A method for enriching and detecting pesticides based on magnetic biochar from garlic straw

Abstract

The present invention relates to the technical field of pesticide analysis and detection, and in particular to a method for enriching and detecting pesticides based on garlic straw magnetic biochar. The present invention uses garlic straw as a carbon source, activates, calcines and carbonizes it, and then mixes it with a trivalent iron salt and a divalent iron salt solution to obtain garlic straw magnetic biochar. The garlic straw magnetic biochar has a large number of pore structures, a high specific surface area, abundant oxygen-containing functional groups, excellent magnetic properties, and has a good adsorption effect on neonicotinoids and strobilurin pesticides. The garlic straw magnetic biochar of the present invention is used in the magnetic solid phase extraction detection of neonicotinoids and strobilurin pesticides in environmental water samples, and the detection recovery rate and precision are excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticide analysis and detection, in particular to a method for enriching and detecting pesticides based on magnetic biochar from garlic straw. Background Art

[0002] Pesticides, as important agricultural chemicals, are widely used to improve crop yield and quality. Neonicotinoids (NEOs), a representative class of insecticides, are widely used in over 120 countries and account for approximately 25% of the global insecticide market. This is due to their broad-spectrum effectiveness in controlling agricultural pests. Neonicotinoids have high water solubility, good fluidity, and a relatively long half-life, so they can remain in the environment, threatening the behavior of aquatic insects, the survival of bees, and even human health.

[0003] Strobilurin fungicides (SFs) are a relatively new class of agrochemicals. Orysastrobin, as a typical SFs, has been successfully used to control rice leaf blast, panicle blast and sheath blight. Considering the persistence of orysastrobin in water and its mobility in soil, orysastrobin tends to accumulate in aquatic environments. Studies have shown that orysastrobin is often detected at high average concentrations in wetlands, and it is significantly toxic to amphibians, aquatic organisms and soil animals. In order to reduce the level of pesticide residues and protect the health of humans and other organisms, many countries and organizations have set maximum residue limits for neonicotinoid insecticides and orysastrobin, ranging from 0.01 mg kg -1 to 10 mg kg -1 Therefore, it is particularly important to develop effective extraction, enrichment, pretreatment and detection methods for neonicotinoids and orysastrobin in trace amounts of environmental water samples. Summary of the Invention

[0004] Based on the above, the present invention provides a method for enriching and detecting pesticides using garlic straw magnetic biochar. The garlic straw magnetic biochar has a well-developed pore structure, a large specific surface area, abundant oxygen-containing functional groups, excellent magnetic properties, and a high adsorption rate for neonicotinoids and strobilurins.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A first aspect of the present invention provides a method for preparing magnetic biochar from garlic straw, comprising the following steps:

[0007] The garlic straw is placed in an alkaline solution for activation, and then calcined and carbonized to obtain garlic straw biochar;

[0008] The garlic straw biochar is dispersed in a mixed solvent of water and ethanol, and then a trivalent iron salt solution is added, followed by a divalent iron salt solution and an alkaline precipitant to react, thereby obtaining the garlic straw magnetic biochar.

[0009] A second aspect of the present invention provides a garlic straw magnetic biochar prepared according to the above preparation method.

[0010] A third aspect of the present invention provides a use of the above-mentioned garlic straw magnetic biochar in the enrichment and detection of neonicotinoid insecticides or strobilurin fungicides.

[0011] A fourth aspect of the present invention provides a method for enriching and detecting pesticides based on the above-mentioned garlic straw magnetic biochar, comprising placing the garlic straw magnetic biochar in a water sample, mixing and oscillating (to enrich the pesticides in the garlic straw magnetic biochar), separating the garlic straw magnetic biochar from the water sample using a magnet, and then desorbing the separated biochar in an acetone solution to obtain an eluate; filtering the eluate and performing high performance liquid chromatography analysis and detection, and calculating the pesticide content according to a standard curve;

[0012] The pesticide is acetamiprid, imidacloprid, thiacloprid or orysastrobin.

[0013] The present invention discloses the following technical effects:

[0014] The present invention uses garlic straw as raw material, activates and calcines it to obtain biochar, and magnetizes it using an in-situ polymerization method. The prepared garlic straw magnetic biochar has a large number of pore structures, a high specific surface area, rich oxygen-containing functional groups, excellent magnetism, and good adsorption effect on neonicotinoids and strobilurins pesticides.

[0015] The garlic straw magnetic biochar of the present invention is used in the magnetic solid phase extraction detection of neonicotinoids and strobilurin pesticides in environmental water samples, with good detection recovery and precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 The surface morphologies of garlic straw biochar and garlic straw magnetic biochar prepared in Example 1 of the present invention; the left picture shows garlic straw biochar, and the right picture shows garlic straw magnetic biochar. DETAILED DESCRIPTION

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0020] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0021] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0022] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0023] Unless otherwise specified, the "%" in the present invention refers to mass percentage.

[0024] A first aspect of the present invention provides a method for preparing magnetic biochar from garlic straw, comprising the following steps:

[0025] The garlic straw is placed in an alkaline solution for activation, and then calcined and carbonized to obtain garlic straw biochar;

[0026] The garlic straw biochar is dispersed in a mixed solvent of water and ethanol, and then a trivalent iron salt solution is added, followed by a divalent iron salt solution and an alkaline precipitant to react, thereby obtaining the garlic straw magnetic biochar.

[0027] In a preferred embodiment of the present invention, the alkaline solution is a mixture of KOH and water in a mass ratio of 1:(1-2). When preparing the alkaline solution, if the mass ratio of KOH to water exceeds the above range, the high concentration of the alkaline solution will destroy the pore structure of the biochar, reducing its specific surface area and pore volume, and thus its adsorption capacity. The low concentration of the alkaline solution will affect the modification effect and fail to effectively modify the pore structure and surface functional groups. The activation time is 17 hours, and stirring is also performed during the activation process.

[0028] In a preferred embodiment of the present invention, the calcination and carbonization temperature is 800° C. and the time is 4.5 hours.

[0029] In a preferred embodiment of the present invention, the volume ratio of water to ethanol in the mixed solvent is 1:1; the trivalent iron salt is ferric chloride; the divalent iron salt is ferrous chloride; and the alkaline precipitant is aqueous ammonia.

[0030] The mass ratio of the garlic straw biochar to the ferric iron salt and the ferrous iron salt is 1:2:1.

[0031] The present invention does not impose any particular limitation on the amount of the mixed solvent. The amount of the mixed solvent is sufficient to fully disperse the garlic straw biochar and to subsequently synthesize Fe3O4 with divalent iron and trivalent iron.

[0032] In a preferred embodiment of the present invention, after adding the ferric salt solution, the mixture is stirred at 70° C. for 15 minutes, then the temperature is raised to 80° C., the ferrous salt solution and the alkaline precipitant are added, and the mixture is reacted at 80° C. for 70 minutes.

[0033] In a preferred embodiment of the present invention, the biochar is poured into a three-necked flask, water and ethanol are added, and the mixture is sonicated for 30 minutes. Ferrous chloride and ferric chloride are then added to the water and sonicated for 30 minutes. The flask is then removed and placed in a blender. The ferric chloride is first added and stirred at 70°C for 15 minutes. The temperature is slowly raised to 80°C, and the ferrous chloride is added, followed by ammonia water, and stirred for 70 minutes. The mixture is then removed and poured into a centrifuge tube, washed three times with ethanol, and dried to produce the garlic straw magnetic biochar.

[0034] A second aspect of the present invention provides a garlic straw magnetic biochar prepared according to the above preparation method.

[0035] A third aspect of the present invention provides a use of the above-mentioned garlic straw magnetic biochar in the enrichment and detection of neonicotinoid insecticides or strobilurin fungicides.

[0036] In a preferred embodiment of the present invention, the neonicotinoid insecticide is acetamiprid, imidacloprid and / or thiacloprid; and the strobilurin fungicide is orysastrobin.

[0037] A fourth aspect of the present invention provides a method for enriching and detecting pesticides based on the above-mentioned garlic straw magnetic biochar, comprising placing the garlic straw magnetic biochar in a water sample, mixing and oscillating (to enrich the pesticides in the garlic straw magnetic biochar), separating the garlic straw magnetic biochar from the water sample using a magnet, and then desorbing the separated biochar in an acetone solution to obtain an eluate; filtering the eluate and performing high performance liquid chromatography analysis and detection, and calculating the pesticide content according to a standard curve;

[0038] The pesticide is acetamiprid, imidacloprid, thiacloprid or orysastrobin.

[0039] In a preferred embodiment of the present invention, the mass volume ratio of the garlic straw magnetic biochar to the water sample is 20 mg:50 mL; the oscillation time is 30 s;

[0040] The parameters of the HPLC analysis and detection were set as follows: chromatographic column: 5 μm, 150×6 mm; flow rate: 1-5 mL min -1 ; Column temperature: 25°C; Injection volume: 20 μL; Mobile phases are A and B; A is a formic acid aqueous solution with a mass concentration of 0.1%; B is methanol; The gradient elution program is as follows: 10% B from 0 to 2 minutes, 10%-40% B from 2 to 5 minutes, 40%-80% B from 5 to 9 minutes, 80% B from 9 to 12 minutes, 80%-10% B from 12 to 14 minutes, and 10% B from 14 to 16 minutes.

[0041] Garlic straw has numerous functional groups on its surface. When KOH is added, it interacts with the functional groups of the aforementioned raw materials, creating a large number of mesopores and micropores during the calcination process. This significantly increases the biochar's specific surface area and reduces its pore size. This results in a fast adsorption rate and high adsorption capacity for neonicotinoid and strobilurin pesticides. Fe₃O₄ has excellent magnetic properties, and Fe₃O₄ biochar is attached to the biochar surface using an in-situ polymerization method, facilitating the adsorption and extraction process.

[0042] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0043] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1

[0045] A method for preparing magnetic biochar,

[0046] Preparation of garlic straw biochar: Garlic straw was washed with deionized water, air-dried, and cut into small pieces. The garlic straw was then placed in a three-necked flask and immersed in a KOH solution (w / v = 1:2) with stirring for 17 hours. The activated garlic straw was then oven-dried at 70°C to obtain the activated garlic straw. The activated garlic straw was then placed in a tube furnace under a nitrogen atmosphere. The furnace was heated to 800°C at a rate of 3°C / min and held for 4.5 hours. The resulting biochar was then washed with 1 mol / L hydrochloric acid solution and distilled water until neutral. Finally, the biochar was dried in a vacuum oven at 70°C for 6 hours to obtain the garlic straw biochar.

[0047] Preparation of garlic straw magnetic biochar: Weigh 200 mg of ferrous chloride, 400 mg of ferric chloride, and 200 mg of garlic straw biochar. Pour the garlic straw biochar into a three-necked flask, add 50 mL of water and 50 mL of ethanol, and sonicate for 30 minutes. The ferrous chloride and ferric chloride are placed in separate centrifuge tubes, each with 5 mL of water and sonicated for 30 minutes to produce ferrous chloride and ferric chloride solutions. Place the three-necked flask in a blender, first add the ferric chloride solution, rinse the centrifuge tube with 5 mL of water, and stir for 15 minutes at 400-600 rpm at 70°C. Heat the mixture to 80°C at a rate of 2°C / min, add the ferrous chloride solution, rinse the centrifuge tube with 5 mL of water, add 5 mL of 25% ammonia, and stir for 70 minutes. Remove the mixture and pour it into a 50 mL centrifuge tube, rinse three times with ethanol, and dry it at 70°C to obtain the garlic straw magnetic biochar.

[0048] The surface morphology of garlic straw biochar and garlic straw magnetic biochar in this example was observed by scanning electron microscopy. Figure 1 As shown in the figure, garlic straw biochar exhibits a honeycomb structure with a smooth surface and a large number of irregular macropores. Compared with the original garlic straw biochar, some small spherical particles were observed on the garlic straw magnetic biochar, resulting in a rougher surface. These tightly bound particles are the introduced Fe3O4. The magnetic Fe3O4 particles adhere to the biochar surface and do not occupy the biochar's adsorption pores. The successful preparation of magnetic garlic straw biochar not only retains the biochar's original rich pore structure, but the introduction of magnetic particles also enables rapid separation of the hybrid material (garlic straw magnetic biochar) and the solution, making the adsorption and extraction of pesticides more convenient.

[0049] Effect Example 1

[0050] A method for enriching and detecting pesticides based on magnetic biochar from garlic straw is as follows:

[0051] Sample Pretreatment: The environmental water samples used in this test were collected from a river near the orchard and from city tap water. Prior to testing, they were filtered through a membrane filter to remove suspended solids, particulate matter, and other impurities, preventing them from interfering with the analytical results. The treated water samples were stored in brown glass bottles and analyzed the same day.

[0052] Pesticide enrichment using magnetic solid-phase extraction: 20 mg of the garlic straw magnetic biochar prepared in Example 1 was accurately weighed into a 50 mL centrifuge tube. 40 mL of the treated water sample was added and initially mixed by vortexing. The mixture was then shaken on an oscillator for 30 seconds. After adsorption, the supernatant was separated using a magnet to recover the garlic straw magnetic biochar. The recovered garlic straw magnetic biochar and 1 mL of acetone solution were added to the centrifuge tube, vortexed for 40 seconds to fully desorb the analytes, and the eluate was collected. This elution process was repeated three times. The eluate was filtered through a 0.22 μm nylon membrane and analyzed by high-performance liquid chromatography (HPLC).

[0053] HPLC detection conditions:

[0054] Chromatographic column: (5 μm, 150 × 6 mm);

[0055] Flow rate: 0.8 mL / min -1 ;

[0056] Column temperature: 25°C;

[0057] Injection volume: 20 μL;

[0058] Mobile phase: 0.1% formic acid-water (A) and methanol (B);

[0059] The gradient elution program was as follows: 10% (B) from 0 to 2 minutes, 10% to 40% (B) from 2 to 5 minutes, 40% to 80% (B) from 5 to 9 minutes, 80% (B) from 9 to 12 minutes, 80% to 10% (B) from 12 to 14 minutes, and 10% (B) from 14 to 16 minutes.

[0060] The standard curve was prepared as follows:

[0061] A 2 μg / mL standard solution of a strobilurin fungicide (orysastrobin) was diluted with ultrapure water to prepare standard solutions with concentrations of 0.02, 0.1, 0.5, 1, 2, 5, and 10 μg / mL. The standard solution was tested and the results were used to generate a standard curve, plotting peak area against concentration.

[0062] A 1 μg / mL standard solution of neonicotinoid insecticides (acetamiprid, imidacloprid, and thiacloprid) was diluted with ultrapure water to prepare standard solutions at concentrations of 0.01, 0.05, 0.25, 0.5, 1, 2.5, and 5 μg / mL. The standard solution was tested and the results were used to generate a standard curve, plotting peak area against concentration.

[0063] The recovery and precision of the pesticides tested are as follows:

[0064] The four pesticides showed good linearity in the range of 0.05-20 ng / mL, and R 2 ≥0.9997. The LODs (limits of detection) and LOQs (limits of quantification) were 0.21-0.75 ng / mL and 1.70-2.60 ng / mL, respectively, with RSDs (relative standard deviations) ranging from 0.30% to 1.90%. At spike levels of 10, 50, and 100 ng / mL, the recoveries of neonicotinoid insecticides (acetamiprid, imidacloprid, and thiacloprid) were 70.2%-99.5%. At spike levels of 20, 100, and 200 ng / mL, the recoveries of the strobilurin fungicide (orysastrobin) were 70%-97.5%.

[0065] The present invention also verifies the recovery rate of garlic straw magnetic biochar on pesticides - methyl parathion, parathion and malathion. The verification method is the same as that of Example 1. The results are statistically shown in Table 1.

[0066] Table 1

[0067]

[0068] As can be seen from Table 1, the garlic straw magnetic biochar of the present invention has a good recovery rate and adsorption effect on neonicotinoids and strobilurins pesticides such as orysastrobin, acetamiprid, imidacloprid and thiacloprid, but has a poor adsorption effect on other pesticides (organophosphorus), which proves that the obtained magnetic biochar has certain specificity.

[0069] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An application of garlic straw magnetic biochar in the adsorption of orysastrobin, characterized in that: The method for preparing garlic straw magnetic biochar comprises the following steps: The garlic straw is placed in an alkaline solution for activation, and then calcined and carbonized to obtain garlic straw biochar; The garlic straw biochar is dispersed in a mixed solvent of water and ethanol, and then a trivalent iron salt solution is added, followed by a divalent iron salt solution and an alkaline precipitant to react, thereby obtaining the garlic straw magnetic biochar; The alkaline solution is a mixed solution of KOH and water in a mass ratio of 1: (1-2); the activation time is 17 hours; stirring is required during the activation process; The calcination temperature is 800 ° C and the time is 4.5 h; In the mixed solvent, the volume ratio of water to ethanol is 1:1; the ferric salt is ferric chloride; the ferrous salt is ferrous chloride; the alkaline precipitant is ammonia water; the mass ratio of the garlic straw biochar to the ferric salt and the ferrous salt is 1:2:1; After adding the ferric salt solution, stir at 70°C for 15 min, then heat to 80°C, add the ferrous salt solution and alkaline precipitant, and react at 80°C for 70 min.

2. The use according to claim 1, characterized in that The garlic straw magnetic biochar is placed in a water sample, mixed and shaken, the garlic straw magnetic biochar in the water sample is separated by a magnet, and then placed in an acetone solution for desorption to obtain an eluate; the eluate is filtered and then subjected to high performance liquid chromatography analysis and detection, and the orysastrobin content is calculated according to a standard curve.

3. The use according to claim 2, characterized in that The mass ratio of the garlic straw magnetic biochar to the water sample is 1:(1000-3000); and the oscillation time is 30 seconds.

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