Magnetic walnut shell biochar material and preparation method and application thereof

Abstract

This invention belongs to the field of environmental monitoring and forensic science testing, specifically relating to a magnetic walnut shell biochar material, its preparation method, and its application. The preparation method involves first pulverizing the walnut shell biochar, modifying it with phosphoric acid, and then loading it with Fe3O4 via a co-precipitation method to obtain the magnetic material. Using this as a magnetic solid-phase extraction adsorbent, combined with gas chromatography-mass spectrometry (GC-MS), it can achieve efficient enrichment and accurate detection of 11 cathinone-type new psychoactive substances in environmental water and urine. The detection process is simple to operate, has a high recovery rate, and strong anti-interference ability.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring and forensic science testing, specifically relating to a magnetic walnut shell biochar material, its preparation method, and its application. Background Technology

[0002] Cathinones are a class of synthetic new psychoactive substances (NPS). Due to their stimulant and hallucinogenic effects, and their relatively low barriers to synthesis and dissemination, their illegal abuse is becoming increasingly prominent. These substances pose a significant threat to the human central nervous system. Short-term abuse can cause symptoms such as increased heart rate and blood pressure, while long-term or excessive exposure can lead to psychological dependence, organ damage, and even death. They enter environmental substrates such as water and urine through the excretion of abusers, posing a potential threat to ecological security and public health. However, environmental water substrates are complex in composition and contain many types of interfering substances, while urine contains low levels of target substances and is often accompanied by interfering metabolites. Therefore, there is an urgent need to develop an efficient pretreatment and accurate detection technology system.

[0003] Currently, the detection of cathinones mainly relies on techniques such as gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). However, the environmental water matrix is ​​complex and contains many coexisting interfering substances. The content of the target substance in urine is low and accompanied by a large number of endogenous metabolites and matrix interference. Direct injection detection is difficult to meet the sensitivity and accuracy requirements. Therefore, sample pretreatment is a key step in the detection process.

[0004] Commonly used pretreatment techniques include liquid-liquid extraction (LLE) and solid-phase extraction (SPE). LLE suffers from drawbacks such as high organic solvent consumption, cumbersome operation, easy emulsification, and unstable recovery rates. Traditional SPE requires packed extraction columns, leading to problems such as column clogging, high adsorbent consumption, long separation time, and difficulty in automation. In recent years, magnetic solid-phase extraction (MSPE) has gained widespread attention due to its advantages of fast separation speed, low organic solvent consumption, and simple operation. However, existing magnetic adsorbents often suffer from high raw material costs, complex preparation processes, poor selectivity for cathinones, and low adsorption capacity, making it difficult to meet the demand for efficient enrichment of trace cathinones in complex matrices. Therefore, there is an urgent need to develop a novel magnetic adsorbent that is readily available, low-cost, has excellent adsorption performance, and facilitates separation, and to establish a supporting efficient pretreatment and precise detection technology system. Summary of the Invention

[0005] To address the problems of high raw material cost, complex preparation process, poor adsorption selectivity for cathinones, and low adsorption capacity in existing magnetic adsorbent technologies, this invention prepares a novel magnetic biochar material using walnut shells as raw material. This material is then used as a magnetic solid-phase extraction (MSPE) adsorbent combined with gas chromatography-mass spectrometry (GC-MS) to establish qualitative and quantitative methods for 11 common cathinones in environmental water and urine. The aim is to provide technical support for environmental monitoring and forensic identification of these substances.

[0006] The purpose of this invention is to provide a method for preparing magnetic walnut shell biochar material, the method comprising the following steps:

[0007] (1) Pulverize the walnut shell biochar to obtain powder raw material; this step increases the specific surface area of ​​the biochar, which can make the subsequent phosphoric acid modification, iron ion adsorption and magnetic loading reaction more complete and uniform. (2) Add phosphoric acid solution to the powder raw material for modification treatment, and then dry it to obtain modified walnut shell biochar. This step further enriches the pore structure of biochar through the etching and activation effect of phosphoric acid, and introduces a large number of active functional groups such as hydroxyl and carboxyl groups on the surface, which greatly improves the adsorption capacity and selectivity of cathinone-like substances. (3) The modified walnut shell biochar is added to an iron source solution for dispersion treatment to obtain a mixed dispersion; this step enables the modified biochar to be fully dispersed in the iron source solution, prevents agglomeration, and allows Fe to be fully dispersed. 3+ Fe 2+ Ions are fully adsorbed onto the pores and active functional group sites on the surface of biochar, providing uniform nucleation sites for the subsequent in-situ generation of Fe3O4 particles. (4) Under an inert atmosphere, an alkaline solution is added dropwise to the mixed dispersion, and then the mixture is heated to react and a reaction solution is obtained. The inert atmosphere in this step can prevent Fe ions from being oxidized, ensure the stoichiometric ratio of Fe3O4, and avoid a decrease in magnetic properties. (5) Wash the product in the reaction solution until neutral and dry it to obtain the magnetic walnut shell biochar material. In this step, repeated washing can remove unreacted iron salts, ammonia and other soluble impurities, and avoid residual impurities from affecting the subsequent adsorption performance GC-MS detection results. The neutral pH can also ensure that the material will not change the acidity or alkalinity of the sample to be tested during the subsequent magnetic solid phase extraction process, and ensure the adsorption efficiency of the target analyte.

[0008] Preferably, in step (1), the walnut shell biochar is pulverized and passed through a 200-mesh sieve to obtain powder raw material. Uniform particle size (passing through a 200-mesh sieve) ensures consistent performance across different batches of products, avoiding uneven reaction and wasted adsorption sites caused by large particles.

[0009] Preferably, in step (2), a 20-90 vol% phosphoric acid solution is added to the powdered raw material, stirred and allowed to stand for 3-5 hours, then filtered to remove the phosphoric acid solution. The mixture is then repeatedly washed with deionized water until the pH is neutral. The resulting solid product is dried at 80-90°C for 10-12 hours, and then cooled to room temperature to obtain modified walnut shell biochar. Washing to neutral removes residual phosphoric acid, preventing acidic impurities from interfering with the subsequent iron salt co-precipitation reaction; drying removes moisture to obtain a stable modified intermediate.

[0010] Preferably, in step (3), FeCl3·6H2O and FeCl2·4H2O are dissolved in water to obtain an iron source solution, and then the modified walnut shell biochar is added and ultrasonically dispersed for 10-20 minutes to obtain a mixed dispersion.

[0011] Preferably, in step (4), under a nitrogen atmosphere, an ammonia solution is added dropwise to the mixed dispersion, and then the mixture is stirred at 80-90°C for 25-30 minutes to obtain a reaction solution. The addition of ammonia provides an alkaline environment, triggering the Fe reaction. 3+ with Fe 2 + The co-precipitation reaction generates Fe3O4 nanoparticles in situ on the surface of biochar.

[0012] Preferably, in step (5), the product in the reaction solution is repeatedly washed with deionized water until the solution pH is neutral, and the resulting solid product is dried at 70-80℃ for 24-30h to completely remove moisture, thus obtaining the magnetic walnut shell biochar material.

[0013] Based on the same technical concept, another aspect of the present invention is to provide a magnetic walnut shell biochar material obtained by the preparation method described above.

[0014] Based on the same technical concept, another aspect of the present invention is to provide the application of the magnetic walnut shell biochar material in the preparation of cathinone-based adsorbents.

[0015] Based on the same technical concept, another aspect of the present invention is to provide a method for detecting cathinone-type novel psychoactive substances, the method comprising the following steps: (I) Pretreatment process for magnetic solid phase extraction (I-1) Take the sample to be tested and adjust the pH to alkaline; (I-2) Add the magnetic walnut shell biochar material to the sample to be tested and vortex it, while using a magnet for adsorption; (I-3) After completion, discard the supernatant and add eluent to elute, and collect the eluent; (II) Post-processing of gas chromatography-mass spectrometry The eluent was analyzed using gas chromatography-mass spectrometry.

[0016] Preferably, the method includes the following steps: (I) Pretreatment process for magnetic solid phase extraction (I-1) Take 5 mL of the environmental water sample or urine sample to be tested into a 10 mL stoppered test tube and adjust the pH to 8-10; (I-2) Add 150 mg of the magnetic walnut shell biochar material to the sample to be tested and vortex for 5 min, while placing a magnet on the outer wall of the bottom of the test tube for adsorption. (I-3) After completion, discard the supernatant and add 1 mL of ethyl acetate as eluent for 5 min, and collect the eluent; (II) Post-processing of gas chromatography-mass spectrometry The eluent was separated using a weakly polar DB-5 MS column as the stationary phase, and then analyzed.

[0017] The beneficial effects of this invention are as follows: 1. Excellent adsorption performance and high enrichment efficiency: Phosphoric acid modification can introduce a large number of active functional groups such as hydroxyl and carboxyl groups on the surface of biochar. Combined with the well-developed pore structure of walnut shell biochar itself, it has a high adsorption capacity for cathinones (the maximum theoretical adsorption capacity for methcathinone reaches 3.32 mg / g). Under optimized adsorption conditions, the recovery rate of the target substance is close to 100%, which is far superior to traditional adsorbents.

[0018] 2. Convenient magnetic separation and significantly improved operation efficiency: The prepared magnetic walnut shell biochar has typical paramagnetic characteristics with a saturation magnetization of 30 emu / g. Under an external magnetic field, it can achieve rapid and thorough separation from the solution system without the need for cumbersome steps such as centrifugation and filtration, which significantly shortens the pretreatment time and reduces the complexity of operation.

[0019] 3. Strong resistance to matrix interference, accurate and reliable detection results: The established magnetic solid-phase extraction-gas chromatography-mass spectrometry method can effectively remove matrix interference from environmental water and urine. The matrix effect of 11 target substances is between 89.56% and 111.44%, with no obvious strong inhibition or enhancement effect. The method has a wide linear range and low detection limit, with intra-day precision ≤9.31% and inter-day precision ≤10.22%, meeting the requirements for qualitative and quantitative detection of trace cathinones.

[0020] 4. Green and economical raw materials, simple and controllable preparation process: Biochar is prepared by using walnut shells, agricultural and forestry waste, as raw materials, realizing the resource utilization of waste and significantly reducing the production cost of adsorbents; Magnetic materials are prepared by a two-step method of phosphoric acid modification + co-precipitation magnetic loading, with fewer process steps, mild reaction conditions, no need for complex equipment, and easy to scale up for industrial production.

[0021] 5. Wide range of applicable matrices and diverse application scenarios: This method is applicable to the detection of cathinones in both environmental water samples and human urine samples, and can provide technical support for multiple fields such as environmental water pollution monitoring, screening of toxins in abusers, and forensic identification. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the magnetic solid-phase extraction process.

[0024] Figure 2 This is a statistical chart showing the adsorption performance of different plant-based biochars.

[0025] Figure 3 This is a statistical chart showing the recovery rate of methcathinone after biochar was modified with different modifiers.

[0026] Figure 4 These are SEM (a) and TEM (b) images of magnetic walnut shell biochar material.

[0027] Figure 5 This is the infrared spectrum of magnetic walnut shell biochar material.

[0028] Figure 6 This is a hysteresis loop diagram of magnetic walnut shell biochar material.

[0029] Figure 7 This is a graph showing the recovery rate of methcathinone under different magnetic solid-phase extraction conditions.

[0030] Figure 8 These are the fitting curves of the Langmuir and Freundlich isothermal adsorption models.

[0031] Figure 9 The selected ion chromatograms are of 11 cathinone-based new psychoactive substances (the compounds corresponding to each peak number are the same as in Table 2). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] (I) Instruments and Reagents (1) The instruments used in the specific embodiments of the present invention are mainly: QP2020 NX gas chromatograph-mass spectrometer (Shimadzu Corporation, Japan); HC-3018 high-speed centrifuge (Anhui Zhongke Zhongjia Scientific Instrument Co., Ltd.); XW-80A micro vortex mixer (Shanghai Huxi Analytical Instrument Co., Ltd.); 2243-CW electronic analytical balance (Sartorius Scientific Instrument Co., Ltd.); novel nano-pulverizer (Dongguan Hailu Intelligent Electric Co., Ltd.); SZCL-2 magnetic stirrer (Gongyi Yuhua Instrument Co., Ltd.); SHA-B constant temperature shaker (Suzhou Guohua Instrument Co., Ltd.); SHB-Ⅲ circulating water multi-purpose vacuum pump (Tianjin Sadelis Experimental Analytical Instrument Manufacturing Plant); DHG-9053A electric heating drying oven (Shanghai Jinghong Experimental Equipment Co., Ltd.); Supra 55 scanning electron microscope (Zeiss AG, Germany); Tecnai GZ F20 transmission electron microscope (FEI Corporation, USA); 5700 Fourier transform infrared spectrometer (Tianjin Zhongke Ruijie Technology Co., Ltd.); ADE Model EV7 System vibrating sample magnetometer (MicroSense, USA).

[0034] (2) The reagents used in the specific embodiments of the present invention are mainly: (2-1) Eleven new cathinone psychoactive substances, including cathinone, methcathinone, N-ethylpentanone, 4-chloroethylcathinone, 1-(4-methylphenyl)-2-(methylamino)-1-pentanone, N-ethylhexanone, 4-chlorobutanone, 4-chloropyrroloacetone, 4-fluoropyrrolohexanone, 4-chloropyrrolopentanone, and 4-chloropyrrolohexanone, were all derived from seized drugs. The chemical structural information of these eleven new cathinone psychoactive substances is shown in Table 1.

[0035] Table 1. Chemical structural information of 11 cathinone-based novel psychoactive substances

[0036] (2-2) Hydrochloric acid, phosphoric acid, potassium hydroxide, hydrogen peroxide (chemically pure, Shenyang Reagent Factory No. 1); nitric acid, sulfuric acid (chemically pure, Shenyang Economic and Technological Development Zone Reagent Factory); ethyl acetate, n-hexane, cyclohexane, acetone, acetonitrile, methanol (analytical grade, Shandong Yuwang Hetianxia New Materials Co., Ltd.); ammonia, FeCl3·6H2O, FeCl2·4H2O (analytical grade, Shenyang Yuwang Chemical Glass Instrument Co., Ltd.); blank water sample was taken from Dingxiang Lake, Shenyang; urine sample was taken from healthy adult male volunteers; deionized water was prepared by a Milli-Q pure water system from the United States.

[0037] (2-3) The 16 kinds of biochar, including walnut shells, apricot shells, peach shells, rice shells, coconut shells, wheat straw, peanut shells, bamboo charcoal, corn cobs, corn stalks, soybean stalks, rapeseed stalks, reed stalks, fir sawdust, coal, and birch, were all purchased from Henan Lize Environmental Protection Technology Co., Ltd.

[0038] (II) Instrument Operating Conditions (1) Chromatographic conditions DB-5MS column (30m × 0.25mm, 0.25μm); injection port temperature 260℃; carrier gas nitrogen, flow rate 1mL / min; split injection, split ratio 20:1; column temperature program: initial temperature 100℃, hold for 3min; increase to 280℃ at a rate of 10℃ / min, hold for 5min.

[0039] (2) Mass spectrometry conditions Electron impact ion (EI) source, electron energy 70 eV; full scan monitoring mode, scan range m / z 40–500; transfer line temperature 280 °C. Other mass spectrometry parameters are shown in Table 2.

[0040] Table 2. GC-MS chromatographic-mass spectrometry parameters of 11 cathinone-based novel psychoactive substances

[0041] Example 1 This embodiment provides a method for preparing magnetic walnut shell biochar material, the preparation method comprising the following steps: (1) Weigh 15g of walnut shell biochar, pulverize it using a nano-pulverizer, pass it through a 200-mesh (0.075 mm) sieve, and place it in a beaker to obtain powder raw material; (2) Add 600 mL of 20% (volume fraction) phosphoric acid solution to the beaker, stir and let stand for 3 h, filter to remove phosphoric acid solution, wash repeatedly with deionized water until pH stabilizes (pH=7), place the obtained solid product in an oven and dry at 80℃ for 12 h, and then cool to room temperature to obtain modified walnut shell biochar. (3) Weigh 2.35g of FeCl3·6H2O and 0.86g of FeCl2·4H2O and dissolve them in 140mL of water. Add 1g of the modified walnut shell biochar and ultrasonically disperse for 10min to obtain a mixed dispersion. (4) Under nitrogen atmosphere protection, add 5% (volume fraction) ammonia solution dropwise to the mixed dispersion to make the pH of the mixture 10, and stir magnetically in an 80℃ water bath for 30 min to obtain the reaction solution; (5) Wash the product in the reaction solution repeatedly with deionized water until the solution is close to neutral. Place the obtained solid product in an oven and dry it at 80°C for 24 hours to obtain dark brown magnetic walnut shell biochar material.

[0042] Example 2 This embodiment provides a method for preparing magnetic walnut shell biochar material, the preparation method comprising the following steps: (1) Weigh 15g of walnut shell biochar, pulverize it using a nano-pulverizer, pass it through a 200-mesh (0.075 mm) sieve, and place it in a beaker to obtain powder raw material; (2) Add 600 mL of 60% (volume fraction) phosphoric acid solution to the beaker, stir and let stand for 5 h, filter to remove phosphoric acid solution, wash repeatedly with deionized water until pH stabilizes (pH=7), place the obtained solid product in an oven and dry at 90℃ for 10 h, and then cool to room temperature to obtain modified walnut shell biochar. (3) Weigh 2.35g of FeCl3·6H2O and 0.86g of FeCl2·4H2O and dissolve them in 140mL of water. Add 1g of the modified walnut shell biochar and ultrasonically disperse for 20min to obtain a mixed dispersion. (4) Under nitrogen atmosphere protection, add 5% (volume fraction) ammonia solution dropwise to the mixed dispersion to make the pH of the mixture 9.5, and stir magnetically in a 90℃ water bath for 25 min to obtain the reaction solution; (5) Wash the product in the reaction solution repeatedly with deionized water until the solution is close to neutral. Place the obtained solid product in an oven and dry it at 70°C for 30 hours to obtain dark brown magnetic walnut shell biochar material.

[0043] Example 3 This embodiment provides a method for preparing magnetic walnut shell biochar material, the preparation method comprising the following steps: (1) Weigh 15g of walnut shell biochar, pulverize it using a nano-pulverizer, pass it through a 200-mesh (0.075 mm) sieve, and place it in a beaker to obtain powder raw material; (2) Add 600 mL of 90% (volume fraction) phosphoric acid solution to the beaker, stir and let stand for 4 h, filter to remove phosphoric acid solution, wash repeatedly with deionized water until pH stabilizes (pH=7), place the obtained solid product in an oven and dry at 85℃ for 11 h, and then cool to room temperature to obtain modified walnut shell biochar. (3) Weigh 2.35g of FeCl3·6H2O and 0.86g of FeCl2·4H2O and dissolve them in 140mL of water. Add 1g of the modified walnut shell biochar and ultrasonically disperse for 15min to obtain a mixed dispersion. (4) Under nitrogen atmosphere protection, add 5% (volume fraction) ammonia solution dropwise to the mixed dispersion to make the pH of the mixture 9.5, and stir magnetically in a water bath at 85℃ for 25 min to obtain the reaction solution; (5) Wash the product in the reaction solution repeatedly with deionized water until the solution is close to neutral. Place the obtained solid product in an oven and dry it at 75°C for 27 hours to obtain dark brown magnetic walnut shell biochar material.

[0044] Example 4 This embodiment provides a method for detecting cathinone-type new psychoactive substances using magnetic walnut shell biochar material prepared in Example 1. The method includes the following steps: (I) Pretreatment process for magnetic solid phase extraction (I-1) Take 5 mL of the environmental water sample to be tested into a 10 mL stoppered test tube and adjust the pH to 8; (I-2) Add 150 mg of the magnetic walnut shell biochar material (prepared in Example 1) to the sample to be tested and vortex for 5 min, while placing a magnet on the outer wall of the bottom of the test tube for adsorption. (I-3) After completion, discard the supernatant and add 1 mL of ethyl acetate as eluent for 5 min, and collect the eluent; (II) Post-processing of gas chromatography-mass spectrometry The eluent was separated using a weakly polar DB-5 MS column as the stationary phase, and then analyzed.

[0045] Comparative Examples 1-15 The difference between Comparative Examples 1-15 and Example 1 is that the types of biochar raw materials are different, while the rest of the operations are the same as in Example 1.

[0046] Comparative Example 1: Comparative Example 1 used apricot shell biochar as raw material.

[0047] Comparative Example 2: Comparative Example 2 used peach shell biochar as raw material.

[0048] Comparative Example 3: Comparative Example 3 used rice husk biochar as raw material.

[0049] Comparative Example 4: Comparative Example 4 used coconut shell biochar as raw material.

[0050] Comparative Example 5: Comparative Example 5 used wheat straw biochar as raw material.

[0051] Comparative Example 6: Comparative Example 6 used peanut shell biochar as raw material.

[0052] Comparative Example 7: Comparative Example 7 used bamboo charcoal biochar as raw material.

[0053] Comparative Example 8: Comparative Example 8 used corn cob biochar as raw material.

[0054] Comparative Example 9: Comparative Example 9 used corn stalk biochar as raw material.

[0055] Comparative Example 10: Comparative Example 10 used soybean straw biochar as raw material.

[0056] Comparative Example 11: Comparative Example 11 used rapeseed straw biochar as raw material.

[0057] Comparative Example 12: Comparative Example 12 used reed straw biochar as raw material.

[0058] Comparative Example 13: Comparative Example 13 used cedar wood chips biochar as raw material.

[0059] Comparative Example 14: Comparative Example 14 used coal-based biochar as raw material.

[0060] Comparative Example 15: Comparative Example 15 used birch biochar as a raw material.

[0061] Comparative Examples 16-30 The difference between Comparative Examples 16-30 and Example 1 is that the type and volume concentration of the modifier in step (2) are different, while the rest of the operations are the same as in Example 1.

[0062] Comparative Example 16: In step (2), a 20% (volume fraction) hydrochloric acid solution was used as a modifier.

[0063] Comparative Example 17: In step (2), a 60% (volume fraction) hydrochloric acid solution was used as a modifier.

[0064] Comparative Example 18: In step (2), a 90% (volume fraction) hydrochloric acid solution was used as a modifier.

[0065] Comparative Example 19: In step (2), a 20% (volume fraction) sulfuric acid solution was used as a modifier.

[0066] Comparative Example 20: In step (2), a 60% (volume fraction) sulfuric acid solution was used as a modifier.

[0067] Comparative Example 21: In step (2), a 90% (volume fraction) sulfuric acid solution was used as a modifier.

[0068] Comparative Example 22: In step (2), a 20% (volume fraction) nitric acid solution was used as a modifier.

[0069] Comparative Example 23: In step (2), a 60% (volume fraction) nitric acid solution was used as a modifier.

[0070] Comparative Example 24: In step (2), a 90% (volume fraction) nitric acid solution was used as a modifier.

[0071] Comparative Example 25: In step (2), a 20% (volume fraction) potassium hydroxide solution was used as a modifier.

[0072] Comparative Example 26: In step (2), a 60% (volume fraction) potassium hydroxide solution was used as a modifier.

[0073] Comparative Example 27: In step (2), a 90% (volume fraction) potassium hydroxide solution was used as a modifier.

[0074] Comparative Example 28: In step (2), a 20% (volume fraction) hydrogen peroxide solution was used as a modifier.

[0075] Comparative Example 29: In step (2), a 60% (volume fraction) hydrogen peroxide solution was used as a modifier.

[0076] Comparative Example 30: In step (2), a 90% (volume fraction) hydrogen peroxide solution was used as a modifier.

[0077] Test characterization example (I) Characterization methods for magnetic walnut shell biochar materials (1) Morphology and particle size determination Scanning electron microscopy (SEM) is used to observe the pore structure of materials, while transmission electron microscopy (TEM) is used to analyze the surface particle distribution and size. SEM uses a high-energy electron beam focused by an electromagnetic lens to scan the material surface, collecting secondary electron signals generated by the interaction of electrons with the material to obtain morphological images. TEM uses an electron gun to emit a high-energy electron beam; as the electrons penetrate the thin material, they interact with atoms, generating signals such as transmitted electrons, scattered electrons, and characteristic X-rays. These signals are collected by detectors and converted into high-resolution images or spectral data, thus achieving atomic-level resolution characterization of the internal structure.

[0078] (2) Fourier transform infrared spectroscopy analysis The prepared magnetic walnut shell biochar material was characterized by Fourier transform infrared spectroscopy to understand its main functional groups.

[0079] (3) Measurement of hysteresis loop The magnetic properties of a material are analyzed by measuring its hysteresis loop using a vibrating sample magnetometer.

[0080] (II) Magnetic Solid Phase Extraction Operation Process The magnetic solid phase extraction operation process is as follows: Figure 1 As shown. Specifically: Take 5.0 mL of environmental water / urine sample into a 10 mL stoppered test tube, add 150 mg of the prepared magnetic walnut shell biochar material (adsorbent) mentioned above, vortex for 5 min, place a magnet on the outer wall of the bottom of the test tube to adsorb the magnetic walnut shell biochar material, and discard the entire supernatant. Add 1.0 mL of ethyl acetate (eluent), vortex for 5 min, press the magnet tightly against the outer wall of the test tube to adsorb the magnetic material, tilt the test tube, collect the ethyl acetate eluent, and inject and determine according to the instrument's operating conditions.

[0081] (III) Solution preparation (1) Preparation of standard solution: Accurately weigh appropriate amounts of 11 cathinone-type new psychoactive substances standards, dissolve and dilute them in methanol to prepare a standard solution with a concentration of 1000 mg / L, and store it at 4℃.

[0082] (2) Preparation of aqueous solution: Take an appropriate amount of blank water sample and add appropriate amounts of standard solutions of 11 cathinone-type new psychoactive substances to obtain a series of aqueous solutions with mass concentrations of 0.02, 0.05, 0.10, 0.50, 1.00, 5.00 and 10.00 mg / L for each target substance.

[0083] (3) Urine preparation: Take an appropriate amount of healthy blank urine sample and add an appropriate amount of standard solutions of 11 cathinone-type new psychoactive substances to obtain a series of spiked urine samples with target substance mass concentrations of 0.02, 0.05, 0.10, 0.50, 1.00, 5.00 and 10.00 mg / L respectively.

[0084] Results Discussion Example (I) Selection of preparation conditions for magnetic walnut shell biochar materials (1) The preparation of magnetic solid-phase extraction materials is the key to the accurate detection of cathinone NPS in environmental water and urine. There are various types of biochar that can be used to prepare such materials. In order to screen the optimal adsorption matrix suitable for the target, this study systematically investigated the adsorption performance differences of 15 plant-based biochars and 1 coal-based biochar, including walnut shell, apricot shell, peach shell, rice shell, coconut shell, wheat straw, peanut shell, bamboo charcoal, corn cob, corn straw, soybean straw, rapeseed straw, reed straw, fir sawdust, coal, and birch (Example 1 and Comparative Examples 1-15).

[0085] Experimental results are as follows Figure 2 As shown, walnut shell biochar exhibits the best performance. This is likely due to the well-developed pore structure and abundant functional groups of walnut shell biochar, resulting in superior adsorption and enrichment properties compared to other types of biochar materials. Based on this, this invention selects to prepare an adsorbent material based on walnut shell biochar for the detection of cathinone NPS in environmental water and urine.

[0086] (2) Compare the effects of acid modification, alkali modification and oxidant modification on the adsorption performance of walnut shell biochar.

[0087] Considering the similarity of the NPS structures of the 11 cathinones selected for testing, environmental water samples and urine samples with a cathinone concentration of 0.5 mg / L were used as the test subjects. The modification effects of walnut shell charcoal materials modified with different concentrations of nitric acid solution, hydrochloric acid solution, sulfuric acid solution, phosphoric acid solution, potassium hydroxide solution, and hydrogen peroxide solution were compared (Example 1 and Comparative Examples 16-30). The recovery rates of cathinone under different modification conditions are as follows: Figure 3 As shown.

[0088] Depend on Figure 3 It is evident that when walnut shell biochar is modified using a 20% (v / v) phosphoric acid solution, the methcathinone recovery rate is close to 100%, significantly superior to other modification methods. Therefore, this invention employs a 20% phosphoric acid solution to modify walnut shell biochar material.

[0089] (II) Characterization of magnetic walnut shell biochar material (magnetic walnut shell biochar material prepared in Example 1) (1) SEM (a) and TEM (b) images of magnetic walnut shell biochar material are shown below. Figure 4 As shown. By Figure 4 As can be seen from the SEM image, the magnetic walnut shell biochar material has a rich pore structure; the TEM image shows that the particles are uniformly distributed on the surface of the walnut shell biochar, with a diameter of about 10 nm, the particles are approximately spherical, and there is no obvious agglomeration.

[0090] (2) Infrared spectrum of walnut shell biochar material as shown in Figure 1 Figure 5 As shown. By Figure 5 It can be seen that, compared with raw walnut shell powder, acid-modified walnut shell biochar material has a higher content of 3416 cm⁻¹. 1 In-plane bending vibration of carboxylic acid -OH occurs at 1618 cm⁻¹. 1 The presence of the stretching vibration of carboxylic acid CO at 582 cm⁻¹ indicates that acid treatment successfully introduced hydroxyl and carboxyl functional groups. Magnetic-modified walnut shell biochar was observed at 582 cm⁻¹. 1 The presence of bending vibrations at the Fe-O-Fe bond angle confirms successful loading of Fe3O4 particles. Simultaneously, the acidity of the solution due to the hydrolysis of FeCl3·6H2O and FeCl2·4H2O during the magnetic modification process leads to variations in the sample's viscosity at 3416 and 1618 cm⁻¹. 1 There is a peak, but its height is lower than that of acid-modified walnut shell biochar. The acid-modified and magnetized walnut shell biochar, however, has a peak height of 3416 cm⁻¹. 1 In-plane bending vibration of carboxylic acid -OH occurs at 1618 cm⁻¹. 1 The stretching vibration of carboxylic acid CO appears at 582 cm⁻¹. 1 The bending vibrations at the Fe-O-Fe bond angle indicate that the material possesses both hydroxyl and carboxyl functional groups, which contributes to its dispersibility in aqueous solutions. Furthermore, combined with... Figure 4 It can be seen that Fe3O4 particles are evenly distributed on the surface of acid-modified walnut shell biochar.

[0091] (3) In order to investigate the magnetic properties of the magnetic walnut shell biochar material, its magnetic characteristics were tested using a vibrating sample magnetometer. The obtained hysteresis loop is shown in the figure. Figure 6 As shown. By Figure 6 It is known that the saturation magnetization of the magnetic walnut shell biochar material is 30 emu / g, exhibiting typical paramagnetic characteristics. Under room temperature conditions, the magnetic moment changes gradually with the magnetic field strength, showing almost zero coercivity and remanence. Moreover, it can achieve rapid and thorough separation from the solution system when an external magnetic field is applied.

[0092] (III) Selection of MSPE Conditions The adsorption and enrichment effects of magnetic solid-phase extraction (MSE) are influenced by multiple factors. Optimizing the extraction conditions is crucial for achieving efficient enrichment and separation of the target analyte. This experiment used an environmental water sample with a 0.5 mg / L cathinone spiking concentration as the analyte. The effects of sample solution acidity and ionic strength (achieved by adjusting the sodium chloride concentration), adsorbent dosage, elution method and time, eluent type and dosage, and elution time on the extraction, purification, and enrichment of cathinone were comprehensively investigated. The recovery rates of cathinone under different MSE conditions were shown below. Figure 7 As shown.

[0093] Depend on Figure 7 It can be seen that the recovery rate of cathinone remains at a high level (close to 100%) when the pH is between 8 and 10, while the recovery rate decreases under other acidic conditions. This is because cathinones have basic functional groups (containing amino groups), which are not easily protonated in an alkaline environment and can maintain molecular stability. However, under strongly alkaline conditions, the excess OH- in the solution... - It can compete with methcathinone molecules for adsorption sites on the surface of biochar, and may also damage the functional group structure of biochar, weakening its adsorption capacity. Therefore, the experiment chose to adjust the pH of water and urine samples and process the samples under the condition of pH=8-10.

[0094] The recovery rate of methcathinone remained consistent under different sodium chloride concentrations, indicating that ionic strength had no effect on the adsorption of methcathinone. Therefore, the experiment was conducted without changing the ionic strength.

[0095] As the dosage of magnetic walnut shell biochar increased from 50 mg to 150 mg, the recovery rate of methcathinone continuously increased. When the dosage of magnetic walnut shell biochar exceeded 150 mg, the recovery rate of methcathinone no longer increased, indicating that a good adsorption effect had been achieved. Considering various factors such as recovery rate and economic benefits, a dosage of 150 mg of magnetic walnut shell biochar was selected to meet the requirements of low dosage and high adsorption performance.

[0096] Compared with adsorption methods such as static setting, shaking, and ultrasound, vortexing resulted in the best recovery rate of methcathinone (close to 100%). Therefore, the experiment chose to use vortexing to process the samples.

[0097] When the vortex adsorption time is between 1 and 5 min, the recovery rate of methcathinone continuously increases. If the adsorption time is further extended, the recovery rate of methcathinone no longer increases. Therefore, the adsorption time selected for the experiment is 5 min.

[0098] Compared with eluents such as n-hexane, cyclohexane, methanol, acetone and acetonitrile, ethyl acetate eluent showed the best recovery rate of methcathinone (close to 100%). Therefore, ethyl acetate was selected as the eluent for the experiment.

[0099] When the eluent volume increased from 0.5 mL to 1.0 mL, the recovery rate of methcathinone increased significantly. However, when the volume increased from 1.0 mL to 3.0 mL, the recovery rate tended to stabilize. Therefore, the eluent volume selected for the experiment was 1.0 mL. When the elution time was extended from 1 min to 5 min, the recovery rate of methcathinone continued to increase. When the elution time exceeded 5 min, the recovery rate showed no significant change. Considering extraction efficiency and time cost, the final elution time selected was 5 min.

[0100] (iv) Adsorption behavior of magnetic walnut shell biochar materials To further investigate the adsorption behavior of the prepared magnetic walnut shell biochar material, this invention examined its isothermal adsorption behavior for methcathinone. 5.0 mL of environmental water samples were taken at methcathinone concentrations of 0.1, 0.5, 1.0, 5.0, 10, 20, 30, 40, 50, 75, and 100 mg / L, and 150 mg of magnetic walnut shell biochar material was added to each. The samples were equilibrated for 24 h at 200 rpm in a constant-temperature water bath at 25°C. The magnetic material was then separated using an adsorption magnet on the outer wall of the test tube. After adsorption according to the magnetic solid-phase extraction procedure, 1.0 mL of ethyl acetate was added, and the mixture was vortexed for 5 min. The mixture was then centrifuged at 10000 rpm for 3 min, and the supernatant was used for analysis. The equilibrium adsorption capacity qe (mg / g) was calculated using the following formula, and the result was 3.32 mg / g.

[0101]

[0102] In the formula: ρ0 represents the mass concentration of methcathinone before adsorption, mg / L; V represents the volume of the eluent, mL; m represents the amount of adsorbent used, mg; ρ e This indicates the mass concentration of methcathinone at adsorption equilibrium, in mg / L.

[0103] The adsorption data were fitted using Langmuir and Freundlich isotherm adsorption models, respectively, and the results are as follows: Figure 8 As shown. By Figure 8 It can be seen that the correlation coefficient R of the curves fitted by the Langmuir and Freundlich isothermal adsorption models is... 2 The values ​​were 0.9942 and 0.9352, respectively, indicating that the adsorption of methcathinone by the magnetic walnut shell biochar material is more consistent with the Langmuir isotherm adsorption model. Its adsorption mechanism is monolayer adsorption, and the calculated maximum theoretical adsorption capacity is 3.32 mg / g, which is close to the measured value of 3.35 mg / g.

[0104] (v) Selection of chromatographic conditions Cathinones are diverse and structurally similar, leading to peak overlap when analyzed using gas chromatography-mass spectrometry (GC-MS). This invention investigated the effects of weakly polar DB-5 MS, moderately polar TG-17 MS, and strongly polar DB-WAX columns of the same specifications on the separation of target analytes. The results showed that the weakly polar DB-5 MS column provided good resolution and peak shape for all 11 target analytes; therefore, the DB-5 MS column was chosen as the stationary phase. The selected ion chromatograms of the 11 cathinone NPS are shown below. Figure 9 As shown. By Figure 9 It can be seen that baseline separation can be achieved for each target analyte, meeting the requirements for qualitative and quantitative analysis.

[0105] (vi) Working curve, limit of detection and limit of quantitation A series of mixed standard solutions were measured according to the instrument's operating conditions. A standard curve was plotted with the mass concentration of each target substance as the abscissa and the corresponding peak area as the ordinate. The limit of detection (3S / N) and limit of quantitation (10S / N) were calculated using signal-to-noise ratios (S / N) of 3 and 10, respectively. The final parameters are shown in Table 3. As shown in Table 3, the correlation coefficients of the 11 cathinone-type new psychoactive substances were all greater than 0.9984, and the limits of detection were 0.01–0.02 mg / L.

[0106] Table 3. Linear parameters, detection limit, and quantification limit in urine.

[0107] (vii) Accuracy, precision, recovery rate and matrix effect experiments Spiked recovery tests were conducted on environmental water and urine samples at three concentration levels according to the experimental method. The tests were performed in parallel over one day (6 measurements) and over 6 days (1 measurement per day). The recovery rate and the relative standard deviation (RSD) of the measured values ​​were calculated. The results are shown in Table 4.

[0108] Table 4 shows that the recoveries of the 11 cathinone-type new psychoactive substances ranged from 83.09% to 109.39%, with intra-day precision (RSD) ≤9.31%, inter-day precision (RSD) ≤10.22%, intra-day accuracy ≤12.12%, and inter-day accuracy ≤16.54%. The matrix effect ranged from 89.56% to 111.44%, with no significant strong inhibition or enhancement effects, indicating that the method has good resistance to matrix interference and can meet the requirements for the detection of cathinone-type substances in environmental water and urine.

[0109] Table 4. Results of the experiments on accuracy, precision, and recovery rate in urine.

[0110] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing magnetic walnut shell biochar material, characterized in that, The preparation method includes the following steps: (1) Pulverize the walnut shell biochar to obtain powder raw material; (2) Add phosphoric acid solution to the powder raw material for modification treatment, and then dry it to obtain modified walnut shell biochar; (3) The modified walnut shell biochar was added to an iron source solution and dispersed to obtain a mixed dispersion; (4) Under an inert atmosphere, an alkaline solution is added dropwise to the mixed dispersion, and then the mixture is heated to carry out the reaction to obtain a reaction solution; (5) Wash the product in the reaction solution until it is neutral and dry it to obtain the magnetic walnut shell biochar material.

2. The method for preparing magnetic walnut shell biochar material according to claim 1, characterized in that, In step (1), the walnut shell biochar is crushed and passed through a 200-mesh sieve to obtain powder raw material.

3. The method for preparing magnetic walnut shell biochar material according to claim 1, characterized in that, In step (2), 20-90 vol% phosphoric acid solution is added to the powder raw material, stirred and allowed to stand for 3-5 hours, then filtered to remove the phosphoric acid solution, and then washed repeatedly with deionized water until the pH is neutral. The obtained solid product is dried at 80-90℃ for 10-12 hours, and after cooling to room temperature, modified walnut shell biochar is obtained.

4. The method for preparing magnetic walnut shell biochar material according to claim 1, characterized in that, In step (3), FeCl3·6H2O and FeCl2·4H2O are dissolved in water to obtain an iron source solution, and then the modified walnut shell biochar is added and ultrasonically dispersed for 10-20 minutes to obtain a mixed dispersion.

5. The method for preparing the magnetic walnut shell biochar material according to claim 1, characterized in that, In step (4), under nitrogen atmosphere protection, ammonia solution is added dropwise to the mixed dispersion, and then the mixture is stirred at 80-90℃ for 25-30 minutes to obtain the reaction solution.

6. The method for preparing magnetic walnut shell biochar material according to claim 1, characterized in that, In step (5), the product in the reaction solution is repeatedly washed with deionized water until the solution pH is neutral, and the resulting solid product is dried at 70-80℃ for 24-30h to obtain the magnetic walnut shell biochar material.

7. Magnetic walnut shell biochar material obtained by the preparation method according to any one of claims 1-6.

8. The application of the magnetic walnut shell biochar material according to claim 7 in the preparation of adsorbents for cathinone-based novel psychoactive substances.

9. A method for detecting cathinone-type new psychoactive substances using the magnetic walnut shell biochar material of claim 7, characterized in that, The method includes the following steps: (I) Pretreatment process for magnetic solid phase extraction (I-1) Take the sample to be tested and adjust the pH to alkaline; (I-2) Add the magnetic walnut shell biochar material to the sample to be tested and vortex it, while using a magnet for adsorption; (I-3) After completion, discard the supernatant and add eluent to elute, and collect the eluent; (II) Post-processing of gas chromatography-mass spectrometry The eluent was analyzed using gas chromatography-mass spectrometry.

10. The method according to claim 9, characterized in that, The method includes the following steps: (I) Pretreatment process for magnetic solid phase extraction (I-1) Take 5 mL of the environmental water sample or urine sample to be tested into a 10 mL stoppered test tube and adjust the pH to 8-10; (I-2) Add 150 mg of the magnetic walnut shell biochar material to the sample to be tested and vortex for 5 min, while placing a magnet on the outer wall of the bottom of the test tube for adsorption. (I-3) After completion, discard the supernatant and add 1 mL of ethyl acetate as eluent for 5 min, and collect the eluent; (II) Post-processing of gas chromatography-mass spectrometry The eluent was separated using a weakly polar DB-5 MS column as the stationary phase, and then analyzed.

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