Method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode

Abstract

The present invention belongs to the field of electrochemiluminescence detection technology, and specifically relates to a method for detecting the concentration of chloride ions in lithium hexafluorophosphate using a Ag3PO4 / Cu‑MOF modified glassy carbon electrode. Specifically, a Ag3PO4 / Cu‑MOF / GCE modified electrode is used as a working electrode, an Ag / AgCl electrode is used as a reference electrode, and a platinum electrode is used as an auxiliary electrode to form a traditional three-electrode system. The detection range of the method for chloride ions is 1.0×10 ‑12 ~1.0×10 ‑4 mol / L, the minimum detection limit can reach 9.1×10 ‑13 mol / L. The method for detecting the concentration of chloride ions in lithium hexafluorophosphate has high sensitivity, strong specificity and simple operation.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemiluminescence detection, and specifically relates to a method for detecting chloride ion concentration in lithium hexafluorophosphate by using a Ag3PO4 / Cu-MOF modified glassy carbon electrode. Background Art

[0002] As the electrolyte of ion sub-batteries, lithium hexafluorophosphate plays a pivotal role in the application of lithium-ion batteries. Since phosphorus pentachloride is the main raw material for the production of lithium hexafluorophosphate, controlling the content of chloride ions in lithium hexafluorophosphate plays a decisive role in the quality management of lithium hexafluorophosphate. The chloride ion content not only affects the stability of lithium-ion batteries, but also causes corrosion of the battery shell and explosion of lithium-ion batteries. Therefore, controlling the content of chloride ions is particularly important for the production process of lithium hexafluorophosphate.

[0003] Currently, the methods reported for detecting chloride ions in lithium hexafluorophosphate include spectrophotometry, ion chromatography and fluorescence. However, these methods are complex, time-consuming, costly and have low detection sensitivity. Electrochemiluminescence (ECL) is chemiluminescence caused by electrochemical reactions. It has attracted widespread attention due to its high sensitivity, strong reaction controllability and simple instrumentation. It is a new analytical method with great development potential. Summary of the invention

[0004] The object of the present invention is to provide a method for detection based on an electrochemiluminescence sensor in order to improve the sensitivity of chloride ion detection in lithium hexafluorophosphate. The present invention fixes silver orthophosphate (Ag3PO4) on Cu-based MOFs. Based on the principle of energy resonance transfer, the electroluminescence intensity of the Ag3PO4 / Cu-MOF / GCE modified electrode is much higher than that of the Ag3PO4 / GCE and Cu-MOF / GCE modified electrodes. When chloride ions are present in the solution to be tested, the chloride ions will cause the quenching of the electrochemiluminescence of the modified electrode Ag3PO4 / Cu-MOF / GCE, and the quenching effect is enhanced as the chloride ion concentration increases, and is proportional to the chloride ion concentration. The present invention not only has the advantages of high sensitivity, strong specificity, wide linear range and simple instrumentation of electrochemiluminescence analysis, but also has important practical significance for the specific detection of chloride ions in lithium hexafluorophosphate.

[0005] In order to achieve the purpose of the present invention, the technical scheme adopted is: using Ag3PO4 / Cu-MOF / GCE modified electrode as working electrode, platinum electrode as auxiliary electrode, Ag / AgCl as reference electrode to form a three-electrode system for detection, and using electrochemiluminescence method to detect the chloride ion concentration in lithium hexafluorophosphate.

[0006] Furthermore, the preparation method of the modified electrode Ag3PO4 / Cu-MOF / GCE comprises the following steps: 1) preparation of Ag3PO4 / Cu-MOF composite material dispersion:

[0007] Ag3PO4 and Cu-MOF are prepared respectively, the prepared Cu-MOF and Ag3PO4 are added into a solvent, ultrasonically dispersed uniformly, centrifuged and washed with an organic solvent and deionized water respectively, and then dried to obtain a yellow-grey powder, i.e., an Ag3PO4 / Cu-MOF composite material, and the Ag3PO4 / Cu-MOF composite material is dispersed in DMF for use;

[0008] 2) Preparation of modified electrode Ag3PO4 / Cu-MOF / GCE:

[0009] The DMF dispersion of the Ag3PO4 / Cu-MOF composite material prepared in step 1) is dropped onto a clean glassy carbon electrode and dried under an infrared lamp to obtain a modified electrode Ag3PO4 / Cu-MOF / GCE capable of selectively detecting chloride ions in lithium hexafluorophosphate.

[0010] Furthermore, in step (1), the mass ratio of Cu-MOF to Ag3PO4 is 2:1; and in step (2), the concentration of the DMF dispersion of Ag3PO4 / Cu-MOF is 3.0 mg / mL.

[0011] Furthermore,

[0012] Preparation of Ag3PO4 / Cu-MOF composite material, including:

[0013] The disodium hydrogen phosphate solution was added dropwise to the silver nitrate solution and stirred vigorously to obtain a yellow milky liquid, which was centrifuged and washed with ultrapure water and dried to obtain a yellow powder, namely Ag3PO4. Copper sulfate pentahydrate (CuSO4·5H2O) and 4-(3-carboxy-1,2,4-H-triazole-1-yl)benzoic acid were added to a mixed solution of N,N-dimethylacetamide (DMF) and acetonitrile, and the blue milky liquid obtained by ultrasonic mixing was poured into a stainless steel autoclave lined with polytetrafluoroethylene for reaction. After the reaction was completed, Cu-MOF was obtained.

[0014] The prepared Cu-MOF and the prepared Ag3PO4 were added to DMF for ultrasonic dispersion; after centrifugal separation, they were washed with deionized water and dried to obtain a yellow-grey powder, i.e., Ag3PO4 / Cu-MOF composite material, and the Ag3PO4 / Cu-MOF composite material was dispersed in DMF so that the concentration of the Ag3PO4 / Cu-MOF dispersion was 3.0 mg / mL.

[0015] The preparation of modified electrode Ag3PO4 / Cu-MOF / GCE includes:

[0016] 5.0 μL of the DMF dispersion of the Ag3PO4 / Cu-MOF composite material was dropped onto a clean glassy carbon electrode and dried under infrared light to obtain a modified electrode Ag3PO4 / Cu-MOF / GCE that can selectively detect chloride ions in lithium hexafluorophosphate.

[0017] Furthermore, the method for detecting the chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode also includes the following steps:

[0018] (1) Prepare 0.05 mol / L K2S2O8 in 0.1 mol / L PBS buffer at pH 7.5;

[0019] Specifically, a PBS buffer solution containing 0.05 mol / L K2S2O8 was prepared using a 0.1 mol / L PBS buffer solution at pH 7.5.

[0020] (2) Preparation of standard solutions with different chloride ion concentrations

[0021] Take a certain amount of 1000ppm chloride ion standard solution and add it to 0.1mol / L PBS buffer solution with pH=7.5 containing 0.05mol / L K2S2O8 to obtain a series of chloride ion standard solutions with different concentrations ranging from 1.0×10 -12 ~1.0×10 -4 mol / L.

[0022] (5) Drawing of standard curve

[0023] The modified electrode Ag3PO4 / Cu-MOF / GCE is used as the working electrode, the platinum electrode is used as the auxiliary electrode, and the Ag / AgCl is used as the reference electrode to form a three-electrode system. The three-electrode system is placed in the above-mentioned 0.1 mol / L pH=7.5 PBS buffer solution containing a series of different concentrations of chloride ions and 0.05 mol / L K2S2O8 and immersed for a certain time (preferably 10 min). In the electrochemical window range of -1.6 to 0 V, a photomultiplier tube high voltage of 800 V and a scan rate of 0.1 V / s is used to perform cyclic voltammetry scanning, and the potential-luminescence intensity curve (E-ECL) is recorded. A linear relationship between the difference in luminescence intensity before and after the addition of chloride ions and the logarithm of the chloride ion concentration is established to obtain the corresponding linear regression equation;

[0024] (6) Sample testing

[0025] The actual sample is first pre-treated and tested under the same electrochemiluminescence test conditions as in step (5) above, and the luminescence intensity is recorded. The concentration of chloride ions in the sample to be tested is calculated using the linear regression equation corresponding to the standard curve obtained in step (5).

[0026] The minimum detection limit that the above method can achieve is 9.1×10 -13 mol / L.

[0027] Compared with the prior art, the significant advantage of the present invention is that Ag3PO4 and Cu-MOF are compounded to form a composite material of Ag3PO4 / Cu-MOF. The composite material of Ag3PO4 / Cu-MOF is then modified on a glassy carbon electrode (GCE) to form an Ag3PO4 / Cu-MOF / GCE modified electrode. The modified electrode is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the platinum electrode is used as the auxiliary electrode to form a traditional three-electrode system. Compared with the ordinary electrochemiluminescence sensor, the detection range of chloride ions of the present invention is 1.0×10 -12 ~1.0×10 -4 mol / L, with higher sensitivity, strong specificity and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a standard curve of the difference in luminescence intensity of the modified electrode Ag3PO4 / Cu-MOF / GCE before and after the addition of chloride ions and the logarithm of the chloride ion concentration. DETAILED DESCRIPTION

[0029] Example

[0030] (1) Preparation of Ag3PO4 / Cu-MOF composite materials:

[0031] To the aqueous solution of AgNO3 (10 mL, 0.6 M), Na2HPO4 aqueous solution (10 mL, 0.2 M) was added dropwise, stirred for 1 h, centrifuged and washed three times with deionized water, and then vacuum dried at 60 ° C to obtain a yellow precipitate, namely Ag3PO4. 0.012 g of 4-(3-carboxy-1,2,4-H-triazole-1-yl)benzoic acid and 0.0125 g of copper sulfate pentahydrate (CuSO4·5H2O) were added to a mixed solution of 4 mL of acetonitrile and 2 mL of deionized water and ultrasonically mixed. The obtained light blue milky liquid was poured into a 50 mL autoclave, heated at 95 ° C for 72 h, fully washed with deionized water and ethanol, and dried at 60 ° C to obtain a light blue powder, namely Cu-MOF.

[0032] The prepared Cu-MOF and the prepared Ag3PO4 were added to DMF for ultrasonic dispersion, and the mass ratio of Cu-MOF to Ag3PO4 was 2: 1. After centrifugal separation, the powder was washed with deionized water and dried to obtain a yellow-gray powder, namely, an Ag3PO4 / Cu-MOF composite material, and the Ag3PO4 / Cu-MOF composite material was dispersed in DMF to obtain an Ag3PO4 / Cu-MOF dispersion with a concentration of 3.0 mg / mL.

[0033] (2) Preparation of modified electrode Ag3PO4 / Cu-MOF / GCE:

[0034] 5.0 μL of the DMF dispersion of the Ag3PO4 / Cu-MOF composite material obtained in step (1) is dropped onto a clean glassy carbon electrode and dried under infrared light to obtain a modified electrode Ag3PO4 / Cu-MOF / GCE electrochemiluminescence sensor that can selectively detect chloride ions in lithium hexafluorophosphate.

[0035] (3) Drawing of standard curve

[0036] The modified electrode Ag3PO4 / Cu-MOF / GCE was used as the working electrode, the platinum electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode to form a three-electrode system. The three-electrode system was immersed in the above-mentioned PBS buffer solution containing a series of different concentrations of chloride ions and K2S2O8 for 10 minutes, and the luminescence intensity was detected using 0.1 mol / L PBS buffer solution with pH = 7.5 containing 0.05 mol / L K2S2O8 as the blank solution.

[0037] The three-electrode system was placed in a series of chloride ion concentrations (1.0×10 -12 mol / L、1.0×10 -11 mol / L、1.0×10 -10 mol / L、1.0×10 -9 mol / L、1.0×10 -8 mol / L、1.0×10 -7 mol / L、1.0×10 -6 mol / L、1.0×10 - 5 mol / L and 1.0×10 -4mol / L) in a 0.1 mol / L PBS buffer solution of pH 7.5 containing 0.05 mol / L K2S2O8, in the electrochemical window range of -1.6 to 0 V, the photomultiplier tube high voltage 800 V, the scan rate 0.1 V / s, cyclic voltammetry scanning, recording the potential-luminescence intensity curve (E-ECL), and establishing a linear relationship between the difference in luminescence intensity before and after the addition of chloride ions and the logarithm of the chloride ion concentration, the corresponding linear regression equation is: △I ECL =12312.6921+960.8102LogC(mol / L), the correlation coefficient (R) is 0.9982. The detection range of the linear regression equation is 1.0×10 -12 ~1.0×10 -4 mol / L, the minimum detection limit is 9.1×10 -13 mol / L.

[0038] (5) Sample testing

[0039] 0.5 g of lithium hexafluorophosphate was accurately weighed and added to 100 mL of 0.1 mol / L PBS buffer solution at pH 7.5 containing 0.05 mol / L K2S2O8 for electrochemiluminescence detection. The concentration of chloride ions in the lithium hexafluorophosphate sample to be detected was calculated according to the linear regression equation corresponding to the above step (4). The results are listed in Table 1. Table 1 also lists the analysis results of ion chromatography. It can be seen from the results that the results obtained by the present invention and the analysis method of ion chromatography are very similar.

[0040] Comparative Example

[0041] (1) Preparation of Cu-MOF / GCE modified electrodes

[0042] 5.0 μL of 3.0 mg / mL Cu-MOF DMF solution was pipetted with a microinjector and drop-coated on the glassy carbon electrode. After baking under an infrared lamp, a Cu-MOF / GCE modified electrode was obtained, which was used as the working electrode for electrochemiluminescence test.

[0043] (2) Drawing of standard curve

[0044] The modified electrode Cu-MOF / GCE was used as the working electrode, the platinum electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode to form a three-electrode system. The three-electrode system was immersed in the above-mentioned PBS buffer solution containing a series of different concentrations of chloride ions and K2S2O8 for 10 minutes, and the luminescence intensity was detected using 0.1 mol / L PBS buffer solution with pH = 7.5 containing 0.05 mol / L K2S2O8 as the blank solution.

[0045] The E-ECL curve was recorded, and a linear relationship between the difference in luminescence intensity before and after the addition of chloride ions and the logarithmic value of the chloride ion concentration was established to obtain the corresponding linear regression equation.

[0046] (3) Sample testing

[0047] 0.5 g of lithium hexafluorophosphate was accurately weighed and added to 100 mL of 0.1 mol / L PBS buffer solution at pH 7.5 containing 0.05 mol / L K2S2O8 for electrochemiluminescence detection. The concentration of chloride ions in the sample to be detected was calculated according to the linear regression equation corresponding to the above step (2). The results are listed in Table 1.

[0048] Table 1 Determination results of chloride ions in lithium hexafluorophosphate (n=3)

[0049]

[0050] Note: 1#, 2# and 3# are different batches of lithium hexafluorophosphate, and the measurement results are the average value of 3 parallel tests.

[0051] As shown in Table 1, the method of the embodiment can stably detect chloride ions in lithium hexafluorophosphate with high sensitivity, but the modified electrode Cu-MOF / GCE is not sensitive enough to chloride ions, so the chloride ions in lithium hexafluorophosphate are not detected. It can be seen from the above results that the present invention is feasible for detecting the chloride ion content in lithium hexafluorophosphate.

[0052] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Technicians in the relevant fields may make various corresponding changes without departing from the scope of the present invention. Therefore, all technical solutions formed by equivalent replacements or equivalent modifications belong to the protection scope of the present invention.

Claims

1. A method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode, characterized in that: The Ag3PO4 / Cu-MOF / GCE modified electrode was used as the working electrode of the electrochemiluminescence test, the platinum electrode was used as the auxiliary electrode, and Ag / AgCl was used as the reference electrode to form a three-electrode system. The electrochemiluminescence method was used to detect the chloride ion concentration in lithium hexafluorophosphate. The preparation method of the modified electrode Ag3PO4 / Cu-MOF / GCE comprises the following steps: (1) Preparation of Ag3PO4 / Cu-MOF composite material dispersion: Ag3PO4 and Cu-MOF are prepared respectively, the prepared Cu-MOF and Ag3PO4 are added into a solvent, ultrasonically dispersed uniformly, centrifuged and washed with an organic solvent and deionized water respectively, and then dried to obtain a yellow-grey powder, i.e., an Ag3PO4 / Cu-MOF composite material, and the Ag3PO4 / Cu-MOF composite material is dispersed in DMF for use; (2) Preparation of modified electrode Ag3PO4 / Cu-MOF / GCE: The DMF dispersion of the Ag3PO4 / Cu-MOF composite material prepared in step (1) is dropped onto a clean glassy carbon electrode and dried under an infrared lamp to obtain a modified electrode Ag3PO4 / Cu-MOF / GCE capable of selectively detecting chloride ions in lithium hexafluorophosphate.

2. The method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode as claimed in claim 1, characterized in that: In step (1), the mass ratio of Cu-MOF to Ag3PO4 is 2:1; in step (2), the concentration of the DMF dispersion of Ag3PO4 / Cu-MOF is 3.0 mg / mL.

3. The method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode according to claim 1, characterized in that: The following steps are also included: (1) First, prepare the PBS buffer solution containing K2S2O8; (2) Preparation of PBS buffer solutions containing different chloride ion concentrations and 0.05 mol / L K2S2O8; Take a certain amount of 1000 ppm chloride ion standard solution and add it to 0.1 mol / L PBS buffer solution with pH=7.5 containing 0.05 mol / L K2S2O8 to obtain a series of chloride ion standard solutions with different concentrations ranging from 1.0×10 -12 ~1.0×10 -4 mol / L; (3) Drawing of standard curve The modified electrode Ag3PO4 / Cu-MOF / GCE was used as the working electrode, the platinum electrode was used as the auxiliary electrode, and Ag / AgCl was used as the reference electrode to form a three-electrode system. The three-electrode system was immersed in the above-mentioned PBS buffer solution containing a series of different chloride ion concentrations and 0.05 mol / L K2S2O8 for a certain period of time, and the luminescence intensity was detected using 0.1 mol / L PBS buffer solution with pH=7.5 containing 0.05 mol / L K2S2O8 as the blank solution; In the electrochemical window range of -1.6~0V, the photomultiplier tube high voltage was 800V, the scanning rate was 0.1V / s, and cyclic voltammetry scanning was performed to record the potential-luminescence intensity curve, and the linear relationship between the difference in luminescence intensity before and after the addition of chloride ions and the logarithmic value of chloride ion concentration was established to obtain the corresponding linear regression equation; (4) Actual sample testing The actual sample detection is first pre-treated and then the pH is adjusted. The luminescence intensity is measured according to the three-electrode system and cyclic voltammetry scanning method in the above step (3), and then substituted into the linear regression equation for calculation to obtain the chloride ion content in the actual sample.

4. The method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode according to claim 3, characterized in that: In step (3), the immersion time of the modified electrode Ag3PO4 / Cu-MOF / GCE is 10 min.

5. The method for detecting chloride ion concentration in lithium hexafluorophosphate using Ag3PO4 / Cu-MOF modified glassy carbon electrode according to any one of claims 1 to 4, characterized in that: The minimum detection limit of chloride ion in lithium hexafluorophosphate is 9.1×10 -13 mol / L.

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