A preparation method of flocculent cobalt sulfide, flocculent cobalt sulfide and its application in organophosphorus pesticide detection

Abstract

The invention belongs to the technical field of detection materials, and discloses a preparation method of flocculent cobalt sulfide, flocculent cobalt sulfide and its application in the detection of organophosphorus pesticides. The preparation method comprises the following steps: mixing a halide salt of cobalt with oleylamine to obtain a solution A; mixing sulfur with oleylamine to obtain a solution B; mixing the solution A with the solution B, and heating the obtained mixture to obtain flocculent cobalt sulfide. The preparation method of flocculent cobalt sulfide of the invention uses a specific raw material to prepare the flocculent cobalt sulfide for the detection of organophosphorus pesticides, and the detection process is simple, and the detection result has high sensitivity and good stability.

Description

Technical Field

[0001] The invention belongs to the technical field of detection materials, and particularly relates to a preparation method of flocculent cobalt sulfide, flocculent cobalt sulfide and application of the flocculent cobalt sulfide in the detection of organophosphorus pesticides. Background Art

[0002] Organophosphorus pesticides are a class of organic substances containing phosphorus and may also contain sulfur. Their chemical structure usually contains carbon-sulfur-phosphorus bonds. The use of organophosphorus pesticides has greatly increased food production and effectively alleviated the increasing food crisis. Therefore, the development of convenient, rapid, sensitive and reliable methods for detecting organophosphorus pesticide residues is of great significance to ensure food safety.

[0003] At present, the main methods for detecting organophosphorus pesticide residues are chromatography (including high performance liquid chromatography, gas chromatography and chromatography-mass spectrometry, etc.), enzyme inhibition method (including rapid test card method and spectrophotometry, etc.) and immunoassay (including enzyme-linked immunosorbent assay, fluorescence immunoassay and chemiluminescence immunoassay, etc.). These detection methods either have high requirements for equipment and require professional personnel to operate and maintain, or have high detection costs and are easily interfered by the external environment to produce false positive results. Compared with the above detection methods, electrochemical sensors have the advantages of convenient operation, fast response and high sensitivity. They include two major categories: bio-enzyme electrochemical sensors and non-enzyme electrochemical sensors. Compared with bio-enzyme sensors with high cost, poor stability and difficulty in preparation, non-enzyme electrochemical sensors have the advantages of low cost, high sensitivity, high stability and easy synthesis.

[0004] Therefore, there is an urgent need to provide a non-enzymatic material and method for detecting organophosphorus pesticides, which makes the detection process simple, the detection results highly sensitive and stable. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a preparation method of flocculent cobalt sulfide, flocculent cobalt sulfide and its application in the detection of organophosphorus pesticides. The flocculent cobalt sulfide of the present invention can be used to detect organophosphorus pesticides, which belongs to a non-enzymatic detection method, has a simple detection process, high sensitivity of the detection result and good stability.

[0006] A first aspect of the present invention provides a method for preparing flocculent cobalt sulfide.

[0007] Specifically, a method for preparing flocculent cobalt sulfide comprises the following steps:

[0008] Mixing the halide salt of cobalt with oleylamine to obtain solution A;

[0009] Mix sulfur and oleylamine to obtain solution B;

[0010] The solution A is mixed with the solution B, and the obtained mixture is subjected to heating reaction to obtain the flocculent cobalt sulfide.

[0011] Preferably, the cobalt halide salt includes at least one of CoCl2, CoBr2, and CoI2, and CoCl2 is more preferred.

[0012] Preferably, the cobalt halogen salt and oleylamine (C 18 H 37 The dosage ratio of N) is 0.01-0.5 mol: 3-10 mL, and more preferably 0.02-0.05 mol: 4-8 mL.

[0013] Preferably, the sulfur and oleylamine (C 18 H 37 The dosage ratio of N) is 0.01-0.5 mol: 3-10 mL, and more preferably 0.02-0.05 mol: 4-8 mL.

[0014] The above-mentioned solution A can be called a cationic solution, and the solution B can be called an anionic solution.

[0015] Preferably, the sulfur is sulfur powder.

[0016] Preferably, the mixing method includes stirring mixing or ultrasonic mixing.

[0017] Preferably, the temperature of the heating reaction is 110-125°C, more preferably 115-120°C.

[0018] Preferably, the heating reaction time is 4-8 hours, more preferably 6-8 hours.

[0019] Preferably, the heating reaction is carried out in a Teflon high temperature reactor.

[0020] Preferably, after the heating reaction is completed, the mixture is naturally cooled to room temperature, and then washed and dried to obtain the flocculent cobalt sulfide.

[0021] Preferably, the washing is performed using anhydrous ethanol for 3-8 times.

[0022] Preferably, the drying is carried out at 40-70° C. for 12-24 hours.

[0023] A second aspect of the present invention provides flocculent cobalt sulfide.

[0024] Specifically, a flocculent cobalt sulfide is prepared by the above preparation method.

[0025] A third aspect of the present invention provides an application of flocculent cobalt sulfide in the detection of organophosphorus pesticides.

[0026] Specifically, the above-mentioned flocculent cobalt sulfide is used in the detection of organophosphorus pesticides.

[0027] Preferably, the application is to first prepare the flocculent cobalt sulfide into a non-enzymatic electrochemical sensor, and then use the non-enzymatic electrochemical sensor to detect organophosphorus pesticides.

[0028] Preferably, the method for preparing the non-enzymatic electrochemical sensor comprises the following steps:

[0029] The flocculent cobalt sulfide is mixed with a perfluorosulfonic acid polymer solution and a solvent, and ultrasonically dispersed to obtain a dispersion liquid, and then the dispersion liquid is coated on the surface of an electrode and naturally air-dried to obtain a composite electrode; a three-electrode system is adopted, with the composite electrode as a working electrode, a platinum wire electrode as an auxiliary electrode, and a silver / silver chloride electrode as a reference electrode to form the non-enzymatic electrochemical sensor.

[0030] Preferably, the solvent includes anhydrous ethanol and water, for example, a solvent consisting of 200-300 μL of anhydrous ethanol and 500-600 μL of distilled water.

[0031] Preferably, the mass concentration of the perfluorosulfonic acid polymer solution (ie, Nafion solution) is 3-5%.

[0032] Preferably, the amount of the perfluorosulfonic acid polymer solution added is 100-200 μL, more preferably 100-150 μL.

[0033] Preferably, the ultrasonic power of the ultrasonic dispersion is 150-180W, and the ultrasonic dispersion time is 1-2 hours.

[0034] Preferably, the electrode is a glassy carbon electrode.

[0035] Preferably, a pipette is used to take 5-10 μL of dispersed droplets and apply them on the electrode surface.

[0036] Preferably, the electrode is a clean, impurity-free glassy carbon electrode that is polished and ultrasonically cleaned with 0.01-0.05 μm Al2O3 powder.

[0037] Preferably, the diameter of the electrode is 1-5 mm.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] The preparation method of the flocculent cobalt sulfide of the present invention uses specific raw materials to prepare the flocculent cobalt sulfide for detecting organophosphorus pesticides, has a simple detection process, high sensitivity of the detection result, a low detection limit and good stability.

[0040] The present invention uses oleylamine to provide a weak alkaline environment and etches flocculent cobalt sulfide to form flocculent cobalt sulfide with many exposed cobalt active sites, thereby having a good detection effect on organophosphorus pesticides. If oleylamine and oleic acid are added at the same time, the weak alkaline environment is changed, which will affect the crystallization degree of flocculent cobalt sulfide, resulting in a decrease in the number of active cobalt sites of flocculent cobalt sulfide, thereby reducing the organophosphorus pesticide detection performance of flocculent cobalt sulfide. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a SEM image of the flocculent cobalt sulfide prepared in Example 1;

[0042] Figure 2 is the X-ray diffraction pattern of the flocculent cobalt sulfide prepared in Example 1;

[0043] Figure 3 The glassy carbon electrode and the flocculent cobalt sulfide / glassy carbon composite electrode were respectively -1 1.0mmol L of potassium chloride -1 Cyclic voltammetry curve measured in potassium ferrocyanide / potassium ferrocyanide solution;

[0044] Figure 4 The square wave voltammetry curves measured in different concentrations of parathion;

[0045] Figure 5 It is a linear relationship diagram between the peak value of square wave voltammetric current and parathion concentration;

[0046] Figure 6 This is the square wave voltammetry curve of different cobalt sulfides under the same detection conditions. DETAILED DESCRIPTION

[0047] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0048] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0049] Example 1

[0050] A method for preparing flocculent cobalt sulfide comprises the following steps:

[0051] During the stirring process, 0.05 mol CoCl2 was added to 5 mL oleylamine (C 18 H 37 N) to form solution A; during stirring, 0.05 mol sulfur powder (S) was added to another 5 mL of oleylamine (C 18 H37 N) to form solution B; under continuous stirring, solution A and solution B are mixed, and stirring is continued for 30 minutes to form a uniform mixture; the mixture is transferred to a 50mL Teflon high-temperature reactor, heat treated at 120°C for 8 hours, naturally cooled to room temperature, washed with anhydrous ethanol for 3 times, and dried at 60°C for 24 hours to obtain flocculent cobalt sulfide (CoS).

[0052] Figure 1 This is a SEM image of the flocculent cobalt sulfide prepared in Example 1; Figure 2 This is the X-ray diffraction pattern of the flocculent cobalt sulfide prepared in Example 1. Figure 1 a) and b) are SEM images at different magnifications. Figure 2 Here 2θ represents the diffraction angle.

[0053] An application of flocculent cobalt sulfide in the detection of organophosphorus pesticides comprises the following steps:

[0054] 10 mg of flocculent cobalt sulfide was added to a mixed solution of anhydrous ethanol (300 μL) + distilled water (600 μL) + 5% mass concentration nafion solution (perfluorosulfonic acid type polymer solution, 100 μL), and ultrasonic dispersion was performed at an ultrasonic power of 180 W for 2 h to obtain a uniform flocculent cobalt sulfide dispersion. Using an Eppendorf 10 μL pipette, 10 μL of the flocculent cobalt sulfide dispersion was evenly dropped on the surface of a clean, impurity-free glassy carbon electrode (GCD, 5 mm in diameter) that was polished and ultrasonically cleaned with 0.05 μm Al2O3 powder, and naturally air-dried for 24 h to form a flocculent cobalt sulfide / glassy carbon composite electrode. A three-electrode system was adopted, with the above-mentioned flocculent cobalt sulfide / glassy carbon composite electrode as the working electrode, the platinum wire electrode as the auxiliary electrode, and the silver / silver chloride electrode as the reference electrode to form a non-enzymatic electrochemical sensor that can be used for the detection of organophosphorus pesticides.

[0055] Figure 3 The glassy carbon electrode and the flocculent cobalt sulfide / glassy carbon composite electrode were respectively -1 1.0mmol L of potassium chloride -1 Cyclic voltammetry curve measured in potassium ferrocyanide / potassium ferrocyanide solution; Figure 3 The "GCD" in the figure corresponds to the cyclic voltammetry curve of the glassy carbon electrode, and the "CoS / GCD" corresponds to the cyclic voltammetry curve of the flocculent cobalt sulfide / glassy carbon composite electrode. Figure 3 It can be seen that the flocculent cobalt sulfide has been coated on the surface of the glassy carbon electrode to form a flocculent cobalt sulfide / glassy carbon composite electrode with good performance.

[0056] The non-enzymatic electrochemical sensor was used for the detection of organophosphorus pesticide (parathion), which included the following steps:

[0057] Determine the optimal pH value of phosphate buffer solution: The prepared flocculent cobalt sulfide / glassy carbon composite electrode was used as the working electrode and placed in 0.1 mol L-1 solution containing 10 μM parathion at pH values ​​of 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0. -1 In phosphate buffer solution, square wave voltammetry was used to detect the response current of parathion, and the detection parameters were set as follows: potential range -0.9 to 0 V, potential step of 5 mV, frequency of 10 Hz, and square wave amplitude of 25 mV. By comparing the response current values ​​under different pH conditions, it was determined that the optimal pH value of the phosphate buffer solution was 8.0.

[0058] Determine the optimal incubation potential of the electrode in parathion solution: The prepared flocculent cobalt sulfide / glassy carbon composite electrode was used as the working electrode and placed in 0.1 mol L parathion solution with a pH value of 8.0 and a concentration of 10 μM. -1 In phosphate buffer solution, the incubation potential was set to -0.8V, -0.7V, -0.6V, -0.5V, -0.4V, -0.3V, -0.2V, and -0.1V, and the response current of parathion was detected by square wave voltammetry. The response current values ​​under different incubation potential conditions were compared, and the optimal incubation potential was determined to be -0.6V.

[0059] Determine the optimal incubation time of the electrode in the parathion solution: The prepared flocculent cobalt sulfide / glassy carbon composite electrode was used as the working electrode and placed in a 0.1 mol L solution containing 10 μM parathion at a pH of 8.0. -1 In phosphate buffer solution, after incubation for 60s, 120s, 180s, 240s, 300s, and 360s at an electrode potential of -0.6 V, the response current of parathion was detected by square wave voltammetry. The response current values ​​under different incubation time conditions were compared, and the optimal incubation time was determined to be 240s.

[0060] Draw a standard curve for parathion.

[0061] The prepared flocculent cobalt sulfide / glassy carbon composite electrode was used as a working electrode and placed in a 0.1 mol L solution of parathion at a pH of 8.0 with concentrations of 0.5 μM, 1 μM, 5 μM, 10 μM, 50 μM, 100 μM, 200 μM, and 500 μM. -1 After incubation for 240 seconds at an electrode potential of -0.6 V in a phosphate buffer solution, the response current of parathion was detected by square wave voltammetry. The relationship between the concentration of parathion and the corresponding peak current value was obtained by linear regression, and the detection standard curve of parathion was drawn, as shown in Figure 2. Figure 4 and Figure 5 (In CThe linear regression equation is: y=11.154(±0.797)x+16.864(±1.360), and the detection limit is 0.413μM.

[0062] Actual sample testing:

[0063] Parathion in apple samples was extracted using acetonitrile at a concentration of 0.1 mol L -1 The phosphate buffer was prepared into a sample solution with a pH value of 8.0, the prepared flocculent cobalt sulfide / glassy carbon composite electrode was placed in the sample solution as a working electrode, and incubated for 240 seconds at a potential of -0.6 V. The response current value of parathion in the sample solution was determined by square wave voltammetry, and the recovery rate was between 96.4% and 102.1%, and the RSD was less than 3%, indicating that the flocculent cobalt sulfide / glassy carbon composite electrode prepared by the present invention has good accuracy in actual sample detection and can be used for the determination of parathion residues in actual samples.

[0064] Based on Example 1, Co(NO3)2 and CoSO4 were used to replace CoCl2 in Example 1, respectively. The other components and processes were the same as those in Example 1. The cobalt sulfide obtained was used as Comparative Examples 1 and 2. The peak value of the response current of parathion was detected by square wave voltammetry. Under the same detection conditions as in Example 1, the results were as follows: Figure 6 As shown, Figure 6 Curve "a" corresponds to the flocculent cobalt sulfide of Example 1; curve "b" corresponds to the cobalt sulfide of Example 1; curve "c" corresponds to the cobalt sulfide of Example 2; and curve "d" corresponds to commercial cobalt sulfide.

[0065] from Figure 6 It can be seen that the flocculent cobalt sulfide prepared in Example 1 has better parathion detection performance than the cobalt sulfide in Comparative Examples 1 and 2.

[0066] For the composite electrodes corresponding to the flocculent cobalt sulfide in Example 1 and the cobalt sulfide in Comparative Examples 1 and 2 with the same loading, under the same test conditions, the response peak current values ​​in Comparative Examples 1 and 2 are significantly lower than those of the flocculent cobalt sulfide in Example 1, indicating that the detection performance of the flocculent cobalt sulfide in Example 1 is better than that of the cobalt sulfide in Comparative Examples 1 and 2.

[0067] The mechanism of the flocculent cobalt sulfide for detecting organophosphorus pesticides is as follows: coordinated unsaturated cobalt ions exist on the surface of the flocculent cobalt sulfide, and the cobalt ions combine with sulfur atoms in the organophosphorus pesticide molecules to form cobalt-sulfur bonds of cobalt in the cobalt sulfide and sulfur in the organophosphorus pesticide molecules, which is conducive to the adsorption of the organophosphorus pesticide molecules on the surface of the cobalt sulfide, and current is generated through charge transfer between the flocculent cobalt sulfide and the organophosphorus pesticide molecules, and the generated current is detected by an electrochemical method, and the electrical signal of the generated current is observed, thereby playing a role in detecting the organophosphorus pesticide molecules.

[0068] When cobalt nitrate or cobalt sulfate is used instead of cobalt chloride to prepare flocculent cobalt sulfide, the nitrate and sulfate ions in cobalt nitrate and cobalt sulfate will form coordination polyhedrons with nitrogen or sulfur atom as the center and oxygen as the coordinating atom. The oxygen in the coordination polyhedron occupies the cobalt position of flocculent cobalt sulfide, resulting in a decrease in the number of cobalt centers in flocculent cobalt sulfide. At the same time, excessive nitrate and sulfate ions will hinder the interaction between cobalt in flocculent cobalt sulfide and sulfur molecules of organophosphorus pesticide molecules due to steric hindrance effect, resulting in a decrease in the number of organophosphorus pesticide molecules adsorbed on the surface of flocculent cobalt sulfide, ultimately leading to poor detection performance.

[0069] In addition, to reveal the stability of the composite electrode (i.e., the flocculent cobalt sulfide / glassy carbon composite electrode of Example 1), the composite electrode was tested daily by square wave voltammetry at a pH of 8.0 with a parathion concentration of 10 μM and a 0.1 mol L -1 Response current in phosphate buffer solution. After 14 days, the peak value of the response current of the composite electrode was 96.2% of the initial measured response current peak value, indicating that the composite electrode has good stability.

[0070] On the basis of Example 1 and within the protection scope of the present application, the raw material dosage, process parameters, etc. in the preparation process of flocculent cobalt sulfide are changed, and the detection effect corresponding to the prepared flocculent cobalt sulfide is similar to that of Example 1.

Claims

1. A method for preparing flocculent cobalt sulfide, characterized in that: The following steps are involved: Mixing the halide salt of cobalt with oleylamine to obtain solution A; Mix sulfur and oleylamine to obtain solution B; The solution A is mixed with the solution B, and the obtained mixture is subjected to heating reaction to obtain the flocculent cobalt sulfide; The ratio of the cobalt halide to oleylamine is 0.01-0.5 mol: 3-10 mL; The usage ratio of sulfur to oleylamine is 0.01-0.5 mol: 3-10 mL; The temperature of the heating reaction is 110-125° C.; the time of the heating reaction is 4-8 hours.

2. The preparation method according to claim 1, characterized in that: The cobalt halide salt includes at least one of CoCl2, CoBr2, and CoI2.

3. The preparation method according to claim 1, characterized in that: After the heating reaction is completed, the mixture is naturally cooled to room temperature, and then washed and dried to obtain the flocculent cobalt sulfide.

4. A flocculent cobalt sulfide, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 3.

5. Use of flocculent cobalt sulfide prepared by the preparation method according to any one of claims 1 to 3 in the detection of organophosphorus pesticides.

6. The use according to claim 5, characterized in that: The application is to first prepare the flocculent cobalt sulfide into a non-enzymatic electrochemical sensor, and then use the non-enzymatic electrochemical sensor to detect organophosphorus pesticides.

7. The use according to claim 6, characterized in that: The preparation method of the non-enzymatic electrochemical sensor comprises the following steps: The flocculent cobalt sulfide is mixed with a perfluorosulfonic acid polymer solution and a solvent, and ultrasonically dispersed to obtain a dispersion liquid, and then the dispersion liquid is coated on the surface of an electrode and naturally air-dried to obtain a composite electrode; a three-electrode system is adopted, with the composite electrode as a working electrode, a platinum wire electrode as an auxiliary electrode, and a silver / silver chloride electrode as a reference electrode to form the non-enzymatic electrochemical sensor.

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