CN110907429B - Surface enhanced Raman spectrum detection method for micro/nano plastic - Google Patents
Surface enhanced Raman spectrum detection method for micro/nano plastic Download PDFInfo
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Abstract
The invention provides a surface enhanced Raman spectrum detection method of micro/nano plastic, which comprises the following steps: preparing a micro/nano plastic solution; preparing nano silver sol: heating a silver nitrate solution to boiling, adding trisodium citrate for reduction reaction, and filtering the reacted solution through a water system microporous filter membrane to obtain the nano silver sol; and mixing the micro/nano plastic solution, the nano silver sol and the coagulant to form a mixed solution, and collecting a surface enhanced Raman spectrum signal of the mixed solution through a spectrometer to realize detection of the micro/nano plastic. The invention uses the silver sol as the surface enhanced Raman spectrum of the active substrate for chemoqualitative analysis of the micro/nano plastic in pure water and seawater, is a very simple, quick and effective micro/nano plastic method, and has certain universality.
Description
Technical Field
The invention relates to the technical field of environmental pollutant detection, in particular to a surface enhanced Raman spectrum detection method of micro/nano plastic.
Background
In recent years, the problem of plastic garbage collection in marine environments has attracted more and more attention to society, and plastics in the environments are broken into microplastic under the composite influence of the actions of sunlight ultraviolet radiation, mechanical damage, weathering corrosion, biodegradation and the like, and microplastic (< 5 mm) is a potential threat to more organisms and even human beings due to easy ingestion by organisms and transfer of food chains.
Currently, there are various detection techniques for analysis of microplastic, among which the common ones include pyrolytic gas chromatography-mass spectrometry, FTIR-fourier infrared spectrometry, raman spectrometry, and the like. However, most of the research is currently investigating microplastic particles of a size greater than 20 μm, and few reports are made on 20 μm and nano plastics. The nano-sized plastic particles cannot be detected due to size limitation, especially for detection of micro/nano plastics in aqueous solution, and there is no convenient and accurate detection method, which results in missing data (quantity, chemical property, etc.) about nano plastics in the environment.
Disclosure of Invention
The invention aims to solve the problem of how to simply and effectively detect micro/nano plastics in water environment to a certain extent.
In order to solve the above problems, the present invention provides a surface enhanced raman spectrum detection method of micro/nano plastic, comprising: preparing a micro/nano plastic solution; preparing nano silver sol: heating a silver nitrate solution to boiling, adding trisodium citrate for reduction reaction, and filtering the reacted solution through a water system microporous filter membrane to obtain the nano silver sol; and mixing the micro/nano plastic solution, the nano silver sol and the coagulant to form a mixed solution, and collecting a surface enhanced Raman spectrum signal of the mixed solution through a spectrometer to realize detection of the micro/nano plastic.
Optionally, the mixed solution comprises silver nanoparticle aggregates, and the silver nanoparticle aggregates are wrapped on the surfaces of the micro/nano plastic microspheres.
Optionally, the silver nanoparticle aggregate has a size of 1500-3000nm.
Optionally, the micro/nano plastic comprises one or more of polystyrene, polyethylene, and polypropylene.
Optionally, when the micro/nano plastic is polystyrene, the preparing the micro/nano plastic solution includes: placing water into a reactor, heating and stirring under nitrogen atmosphere, removing oxygen in the water, adding styrene monomer into the reactor, stirring uniformly, adding 2, 2-azo-bis (2-methylpropyl-mi) dihydrochloride solution, reacting for 9-11 hours, carrying out suction filtration or dialysis on the reacted solution, drying to obtain polystyrene powder, and finally dispersing the polystyrene powder in pure water or seawater to obtain the micro/nano plastic solution.
Optionally, the volume ratio of the micro/nano plastic solution to the nano silver sol is 1:1.
Optionally, the concentration of the micro/nano plastic and the surface enhanced raman spectrum signal are in a linear function relation; wherein, when the micro/nano plastic is polystyrene with the particle size of 100nm, the concentration of the micro/nano plastic is positively correlated with the surface enhanced Raman spectrum signal; when the micro/nano plastic is polystyrene with the particle size of 500nm, the concentration of the micro/nano plastic is inversely related to the surface-enhanced Raman spectrum signal.
Alternatively, when the micro/nano plastic is polystyrene with a particle size of 100nm and the concentration in pure water is 0.8mg/mL, the detection limit of the micro/nano plastic is 20 μg/mL; when the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration in pure water is 0.08mg/mL, the detection limit of the micro/nano plastic is 0.188mg/mL.
Alternatively, when the micro/nano plastic is polystyrene with a particle size of 100nm and the concentration in seawater is 1.6mg/mL, the detection limit of the micro/nano plastic is 30 mug/mL; when the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration in seawater is 0.08mg/mL, the detection limit of the micro/nano plastic is 0.287mg/mL.
Optionally, the coagulant is sodium chloride.
Compared with the prior art, the surface enhanced Raman spectrum detection method of the micro/nano plastic provided by the invention has the following advantages:
(1) According to the invention, silver sol is selected as an active substrate, and a coagulant is added to enhance signals of Raman spectrum, so that detection of micro/nano plastics in water environment is realized, the detection method has simple steps, no complex pretreatment process is adopted, the detection time is short, the detection method is not only suitable for detecting nano plastics smaller than 1 mu m, but also detecting micro plastics with larger size, and in addition, the detection method is little influenced by seawater environment and has certain universality.
(2) The surface enhanced Raman spectrum detection method of the micro/nano plastic optimizes the step parameters aiming at different micro/nano plastics and further improves the detection accuracy.
Drawings
FIG. 1 is a schematic flow chart of a method for detecting surface enhanced Raman spectrum of micro/nano plastic according to an embodiment of the invention;
FIG. 2 (a) is a graph comparing the SERS spectral intensities of 100 nPS and 500 nPS spheres at different silver sol to sample volume ratios; FIG. 2 (b) is a graph comparing the intensity of SERS spectra of 100 nPS and 500 nPS spheres at different NaCl concentrations; FIG. 2 (c) is a graph of the contrast of the SERS spectral intensities of 100nmPS spheres at different low concentrations of samples; FIG. 2 (d) is a graph comparing the intensity of SERS spectra of 500nmPS spheres at different high concentrations of sample;
FIG. 3 shows a measurement at 1295cm -1 And 807cm -1 A SERS intensity change graph of 10 mu mPE and PP within 10min, wherein (a) is PE+5mL of water mixed solution, PE+5mL of water+CTAB mixed solution, PE+5mL of water+CTAB+silver sol mixed solution; FIG. 3 (b) is a mixture of PP+5mL of water, a mixture of PP+5mL of water+CTAB, and a mixture of PP+5mL of water+CTAB+silver sol;
FIG. 4 (a) is a graph of the comparison of the SERS spectral intensities of 100nmPS spheres at different concentrations of samples; FIG. 4 (b) is a graph comparing the SERS spectrum intensities of 500nmPS spheres at different concentrations of samples; FIG. 4 (c) is a SERS spectrum of seawater, 10. Mu. MPE spheres dispersed in a surfactant, and 10. Mu. MPE spheres after addition of silver sol;
FIG. 5 (a) is a TEM image of single dispersed silver nanoparticles; FIG. 5 (b) is a TEM image of silver nanoclusters; FIG. 5 (c) is a DLS map of single dispersed silver nanoparticles; FIG. 5 (d) is a DLS map of silver nanoclusters;
FIG. 6 (a) is a TEM image of a single dispersed 500nmPS sphere; FIG. 6 (b) is a TEM image of silver sol adsorbed on 500nmPS spheres;
FIG. 7 is a Raman spectrum of seawater according to an embodiment of the present invention;
FIG. 8 is an ultraviolet-visible absorption spectrum of a silver sol according to an embodiment of the present invention.
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
In addition, the terms "comprising," "including," "containing," "having" and their derivatives are not limiting, as other steps and other ingredients not affecting the result may be added. Materials, equipment, reagents are commercially available unless otherwise specified.
In addition, although the steps in the preparation are described in the forms of S1, S2, S3, etc., the description is only for the convenience of understanding, and the forms of S1, S2, S3, etc. do not represent a limitation of the sequence of the steps.
Some researchers refer to particles smaller than 1 μm in size as nano-plastics, while others consider that at least 50% of particles must have at least one particle smaller than 100nm in size as nano-plastics, which in the present invention is defined as plastic particles below 1 μm.
In the prior art, the pyrolysis-GC/MS technique, which can identify the chemical composition of microplastic polymers by analyzing their characteristic thermal degradation products, accurately determine the polymer type by comparing with the pyrolysis reference map of known pure polymers, has the advantage that no pretreatment of the sample is required, and the polymer type and the related organic plastic additives can be determined simultaneously, microplastic particles as low as 100 μm can be detected, but the nanoplastic below 1 μm cannot be detected. Microplastic particles with sizes as low as between 10-20 μm were detected by Fourier Transform Infrared (FTIR) spectroscopy, nor were nanoplastic particles below 1 μm detected. Whereas raman spectroscopy has a better response to nonpolar plastic functional groups, conventional raman spectroscopy is able to detect microplastics as low as 1 μm, whereas for micro/nano plastics in aqueous solution, the raman signal detected with conventional raman spectroscopy is very weak or even absent, even at very high concentrations.
At present, in a new report, polystyrene (PS) microplastic and nano-plastic in natural water are quantitatively analyzed by using an LC-HRMS (liquid chromatography-high resolution mass spectrometry) technology, and the method has high sensitivity and is successfully used for analyzing a plurality of actual samples, however, the method is only suitable for PS detection, and the sample is complicated in early treatment, complicated in operation process and not suitable for large-size plastic particles, so that the method has a certain limitation.
In order to solve the problems, the invention provides a method for detecting the surface enhanced Raman spectrum of the micro/nano plastic, which is used for detecting the micro/nano plastic in the water environment more conveniently and rapidly, and silver sol is selected as an active substrate and a coagulant is added to enhance signals of the Raman spectrum, so that the detection of the micro/nano plastic in the water environment is realized. The detection method has the advantages of simple steps, no complex pretreatment process, short detection time, suitability for detecting nano plastics smaller than 1 mu m, capability of detecting micro plastics with larger size, little influence of seawater environment and increased detection universality.
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
Referring to fig. 1, the embodiment of the invention provides a surface enhanced raman spectrum detection method of micro/nano plastic, which comprises the following steps:
s1, preparing a micro/nano plastic solution;
s2, preparing nano silver sol: adding silver nitrate solution into a flask, stirring, heating to boiling, adding trisodium citrate for reduction reaction, and filtering the reacted solution through a water system microporous filter membrane to obtain colloidal nano silver sol;
s3, mixing the micro/nano plastic solution, the nano silver sol and the coagulant to form a mixed solution, and collecting surface-enhanced Raman spectrum signals of the mixed solution through a spectrometer to realize detection of the micro/nano plastic.
Wherein, the micro/nano plastics mentioned in the embodiment of the present invention include one or more of Polystyrene (PS), polyethylene (PE) and polypropylene (PP), and although in step S1, the preparation of the micro/nano plastic solution is mentioned, it is understood that this includes obtaining the micro/nano plastic solution by directly mixing the micro/nano plastic powder with pure water or seawater, or obtaining the micro/nano plastic solution by preparing the micro/nano plastic first and then mixing the prepared micro/nano plastic with pure water or seawater; here, the present invention is not particularly limited, and may be selected according to actual needs.
To specifically illustrate the reliability of the detection method of the present invention, preferably, when the micro/nano plastic is polystyrene, step S1 prepares a micro/nano plastic solution, comprising the steps of:
placing water into a reactor, heating and stirring under nitrogen atmosphere, removing oxygen in the water, adding styrene monomer into the reactor, stirring uniformly, adding 2, 2-azo bis (2-methylpropyl-mi) dihydrochloride (AIBA) solution, reacting for 9-11 hours, carrying out suction filtration or dialysis on the reacted solution, drying to obtain polystyrene powder, and finally dispersing the polystyrene powder into ultrapure water or seawater to obtain the micro/nano plastic solution.
Specifically, the step of synthesizing Polystyrene (PS) spheres of 100nm or 500nm comprises: the aqueous solution was placed in a reactor, purged with nitrogen, vigorously stirred at 600rpm, heated at 90 ℃ (100 nm) or 55 ℃ (500 nm) for 30 minutes to remove the dilute oxygen from the solution, and then styrene monomer was added to the reactor. The system was maintained for another 10 minutes to ensure uniform dispersion of styrene in the aqueous solution, and then AIBA previously dissolved in water was added to the styrene-aqueous solution mixed solution, followed by incubating the mixture at 90℃or 55℃for 10 hours under a nitrogen atmosphere, and finally the reacted solution was cooled to room temperature, and then the solution was suction-filtered (500 nm) or dialyzed (100 nm) and dried, thereby obtaining a 100nm or 500nm PS sphere solid powder sample.
Although the present embodiment is specifically described by taking the preparation method of PS spheres of 100nm and 500nm as an example, it is understood that the reaction temperature is inversely proportional to the particle size of PS spheres prepared, for example: 100nm PS spheres were prepared at 90℃and 500nm PS spheres were prepared at 55℃under the same conditions. Therefore, according to actual demands, PS balls with different particle sizes can be prepared by controlling the temperature.
In addition, PE and PP microplastic solid powders can be obtained by purchasing, PE and PP microplastics adopted in the embodiment of the invention are purchased from plastic limited company, the sizes of the PE and the PP microplastics are concentrated at about 10 mu m, and the PP and the PE powders are respectively dispersed in ultrapure water and seawater (50 mg/10 mL), and as the two microplastics cannot be uniformly dispersed in water, the added surfactant can be used for helping the uniform dispersion of the microplastic.
In the step S2, silver sol is selected as an SERS active substrate, and the SERS active substrate is prepared by a chemical reduction method, specifically, the method comprises the steps of firstly placing 100mL of 0.18g/L silver nitrate AgNO3 solution into a 250mL round bottom flask, adding a rotor, placing into a heat-collecting constant-temperature heating magnetic stirrer, heating at 120 ℃ by using an oil bath, immediately adding 2.0mL of 1% trisodium citrate for reduction after the solution boils, wherein sodium citrate plays a role in reducing and can also prevent formed nanoparticles from aggregating. The solution is kept for 1h under boiling, then naturally cooled to room temperature, and filtered by a 0.22 mu m water system microporous filter membrane to obtain uniform phase colloidal silver nano particles, and the colloidal silver nano particles are stored in a dark place at the temperature of 4 ℃ for standby.
In the step S3, firstly mixing the micro/nano plastic with the coagulant, then mixing the mixture of the micro/nano plastic and the coagulant with silver sol, shaking uniformly to obtain mixed solution, finally taking 20 mu L of the mixed solution as a sample to be measured, placing the sample to be measured under a micro laser Raman detector, enabling laser to irradiate near the highest point of the convex surface of the mixed liquid drop as much as possible, and collecting SERS spectrum signals.
The embodiment of the invention adopts a portable Raman spectrometer (Ocean Optics, SR-510 Pro), and all SERS spectrums are subjected to baseline correction. The parameters of the SERS spectrum are set as: excitation wavelength 785nm, laser power about 105mW, optical resolution 1um -1 Scanning range is 500-2500cm -1 The exposure time for SERS measurement was 2-20s, and each acquisition was repeated 3 more times to calculate the average.
The mass fractions of the micro/nano plastic solution, the nano silver sol and the coagulant have great influence on the collected surface enhanced Raman spectrum signals (SERS signals), so that the proportion of each component is optimized through the following experiment in order to further improve the accuracy of the detection method disclosed by the embodiment of the invention.
S31, influence of proportion SERS light intensity of micro/nano plastic solution and nano silver sol
Silver sol is a liquid SERS substrate, can be mixed with a sample solution to be tested in any proportion during use, and has great influence on SERS signals in different proportions. This is because when the silver sol is too small, it is insufficient to generate enough hot spots, failing to sufficiently enhance the raman signal of the sample molecules; when the silver sol is too much, the sample is precipitated due to the adsorption of too many silver nanoparticles, and the best detection effect cannot be obtained, so that the best detection effect can be achieved only when the silver sol and the sample to be detected are kept in a proper ratio.
According to the embodiment of the invention, 500nmPS spheres are selected as the micro/nano plastic, the volume ratio of the PS spheres to the nano silver sol is 1:4, 1:3, 1:2, 1:1, 2:1, 3:1 and 4:1 according to the preparation method of the step S3, 7 samples to be detected are prepared, and SERS detection is carried out respectively.
Referring to fig. 2 (a), when the volume ratio of the 100nmPS and 500nmPS sphere aqueous solution to the nano silver sol is 1: at 1, SERS spectra of 100 nPS and 500 nPS spheres were 998cm -1 The characteristic peak intensity is the largest, namely when the volume ratio of the micro/nano plastic solution to the nano silver sol is 1:1 under the same condition, the SERS spectrum detection method of the micro/nano plastic can obtain the best detection effect.
S32 influence of the coagulant on the SERS light intensity
The coagulant may promote coagulation of the sol, thereby greatly enhancing SERS signals, and may be: sodium chloride, nitric acid, trichloroacetic acid, or the like, and in the embodiment of the present invention, preferably, the coagulant is a NaCl solution. Since the concentration of the coagulant is closely related to the SERS activity of the nanosilver sol. According to the embodiment of the invention, the influence of chloride ions on the SERS detection effect of the sample to be detected is represented by configuring NaCl solutions with different concentrations, and specifically, the concentration of the NaCl solutions in the sample to be detected is respectively as follows: 0mol/L, 0.1mol/L, 0.25mol/L, 0.5mol/L, 0.75mol/L, 1mol/L, 2mol/L, 3mol/L, 4mol/L.
Referring to FIG. 2 (b), when the concentration of NaCl solution is 0.25mol/L, the characteristic peak intensities of SERS spectra of 100 nPS and 500 nPS spheres are all the maximum, that is, the concentration of NaCl solution is 0.25mol/L under the same condition, the best detection effect can be obtained by the SERS spectrum detection method of micro/nano plastics.
S33, influence of micro/nano plastic concentration in pure water solution on SERS light intensity
According to the tests of steps S31 and S32, 0.25mol/L NaCl is used as a coagulant, and the volume ratio of 100nmPS and 500nmPS spheres to nano silver sol is 1:1, and the micro/nano plastics are dispersed in pure water, and the influence of the micro/nano plastics concentration in the pure water solution on the SERS detection effect of the sample to be detected is represented by configuring different micro/nano plastics concentrations, specifically, the micro/nano plastics concentration in the sample to be detected is respectively: 0mg/mL, 0.04mg/mL, 0.08mg/mL, 0.16mg/mL, 0.2mg/mL, 0.4mg/mL, 0.8mg/mL, 1.6mg/mL, 2mg/mL, 2.4mg/mL.
Referring to fig. 2 (c) and (d), the concentration of the micro/nano plastic and the surface enhanced raman spectrum signal are in a linear function relation; when the micro/nano plastic is polystyrene with the particle size of 100nm, the concentration of the micro/nano plastic is positively correlated with the surface enhanced Raman spectrum signal; when the micro/nano plastic is polystyrene with the particle size of 500nm, the concentration of the micro/nano plastic is positively correlated with the surface enhanced Raman spectrum signal.
Specifically, when the micro/nano plastic is polystyrene with a particle size of 100nm and the concentration in the pure water solution ranges from 0 to 0.8mg/mL, the optimal enhancement concentration is 0.8mg/mL. When the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration range in pure water solution is 0.08-1.6mg/mL, the optimal enhancement concentration is 0.08mg/mL.
As can be seen from FIG. 2 (c), the SERS spectral intensity increases with increasing concentration of 100nmPS spheres over the 0-0.8mg/mL concentration range, with a linear relationship defined as: y=1193.027+17842.240x, where y is the spectral intensity and x is the concentration of PS spheres (mg/mL), the correlation coefficient of this equation is 0.96.
As can be seen from FIG. 2 (d), the SERS spectral intensity decreases with increasing concentration of 500nmPS spheres over the 0.08-1.6mg/mL concentration range, with a linear relationship defined as: y= 14317.140-9294.720x, where y is the spectral intensity and x is the concentration of PS spheres (mg/mL), the correlation coefficient of this equation is 0.90.
From this, it can be seen that the characteristic peak intensity of the SERS spectrum of 100nmPS spheres is maximum when the concentration of micro/nano plastics in pure water is 0.8 mg/mL; when the concentration of the micro/nano plastic in pure water is 0.08mg/mL, the characteristic peak intensity of the SERS spectrum of the 500nmPS sphere is maximum. Namely, under the same condition, when the concentration of 1500nmPS spheres in pure water is 0.4mg/mL, the optimal detection efficiency can be obtained by the SERS spectrum detection method of the micro/nano plasticAnd (5) fruits. The enhancement factor at this concentration was 5.0 x 10 by the calculation formula 2 And the minimum detection limit was calculated to be 20. Mu.g/mL. When the concentration of the 500nmPS sphere in the pure water solution is 0.08mg/mL, the optimal detection effect can be obtained by the SERS spectrum detection method of the micro/nano plastic. The enhancement factor at this concentration was 4 x 10 by the calculation formula 4 And the minimum detection limit was calculated to be 0.188mg/mL.
S34, influence of micro/nano plastic concentration in seawater solution on SERS light intensity
Seawater itself has a strong background (as shown in fig. 7), and various impurities such as microorganisms and minerals may be present in the seawater, so that raman detection of micro/nano plastics in the seawater may become more difficult.
In order to characterize the detection method provided by the embodiment of the invention for detecting the micro/nano plastics in the sea water and the influence of the micro/nano plastics concentration in the sea water solution on the SERS light intensity, referring to the optimal ratio of the nano silver sol in the pure water to the sample to be detected, 100nmPS and 500nmPS spheres with different concentrations (the ratio of 10mgPS added into 5mL of water) are dispersed in the sea water according to the following steps of 1: the volume ratio of 1 mixes nano silver sol and micro/nano plastic solution, and the SERS intensity of 100 nPS and 500 nPS balls is not interfered by seawater, and compared with the SERS signals of the conventional Raman spectrum 100 nPS and 500 nPS balls, the SERS intensity of the 100 nPS and 500 nPS balls is greatly enhanced.
When the concentration range of the micro/nano plastic in the aqueous solution is 0-1.6mg/mL, the concentration of the micro/nano plastic and the surface enhanced Raman spectrum signal are in a linear function relation, the concentration of the 100nmPS plastic and the surface enhanced Raman spectrum signal are in positive correlation, and the concentration of the 500nmPS plastic and the surface enhanced Raman spectrum signal are in negative correlation.
Specifically, when the micro/nano plastic is polystyrene with the particle size of 100nm and the concentration range in the seawater solution is 0-1.6mg/mL, the optimal enhancement concentration is 1.6mg/mL, and the detection limit of the micro/nano plastic under the optimal concentration is 30 mug/mL. When the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration range in the seawater solution is 0.08-1.6mg/mL, the optimal enhancement concentration is 0.08mg/mL, and the detection limit of the micro/nano plastic under the optimal concentration is 0.287mg/mL.
As can be seen from FIG. 4 (a), the SERS spectral intensity increases with increasing concentration of 100nmPS spheres over the 0-1.6mg/mL concentration range, with a linear relationship defined as: y=1712.875+15111.229 x, where y is the spectral intensity and x is the concentration of PS spheres (mg/mL), the correlation coefficient R of this equation 2 0.925.
As can be seen from FIG. 4 (b), the SERS spectrum intensity decreases with increasing concentration of 500nmPS sphere in the concentration range of 0.08-1.6mg/mL, and the characteristic peak intensity of the SERS spectrum of 500nmPS sphere is maximum at 0.08mg/mL.
From this, it can be seen that the characteristic peak intensity of the SERS spectrum of 100nmPS spheres was maximum when the concentration of the micro/nano plastic in seawater was 1.6 mg/mL. When the concentration of the micro/nano plastic in the seawater is 0.08mg/mL, the characteristic peak intensity of the SERS spectrum of the 500nmPS sphere is maximum. Namely, under the same conditions, when the concentration of the 100nmPS sphere in the seawater solution is 1.6mg/mL, the SERS spectrum detection method of the micro/nano plastic can obtain the optimal detection effect; the enhancement factor at this concentration was 7 x 10 by the calculation formula 2 And the minimum detection limit was calculated to be 30. Mu.g/mL. When the concentration of the 500nmPS sphere in the seawater solution is 0.08mg/mL, the optimal detection effect can be obtained by the SERS spectrum detection method of the micro/nano plastic, and the enhancement factor under the concentration is 1.1 x 10 through a calculation formula 4 。
Accordingly, when the micro/nano plastic was 10. Mu.mPE, 10. Mu.mPE spheres of different concentrations (in a ratio of 50mgPE added to 10mL of water) were dispersed in seawater and detected by the detection method of 500nmPS spheres described above. As a result, as shown in fig. 4 (c), PE was dispersed in a solution with a surfactant, and its conventional raman signal was weak; and after the nano silver sol is added, the SRES signal of PE is greatly enhanced.
In conclusion, the surface enhanced Raman spectrum detection method of the micro/nano plastic provided by the invention can conveniently and accurately detect the micro/nano plastic in the seawater, and shows that the method has certain universality.
SERS detection of S35 and micron plastics
The micron plastic of the embodiment of the invention comprises 10 mu m PE and 10 mu m PP, the 10 mu m PE and the 10 mu m PP are respectively dispersed in the form of powder into an aqueous solution (50 mgPE or PP is added into 10mL of pure water), and a surfactant is added into the solution to ensure that the micron plastic is dispersed more uniformly, wherein the surfactant is cetyl trimethyl ammonium bromide (CTBA), and the volume ratio of the micron plastic to the surfactant is 1:200. the SERS intensity of the sample was then tested after mixing the PE/PP solution with 1mol/L NaCl solution and nano-silver sol.
Because the aggregation of the nano silver sol on the surface of the micro plastic needs a certain time, the Raman signal of the micro plastic can be enhanced only when the aggregation reaches a certain degree, and therefore, in the detection process, the Raman signals of PE and PP are acquired once every 60s and are continuously acquired for 10 times.
As shown in fig. 3 (a) (b), the raman signals of PE and PP added with the nano silver sol are greatly enhanced, that is, even though the size of the microplastic is large, the raman signals are greatly enhanced due to the hot spots generated on the surface of the microplastic by the silver sol. That is, the surface enhanced Raman spectrum detection method of the micro/nano plastic provided by the embodiment of the invention is not only suitable for detecting nano plastic smaller than 1 μm, but also can detect micro plastic with larger size.
Furthermore, for different types of plastic particles, the identification is based on their main characteristic vibration peaks. For example, polystyrene (PS) has Raman spectra of mainly 622, 790, 1000, 1029, 1152, 1177 and 1590cm -1 Several major peaks, the strongest peak being 1000cm -1 The vibration peak is caused by respiratory vibration of the benzene ring; whereas the raman spectra of Polyethylene (PE) are mainly 1059, 1125, 1289 and 1429cm -1 Several major vibrational peaks; the Raman spectra of polypropylene (PP) are mainly 809, 841, 971, 1149, 1166, 1322 and 1451cm -1 Several major vibrational peaks. It will thus be appreciated that different types of plastic particles may also be identified by the method of the present embodiment.
S36, characterization analysis of nano silver sol
By passing throughAs can be seen from the measurement of the optical absorption characteristics of the nano silver sol prepared in the step S2 by the ultraviolet-visible spectrophotometer and the combination of the graph shown in FIG. 8, the maximum absorption peak of the nano silver sol is 407cm -1 The half-width of the silver sol is narrow, and no other impurity peak appears, so that the particle size distribution of the prepared silver sol nanoparticles is considered to be uniform.
The coagulant sodium chloride can coagulate the silver sol, the sodium chloride is added into the nano silver sol, and the aggregation state of silver sol particles is judged by representing the particle sizes of the system before and after aggregation. Examination of silver sol particles and silver nanoparticle aggregates using a transmission electron microscope (TEM, tecnaiG2F 20S), combined with the illustration of fig. 5 (a), it can be seen that most of the silver nanoparticles were about 60nm in diameter and in a single dispersed state; as shown in fig. 5 (b), after adding sodium chloride, the silver nanoparticles are aggregated together to form a silver aggregate structure.
To further systematically investigate the particle size distribution of silver nanoparticles before and after aggregation, a dynamic light scattering technique (Dynamic Light Scattering) was used to characterize the particle size distribution of silver nanoparticles. As a result, as shown in FIG. 5 (c), the silver nanoparticles prepared in step S2 were mainly distributed in the range of 50-100nm in particle diameter and 60nm in average diameter. As shown in FIG. 5 (d), after the addition of sodium chloride to aggregate the sol, the size of the silver nanoparticle aggregates was mainly distributed between 1500 and 3000nm, i.e., increased by approximately 30 times over before the addition of sodium chloride.
In step S3, by adding the coagulant, the mixed solution formed by mixing the micro/nano plastic solution, the nano silver sol and the coagulant includes not only silver nanoparticles but also silver nanoparticle aggregates, and both the silver nanoparticles and the silver nanoparticle aggregates are wrapped on the surface of the micro/nano plastic balls. When the sample to be detected adsorbs the metal (commonly used gold or silver) structure surface with nano-scale roughness, hot spots generated between silver nano particles act on the micro/nano plastic surface, so that the weak signal of the sample to be detected is greatly enhanced. Therefore, whether the particle size of the plastic particles in the water environment is large or small, detection can be carried out, even if the particles are microplastic with larger particle size, the silver sol aggregate can generate more hot spots on the surface of the microplastic so as to enhance SERS signals, and the detection accuracy is improved.
In addition, as shown in fig. 6, the change of PS sphere solution before and after adding nano silver sol was characterized using transmission electron microscope TEM, and as can be seen from fig. 6 (a), PS spheres were about 500nm in diameter and in a single dispersed state. As can be seen from fig. 6 (b), after the nano silver sol is added, the surface of the PS spheres is wrapped with a large amount of silver nanoparticles and silver nanoparticle aggregates, which also laterally illustrates that the raman signal of the PS spheres is greatly enhanced after the nano silver sol is added.
In summary, it can be seen that the surface enhanced raman spectrum detection method of the micro/nano plastic provided by the embodiment of the invention uses silver sol as the Surface Enhanced Raman Spectrum (SERS) of the active substrate for chemoqualitative analysis of the micro/nano plastic in pure water and seawater, is a very simple, rapid and effective micro/nano plastic method, and can effectively detect plastic particles ranging from nano-scale to micro-scale size by adding the coagulant, and can also identify different types of plastic particles; meanwhile, the chemical identification of the micro/nano plastic in the sea water is hardly influenced by the complex matrix in the marine environment. In addition, the detection method does not have a complex pretreatment process, and the direct and rapid detection of the microplastic and the nano-plastic in the water environment is realized in the future based on the surface-enhanced Raman spectrum.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (6)
1. The surface enhanced Raman spectrum detection method of the micro/nano plastic is characterized by comprising the following steps of:
preparing a micro/nano plastic solution;
preparing nano silver sol: heating a silver nitrate solution to boiling, adding trisodium citrate for reduction reaction, and filtering the reacted solution through a water system microporous filter membrane to obtain nano silver sol, wherein the nano silver sol is uniform-phase colloidal silver nano particles, and the particle size distribution of the silver nano particles is in the range of 50-100 nm;
mixing the micro/nano plastic solution, the nano silver sol and a coagulant to form a mixed solution, wherein the volume ratio of the micro/nano plastic solution to the nano silver sol is 1:1, the coagulant is NaCl with the concentration of 0.25mol/L, the mixed solution comprises silver nano particles and silver nano particle aggregates, the size of the silver nano particle aggregates is 1500-3000nm, and the silver nano particles and the silver nano particle aggregates are wrapped on the surface of the micro/nano plastic;
and collecting surface enhanced Raman spectrum signals of the mixed liquid through a spectrometer to realize detection of the micro/nano plastic.
2. The method of claim 1, wherein the micro/nano plastic comprises one or more of polystyrene, polyethylene, and polypropylene.
3. The method for surface-enhanced raman spectroscopy of micro/nano plastic according to claim 2, wherein when the micro/nano plastic is polystyrene, the preparing the micro/nano plastic solution comprises:
placing water into a reactor, heating and stirring under nitrogen atmosphere, removing oxygen in the water, adding styrene monomer into the reactor, stirring uniformly, adding 2, 2-azo-bis (2-methylpropyl-mi) dihydrochloride solution, reacting for 9-11 hours, carrying out suction filtration or dialysis on the reacted solution, drying to obtain polystyrene powder, and finally dispersing the polystyrene powder in pure water or seawater to obtain the micro/nano plastic solution.
4. The method for detecting the surface-enhanced raman spectrum of the micro/nano plastic according to claim 3, wherein the concentration of the micro/nano plastic and the surface-enhanced raman spectrum signal are in a linear function relation;
wherein, when the micro/nano plastic is polystyrene with the particle size of 100nm, the concentration of the micro/nano plastic is positively correlated with the surface enhanced Raman spectrum signal;
when the micro/nano plastic is polystyrene with the particle size of 500nm, the concentration of the micro/nano plastic is inversely related to the surface-enhanced Raman spectrum signal.
5. The surface-enhanced raman spectroscopy detection method of micro/nano plastic according to claim 4, wherein when the micro/nano plastic is polystyrene with a particle size of 100nm and the concentration in pure water is 0.8mg/mL, the detection limit of the micro/nano plastic is 20 μg/mL; when the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration in pure water is 0.08mg/mL, the detection limit of the micro/nano plastic is 0.188mg/mL.
6. The surface enhanced raman spectrum detection method of micro/nano plastic according to claim 4, wherein when the micro/nano plastic is polystyrene with a particle size of 100nm and the concentration in sea water is 1.6mg/mL, the detection limit of the micro/nano plastic is 30 μg/mL; when the micro/nano plastic is polystyrene with the particle size of 500nm and the concentration in seawater is 0.08mg/mL, the detection limit of the micro/nano plastic is 0.287mg/mL.
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