Preparation method and application of high-selectivity chlorpyrifos biochar surface molecularly imprinted polymer

Abstract

This invention relates to a method for preparing a highly selective molecularly imprinted polymer on the surface of chlorpyrifos biochar and its application. The invention uses modified biochar as a carrier, chlorpyrifos as a template, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent to synthesize a molecularly imprinted polymer with three-dimensional cavities on the surface of the modified biochar. Compared with traditional methods for preparing molecularly imprinted polymers, the method of this invention uses inexpensive straw biochar as a carrier, making it simple and low-cost. The obtained chlorpyrifos biochar surface molecularly imprinted polymer has advantages such as strong adsorption capacity, high specificity and selectivity, high porosity, high specific enrichment efficiency, and fast adsorption equilibrium and desorption rates. Its application in the specific identification, efficient separation, enrichment, and detection of chlorpyrifos residues in environmental water samples broadens the detection range of chlorpyrifos molecules, lowers the detection limit, and improves sensitivity.

Description

Technical Field

[0001] This invention belongs to the fields of materials preparation technology and pesticide residue chemistry, specifically relating to a method for preparing and applying a chlorpyrifos (CPF) molecularly imprinted polymer (CPF-BC-MIP) synthesized on the surface of biochar (BC) using non-covalent molecular imprinting technology. Background Technology

[0002] Chlorpyrifos (CPF) is a non-systemic broad-spectrum organophosphate insecticide developed by Dow AgroSciences. It possesses contact, stomach poison, and fumigation action, and is characterized by high efficiency, safety, and low environmental impact. Since its development and market launch in the United States in 1965, it has remained a consistently popular pesticide worldwide. CPF has wide-ranging agricultural applications, controlling crop and soil pests, and is also used in the sanitation sector to control termites and household pests. While CPF's effectiveness as a highly effective insecticide is widely recognized, its toxicity poses significant risks to human health, the environment, and other organisms. Reports indicate that CPF is a suspected endocrine disruptor; low-dose residues (μg / L-ng / L) exhibit significant biotoxicity, potentially causing harm to the endocrine, respiratory, nervous, or immune systems. CPF is also linked to cancer development; long-term exposure may increase the risk of lung cancer. In the United States, New Zealand, and other countries, it has been classified as a "restricted use" pesticide. Studies have shown that the concentration of chlorpyrifos (CPF) in farmland drainage in China can reach as high as 26.1 μg / L. CPF can easily enter free water bodies through farmland drainage, further spreading and accumulating in the environment, posing a risk to the health of humans and animals.

[0003] Currently, both domestically and internationally, most methods for enriching and detecting organophosphorus pesticides, antibiotics, and other pollutants in environmental water samples utilize liquid-liquid extraction for sample pretreatment. For example, dispersive liquid-liquid microextraction (DLME-SFO) is used to determine chlorpyrifos residues in green tea; nickel-metal-organic framework (Ni-MOF) solid-phase extraction followed by high-performance liquid chromatography-mass spectrometry (HPLC-MS / MS) is used to detect organophosphorus pesticide residues in wheat samples; and solid-phase microextraction and dispersive liquid-liquid microextraction based on suspended organic droplet solidification (DLLME-SFO) are used to extract chlorpyrifos, methyl chlorpyrifos (CPM), and their main degradation product 3,5,6-trichloro-2-pyridinol (TCP) from tomato and cucumber samples, followed by HPLC-UV detection. These methods for extracting, purifying, and detecting chlorpyrifos often involve extraction with organic solvents, liquid-liquid partitioning, and then column chromatography. These methods suffer from significant emulsification, require large amounts of solvent and time, and are characterized by low efficiency and high detection costs.

[0004] Sample pretreatment techniques are a crucial prerequisite for ensuring the high efficiency of trace pesticide residue detection. Commonly used sample pretreatment methods include solid-phase extraction (SPE), stir bar adsorption extraction, solid-phase microextraction, and liquid-liquid extraction. Dispersive solid-phase extraction (DSPE) is a sample pretreatment method based on solid-phase extraction. The adsorbent can be directly added to the sample solution, followed by extraction and desorption. Compared with traditional SPE methods, it eliminates the need for complex processes such as activation, rinsing, and elution in solid-phase extraction. Therefore, this method has advantages such as simple operation (extraction and purification processes only require shaking and high-speed centrifugation), speed, and economy. DSPE can also effectively increase the active surface area between the analyte and the adsorbent, thereby better enriching the target analyte.

[0005] Molecular imprinting, as a novel molecular recognition technology, not only provides specific molecular recognition sites for target molecules compared to natural receptors, but also exhibits significant chemical advantages, such as good chemical stability, simple and economical preparation methods, and reusability. When the target molecule polymerizes with the functional monomer, multiple interaction sites are formed. After the target molecule is eluted, a three-dimensional cavity with multiple interaction sites is formed in the polymer, matching the spatial configuration of the target molecule. Such a cavity will have selective recognition properties for the target molecule and its analogues. However, although molecularly imprinted polymers have unique advantages, they still suffer from drawbacks such as the incomplete removal of template molecules and the susceptibility of recognition sites to destruction after polymerization.

[0006] Many new pesticide extraction technologies have emerged recently, such as accelerated solvent extraction, solid-phase microextraction, supercritical fluid extraction, and purge distillation. However, these technologies require specialized and expensive equipment, making widespread adoption difficult. Conventional solid-phase extraction (SPE) has become a widely used pesticide pretreatment technique in recent years due to its low solvent consumption and simplicity, but it suffers from poor selectivity, complex procedures, and low chlorpyrifos recovery rates. For detection, gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) are commonly used. While expensive large-scale instruments are used to lower the detection limit and improve sensitivity, using polymers prepared using molecular imprinting technology as materials for dispersed solid-phase extraction allows for the separation and extraction of chlorpyrifos target compounds. Combining this with a conventional, affordable high-performance liquid chromatograph with ultraviolet detector (HPLC-PDA) can achieve high selectivity and sensitivity, thereby reducing detection costs. Summary of the Invention

[0007] To address the aforementioned technical problems of poor selectivity, low sensitivity, and high detection costs in the detection of chlorpyrifos, the present invention aims to provide a highly selective chlorpyrifos biochar surface molecularly imprinted polymer and its preparation method. This polymer can be used as an adsorbent material in dispersed solid-phase extraction, shortening the pretreatment time of trace chlorpyrifos pesticide residue samples in aquatic environments, improving detection efficiency and accuracy, and is economical and practical.

[0008] The chlorpyrifos biochar surface molecularly imprinted polymer synthesized by the preparation method of the present invention can form binding sites on the surface of biochar carrier, making it easier to elute and recombine the target analyte. The modified biochar has a high specific surface area and high adsorption capacity. The adsorption mechanism of chlorpyrifos on the surface of biochar mainly includes the following aspects: (1) Due to the abundance of functional groups on the surface of plant-derived biochar materials, hydrogen bonding will occur when chlorpyrifos has hydrogen bond donors or hydrogen bond acceptors, thus being adsorbed; electrostatic interaction is the attraction between the charged adsorbate and the adsorbent; (2) Based on the negative logarithm of the ionization constant of chlorpyrifos and the isoelectric point data of the surface of plant-derived biochar materials, the electrostatic interaction between pesticide and biomass materials can be controlled by adjusting the pH value of the solution; (3) π-π interaction is a weak interaction that often occurs between aromatic rings; (4) Pore filling is related to the size of chlorpyrifos molecules and the pore size and porosity of the material surface, and is a kind of physical adsorption. Due to its extremely high specific surface area and stable chemical properties, this invention uses BC as a supporting material for adsorbents (MIPs) for the enrichment and detection of chlorpyrifos samples.

[0009] This invention uses CPF as a template molecule, acetonitrile as a stabilizer, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent, and 2,2-azobisisobutyronitrile (AIBN) as an initiator to synthesize a molecularly imprinted polymer on the surface of straw biochar. The target molecule CPF is then eluted using acetic acid-methanol to synthesize CPF-BC-MIP. Subsequently, a sample pretreatment method based on molecularly imprinted dispersion solid-phase extraction (CPF-BC-MIP-DSPE) of straw biochar surface was established. Combined with high-performance liquid chromatography, selective enrichment and detection of chlorpyrifos pesticide residues were achieved. Finally, the established method was used to enrich and detect trace amounts of chlorpyrifos pesticide residues in environmental water samples.

[0010] The method for preparing the chlorpyrifos biochar surface molecularly imprinted polymer of the present invention includes the following steps:

[0011] (1) Preparation of biochar;

[0012] (2) Preparation of modified biochar (BC);

[0013] (3) Prepare chlorpyrifos biochar surface molecular imprinted polymer by non-covalent molecular imprinting synthesis technology.

[0014] Furthermore, the preparation method of the chlorpyrifos BC surface molecularly imprinted polymer of the present invention includes the following steps:

[0015] (1) Preparation of biochar

[0016] First, wash and dry the straw, then grind it into powder. Then, place the straw powder in a tube furnace for pyrolysis. After heating is stopped and the temperature is lowered, take out the straw biochar, wash it again, dry it, and seal it for later use.

[0017] (2) Preparation of modified biochar

[0018] Biochar materials were modified using a chemical activation method.

[0019] (3) Preparation of chlorpyrifos BC surface molecularly imprinted polymer by non-covalent molecular imprinting synthesis technology

[0020] Since CPF and MAA can be effectively bound together through hydrogen bonds, ion interactions, and π-π stacking effects, CPF was used as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the crosslinking agent, and modified biochar as the carrier. The mixture was subjected to a polymerization reaction at 65 °C. After the reaction was completed, the polymer was removed, washed with methanol, ground, and the polymer obtained by sieving was used to elute the target molecules with a mixture of methanol and acetic acid. Finally, a highly selective chlorpyrifos BC surface molecularly imprinted polymer was obtained.

[0021] In the above method, the specific conditions for preparing biochar in step (1) are as follows:

[0022] After washing, the straw was dried in a 40℃ oven and then ground into powder. The straw powder was passed through a 60-mesh sieve and then pyrolyzed in a tube furnace at a rate of 10℃ / min to 350℃ for 35 min. A nitrogen atmosphere was maintained during pyrolysis to remove oxygen interference. After holding at this temperature for 6 h, the sample was removed. The sample was washed with ultrapure water to remove impurities and dried in an 80℃ oven. After cooling, the straw biochar was removed, sealed in a plastic bag, and stored in the dark before use.

[0023] The specific conditions for modifying biochar materials by chemical activation in step (2) are as follows: the biochar materials are impregnated with a mixture of chemical reagents (ZnCl2:H2SO4:HNO3=4:3:3, v / v) to carry out the activation reaction. These activators can improve the surface structure of the biochar materials and generate hydrophilic functional groups on their surface to enhance their adsorption performance.

[0024] Preferably, the specific conditions for preparing the chlorpyrifos BC surface molecularly imprinted polymer by non-covalent molecular imprinting synthesis technology in step (3) are as follows:

[0025] S1: Using 0.4 mmol CPF as the template molecule and 1.5 mmol MAA as the functional monomer, add it to 15 mL of chromatographic grade acetonitrile until the CPF is completely dissolved, and then add 6 g of modified biochar.

[0026] S2: Add 8 mmol EGDMA as a crosslinking agent and 15 mg AIBN as an initiator to S1, mix well, sonicate for 10 min, then purge with nitrogen for 10 min. Repeat the sonication and nitrogen purging process three times.

[0027] S3: Finally, purge with nitrogen for 15 min and place at 65 ℃ for polymerization reaction for 18 h. The CPF and MAA in the polymer can be effectively combined through hydrogen bonds, ionic interactions, and π-π stacking effects.

[0028] S4: After the reaction is complete, the polymer is taken out, then centrifuged and washed three times with methanol to ensure that there is no residue of initiator and unreacted monomer. Then the block polymer is ground to pass through a 400-mesh sieve to obtain μm-sized microspheres.

[0029] S5: The polymer passing through the sieve is eluted with a water / acetic acid (8:2, v / v) mixture to remove the target molecules and the template molecule CPF until CPF is no longer detectable in the eluent by HPLC-PDA. Finally, the polymer particles are washed three times with deionized water and dried under vacuum at 60 °C to constant weight to obtain the chlorpyrifos biochar surface molecularly imprinted polymer (CPF-BC-MIP).

[0030] In contrast, the present invention also prepared a non-molecularly imprinted polymer on the surface of chlorpyrifos biochar (CPF-BC-NIP), the preparation process of which is the same as the above process, except that no CPF template molecules are added during the synthesis process, and the other steps are the same as the preparation process of the molecularly imprinted polymer in steps S1-S5 above.

[0031] The application of the chlorpyrifos biochar surface molecularly imprinted polymer prepared by the above method in the detection of chlorpyrifos residues in environmental water samples.

[0032] The chlorpyrifos biochar surface molecularly imprinted polymer prepared by the above method is characterized by using modified biochar as a carrier, CPF as a template molecule, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent to synthesize a molecularly imprinted polymer with three-dimensional cavities on the surface of the modified biochar. The molecularly imprinted polymer has three-dimensional imprinted sites on the biochar surface, exhibiting specific recognition ability for the chlorpyrifos template molecule. The modified biochar is generated from straw through pyrolysis and activated by impregnation with a mixture of ZnCl2, H2SO4, and HNO3. This novel biochar composite material not only possesses the strong adsorption capacity of biochar but also endows it with strong specificity and selectivity. Specific surface area and porosity analysis experiments demonstrate that the chlorpyrifos biochar surface molecularly imprinted polymer prepared by this biochar matrix material surface imprinting technology has higher porosity, stronger specificity, and better enrichment effect.

[0033] The application of the chlorpyrifos biochar surface molecularly imprinted polymer prepared by the above method as a dispersed solid-phase extraction adsorbent material for the enrichment and detection of chlorpyrifos pesticide residues in environmental water samples is also within the scope of protection of this invention.

[0034] The beneficial effects of this invention are reflected in:

[0035] (1) The preparation method of the present invention is simple and low cost. The obtained chlorpyrifos biochar surface molecular imprinted polymer can obtain three-dimensional imprinted sites by introducing templates on the BC surface, thereby generating specific recognition ability for template molecules. It has the advantages of strong adsorption capacity, high specificity and selectivity, high porosity, high specific enrichment efficiency, adsorption equilibrium and fast desorption rate.

[0036] (2) The sample pretreatment technology of dispersion solid phase extraction has enabled the specific identification, efficient separation and enrichment detection of chlorpyrifos in environmental water samples.

[0037] (3) The polymer material prepared by the present invention can be recycled multiple times, which reduces the cost of enrichment detection and has good economic and social benefits. Attached Figure Description

[0038] Figure 1 This is a schematic diagram illustrating the preparation process and principle of the chlorpyrifos biochar molecularly imprinted polymer of the present invention.

[0039] Figure 2 The SEM characterization of the BC, CPF-BC-NIP, and CPF-BC-MIP materials prepared in Example 1 is shown.

[0040] Among them, A: BC (1.0K×), B: BC (2.0K×), C: BC (5.0K×); D: CPF-BC-NIP (5.0K×), E: CPF-BC-MIP (5.0K×), F: CPF-BC-MIP (5.0K×).

[0041] Figure 3 Isotherms of N2 adsorption capacity for BC and CPF-BC-NIP and CPF-BC-MIP composites.

[0042] Figure 4 The pore size distribution curves are for CPF-BC-MIP and CPF-BC-NIP.

[0043] Figure 5 FT-IR characterization of BC(a) and CPF-BC-MIP(b) composites.

[0044] Figure 6TGA characterization of BC(a), CPF-BC-NIP(b) and CPF-BC-MIP(c) composites.

[0045] Figure 7 This describes the effect of the pH value of the extraction solution on CPF adsorption.

[0046] Figure 8 This describes the effect of extraction time on CPF adsorption.

[0047] Figure 9 This describes the effect of extraction temperature on CPF adsorption.

[0048] Figure 10 This describes the effect of the type of desorption reagent on CPF adsorption.

[0049] Figure 11 This describes the effect of desorption time on CPF adsorption.

[0050] Figure 12 This is a comparison of the selectivity factors of CPF-BC-MIP.

[0051] Figure 13 This is a diagram showing the repeated adsorption-regeneration of CPF-BC-MIP.

[0052] Figure 14 This is a selective enrichment chromatogram of soil spiked with 2.0 μg / mL.

[0053] a: CPF-BC-NIP-DSPE; b: CPF-BC-MIP-DSPE.

[0054] Figure 15 This is a diagram illustrating the sample pretreatment process of CPF-BC-MIP-DSPE-HPLC-PDA. Detailed Implementation

[0055] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0056] Example 1: Preparation of molecularly imprinted polymer on the surface of chlorpyrifos BC

[0057] (1) Preparation of biochar

[0058] After washing, the straw was dried in a 40℃ oven and then ground into powder. The straw powder was passed through a 60-mesh sieve and then pyrolyzed in a tube furnace at a rate of 10℃ / min to 350℃ for 35 min. A nitrogen atmosphere was maintained during pyrolysis to remove oxygen interference. After holding at this temperature for 6 h, the sample was removed. The sample was washed with ultrapure water to remove impurities and dried in an 80℃ oven. After cooling, the straw biochar was removed, sealed in a plastic bag, and stored in the dark before use.

[0059] (2) Preparation of modified biochar

[0060] Biochar materials were modified using a chemical activation method. Solutions of ZnCl2 (0.1 mol / L), H2SO4 (2 mol / L), and HNO3 (0.5 mol / L) were prepared and used for the activation reaction. The biochar materials were then impregnated with the prepared chemical reagent mixture (ZnCl2:H2SO4:HNO3 = 4:3:3, v / v) for 12 hours. These activators improve the surface structure of the biochar materials and generate hydrophilic functional groups on their surface to enhance their adsorption performance. After the modification reaction was completed, the materials were washed three times with water and then air-dried at room temperature before use.

[0061] (3) Preparation of molecularly imprinted polymers on the surface of chlorpyrifos BC

[0062] First, 0.4 mmol CPF was used as the template molecule and 1.5 mmol MAA as the functional monomer, both added to 15 mL of chromatographic grade acetonitrile until the CPF was completely dissolved. Then, 6 g of modified biochar was added. Next, 8 mmol EGDMA was added as a crosslinking agent and 15 mg AIBN as an initiator, respectively. After mixing thoroughly, the mixture was sonicated for 10 min, followed by nitrogen purging for 10 min. This sonication and nitrogen purging process was repeated three times. Finally, nitrogen purging was applied for 15 min, and the mixture was placed at 65 °C for polymerization for 18 h. The CPF, MAA, and modified biochar in the polymer can effectively bind through hydrogen bonds, ion interactions, and π-π stacking effects. This principle and synthesis process are as follows: Figure 1 As shown. Finally, after the reaction was complete, the polymer was removed, centrifuged, and washed three times with methanol to ensure no initiator or unreacted monomer residues remained. The block polymer was then ground to pass through a 400-mesh sieve to obtain μm-sized microspheres. The polymer passing through the sieve was eluted with a methanol / acetic acid (V / V=8:2) solvent mixture to remove the template molecule CPF until CPF was undetectable in the eluent by HPLC-PDA. The polymer particles were repeatedly precipitated with acetone to remove suspended powder, washed three times with deionized water, and vacuum dried at 60 °C to constant weight to obtain the chlorpyrifos biochar surface molecularly imprinted polymer (CPF-BC-MIP).

[0063] Comparative Example 1:

[0064] The preparation process of the non-molecularly imprinted polymer (CPF-BC-NIP) on the surface of straw-modified biochar is the same as the above process, except that no CPF template molecules are added during the synthesis process. The other steps are the same as the preparation process of the imprinted polymer in Example 1.

[0065] In this invention, the physical structure and thermal stability of the molecularly imprinted polymer on the surface of the prepared chlorpyrifos biochar were characterized by cold field emission scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and specific surface area and porosity analysis experiments.

[0066] (1) SEM characterization of composite materials

[0067] During the experiment, the BC, CPF-BC-NIP, and CPF-BC-MIP composites were characterized by SEM. The SEM results showed the surface structure characteristics of BC, CPF-BC-MIP, and CPF-BC-NIP, as shown in the figure. Figure 2 BC (AC) exhibits the smoothest surface, fewest pores, and no polymer within the pores. Compared to CPF-BC-NIP (D), CPF-BC-MIP (E and F) materials have a rougher surface and more pores containing porous polymers (three-dimensional cavities), while the CPF-BC-MIP surface has more layered wrinkles. Compared to BC, both CPF-BC-MIP and CPF-BC-NIP show increased total pore volume and micropore volume, indicating the presence of more chlorpyrifos adsorption sites. These pores can effectively adsorb CPF, maximizing the effect of dispersed solid-phase extraction.

[0068] (2) BET characterization of composite materials

[0069] Table 1. Structural characteristics of BC, CPF-BC-MIP, and CPF-BC-NIP

[0070]

[0071] Table 1 presents the structural characteristics of three biochar composite materials: BC, CPF-BC-MIP, and CPF-BC-NIP. The table shows that the specific surface area of ​​the three biochar composites increases sequentially (BC < CPF-BC-NIP < CPF-BC-MIP), with CPF-BC-MIP having the largest specific surface area, almost 13 times that of BC. This large specific surface area facilitates adsorption reactions with chlorpyrifos molecules. The increased specific surface area is attributed to the synthesis of molecularly imprinted polymers with three-dimensional cavities on the surface. Compared to BC and CPF-BC-NIP, CPF-BC-MIP exhibits increased total pore volume and micropore volume, indicating the presence of more chlorpyrifos adsorption sites. Therefore, if… Figure 3 The N2 adsorption isotherm results show that, compared with BC and CPF-BC-NIP, CPF-BC-MIP has the highest adsorption capacity, followed by CPF-BC-NIP, while BC has the lowest adsorption capacity. BET results show that the average pore sizes of BC, CPF-BC-MIP, and CPF-BC-NIP are 1.8556 nm, 2.4668 nm, and 2.6946 nm, respectively. Most pores have irregular shapes and rougher surfaces. The organic reagents used in the molecular imprinting synthesis process corrode the biochar, increasing its pore size to mesoporous, which further facilitates the adsorption of chlorpyrifos target molecules. Figure 4 The results showed that the mesopore sizes of CPF-BC-MIP and CPF-BC-NIP were 3.7888 nm and 3.9826 nm, respectively. The pore size of CPF-BC-MIP was slightly smaller than that of CPF-BC-NIP, indicating that it has better hydrophilicity and is more conducive to adsorbing chlorpyrifos in water.

[0072] (3) FTIR characterization of composite materials

[0073] Fourier transform infrared spectroscopy Figure 5 a shows BC, at 3429, 1626 cm. -1 Stretching vibrations of -C=O and COC were observed at 3000 cm⁻¹. -1 The presence of peaks above indicates that BC exhibits saturated CH stretching vibrations. Figure 5 b is the spectrum of CPF-BC-MIP, showing the main adsorption peak at 3440 cm⁻¹. -1 The nearby band belongs to the vibrational and bending modes of OH, 2991 cm. -1 The adsorption band at 3440 cm⁻¹ is a characteristic peak of the stretching vibration of CH₄. -1 A characteristic absorption peak appeared at [location], corresponding to the stretching vibration of the hydroxyl group (OH). The hydroxyl group is a characteristic functional group of molecular imprinting, which has the functions of deprotonation and repulsion of anionic contaminants. Figure 5 b indicates that CPF-BC-MIP has new oxygen-containing functional groups, and the biochar exhibits a new peak in the spectral fingerprint region after EDMA surface cross-linking. Furthermore, in addition to the characteristic absorption peaks in a, b also contains the characteristic absorption peak of the imprinted molecule (1720 cm⁻¹). -1 1447 cm -1 1251 cm -1 and 941 cm -1 This demonstrates that the molecular imprinting crosslinking was successful and that the functional monomers were successfully polymerized on the carbon surface.

[0074] (4) Thermogravimetric analysis (TGA) characterization of composite materials

[0075] Thermogravimetric analysis was performed on the BC, CPF-BC-NIP and CPF-BC-MIP composites, and their thermogravimetric curves are shown in the figure. Figure 6 Curve a shows that between 60-120 °C, the weight percentage of BC decreases by approximately 4.56% with increasing temperature. This is likely due to the easy decomposition of oxygen-containing groups such as -OH and -COOH on the BC surface at high temperatures, leading to a decrease in weight percentage. Curve b shows that when the temperature rises to between 100-200 °C and 200-400 °C, the mass of the CPF-BC-NIP composite gradually decreases, with a weight percentage reduction of approximately 21.71% and 9.41%, respectively. This is mainly because the CPF-BC-NIP material lacks a template molecule (chlorpyrifos) and therefore cannot polymerize; it is likely that only functional monomers and crosslinking agents decompose. Curve c shows good thermal stability between 100-200 °C, possibly due to the polymerization of an organic polymer layer on the BC surface. However, when the temperature rises to between 200-400 °C, the mass of the CPF-BC-MIP composite gradually decreases, with a weight percentage reduction of approximately 28.83%. This is mainly due to the decomposition of the polymer on the BC surface. The fact that BC, CPF-BC-NIP and CPF-BC-MIP composites have different thermal stability also proves that the CPF-BC-MIP composite has been successfully prepared.

[0076] Example 2: Optimization of Dispersive Solid Phase Extraction Conditions

[0077] To achieve optimal enrichment and detection of CPF, a dynamic equilibrium is reached between CPF adsorption and desorption during DSPE. Therefore, the DSPE extraction conditions need to be optimized (pH of the extraction solution, extraction time, extraction and adsorption temperature, type of desorption solvent, and desorption time). 50 mg of CPF-BC-MIP particles and a series of 2.0 μg / mL spiked chlorpyrifos solutions were used to study the extraction performance of DSPE under different experimental conditions. All experiments were performed in triplicate, and the average result was used to optimize and evaluate the selective enrichment effect.

[0078] (1) Optimization of extract pH

[0079] The pH of the sample significantly affects extraction efficiency. A suitable sample solution pH can improve extraction efficiency and reduce matrix interference. In this experiment, the effect of solution pH on extraction efficiency was investigated within a pH range of 2.0 to 12.0. Figure 7As shown, the extraction efficiency was highest at pH 6.0; however, the CPF extraction effect was almost negligible in the pH range of 8.0 to 12.0. The reason for this significant phenomenon may be as follows: when the sample pH is below 6.0, they are neutral molecules, and the analyte CPF exhibits high selective adsorption capacity with CPF-BC-MIP particles through molecularly imprinted pore selection, hydrophobic interactions, and π-π interactions, resulting in the largest peak area. When the pH increases above 6.0, the analyte is protonated. In this case, molecularly imprinted pore selection, hydrophobic interactions, and π-π interactions are suppressed, and the selective adsorption between CPF and CPF-BC-MIP particles is lost. Therefore, the extraction efficiency of CPF is low.

[0080] (2) Optimization of extraction time

[0081] In the CPF-BC-MIP-DSPE method, to achieve the maximum CPF extraction efficiency of the analyte at equilibrium, extraction time curves were studied within the range of 10-60 min. For example... Figure 8 As shown, the peak area of ​​the target analyte increases from 10 to 40 min, reaching its maximum at 40 min. After 40 min, the peak area gradually decreases. This phenomenon may be due to the loss of CPF caused by the prolonged extraction time, which is detrimental to the adsorption between CPF and CPF-BC-MIP particles. Therefore, we chose 40 min as the dispersion solid-phase extraction time.

[0082] (3) Extraction and adsorption temperature

[0083] Temperature changes also affect adsorption efficiency during the adsorption process. In the adsorption experiment using CPF-BC-MIP, the sealed container was placed in a constant-temperature shaking incubator for adsorption by shaking. Experiments were conducted at temperatures of 20 ℃, 30 ℃, 40 ℃, 50 ℃, and 60 ℃. The residual CPF concentration after the reaction was detected using HPLC-PDA. Figure 9 The data shows that within the temperature range of 20 ℃ to 40 ℃, the adsorption capacity of CPF by CPF-BC-MIP gradually increases with increasing temperature. CPF-BC-MIP reaches its maximum adsorption capacity at 50 ℃, and the adsorption efficiency decreases with increasing temperature. Therefore, the optimal adsorption temperature is 40 ℃.

[0084] (4) Optimization of desorption reagent types

[0085] The role of the desorbent is to loosen the bond between the template and the monomer by altering chemical bonds, allowing the template to be eluted in a high-speed, unstable solution environment. Different desorbents are suitable for different polymers; therefore, different types of desorbents have a significant impact on desorption and recovery of the target analyte. This study investigated the elution of the target analyte CPF using a series of desorbents (acetic acid-water (10 / 90, v / v), acetic acid-methanol (10 / 90, 20 / 80, and 30 / 70, v / v), acetic acid-acetonitrile (20 / 80, v / v), and acetic acid-acetone (20 / 80, v / v)). CPF is readily soluble in methanol, and the inherent polarity of the methanol solution is insufficient to elute the template molecules. The hydrolysis of a small amount of acetic acid to generate hydrogen ions facilitates the dissociation of the template molecules from the polymer. The acetic acid in methanol promotes the penetration of the eluent into the CPF-BC-MIP particles, allowing for more thorough contact between the eluent and the adsorbed CPF. Furthermore, acetic acid in the eluent also helps to break the hydrogen bonds between CPF and CPF-BC-MIP. The acidity of the eluent increases with the amount of acetic acid added. If the acidity is too high, the vacancy structure of the polymer may be destroyed, which may reduce the performance of the microspheres. The results are as follows: Figure 10 The results showed that acetic acid-methanol (20 / 80, v / v) could achieve satisfactory extraction results. Therefore, acetic acid-methanol (20 / 80, v / v) was chosen as the desorption reagent and used in subsequent experiments.

[0086] (5) Optimization of desorption time

[0087] Following CPF-BC-MIP extraction, the target compound CPF was desorbed using a 20% acetic acid aqueous solution via vortexing. The effect of a series of desorption times on the extraction efficiency was investigated within the range of 10-50 min at room temperature to ensure complete desorption of all CPF from the three-dimensional pores of the CPF-BC-MIP. The maximum peak area of ​​CPF was reached at 35 min (e.g., ...). Figure 11 As shown in the figure, when desorption exceeds 35 min, the peak area of ​​CPF gradually decreases, which may be because the desorbed analyte CPF can be re-adsorbed by the CPF-BC-MIP particles. However, using a shorter desorption time does not result in complete desorption. Therefore, 35 min was chosen as the optimal desorption time for the DSPE method.

[0088] Based on the above experimental results, the extraction conditions for the DSPE method are as follows: pH of the extraction solution is 6; extraction time is 40 min; extraction temperature is 40 ℃; desorption solvent is acetic acid-methanol (20 / 80, v / v); desorption time is 35 min.

[0089] Example 3: Performance evaluation of CPF-BC-MIP

[0090] (1) Examination of the selectivity of CPF-BC-MIP

[0091] To evaluate the selectivity of CPF-BC-MIP particles for the target molecule CPF, four organophosphorus compounds (PAM, TLM, and DCV) were selected. Figure 12 A) This applies to selective enrichment comparisons because CPF has a similar molecular structure to these compounds and often coexists with them in real samples. The selectivity factor (SFs) is calculated using: SFs = A M / A N A M and A N The peak areas represent the chromatographic peak areas of the four head organophosphates after treatment with CPF-BC-MIP and CPF-BC-NIP particles, respectively.

[0092] from Figure 12 As shown in Figure B, CPF-BC-MIP particles exhibit the highest SFs for CPF, with an average of 4.24 and an RSD of 7.8% (n=3). In contrast, the average SFs for TLM, PAM, and DCV are 1.16 (RSD=9.6%, n=3), 0.47 (RSD=4.5%, n=3), and 0.23 (RSD=2.7%, n=3), respectively. Clearly, the extraction selectivity of CPF-BC-MIP particles is significantly better than that of the other three organophosphorus pesticides. This suggests that CPF-BC-MIP particles demonstrate a stable and selective adsorption capacity for CPF. This may be attributed to the unique molecular structure of CPF perfectly integrating with the three-dimensional pore shape of the CPF-BC-MIP particles, while PAM, TLM, and DCV cannot be specifically bound and adsorbed into the pores. Therefore, it can be concluded that CPF-BC-MIP particles exhibit good selectivity and enrichment for the template molecule CPF.

[0093] (2) Reusability of CPF-BC-MIP

[0094] To investigate the reusability of CPF-BC-MIP particles, continuous adsorption-regeneration cycles were performed using the same CPF-BC-MIP particles. In each cycle, the CPF-BC-MIP particles were continuously regenerated under vortex conditions with 25 mL of acetic acid-methanol (20 / 80, v / v) and 10 mL of methanol. The use of a large amount of solvent reduced overload effects and interference between each adsorption-regeneration process. The desorption buffer was used for HPLC detection of CPF residues until CPF was no longer detectable. The desorption efficiency was assessed by the recovery rate of the target analyte, CPF. Figure 13The figures show the recovery rates of CPF after different desorption cycles. It can be seen that the recovery rate reaches 91.8% after the first desorption, and the recovery rate changes very little after recirculation. The recovery rate remains stable above 83.6% after 6 desorption cycles. These results indicate that CPF-BC-MIP particles are stable and can be used as an adsorbent for extracting target analytes from environmental water samples.

[0095] Example 4: Selective adsorption and enrichment effect of CPF-BC-MIP-DSPE

[0096] CPF-BC-MIP and CPF-BC-NIP particles were used in DSPE experiments to extract a mixed solution of environmental water samples spiked with 2.0 μg / mL CPF and TLM (which has the most similar molecular structure to CPF). The chromatograms of their selective enrichment effects are shown below. Figure 14 As shown in the figure, curve a uses CPF-BC-NIP particles for DSPE pretreatment, but it has almost no selective enrichment of CPF. Compared with CPF-BC-NIP, after enrichment with CPF-BC-MIP-DSPE, curve b shows that the peak area of ​​CPF is significantly increased, and there is obvious selective enrichment of CPF. The three-dimensional pores and matching recognition sites of CPF-BC-MIP improve the extraction selectivity of CPF. For the adsorption capacity of CPF-BC-NIP, the non-specific adsorption of BC is the main factor. However, due to the difference in molecular structure between TLM and CPF, TLM cannot be specifically recognized by the imprinted pores of CPF-BC-MIP, resulting in almost no extraction selectivity of CPF-BC-MIP for TLM.

[0097] Example 5: Application of CPF-BC-MIP

[0098] The chlorpyrifos activated carbon surface molecularly imprinted polymer from Example 1 was used to determine chlorpyrifos pesticide residues in environmental water samples.

[0099] (1) Sample extraction

[0100] After taking environmental water samples (such as Baisha River and tap water), they were first filtered through a 0.45 μm filter membrane, then through a 0.22 μm filter membrane, and then stored at 4 ℃.

[0101] (2) Dispersive solid-phase extraction

[0102] First, adjust the pH of 30 mL of environmental water sample to 6.0. Then, add 50 mg of CPF-BC-MIP and place in a 40 °C constant temperature shaking incubator for adsorption for 40 min. After extraction, centrifuge and slowly discard the supernatant. Add 10 mL of acetic acid-methanol (20 / 80, v / v), vortex for desorption for 35 min, and centrifuge to precipitate. Finally, concentrate the supernatant to 1 mL through a 0.22 μm filter membrane using nitrogen blowing. Transfer the supernatant to a sample vial for HPLC-PDA analysis. The entire extraction process is as follows: Figure 15 As shown.

[0103] Conclusion: Under optimal extraction conditions, the quantitative parameters of the CPF-BC-MIP-DSPE method were evaluated using HPLC-PDA data, including: linear range, linear equation, and correlation coefficient (R²). 2 The limits of detection (LOD), limit of quantitation (LOQ), and relative standard deviation (RSD) were determined, and the results are shown in Table 2.

[0104] Table 2 Quantitative evaluation of CPF using the CPF-BC-MIP-DSPE method

[0105]

[0106] The results in Table 2 show that the CPF-BC-MIP-DSPE method exhibits good stability. The linear equation for CPF is y = 248.68x + 42190 (where y represents the peak area of ​​CPF and x represents the concentration of the CPF standard solution); the linear range is 4–1500 ng / mL; and the linear correlation coefficient is 0.9982. We determined the limits of detection and quantitation for CPF using the calculated signal-to-noise ratio (S / N), which were 1 ng / mL (S / N = 3) and 4 ng / mL (S / N = 10), respectively. The accuracy of the CPF-BC-MIP-DSPE-HPLC method was investigated by performing intra-day precision (6 measurements on the same day) and inter-day precision (3 measurements on the same day for 3 consecutive days). The results are shown in Table 2. The intra-day precision RSD for CPF was 4.7%, and the inter-day precision RSD for CPF was 6.2%. These data indicate that the proposed method is acceptable and stable for the selective extraction of CPF.

[0107] The chlorpyrifos-activated carbon surface molecularly imprinted polymer of this invention was used as an adsorbent in dispersion solid-phase extraction to adsorb chlorpyrifos pesticide residues in environmental water samples, which were then detected by HPLC. To evaluate the accuracy of the established analytical method, spiked recoveries were used to analyze real environmental water samples from Baisha River (Chengyang District, Qingdao City, Shandong Province) and laboratory tap water samples. Filtered samples were added with a mixture of CPF and TLM at concentrations of 10 ng / mL, 100 ng / mL, and 1000 ng / mL, followed by extraction using the previously optimized and analyzed method. Analysis of the Baisha River samples showed recoveries ranging from 81.2% to 103.6%, and RSDs (n=3) ranging from 4.2% to 9.2%, with specific data listed in Table 3.

[0108] Table 3 Results of spiked recovery of Baisha River samples

[0109]

[0110] The recovery rate for tap water samples was 83.7-102.6%, and the RSD (n=3) ranged from 5.2-7.6%. Specific data are listed in Table 4.

[0111] Table 4. Results of Spike Recovery Rate Measurement in Tap Water Samples

[0112]

[0113] The above recovery results indicate that the sample matrix components of environmental water samples have a negligible impact on the enrichment and detection of CPF. This demonstrates the application of the chlorpyrifos activated carbon surface molecularly imprinted polymer material of this invention in the detection of chlorpyrifos pesticide residues in environmental water samples.

[0114] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly selective chlorpyrifos biochar surface molecularly imprinted polymer, characterized in that, Includes the following steps: (1) Preparation of biochar After washing, the straw was dried in an oven at 40℃ and then ground into powder. The straw powder was passed through a 60-mesh sieve and then pyrolyzed in a tube furnace at a rate of 10℃ / min to 350℃ for 35 min. During the pyrolysis process, a nitrogen atmosphere was maintained to remove oxygen interference. After holding at this temperature for 6 h, the sample was removed. The sample was washed with ultrapure water to remove impurities and dried in an oven at 80℃. After cooling, the straw biochar was removed, sealed in a plastic bag, and stored in the dark before use. (2) Preparation of modified biochar The biochar material was activated by impregnating it with a mixture of ZnCl2, H2SO4, and HNO3 to achieve chemical modification of the biochar material. (3) Preparation of chlorpyrifos-biochar surface molecularly imprinted polymer by non-covalent molecular imprinting synthesis technology Using modified biochar as a carrier, chlorpyrifos as a template molecule, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent, the polymer was subjected to a polymerization reaction at 65 °C. After the reaction was completed, the polymer was removed, washed with methanol, ground, and the polymer obtained by sieving was eluted with a mixture of methanol and acetic acid to remove the target molecules. Finally, a highly selective chlorpyrifos biochar surface molecularly imprinted polymer was obtained.

2. The method for preparing the highly selective chlorpyrifos biochar surface molecularly imprinted polymer as described in claim 1, characterized in that, Step (3) includes: S1: Using 0.4 mmol CPF as the template molecule and 1.5 mmol MAA as the functional monomer, add it to 15 mL of chromatographic grade acetonitrile until the CPF is completely dissolved, and then add 6 g of modified biochar. S2: Add 8 mmol EGDMA as a crosslinking agent and 15 mg AIBN as an initiator to S1, mix well, sonicate for 10 min, then purge with nitrogen for 10 min. Repeat the sonication and nitrogen purging process three times. S3: Finally, blow nitrogen for 15 min and place it at 65 ℃ for polymerization reaction for 18 h; S4: After the reaction is complete, the polymer is taken out, then centrifuged and washed three times with methanol to ensure that there is no residue of initiator and unreacted monomer. Then the block polymer is ground to pass through a 400-mesh sieve to obtain μm-sized microspheres. S5: Elute the polymer passing through the sieve with a water / acetic acid mixture to remove the target molecules and the template molecule CPF until HPLC-PDA can no longer detect CPF in the eluent; finally, wash the polymer particles three times with secondary water and dry them at 60 °C until the weight no longer changes.

3. The method described in claim 1 yields a molecularly imprinted polymer on the surface of chlorpyrifos biochar, characterized in that... Using modified biochar as a carrier, chlorpyrifos as a template molecule, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent, a molecularly imprinted polymer with three-dimensional cavities is synthesized on the surface of modified biochar. The molecularly imprinted polymer has three-dimensional imprinted sites on the surface of modified biochar, which can specifically recognize the chlorpyrifos template molecule.

4. The application of the chlorpyrifos biochar surface molecularly imprinted polymer prepared by the preparation method described in claim 1 in the detection of chlorpyrifos residues in environmental water samples.

5. The application of the chlorpyrifos biochar surface molecularly imprinted polymer prepared by the preparation method described in claim 1 as a dispersed solid-phase extraction adsorbent material for the enrichment and detection of chlorpyrifos pesticide residues in environmental water samples.

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