nm polystyrene nano-plastic solution with a concentration of 25 mg / L, and the one-time removal rate can reach 98%.

[0045] Example 5 Desorption and Reuse

[0046] (1) Put the adsorbed material into 0.1 mol / L hydrochloric acid solution, shake for 2 h, ultrasonic for 1 h, and stand for more than 6 h. Micro-nano plastics will gradually separate from the adsorbent particles.

[0047] (2) Put the magnet outside the solution, and transfer the adsorbent particles out. Repeat the desorption operation more than twice to ensure complete desorption.

[0048] (3) Based on the above method, the 100 nm polystyrene nano-plastic solution with a concentration of 25 mg / L is repeatedly adsorbed. The first removal rate is as high as 98%, and the removal rate slightly decreases with the increase of the number of uses. The removal rate of the sixth time is still as high as 86%. It shows that the adsorbent can be repeatedly used, which can effectively reduce the economic cost.

[0049] In summary, the Fe3O4@C nanoparticles prepared by the application have a core-shell structure, the inner core is ferroferric oxide, the outer layer is a carbon shell, the overall size is 150±10 nm, the carbon shell thickness is about 15-18 nm, the carbon shell tightly wraps the inner core without gaps, the carbon shell provides good protection for the ferroferric oxide inner core, the Fe3O4@C nanoparticles are surface modified to introduce positively charged imidazole groups and alkyl chains, the molecular structure is stable, the acid resistance is good (long-term use in an acidic solution with pH=1), the material can be used in a complex water environment, has superparamagnetism, good dispersibility, can be aggregated under the action of a magnet, and can be dispersed again after the magnet is removed; can efficiently and quickly adsorb micro-nano plastic, and can be reused after desorption treatment, therefore, the material has the advantages of economy, environmental protection, durability, low cost, efficient adsorption of micro-nano plastic in water, and provides an effective solution for the repair of micro-nano plastic pollution in water.

Claims

1. A method for preparing a micro- and nano-plastic adsorbent in water, characterized by, Comprising the following steps: Step 1, preparation of Fe3O4@C nanoparticles Ferrocene powder was dispersed in acetone and stirred until uniformly dispersed, then 30% hydrogen peroxide was added, and stirring was continued for 30 min before being transferred to a hydrothermal reactor, which was then placed in an oven at 210 ℃ for 48 h. After natural cooling, the black product was washed by centrifugation with acetone to remove excess ferrocene, and finally dried in an oven at 60 ℃ for 12 h or more to obtain Fe3O4@C nanoparticles with a superparamagnetic core-shell structure; Step 2, surface amidation of Fe3O4@C nanoparticles to introduce imidazole groups Fe3O4@C nanoparticles were dispersed in deionized water and ultrasonically dispersed for 2 h, then EDC solution and NHS solution were added, and the nanoparticles were magnetically stirred for 1 h or more to activate and stabilize the carboxyl groups on the surface of the nanoparticles. 1- (3 -aminopropyl) imidazole was added, and the mixture was heated and magnetically stirred for 2 h or more. The supernatant was removed by centrifugation, and the precipitate was washed with deionized water three times or more and dried at 60 ℃ for 10 h to obtain Fe3O4@C nanoparticles with imidazole groups introduced. The EDC solution and NHS solution were prepared by MES buffer, and the buffer pH was 6. The volume ratio of the EDC solution and NHS solution was 1:1, which served as an activator to improve the activation efficiency of the surface carboxyl groups; Step 3, dispersing the Fe3O4@C nanoparticles with imidazole groups in bromododecane, and ultrasonically dispersing until uniformly dispersed, then transferring to a flask and heating at 110 ℃ under N2 protection for 18 h or more with magnetic stirring and condensation reflux. After heating, the mixture was naturally cooled; The supernatant was removed by centrifugation, and the precipitate was washed with ethanol or acetone three times and dried at 60 ℃ for 10 h or more to obtain Fe3O4@C nanoparticles with positive charges and alkyl chain modification.

2. The method according to claim 1, wherein, In step 3, 1- (3 -aminopropyl) imidazole was used to react with the surface carboxyl groups, and excess imidazole was used to ensure full reaction. This step can be performed at 80 ℃ under heating conditions to save reaction time and improve reaction efficiency.

3. The application of the micro-nano plastic adsorbent prepared by the preparation method of claim 1 to remove micro-nano plastics in water, characterized in that, Specifically comprising the following steps: Step 1, adding superparamagnetic nanoparticles with dodecyl chain and positive charges to a container containing a solution to be removed from micro-nano plastic, and thoroughly stirring to mix uniformly; Step 2, placing a magnet outside the container, and the magnetic particles of micro-nano plastic quickly gather on the inside of the container near the magnet, and the solution becomes clear within 3 minutes; Step 3, maintaining the adsorption of the magnet, and discharging the pure water after removing the micro-nano plastic, which realizes the rapid and efficient removal of micro-nano plastic in water. To ensure sufficient removal, the operation is repeated two times or more.

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