A method for analyzing the ionic and particle states of metal nanoparticles in water

Abstract

The present invention belongs to the technical field of environmental analytical chemistry, and specifically relates to a method for analyzing the ionic state and particle state of metal nanoparticles in water. The present invention proposes a method of electron microscope coupling energy spectrum identification-filtration membrane separation and extraction of ionic state-ionic state and mixed state acid hydrolysis-microwave digestion-acid removal and volume fixation-quantitative detection and analysis, while abandoning the sample pretreatment method of hydrofluoric acid digestion of titanium dioxide and zinc oxide, which is safer to operate. The method of the present invention overcomes the dependence and limitations of advanced instruments such as spICP-MS, reduces the cost of testing and analysis, and overcomes the errors caused by the conversion of particle number concentration and ion mass concentration and the requirement for homogenization of water sample particles. At the same time, the present invention innovatively forms a simple, accurate, and high-recovery analysis method based on existing equipment, overcomes the bottleneck of difficult quantitative comparison of ionic state and particle state, makes up for the lack of standardized process of nanoparticle biological quantification, and has good generalizability.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental analytical chemistry, and in particular relates to a method for analyzing the ionic state and particle state of metal nanoparticles in water. Background Art

[0002] Currently, there are more than 5,000 consumer products based on nanoparticles in commercial use in the global market, and the transaction volume is expected to reach US$125.7 billion by the end of 2024. Among the different types of nanoparticles, metals (such as Ag, Cu), metal oxides (such as TiO 2 , ZnO) and other metal-containing nanoparticles such as quantum dots (QDs) can be classified as metal nanoparticles (MNPs). These MNPs are produced in huge quantities and are widely used in medicine, catalysis, photonics, electronics, and environmental remediation due to their wide range of applications and wide range of fields, resulting in the highest predicted concentration in the environment. As the release of MNPs in the aquatic environment gradually increases, they are inevitably affected by the environmental medium, which in turn causes changes in their physical and chemical properties and state of occurrence. Moreover, the particle and ion states released from MNPs will be enriched in aquatic organisms, which will not only cause obvious damage to aquatic organisms, but also affect the migration, transformation, and bioaccumulation of other pollutants, thereby endangering human health and the ecological environment. Therefore, it is necessary to establish a method for analyzing the concentration of metal nanoparticles in water environments and study the concentration of ZnO-NPs and TiO 2 The distribution of -NPs in the water environment is of great significance for evaluating the safety of metal nanoparticles to organisms. By establishing a method for accurately analyzing the concentration of MNPs in the particle and ion states in water, the enrichment law of soluble MNPs in aquatic organisms is studied, which is of great significance for evaluating the safety of metal nanoparticles to organisms.

[0003] According to existing research, the detection, separation and identification of nanoparticles in environmental water bodies face many challenges, especially how to distinguish between particulate and ionic components and evaluate their toxic effects. In recent years, many advanced analytical methods have been gradually applied to the characterization and detection of metal nanoparticles, such as SP-ICP-MS (single particle inductively coupled plasma mass spectrometry) and HFUF (hollow fiber ultrafiltration) technology. For example, Chinese invention patent CN 113933375B proposes a method of online coupling of HFUF and SP-ICP-MS to effectively remove metal ions and retain nanoparticles, especially showing good application prospects in removing high-salt matrix and macromolecular substances. In addition, Chinese invention patent CN 114354464A proposes a quantitative analysis method based on hyperspectral similarity coefficient, which can quickly and accurately analyze the similarity between different metal nanoparticle spectral libraries. Although the accuracy and universality of these methods have been verified, they still need to rely on high-precision equipment. Therefore, there is an urgent need for a standardized method that is easy to operate and has low equipment dependence to achieve efficient identification and detection of ionic and particulate components of nanoparticles in water bodies.

[0004] In recent years, some studies have developed nanoparticle detection methods based on magnetic microsphere enrichment and immune response. For example, Chinese invention patent CN 117630154A proposed a differential counting analysis method for single-particle inductively coupled plasma mass spectrometry. This method abandons the cumbersome sample washing steps and greatly simplifies the operation process, but requires precious metal probes and sp-ICP-MS, which are relatively expensive. The method for estimating the toxicity contribution rate of metal nanoparticles nano-effects and ion effects proposed by CN 106018688 B decomposes the toxic effects of nanoparticles into ion effects and nano-effects through cell immune experiments, further promoting the accuracy of research on the environmental effects of nanoparticles. However, this method can only estimate the toxicity contribution of a single type of soluble nanoparticles, but cannot identify and estimate multi- or mixed nanoparticles. It can be seen that if a method for detecting, identifying and separating nanoparticles with low equipment dependence, simple operation and high repeatability can be developed, it is expected to effectively address the technical bottlenecks in the current research on environmental nanoparticles and has broad application prospects. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for simultaneously identifying soluble and insoluble metal nanoparticle elemental components in a water sample and a sample pretreatment method for separating and digesting ionic and particulate components. The method can be used for the simultaneous quantitative analysis of ionic and particulate states of metal nanoparticles, and there is no need to use hydrofluoric acid throughout the process. The operation is safe and simple, and it is easy to standardize and promote.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for simply and accurately analyzing the ionic state and particle state of metal nanoparticles in water, the method comprising the following steps:

[0008] S1. Identification of metal nanoparticles:

[0009] S11, mixing the mixed solution containing soluble and insoluble metal nanoparticles, and dropping it onto the surface of a copper mesh for adsorption and air drying for later use;

[0010] S12, using a transmission electron microscope (JEM-1400Plus, Japan) to observe the particle morphology of the dried copper mesh, measure the particle size, and take photos for record;

[0011] S13, select the identification area of ​​S12, perform EDS energy spectrum scanning, and identify the type and distribution degree of each metal particle in the agglomerated mixture;

[0012] S2. Separation and extraction of ionic metal solutions:

[0013] After mixing the freshly prepared mixed nanoparticle solution in S11, filter it through a 0.22 μm filter membrane to remove large suspended particles in the water body to prevent clogging and reduce the filtering effect of the nano-scale filter membrane, and then filter it through a 20 nm filter membrane to extract and collect the ionic solution;

[0014] S3. Preparation of the solution to be digested:

[0015] The nano-mixed solution prepared in S11 and the ionic metal solution extracted in S2 are respectively added to microwave digestion tubes to be digested, concentrated nitric acid and concentrated hydrochloric acid are prepared as a digestion solution, and the obtained digestion solution is added to the digestion tube to form a solution to be digested;

[0016] S4. Microwave digestion:

[0017] The solution to be digested in the digestion tube described in S3 was placed in a microwave digestion instrument (CEM Mars6, USA), and the temperature was increased gradually according to the set temperature increase program. After reaching the set temperature, microwave digestion was performed for more than 10 minutes, and the solution was naturally cooled to room temperature.

[0018] S5, remove acid and set volume:

[0019] The digestion solution obtained by cooling in S4 is transferred to a graphite digestion tube, which is placed in a graphite digestion furnace with its opening opened, and the acid is driven out by heating at a temperature of 170-190°C until only 1-2 mL of digestion solution is left. Finally, the remaining digestion solution is diluted to a fixed volume to obtain a simple matrix metal test solution;

[0020] S6. Detection and analysis:

[0021] S61, subjecting the metal test solution obtained in S5 to ICP-OES analysis and detection, and calculating the recovery rate;

[0022] S62. Calculate the concentration of the particulate metal by using the total metal concentration and the ionic metal concentration of the metal test solution obtained in S5, that is, [particulate metal] = [total metal concentration] - [ionic metal].

[0023] Preferably, the mixed solution containing soluble and insoluble metal nanoparticles in S11 is a mixture of soluble nano zinc oxide particles (ZnO) and insoluble nano titanium dioxide particles (TiO 2 ) mixed solution.

[0024] The present invention uses soluble nano zinc oxide particles (ZnO) and insoluble nano titanium dioxide (TiO 2 ) mixed water sample as an example, a method of electron microscope coupled energy spectrum identification - membrane separation and extraction of ionic state - acid hydrolysis of ionic state and mixed state - microwave digestion - acid removal and volume fixation - quantitative detection and analysis was proposed. This method can be used for digestion determination of nano titanium dioxide and nano zinc oxide at the same time, without the need to use hydrofluoric acid throughout the process, with high net efficiency, safe and simple operation, high metal recovery rate, and can be used for simultaneous quantitative analysis of ionic state and particle state of metal nanoparticles, which is convenient for standardization and promotion.

[0025] Preferably, the sizes of the nano titanium dioxide and nano zinc oxide are 30-50 nm and 40-60 nm respectively.

[0026] Preferably, in the digestion solution described in S3, the volume ratio of concentrated nitric acid to concentrated hydrochloric acid is 1:3.

[0027] Preferably, the gradient temperature increase program in S4 is to first increase the temperature to 120°C within 15 minutes, maintain for 5 minutes, then increase the temperature to 150°C within 5 minutes, maintain for 5 minutes, and finally increase the temperature to 180°C within 5 minutes, and maintain for 10 minutes.

[0028] Preferably, the power of microwave digestion in S4 is 1200-1600W.

[0029] Preferably, in S3, the volume ratio of the nano-mixed solution or the ionic metal solution to the digestion solution is 1:4.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The invention discloses a method for synchronously determining the content of ionic and particle components of mixed metal nanoparticles in a water environment. The method comprises the following steps: firstly, a water sample is dripped into a copper mesh for precipitation, and a projection electron microscope coupled to an X-ray energy spectrum (TEM-EDS) is used to analyze and identify the metal type, particle morphology and size of the metal nanoparticles in the water body; for a sample containing soluble metal nanoparticles, an ionic component solution released by the soluble metal nanoparticles is extracted by filtering through a 20-nanometer filter membrane; a concentrated nitric acid digestion solution is added to the extracted ionic component solution, and a digestion solution of concentrated nitric acid and concentrated hydrochloric acid (3:1) is added to an unfiltered water sample (containing particle and ionic states); the water sample added with the digestion solution is digested according to a set microwave digestion program to obtain a sample digestion solution; a clarified sample is obtained by high-temperature digestion in a graphite furnace to drive out the acid and dilute the clarified sample to a fixed volume; and an inductively coupled plasma optical emission spectrometer (ICP-OES) is used to determine the metal element content of the sample digestion solution, and the total concentration, ionic and particle component concentrations in the water sample are calculated.

[0032] The present invention designs a synchronous determination and analysis method of the ionic state and particle state of metal nanoparticles in mixed water samples without the need for advanced instruments such as sp-ICP-MS, reduces the test and analysis costs, overcomes the errors caused by the conversion of particle number concentration and ion mass concentration, and overcomes the requirement for homogenization of water sample particles. At the same time, the digestion method involved in the analysis method abandons the sample pretreatment method of hydrofluoric acid digestion, avoids the danger of the experimenter being exposed to hydrofluoric acid, the method is simpler, and the operation process is safer. In addition, the method adopts microwave digestion, abandons the traditional strategy of firing samples with a muffle furnace, can better control temperature changes and temperature gradients, can better cope with complex samples from different sources, can well remove interfering ions, and improves the recovery rate. The present invention innovatively forms a simple, accurate, and high-recovery analysis method based on existing equipment, overcomes the bottleneck that the ionic state and the particle state are difficult to quantitatively compare, makes up for the lack of a standardized process for the quantitative bio-quantification of nanoparticles, and has good promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The operational flow chart from sample processing to digestion and detection is shown;

[0034] Figure 2 This is a TEM-EDS surface scan image of a mixed solution of nano-titanium dioxide and nano-zinc oxide;

[0035] Figure 3 The recovery rate of nano-titanium dioxide under different digestion solution combinations and different powers;

[0036] Figure 4 The recovery rate of nano zinc oxide under different digestion solution combinations and different powers;

[0037] Figure 5The results are a comparison of the concentrations of different forms of nano zinc oxide (mixed overall, ionic state and particle state) in the mixed solution. DETAILED DESCRIPTION

[0038] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0040] Example: A method for identifying, separating and digesting a mixed water sample of nano-titanium dioxide and zinc oxide, as well as a sample pretreatment and analysis method for determination and analysis

[0041] like Figure 1 As shown, the method comprises the following steps:

[0042] 1. Identification of metal nanoparticles

[0043] 1.1. 40nm ZnO and 50nm TiO with a concentration of 1mg / L 2 After the mixed solution of nanoparticles was ultrasonically dispersed for 15 minutes, 200 μL of the sample was immediately dropped onto the surface of the copper mesh for precipitation, and then placed under a heating lamp to evaporate the water for later use;

[0044] 1.2. Place the dried copper mesh into the sample holder of a transmission electron microscope (JEM-1400Plus, Japan), evacuate the vacuum, adjust the parameters to search for and determine the heterogeneous agglomerated particle area, observe the particle morphology, measure the particle size, and take photos for record;

[0045] 1.3. Select the identification area in step 1.2 and perform EDS spectrum scanning to identify the type and distribution of each metal particle in the agglomerated mixture. Figure 2 As shown in the figure, in the heterogeneous aggregation of nanoparticles, the particulate TiO 2 Obviously more than granular ZnO, both are nearly spherical.

[0046] 2. Separation and extraction of ionic metal solutions

[0047] 2.1. Ultrasonic mix the freshly prepared mixed nanoparticle solution in step 1.1, and then extract 5 mL of the mixed solution using a syringe;

[0048] 2.2. Filter the nanoparticle mixture in step 2.1 through a 0.22 μm filter membrane to remove large suspended particles in the water to prevent clogging and reduce the filtering effect of the nano-scale filter membrane;

[0049] 2.3. The solution extracted in step 2.2 is further filtered through a 20 nm filter membrane to extract and collect the ionic solution.

[0050] 3. Preparation of digestion solution

[0051] Take 2 mL of the mixed nanoparticle suspension prepared in step 1.1 and the ionic solution extracted in step 2, and add them into digestion tubes respectively; prepare 8 mL of digestion solution (aqua regia) with concentrated nitric acid (65%-68%) and concentrated hydrochloric acid (36%-38%) in a volume ratio of 1:3, and add the obtained aqua regia solution into the digestion tube to form 10 mL of digestion solution.

[0052] To determine the suitability of the digestate, other acid addition schemes were also tested, including HNO 3 +HCl+HClO 4 (1:3:1),HNO 3 +HF+HClO 4 (4:1:1),HNO 3 +H 2 O 2 +HClO 4 (4:1:1),HNO 3 +H 2 O 2 +HF(4:1:1),HNO 3 +H 2 O 2 +(H 2 SO 4 +(NH 4 ) 2 SO 4 )(4:1:5, where (H 2 SO 4 +(NH 4 ) 2 SO 4 ) was prepared in advance with a mixing ratio of 35mL:4g and boiled).

[0053] 4. Microwave digestion

[0054] The solution to be digested in the digestion tube described in step 3 was placed in a microwave digestion instrument (CEM Mars6, USA). After assembling the microwave digestion tank, the microwave parameters were adjusted and microwave digestion was started. The specific microwave heating program, duration and operating power are shown in Table 1. After digestion for 10 minutes, it was naturally cooled to room temperature.

[0055] In order to determine the suitability of the selected microwave digestion power, powers of 800 W and 1200 W were also tested as controls.

[0056] Table 1 Microwave parameters for microwave digestion

[0057]

[0058]

[0059] 5. Remove acid and set volume

[0060] The digestion solution obtained by cooling in step 4 was transferred to a graphite digestion tube (high borosilicate glass tube), and then opened and placed in a DTD-40 graphite constant temperature digester (Changzhou Pusen Electronic Instrument Factory), and the heating temperature and duration (180°C, 5min) were adjusted to perform the acid-driving operation, and it was appropriate to heat and drive out the acid until only 2mL of the digestion solution remained; finally, the remaining digestion solution was taken out and diluted to 5mL, and the wall of the digestion tube was rinsed with ultrapure water 2-3 times during the volume fixing process to obtain a titanium\zinc ion test solution with a simple matrix, which was stored in a 15mL centrifuge tube and labeled for ICP-OES sampling.

[0061] 6. Detection and analysis

[0062] Agilent metal mixed standard solution was used to construct Ti and Zn standard curves and set parameters. The titanium\zinc ion test solution obtained in step 5 was subjected to ICP-OES analysis and detection, and the recovery rate was calculated. The titanium / zinc ion concentration was determined by the above steps, and the recovery rates were obtained under various acid addition schemes and microwave digestion powers. Figure 3 , Figure 4 The results show that the digestion solution of concentrated nitric acid and concentrated hydrochloric acid (3:1) can ensure the nano-TiO 2 The high recovery rate of nano-ZnO and the relatively simple acid addition scheme without the need to add reagents with high health risks such as HF are the best digestion scheme.

[0063] For soluble metal nanoparticle zinc oxide, the total element concentration in the mixed solution (0.64 mg / L) and the extracted ion concentration (0.44 mg / L) can be directly obtained from the above steps, and the particle concentration (0.20 mg / L) can be obtained by calculation, that is, [particle state] = [total concentration] - [ion state]. Figure 5 As shown in Figure 2, the ionized Zn content is about twice that of the particulate Zn content, which is consistent with the result that the particulate Zn content is less in the electron microscope coupled energy spectrum. The determination of this occurrence form component will help in the subsequent quantitative analysis of bioaccumulation and toxicity.

[0064] In summary, the method of the present invention overcomes the dependence and limitations of advanced instruments such as spICP-MS, reduces the cost of testing and analysis, and overcomes the errors caused by the conversion of particle number concentration to ion mass concentration and the requirement for homogenization of water sample particles. At the same time, the present invention innovatively forms a simple, accurate, and high-recovery analysis method based on existing equipment, overcomes the bottleneck of difficult quantitative comparison of ionic and particle states, makes up for the lack of standardized process for biological quantitative analysis of nanoparticles, and has good promotion.

[0065] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for analyzing the ionic and particle states of metal nanoparticles in water, characterized in that: The following steps are involved: S1. Identification of metal nanoparticles: S11, mixing the mixed solution containing soluble and insoluble metal nanoparticles, and dropping it onto the surface of a copper mesh for adsorption and air drying for later use; S12, using a transmission electron microscope to observe the particle morphology of the dried copper mesh, measure the particle size, and take photos for record; S13, select the identification area of ​​S12, perform EDS energy spectrum scanning, and identify the type and distribution degree of each metal particle in the agglomerated mixture; S2. Separation and extraction of ionic metal solutions: The freshly prepared mixed nanoparticle solution in S11 was mixed, filtered through a 0.22 μm filter membrane to remove large suspended particles in the water, and then filtered through a 20 nm filter membrane to extract and collect the ionic solution; S3. Preparation of the solution to be digested: The nano-mixed solution prepared in S11 and the ionic metal solution extracted in S2 are respectively added to a microwave digestion tube for digestion, wherein the nano-mixed solution uses concentrated nitric acid and concentrated hydrochloric acid as digestion solutions, and the ionic metal solution uses concentrated nitric acid as digestion solution, and the digestion solutions are added to the digestion tube to form a solution to be digested; S4. Microwave digestion: The solution to be digested in the digestion tube in S3 is placed in a microwave digestion instrument, and the temperature is gradually increased according to the set temperature increase program. After reaching the set temperature, microwave digestion is performed for more than 10 minutes, and the solution is naturally cooled to room temperature; S5, remove acid and set volume: The digestion solution obtained by cooling in S4 is transferred to a graphite digestion tube, which is placed in a graphite digestion furnace with its opening opened, and the acid is driven out by heating at a temperature of 170-190°C until only 1-2 mL of digestion solution is left. Finally, the remaining digestion solution is diluted to a fixed volume to obtain a simple matrix metal test solution; S6. Detection and analysis: S61, subjecting the metal test solution obtained in S5 to ICP-OES analysis and detection, and calculating the recovery rate; S62. Calculate the concentration of the particulate metal by using the total metal concentration and the ionic metal concentration of the metal test solution obtained in S5, that is, [particulate metal] = [total metal concentration] - [ionic metal].

2. A method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1, characterized in that: The mixed solution containing soluble and insoluble metal nanoparticles in S11 is a mixed solution containing soluble nano zinc oxide particles and insoluble nano titanium dioxide particles.

3. A method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1 or 2, characterized in that: The sizes of the nano titanium dioxide and nano zinc oxide are 30-50nm and 40-60nm respectively.

4. The method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1, characterized in that: In S3, the volume ratio of concentrated nitric acid to concentrated hydrochloric acid is 1:

3.

5. The method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1, characterized in that: The gradient temperature program in S4 is to first increase the temperature to 120°C within 15 min, maintain it for 5 min, then increase the temperature to 150°C within 5 min, maintain it for 5 min, and finally increase the temperature to 180°C within 5 min, maintain it for 10 min.

6. The method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1, characterized in that: The power of microwave digestion in S4 was 1200-1600W.

7. The method for analyzing the ionic and particle states of metal nanoparticles in water according to claim 1, characterized in that: In S3, the volume ratio of the nano-mixed solution or the ionic metal solution to the digestion solution is 1:4.

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