Preparation method and application of a magnetic organic framework-ionic liquid composite

Abstract

This invention discloses a method for preparing a magnetic organic framework-ionic liquid composite material and its application. The main components of this magnetic organic framework-ionic liquid composite material are iron(III) oxide nanoparticles, zeolite imidazole framework-8, and an ionic liquid. It is immiscible with ethanol, exhibiting aggregated droplet form in ethanol. After shaking and dispersion, it can rapidly recombine into droplets. Furthermore, the material possesses adsorption properties for heavy metal ions, enabling the removal of Cd ions from ethanol. 2+ Cu 2+ Hg 2+ Simultaneous adsorption of three heavy metal ions. These ions are magnetically adsorbed onto the surface of a magnetic glassy carbon electrode, enabling one-step electrode surface material modification. Subsequently, differential pulse voltammetry can be used to achieve the adsorption of Cd ions. 2+ Cu 2+ Hg 2+ Simultaneous electrochemical detection of three heavy metal ions.

Description

A method for preparing a magnetic organic framework-ionic liquid composite material and its application. Technical Field

[0001] This invention pertains to analytical detection technology, specifically relating to the simple synthesis of a magnetic droplet composite material with adsorption properties and its application in the simultaneous detection of multiple heavy metal ions. Background Technology

[0002] The depletion of petroleum fuels and related ecological problems have prompted many countries to focus on clean and renewable alternatives to gasoline and diesel fuels. Ethanol, due to its biodegradable and renewable characteristics, is considered a promising alternative fuel for automotive engines. As a biofuel, improving ethanol fuel quality is of great significance from environmental, technological, and economic perspectives. Cadmium, copper, and mercury, common heavy metal pollutants, are also present in ethanol fuel. Trace amounts of heavy metal ions in ethanol fuel accelerate corrosion reactions, promote the formation of fuel deposits, catalyze oxidation reactions in hydrocarbon mixtures, and reduce the efficiency of catalytic converters used in automotive exhaust systems. Therefore, designing a sensitive method for detecting heavy metal ions in ethanol is of great importance.

[0003] Many studies employ spectroscopic techniques, such as atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (AES-ICP), inductively coupled plasma mass spectrometry (MS-ICP), ultraviolet-visible spectrophotometry (UV-Vis), and energy-dispersive X-ray fluorescence (ED-XRF). These spectroscopic techniques require sample pretreatment and expensive testing equipment. Electrochemical analysis methods offer advantages such as high sensitivity, convenient detection, and the ability to simultaneously detect multiple ions, making them an ideal choice for the simultaneous analysis and detection of multiple heavy metal ions.

[0004] In electrochemical analysis, suitable electrode materials are crucial for achieving rapid and sensitive detection. Metal-organic frameworks (MOFs) are porous materials composed of inorganic ions or groups linked to organic ligands. As adsorbents, MOFs can present separation difficulties in solution, hindering practical applications. Combining MOFs with magnetic nanomaterials, utilizing the magnetic properties of the materials and adsorption through an external magnetic field, allows for rapid collection. Ionic liquids (ILs) are salts formed by the pairing of asymmetric organic cations with inorganic or organic anions, typically liquid at room temperature. ILs are used as reaction media in MOF synthesis and influence the structural characteristics of MOFs. Summary of the Invention

[0005] To address the above problems, this invention provides a method for preparing a magnetic organic framework-ionic liquid composite material and its application.

[0006] The specific plan is as follows:

[0007] A method for preparing a magnetic organic framework-ionic liquid composite material includes the following steps:

[0008] Step (1): Prepare a sodium polystyrene sulfonate (PSS) solution;

[0009] Step (2): Add nano Fe3O4 to the PSS solution in step (1), mix with ultrasonication, collect the material by magnetic attraction with a magnet, wash with deionized water to obtain a solid intermediate product;

[0010] Step (3): Dissolve a certain amount of Zn(CH3COO)2 and 2-methylimidazolium in 1-ethyl-3-methylimidazolium tetrafluoroborate (ionic liquid, IL) to form a mixed solution;

[0011] Step (4): Disperse the solid intermediate product obtained in step (2) in the mixed solution of step (3), heat and stir in a water bath at 50°C for 3 hours to obtain a brown suspension.

[0012] Step (5): Centrifuge the product obtained in step (4) and wash it with ethanol several times to obtain the composite material product.

[0013] Furthermore, in step (1), the concentration of sodium polystyrene sulfonate (PSS) solution is 0.3%;

[0014] Furthermore, in step (2), the nano Fe3O4 is approximately 20 nm in size;

[0015] Furthermore, in step (3), Zn(CH3COO)2 is 35.8 mg, 2-methylimidazole is 134.6 mg, and 1-ethyl-3-methylimidazole tetrafluoroborate is 3.0 mL.

[0016] A magnetic organic framework-ionic liquid composite material, mainly composed of iron oxide nanoparticles, zeolite imidazole framework-8, and an ionic liquid, is immiscible with ethanol. The material forms immiscible droplets in ethanol and can rapidly re-aggregate after being dispersed by shaking, achieving rapid adsorption of Cd from ethanol. 2+ Cu 2+ Hg 2+ The purpose of this study is to target three heavy metal ions; and this composite material can be magnetically adsorbed onto the surface of a magnetic glassy carbon electrode through a magnetic absorption collector, achieving one-step electrode surface modification. Subsequently, differential pulse voltammetry can be used to detect Cd in ethanol. 2+ Cu 2+ Hg 2+ Simultaneous electrochemical detection of three heavy metal ions.

[0017] An application of a magnetic organic framework-ionic liquid composite material for the simultaneous electrochemical detection of heavy metal ions in ethanol, comprising the following steps:

[0018] Step S1: Add a certain amount of magnetic organic framework-ionic liquid composite material to a Cd-containing container. 2+ Cu 2+ Hg 2+ In ethanol, heavy metal ions are adsorbed by shaking (10s);

[0019] Step S2: Using the magnet built into the magnetic glassy carbon electrode, the magnetic organic framework-ionic liquid composite material after the heavy metal ions were adsorbed in step S1 is modified onto the magnetic glassy carbon electrode.

[0020] Further, the Cd mentioned in step S1 2+ Cu 2+ Hg 2+ The concentration ranges from 1 to 100 μmol / L.

[0021] Furthermore, using a modified magnetic glassy carbon electrode as the working electrode, a platinum rod electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, with an acetate-sodium acetate buffer solution as the electrolyte, the content of three heavy metal ions in ethanol was determined by differential pulse voltammetry.

[0022] Furthermore, the concentration of the acetate-sodium acetate buffer solution is 0.1 mol / L, and the pH is 4.

[0023] The beneficial effects of this invention are as follows: the composite material synthesized by this invention has adsorption properties, exhibiting immiscible droplet form in ethanol solution, and can rapidly re-aggregate after being shaken and dispersed, thus achieving rapid adsorption of Cd from the organic solvent ethanol. 2+ Cu 2 + Hg 2+ The purpose of this study is to detect three heavy metal ions. This material simplifies the layer-by-layer modification of the electrode surface, enabling one-step electrode surface material modification. Differential pulse voltammetry was used to achieve the detection of Cd. 2+ Cu 2+ Hg 2+ Simultaneous electrochemical detection of three heavy metal ions. Attached Figure Description

[0024] Figure 1 shows a scanning electron microscope image of the composite material Fe3O4 / ZIF-8 / IL of the present invention. The left image is 100 μm and the right image is 5 μm.

[0025] Figure 2 is an X-ray diffraction pattern of the composite material Fe3O4 / ZIF-8 / IL of the present invention.

[0026] Figure 3 is a feasibility test diagram of the application of the composite material Fe3O4 / ZIF-8 / IL in the simultaneous electrochemical detection of heavy metal ions in ethanol.

[0027] Figure 4 shows the condition optimization diagram for the application of the composite material Fe3O4 / ZIF-8 / IL in the present invention for the simultaneous electrochemical detection of heavy metal ions in ethanol, where a and b represent the effects of buffer solution pH and ethanol dosage on the electrochemical signal, respectively.

[0028] Figure 5 shows the detection results of the simultaneous electrochemical detection of heavy metal ions in ethanol using the composite material Fe3O4 / ZIF-8 / IL, which exhibits characteristic development of the present invention. The results are obtained using a 0.1 mol / L acetate-sodium acetate buffer solution at pH 4, and the application of the present invention for different concentrations of Cd... 2+ Cu 2+ Hg 2+ The response curve and standard curve of differential pulse voltammetry are shown, where a, c, and e are the Fe3O4 / ZIF-8 / IL complex used to detect 1–100 μmol / L d. 2+ Cu 2+ Hg 2+ The DPV response of the ethanol solution, where b, d, and f are the results of simultaneous determination of different concentrations of Cd. 2+ Cu 2+ Hg 2+ Standard curve graph of time. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] This invention provides a method for preparing a magnetic organic framework-ionic liquid composite material, characterized by comprising the following steps:

[0031] Step (1): Prepare a sodium polystyrene sulfonate (PSS) solution (concentration 0.3%);

[0032] Step (2): Add nano Fe3O4 (20nm) to the PSS solution in step (1) and mix with ultrasound; then collect the material by magnetic attraction with a magnet, wash with deionized water to obtain a solid intermediate product;

[0033] Step (3): Dissolve 35.8 mg of Zn(CH3COO)2 and 134.6 mg of 2-methylimidazolium in 3.0 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate to form a mixed solution;

[0034] Step (4): Disperse the solid intermediate product obtained in step (2) in the mixed solution of step (3), and heat and stir in a 50°C water bath for 3 hours to obtain a brown suspension;

[0035] Step (5): Centrifuge the product obtained in step (4) and wash it with ethanol several times to obtain the composite material product.

[0036] Figure 1 shows a scanning electron microscope image of the composite material Fe3O4 / ZIF-8 / IL.

[0037] The composite material exhibits good dispersibility, relatively uniform material size, and a fairly regular morphology. ZIF-8 synthesized in an IL environment retains its crystal structure.

[0038] Figure 2 shows the X-ray diffraction pattern of the Fe3O4 / ZIF-8 / IL composite material.

[0039] The characteristic diffraction peaks of the synthesized Fe3O4 / ZIF-8 / IL material at 2θ = 30.09°, 35.42°, 43.05°, 53.39°, 56.94°, 62.51°, and 73.95° correspond to the (220), (311), (400), (422), (511), (440), and (533) crystal planes, indicating that the Fe3O4 structure was maintained during the synthesis of Fe3O4 / ZIF-8 / IL. Furthermore, the characteristic diffraction peaks at 2θ = 7.28°, 10.16°, 12.62°, 14.7°, 16.28°, and 18.04° correspond to the (011), (002), (112), (022), (013), and (222) crystal planes of ZIF-8, respectively. The crystal structure of ZIF-8 synthesized in an IL environment was preserved. Due to the influence of IL, the peak intensity of ZIF-8 in the composite material differed from that of standard ZIF-8. In summary, the synthesized Fe3O4 / ZIF-8 / IL retained the magnetic separation ability of Fe3O4 and possessed the high-efficiency adsorption performance of ZIF-8. The addition of IL caused the composite material to exhibit immiscible droplet form in ethanol.

[0040] Figure 3 shows a feasibility test diagram for the simultaneous electrochemical detection of heavy metal ions in ethanol, based on the characteristics of the composite material Fe3O4 / ZIF-8 / IL.

[0041] Heavy metal ions readily undergo redox reactions. When heavy metal ions react with elemental heavy metals, corresponding peaks appear in electrochemical tests. The peak potentials differ depending on the type of heavy metal ion, allowing for differentiation. As shown in the figure, three electrochemical dissolution peaks are observed at -0.8V, -0.1V, and 0.2V. Based on the redox potentials of the three ions, the electrochemical dissolution peak at -0.8V indicates that it is Cd. 2+The electrochemical dissolution peak at -0.1V is Cu. 2+ The electrochemical dissolution peak at 0.2V is Hg. 2+ The constructed electrochemical sensor can simultaneously detect three heavy metal ions, Cd. 2+ Cu 2+ Hg 2+ .

[0042] Figure 4 shows the optimization of the effect of buffer solution pH and ethanol solution volume on the electrochemical signal when the electrochemical sensor constructed with Fe3O4 / ZIF-8 / IL detects multiple heavy metal ions.

[0043] To obtain the optimal sensing performance of the electrochemical sensor constructed from Fe3O4 / ZIF-8 / IL material, factors affecting the sensor signal were identified and optimized during the experiment. These factors included electrolyte pH (3–7) and the volume of ethanol solution (1–5 mL). Differential pulse voltammetry was used to record the dissolution peaks of heavy metal ions under different conditions, with each experiment repeated three times under the same conditions. As shown in Figure a, the largest electrochemical signal was obtained when the pH of the NaAc-HAc buffer solution was 4. Excessively strong or weak acidity may affect the material's performance, leading to unstable electrochemical signals and failing to achieve optimal detection results. With a fixed amount of ethanol solution added to the material, a higher concentration of heavy metal ions in the solution resulted in a stronger electrochemical signal. The optimal electrochemical signal was obtained when the ethanol solution volume of heavy metal ions was 2 mL. When the solution volume exceeded 2 mL, the material might not be able to effectively adsorb heavy metal ions in a short time due to the larger solution volume, leading to a decrease in the electrochemical signal.

[0044] Figure 5 shows the application of the composite material Fe3O4 / ZIF-8 / IL of the present invention for the simultaneous electrochemical detection of heavy metal ions in ethanol.

[0045] Take 2 μL of Fe3O4 / ZIF-8 / IL liquid material and 2 mL of Cd at different concentrations. 2+ Cu 2+ Hg 2+ Ethanol solutions (1, 10, 30, 50, 80, 100 μmol / L) were used. Magnetic materials were dropped into solutions containing heavy metal ions, and the solution was gently vibrated to disperse the materials. After rapid aggregation, the materials were modified onto the surface of a magnetic glassy carbon electrode. Finally, differential pulse voltammetry (DPV) was used to measure the electrochemical signals generated by the three ions. Each experiment was performed three times under the same conditions. As shown in the figure, it can be clearly seen that Cd... 2+ The electrochemical dissolution peak of Cu is at -0.8V. 2+ The electrochemical dissolution peak is at -0.1V, Hg2+ The electrochemical dissolution peak is at 0.2 V, and the peak values ​​of the electrochemical signals of the three ions increase with increasing ion concentration. Based on the known concentrations of the three heavy metal ions and the experimentally measured peak values ​​of the dissolution at these concentrations, we established a concentration-peak value standard curve. As shown in the figure, Cd 2+ Cu 2+ Hg 2+ The peak values ​​of the three ions showed a good linear relationship with their concentrations in the range of 1–100 μmol / L, with Cd... 2+ The linear regression equation is y = 0.1730x - 0.12125 (R²). 2 =0.999), Cu 2+ The linear regression equation is y = 0.07223x - 0.039675 (R²). 2 =0.997), Hg 2+ The linear regression equation is y = 0.5243x - 0.4828 (R²). 2 =0.998), (where x is Cd) 2+ Cu 2+ Hg 2+ The concentration of Cd is given by y, where y is the corresponding electrochemical peak value. This electrochemical sensor detects Cd... 2+ Cu 2+ Hg 2+ The detection limits were 254.39 nM, 415.34 nM, and 9.458 nM, respectively. The electrochemical peak value of a prepared heavy metal ion solution of unknown concentration can be determined using the above method. Substituting the obtained peak value into a linear regression equation yields the concentration of heavy metal ions in the unknown solution, thus enabling the detection of heavy metal ion concentration.

Claims

1. A method for simultaneous electrochemical detection of cadmium, copper, and mercury ions in ethanol, characterized in that, The steps include: Step S1: Adding a certain amount of magnetic organic framework-ionic liquid composite material to a Cd-containing container. 2+ Cu 2+ Hg 2+ In ethanol, shake for 10 s; Step S2: Use the magnet built into the magnetic glassy carbon electrode to attract the magnetic organic framework-ionic liquid composite material after the adsorption of heavy metal ions in step S1 to the surface of the magnetic glassy carbon electrode to achieve the modification of the electrode surface material; The preparation method of the magnetic organic framework-ionic liquid composite material includes the following steps: Step (1): Prepare a sodium polystyrene sulfonate PSS solution; Step (2): Add nano Fe3O4 to the PSS solution in step (1) and mix it with ultrasound; Then collect the material by magnetic attraction with a magnet, wash it with deionized water, and obtain a solid intermediate product; Step (3): Dissolve a certain amount of Zn(CH3COO)2 and 2-methylimidazolium in 1-ethyl-3-methylimidazolium tetrafluoroborate to form a mixed solution; Step (4): Disperse the solid intermediate product obtained in step (2) in the mixed solution in step (3), heat and stir in a 50 ℃ water bath for 3 h to obtain a brown suspension; Step (5): Centrifuge the product obtained in step (4), wash it with ethanol several times to obtain the composite material product.

2. The method for simultaneous electrochemical detection of cadmium, copper, and mercury ions in ethanol according to claim 1, characterized in that, In step (1), the concentration of PSS solution is 0.3%; in step (2), the nano Fe3O4 is 20 nm; in step (3), Zn(CH3COO)2 is 35.8 mg, 2-methylimidazole is 134.6 mg, and 1-ethyl-3-methylimidazole tetrafluoroborate is 3.0 mL.

3. The method for simultaneous electrochemical detection of cadmium, copper, and mercury ions in ethanol according to claim 1, characterized in that, Using a modified magnetic glassy carbon electrode as the working electrode, a platinum rod electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, the content of three heavy metal ions in ethanol was determined by differential pulse voltammetry.

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